Are Europa’s Plumes Really There?

by Paul Gilster on December 22, 2014

A new study of data from the Cassini Saturn orbiter has turned up useful information about, of all places, Europa. Cassini’s 2001 flyby of Jupiter en route to Saturn produced the Europa data that were recently analyzed by members of the probe’s ultraviolet imaging spectrograph (UVIS) team. We learn something striking: Most of the plasma around Europa is not coming from internal activity being vented through geysers, but from volcanoes on Jupiter’s moon Io. Europa actually contributes 40 times less oxygen to its surrounding environment than previously thought.

These findings cast one Europa mission possibility in a new light. In 2013, researchers using the Hubble Space Telescope reported signs of plume activity, which immediately called the example of Enceladus to mind. If Europa were venting materials from an internal ocean, a possible mission scenario would be to fly a probe through the plume, just as the Cassini team has done with its probe at Enceladus. The latter also has strong signs of an internal ocean, but its geysers are far more substantial than what Hubble has observed at Europa. The new Cassini data indicate that at least in 2001, the UVIS instrument could detect no plume activity on Europa.


Image: Europa is a high value target in any case, but plumes would offer useful options for future spacecraft to study. Credit: NASA/JPL-Caltech/SETI Institute.

In the mix here is the kind of plasma observed in Europa’s orbit. The UVIS instrument saw hot plasma there, a stark contrast to the cold, dense gas that marks out the orbit of Enceladus. The Enceladan plumes account for this gas, which slows down electrons being dragged through it by Saturn’s magnetic field, lowering the temperature of the plasma. If something similar is happening at Europa, there is little sign of it. Cassini could find no evidence that large amounts of water vapor were being injected into Europa’s orbit, so any Europan plume activity is minimal. Amanda Hendrix (Planetary Science Institute) is a Cassini UVIS team member who co-authored the new study:

“It is certainly still possible that plume activity occurs, but that it is infrequent or the plumes are smaller than we see at Enceladus. If eruptive activity was occurring at the time of Cassini’s flyby, it was at a level too low to be detectable by UVIS.”

Even the tenuous atmosphere around Europa, millions of times thinner than Earth’s atmosphere, turns out to be about 100 times less dense than previously believed, according to these results. So the Hubble findings point to the need for further study, to determine whether there is intermittent plume activity or not. Maybe what had been thought to be 200-kilometer high jets of water are an extreme rarity, or perhaps they were the result of a mistaken original analysis.

This story isn’t over, because New Scientist is reporting that scientists who discovered the original Europa plume are working on an rebuttal of the Cassini findings. The magazine quotes Kurt Retherford (Southwest Research Institute), one of the plume discoverers, as saying that Cassini was simply too far from Jupiter to get an adequate reading of Europa’s plume activity, adding “We would say using their technique, they couldn’t possibly find water.”

A future mission may be what it takes to make sense of observations that were at the outside of Hubble’s envelope and may not be repeated until we can get a closer look. If Europa isn’t venting water into space, its status as a highly interesting astrobiology target is hardly compromised, but a flyby through a plume will disappear from our list of mission possibilities. Can Hubble make a repeat, definitive observation to settle this?

The Cassini findings were presented on December 18 at the American Geophysical Union fall meeting in San Francisco. The paper is Shemansky et al., “A New Understanding of the Europa Atmosphere and Limits on Geophysical Activity,” Astrophysical Journal Vol. 797, No. 2 (2014), p. 80 ff. (abstract).



Interstellar: Herald to the Stars or a Siren’s Song?

by Paul Gilster on December 19, 2014

Not long after I published my thoughts on Chris Nolan’s film Interstellar, Centauri Dreams regular Larry Klaes weighed in with his own take. Views on Interstellar have been all over the map, no surprise given how personal film criticism can be (take a look at the critical reception of Bladerunner over the years). I like the point/counterpoint aspect of what Larry does here, and while I imagine most readers have seen the movie by now, his criticisms may provoke a few more viewings and, I hope, a look at Kip Thorne’s excellent book on science in the making of the film.

By Larry Klaes

When I first heard about the existence of the film Interstellar, I was initially hopeful yet cautious. Most science fiction, especially these days, is some variation on Star Wars, which is often about as scientific and science fictional as the Harry Potter series. Yet Christopher Nolan and his team insisted they were striving hard to stick to REAL science with their production: They even had the famous Caltech astrophysicist Kip Thorne on their side, the very man who convinced none other than Carl Sagan to go with a wormhole rather than a black hole as the means to propel Ellie Arroway across space and time to meet the ETI in his 1985 novel (and 1997 film) titled Contact.

My real hope was that Interstellar would both portray a realistic method of travel among the stars based on currently known and plausible science and technology (no ambiguous hyper drives or nearly magical wormholes) and ignite the public’s passion for true interstellar exploration – along with overall space exploration and colonization in the process. A decent and maybe even original story with characters I genuinely cared about would be nice, too. Something to counterbalance the last three decades of fantasy and soap opera that Star Wars and Star Trek had done to science fiction after the golden age of the cinematic genre in the 1960s and early 1970s.


The cry and hue that the story of Interstellar was based on real science and was very similar to the classic 2001: A Space Odyssey thrust upon the world by Stanley Kubrick and Arthur C. Clarke 46 years earlier only grew as the date of its general release approached. My gut feeling that Interstellar was not going to be a straightforward science film of fiction also grew, but I kept hoping to be wrong, that somehow we were going to have a cinematic creation of the genre worthy of 2001 or at least in the same room as Kubrick’s masterpiece. Heck, I would be happy if Interstellar was in the same building or at least on the same street as the original 2001: A Space Odyssey.

When I finally saw Interstellar on the big screen I sadly realized my underlying fears were true. In a number of ways the film was even worse than I predicted and not just because it felt like I was watching something created by an amateur filmmaker whom the studios had given a big budget to and told to do as he pleased. My hopes of giving the general nonscientific public an anchor to see and appreciate how we might really send our species to the stars one day were also dashed.

Now I may be wrong, for Interstellar did do a lot of positive cheerleading for the cause of science and expansion into space and that could be enough to tip the scales or at least contribute to humanity getting off this rock permanently. Nevertheless I feel the way Nolan and company went about showing how people might spread into the Cosmos could ultimately undermine the enterprise with unrealistic and even damaging expectations.

Is Interstellar a cinematic herald that will turn the public’s interest and support towards a destiny in space? Or is it an unwitting siren’s song that will lure in unwary viewers to expect our journeys and colonization of the Cosmos to be like the fantastical paths in the film, only to lead them to unfulfilled dreams, disappointment, and ultimately turn away from what has long been called the Final Frontier?

Now to elaborate….

Let’s Put On a Show!

First the film itself. I am not a big fan of Christopher Nolan’s work even though I know he has a rather rabid fan base. I feel most of his films, while nice looking and not lacking in action, are rather heavy-handed in their messages, which themselves are given a gravity I find undeserving overall. About the only film of Nolan’s that did do more than just temporarily entertain me was The Dark Knight from his Batman trilogy and that was mainly due to the late actor Heath Ledger’s amazing performance as the psychopathic villain The Joker.


In any event I expected a director and producer of Nolan’s experience to come up with something better than what I witnessed on the big screen. Yes Nolan was clearly influenced by 2001 and many parts of Interstellar were both emulations and tributes to the 1968 cinematic landmark, but ultimately that is essentially what Interstellar felt like, a tribute by someone who thought they could make a 2001 level science fiction film for this generation but ultimately fell short. It was both a bit surprising and disappointing.

Across the Internet many people were quite vocal in praising and defending Interstellar and that of course is their right. I noted in particular how many were adamant both that it was “just a film” as if this were some deep revelation and that any poor or inaccurate portrayals of science should not matter, usually reverting back to the “just a film” reason or Interstellar not being a documentary as the most common excuses. No, Interstellar was not a terrible film and it was obvious that Nolan et al tried very hard to make good science fiction cinema. Perhaps that is what makes it all the sadder that for all their talent and budget they could not match what they tried to emulate or even as a lesser science fiction film, not even in the three hours they had to tell their story. And when one has spent hundreds of millions of dollars and years on a project and loaded it with important messages for a wide audience, then Interstellar is NOT “just a film.”

To me it felt like Nolan said to himself “Hey, I can write science fiction!” and then proceeded to show why and how making a good creation of the genre is not as easy as the fluff the public has been fed since 1977. I also blame this on why certain segments of the public think Interstellar is so wonderful: When you have been fed a near steady diet of hamburger for decades, suddenly being given a better made hamburger (yet a hamburger nonetheless) makes you think you are dining on a porterhouse steak. Or cooking up one, apparently.

I am not going to delve much into the science portrayed in Interstellar as many have already done so (Google the words ‘interstellar science’) and amazingly even a science book by Kip Thorne himself was produced on the very subject, which perhaps may be the best thing to come out of this whole effort. I do not want to detract from the main points I really want to make about Interstellar next in this piece. Besides, there will still be enough of my comments on the science of Interstellar in the process.

When You Wish Upon a Wormhole…

I was honestly quite bothered by the way Interstellar went about saying and showing how humanity may one day achieve the stars. The first issue is their reason for spreading into deep space: In the film it is not due to humanity’s desire for knowledge or adventure, it is primarily one of survival. Now while needing to evacuate Earth and the Sol system is one legitimate reason for developing a means of interstellar transportation and colonization, there are two problems with this scenario: One is that it is often considered to be the ONLY legitimate reason for sending humans to the stars. The other is that if humanity and our planet are in some kind of dire trouble where the only alternative is to evacuate, the odds are probably rather high that humanity will already be in a state where building any kind of interstellar vessel, even a slow-moving multigenerational starship, may no longer be an option. So if we are ever to develop a real interstellar capability, perhaps we should start conducting one while our civilization is not in a major state of crisis or outright impending doom.

In the near future, a disease called only the Blight has decimated most crops across Earth and is steadily increasing the amount of nitrogen in our planet’s atmosphere. This in turn has led to many aspects of the society falling towards doom, including space travel in general and NASA in particular. The slow march to extinction for the human species appears to be inevitable and the efforts at preservation shown in Interstellar are only buying time.

Then suddenly it is revealed (by methods which feel like nothing less than the supernatural) that NASA isn’t gone but merely hiding underground (literally) to escape a skeptical and increasingly ignorant and panicky public while what is left of the United States government secretly funds the space agency for several plans it has to save the human race, or at least some of it. One part of the plan involves flying up to a spaceship in Earth orbit which will then take a crew of brave astronauts (and a collection of frozen and fertilized human eggs as the backup part of the plan) to travel to a wormhole which appeared near the planet Saturn some decades ago. From there the astronauts will use the wormhole to journey to a solar system in another galaxy and check out three worlds circling a black hole to see if initial reports beamed back from earlier expeditions there do indeed prove these alien planets to be viable places for human colonization.


It has already been stated multiple times elsewhere about the concerns one might understandably have about venturing to planets in the gravitational grip of a black hole. We have also been informed more than once how Thorne made some actual new scientific revelations about this type of celestial object while helping the filmmakers create a realistic black hole. What bothers me deeply is that the public will have even more firmly entrenched in their minds that cosmic wormholes are probably the only way humanity will ever achieve interstellar travel (the other faster than light speed contenders are of course warp drives and hyperdrives).

What may be even more harmful is that the wormhole was apparently not a natural cosmic formation but placed deliberately near the ringed gas giant world by some unknown advanced entities from the future in our Sol system for use by their distant human ancestors from the struggling Earth. This will merely add reinforcement to those who think humans both in the past and present are not bright enough to solve their own problems and build wondrous devices in the process, that some outside force like advanced aliens or future humans must intervene or all is lost. This is an insult to the intelligence and ingenuity of our ancestors and present ourselves, who have done and learned some amazing things without any external assistance and beaten some very strong odds against us and our societies.

Anyone who has done more than a very casual read of Centauri Dreams knows there are multiple methods for interstellar travel which are plausible and do not invoke help from remote human descendants or superior ETI and do not require abilities that seem to be almost magical in their powers. Ironically the new television miniseries called Ascension, which I thought would be little more than an imitation of Mad Men set in space for the novelty, involves a multigenerational starship with Orion nuclear pulse propulsion – both forms of star voyaging which we could build either now or in the rather near future.

It is obvious that Nolan, feeling he had to have a means for star travel grand enough to match his visions and huge film budget ($165 million, which does not even include marketing costs), while lacking a strong background in science and technology (he even says as much in Thorne’s science companion book), went for what he thought would invoke the wonder and magic of the Cosmos for his audience. Maybe it did, but maybe it also left the general public thinking there is only one real way to attain the vast realm beyond the Sol system. This implies that we should let the smart people of the future do all the grunt work to hopefully come up with a device that seems to solve the physics and technical issues resident with wormholes with little effort.

This concern of mine has a real world basis in the reactions of the press and public to some of the more recent interstellar workshops and conferences. While these wonderful and groundbreaking events have many real experts discussing about and working upon a wide range of interstellar methods of propulsion and exploration which involve real physics and technology, the media instead tends to focus on those presentations about warp drives and wormholes, both of which suffer from some major obstacles in reality.

However, thanks to certain popular genres, this does not stop the general public from overly attaching their attention and excitement onto hypothetical means of reaching the stars which may not come to fruition for a very long time, if ever. Witness the hype about the belief that NASA is developing a warp drive, when in reality there is just one person working on the subject on a very limited budget and has so far produced a few academic papers from it all. Meanwhile the more plausible methods such as the aforementioned Orion, fusion propulsion, laser sails, and antimatter, are left standing off to the side, diminished by the very artificial glare of the flashier warp drives and wormholes. Yet Orion and its brethren, while certainly having some issues of their own, give us much better chances of actually getting us to Alpha Centauri and beyond, even if it will take years to centuries rather than minutes or seconds.

Despite what may seem at first to be incongruent to common sense, many people do get much of their “education” about the world from films and television whether they think so or not (or like It or not); whether it is accurate or not is another matter, yet they still absorb it and take what the film shows as the way something is, especially if it is a place or object unfamiliar to their everyday experiences. This certainly includes space science and astronomy, as these subjects are often either taught sparingly in the public school systems or not at all. This is why the general public and the media by extension focus so much on using warp drives or hyperdrives or wormholes as the most popular and expected means of deep space propulsion. These are not only the most complex methods but also perhaps the most unrealistic, but when your education comes from Hollywood, that hardly matters – except when it comes to supporting groups that are trying to make interstellar travel a reality.


Just So Long as We Look Really Cool

Then there is the issue of where the expedition in Interstellar was going to start a new civilization for humanity. Forget for a moment that the best candidate planets are circling a giant black hole, perhaps one of the worst places to be near in the Universe between the constant threat of being torn apart and then crushed into a singular dot and the massive amounts of radiation from all the x-rays being generated as celestial debris is constantly being pulled into the black hole and heating up immensely in the process. There is also the general lack of any light from an object with a mass strong enough to keep any photons from escaping but why quibble at this point? The worlds around the black hole named Gargantua seem to get enough illumination somehow so that the visiting astronauts can see what they are doing and getting into.

No, my even greater issue with the scenario is that apparently there was not a single world of the 400 billion star systems in our own Milky Way galaxy which were good enough to resettle what was left of our species. This despite the fact that even in our early stages of knowledge about real exoplanets we can now comfortably estimate there are billions of habitable worlds in the Milky Way: With those kinds of odds at least some of them should be good enough for terrestrial life to settle upon, or at the least be made viable for colonization. Instead the superior future humans (or whatever they really are exactly) chose a galaxy so remote that the people doing the initial exploring do not even know where it is In the Universe. So if something went wrong, the people on either side of the wormhole are literally stuck with no other apparent options.

In many science fiction films and television series which deal with deep space, Hollywood has often made no distinction between a solar system and a galaxy. While the makers of Interstellar were aware of these two very different kinds of celestial objects, the fact that they still had our main characters whiz off not to another solar system in the Milky Way but another entire galaxy many millions if not perhaps billions of light years away probably blurred the distinction for many in the audience, who sadly have little better knowledge of astronomy than a typical Hollywood producer.

For that matter, this film should have properly been called Intergalactic rather than Interstellar, since any travel outside the Sol system by the astronauts led not to another star system in our galaxy but another entire stellar island. I see this as a missed educational opportunity for a cinematic production team which boasted how scientific their film is and hoped it would inspire millions of viewers.

What is Love? Baby Don’t Hurt Me

Perhaps there is one thing more derailing about Interstellar than a near magical wormhole sent from the future and that is the film’s take on the concept of love. And the fifth dimension. Of the many instances where Nolan tried to channel Kubrick’s 2001, perhaps the biggest example was near the end of the film, when our hero astronaut named Cooper rides into the black hole called Gargantua and somehow ends up inside an infinite bookcase where he attempts to communicate with his daughter named Murphy using Morse code. She in turn goes on to create what I can only surmise is some form of cavorite – the antigravity material written about in the 1901 science fiction novel The First Men in the Moon by H. G. Wells – which somehow saves what is left of the human race by getting them off Earth and into giant space colonies, one of which ends up around the ever-photogenic Saturn.

This then begs the question: Why did we spend the vast majority of the film focused on trying to save humanity by colonizing some really distant alien worlds when we ended up living in massive space cities in our Sol system after all?

Much of the film’s latter parts can only be described as a metaphysical mess which were actually made worse when Nolan tried to throw in explanations to make it all seem somehow plausible along with dramatic and heartwarming. Sure, Kubrick also went seemingly transcendent with the famous Stargate sequence in 2001, but at least he had the good sense to speak only with images and let the viewers decide what was going on. Nolan fell into the trap that most cinematic and television producers make these days and that is they feel they have to explain EVERYTHING. Even if it is a bunch of metaphysical technobabble.

All Nolan really did was reinforce my concern that the public will think we can reach the stars only if we do the future technological equivalent of clicking our heels together three times and wishing really hard.


And this thing called love. I literally started to sink into my theater chair when I heard the character of Brand played by Anne Hathaway declare with dead seriousness that love is not just a chemical reaction or a genetic drive to continue the species but a physical, tangible force that can transcend space and time and unite two people despite any and all odds including deep, deep space. This is how she knew her lover was still alive on one of the worlds circling that black hole.

I know love can make people do amazing, crazy, and stupid things, but Nolan really went off into the deep end of the pseudoscientific swimming pool here. This notion about love is the kind of thing one expects from a Lifetime or Hallmark Channel production, not an expensive epic wannabe that continually boasts about how scientific it is – and then immediately dances down the magical mystery tour path. If they had stuck with the melodramatic message that love can drive and unite two people even if they are very far apart in space and time in the metaphorical sense, that would have worked. But then they went the pseudoscience route, which really undermined Nolan’s repeated claims about how science-oriented Interstellar is.

How Not to Buy the Farm

For a film that I assumed wanted to inspire the average Joe and Jane to support space exploration, I was left rather wondering about their treatment of farmers and farming in general. Cooper’s son, Tom, is designated by the local school system – the same one that said the Apollo lunar landings were a hoax, please note – as being smart enough for farming. Cooper takes this pretty much as a given and for the rest of the film we see our hero astronaut bonding over and over with his daughter, the smart one who grows up to become the scientist who solves the “gravity problem” – whatever the heck that was anyway. As an astronaut who desperately wants to get back into space, everything else, including working in the terrestrial dirt, is second rate.

Not too many generations ago, most people were farmers. And even though the number of participants in this occupation are much less these days, there are still plenty more whose jobs are much closer to farming than those of science. So why does Interstellar implicitly put down the average Joe and Jane even if it thinks it doesn’t mean to? Son Tom grows up to become the farmer he was more or less assigned to be, one who is so focused on his trade that even when his sister and her boyfriend warn Tom that he and his family have to consider leaving their home and fields due to health problems from all the dust caused from the Blight, his reaction is a very negative one tinged with growing hostility.

In the end we don’t know what becomes of Tom or his family in the later years, because Cooper’s bond is mainly with his scientist daughter and not the son he pretty much wrote off the day the school determined he was good enough for farming.

While I for one was very happy to see a film which verbally promoted and elevated space and those who want to explore it, I was also surprised at all the underlying negativity towards what I guess can best be described as Middle America. If anything Nolan should have been trying to find ways to show folks who were not science minded or ever considered the possibilities that space holds for our species and our planet that they too could participate in the Great Adventure; that space truly does hold the keys to our future. Instead we get Cooper making comments such as: “We used to look up at the sky and wonder at our place in the stars, now we just look down and worry about our place in the dirt.” He may have been largely right both for his world and ours, but putting up a further divide between the two modes of thought that also treats Earth as something separate from the rest of the Universe, which as a big ball of rock circling a star through space certainly means it is not, is not going to help the cause in our world to get off that dirt – or use space to help it, for that matter.

Oh Look, O’Neil’s Space Colonies – Hey, Wait, Come Back!

Despite the fact that it kind of felt like defeating the whole point of spending so much time and effort with those astronauts trying to find a new world to colonize on the other side of that mysterious wormhole, I was rather pleased to see the scenes near the end taking place aboard an honest-to-goodness O’Neil space colony.

In the 1970s we were presented with huge artificial space cities looking like either long cylinders or wheels with spokes. Thousands of people were going to live on them and construction would begin by the start of the 21st Century: The Bicentennial issue of National Geographic Magazine devoted an article to the concept, complete with very nice artwork showing how we could all be living in these floating space colonies fifty years hence – that is how serious and widespread the idea was becoming, at least in the minds of space fans
Of course just like the manned missions to Mars, we are still waiting for them to happen, but the ideas have taken on a form of reality in science fiction cinema. The Stanford torus version of the O’Neil space colony is a key player in the 2013 film Elysium, although it isn’t doing space utilization any favors by showing that only the rich and powerful get to live way up in Earth orbit while everyone else gets to struggle for existence on a dying planet.

For Interstellar, the space colony is for everyone, or at least all those who could manage to survive long enough to escape Earth and start new lives on these huge artificial worlds thanks to Cooper’s scientist daughter solving the “gravity problem”, whatever that was exactly. Again, why the film did not depict humanity expanding into the Sol system, which would have been a lot easier than even more conventional forms of interstellar travel let alone a wormhole that appears by virtual magic, I still do not quite understand. Just as I do not understand why those future humans let machines, resources, and lives be wasted attempting to colonize a few really distant and rather inhospitable alien planets which being from the future they should have known about already. So that Cooper and Brand could hook up on the one planet that was livable? I know Brand also had all those Plan B frozen fertilized eggs with her as well, so maybe they were supposed to start a new branch of the human race in another galaxy, but I did not see how exactly they were going to gestate all those eggs and then raise the children into successful adulthood on their own? Were those monolithic robots supposed to help?

We the audience did get a more satisfying and plausible answer to solving the dilemma of settling space with those big artificial colony worlds, but it took most of the three hour long film going down some rather murky and even dead end roads to get there. I wondered how many viewing Interstellar could appreciate or even remember what an O’Neil colony was and what it promised humanity by then? And what about settling actual worlds in our Sol system, namely the Moon and Mars? Did they get colonized and Nolan just didn’t bother to have anyone mention it? Are the planetoids and comets colonized too? Why didn’t they get at least a mention considering just how important their roles will be when real space colonies come along? I think a real opportunity to present how we could colonize our celestial neighborhood was missed here.

Teaching Them to Long for the Endless Immensity of the Sea

Ironically, for all my views on and concerns about Intergalactic – I mean Interstellar – my fondest hope is that I am wrong when it comes to the film succeeding in its intentions, that Nolan’s effort does pay off with the public supporting space in their minds, with their words, and with their wallets. Especially those who so vocally defended Interstellar. We have enough pretend space programs and actors portraying astronauts; we need to do our part to show how much more amazing and exciting the real Universe is and can be.

Perhaps the author of The Little Prince, Antoine de Saint-Exupery, has it right about how to get the public interested in settling the stars when he said the following:

“If you want to build a ship, don’t drum up people to collect wood and don’t assign them tasks and work, but rather teach them to long for the endless immensity of the sea.”

And while you are at it, as Interstellar said multiple times, do not go gentle into that good night. Rather, go boldly with a sense of adventure and purpose, all of which space can give us – and which we can do on our own with our minds and tools. We are the ones who will create the future, not the other way around.



A New Look at High Obliquity Exoplanets

by Paul Gilster on December 18, 2014

Looking forward from winter into spring in North America — unfortunately still a few months out — I can thank Earth’s obliquity for a seasonal change I enjoy more every year. Obliquity is the angle that our planet’s rotational axis makes as it intersects the orbital plane, which in the case of Earth is 23.5°, so that when we reach the summer solstice, the north pole of the planet tilts toward the Sun by this angle. At winter solstice, the pole is tilted away by the same amount.

Our Solar System’s most extreme case of obliquity is Uranus, where the angle is a whopping 97.8°. Imagine a planet where the north pole points all but directly at the Sun, cycling through a year where the southern pole will eventually do the same. I’m reminded of Stephen Baxter’s novel Ark (Roc, 2011). Here, interstellar travelers come to a planet they hopefully designate Earth II (82 Eridani is its primary). Alas, the obliquity turns out to be 90 degrees, kicking off extreme seasonality. In this passage, one of the characters explains the problem to the rest of the crew:

“Every part of the planet except an equatorial strip will suffer months of perpetual darkness, months of perpetual light. Away from the equator you’ll suffer extreme heat, aridity, followed by months of Arctic cold—we estimate the surface temperature will drop to a hundred degrees below across much of the space-facing hemisphere, and there’ll be one hell of a blanket of snow and ice. Even the equator would be a challenge to inhabit, for even at the height of summer in either hemisphere the sun would be low, the heat budget minimal, the climate wintry.”

Is a planet with 90 degree obliquity in any sense habitable? It’s a question the crew debate and I won’t spoil what they find out. But I will point to a new study out of MIT that looks at planetary obliquity and finds that, depending on the world, habitable conditions may emerge. The work of David Ferreira (University of Reading, UK), Sara Seager (MIT) and colleagues, the paper in Icarus uses a three-dimensional computer model to simulate interactions between atmosphere, ocean and sea ice over a 3000-meter deep ocean. Shallower, more simplified oceans at 200, 50 and 10 meters in depth were also plugged into the mix for comparison.

The model assumes an Earth-sized planet at a similar distance from its star, one that is completely covered in water. Simulating three planetary obliquities — 23 degrees, 54 degrees and 90 degrees — the researchers found that a global ocean as shallow as 50 meters would absorb so much solar energy throughout the polar summer, releasing it back into the atmosphere during the winter, that the climate would remain relatively mild, with temperatures comfortably spring-like year round. It’s a result that no one on the team had anticipated.

“We were expecting that if you put an ocean on the planet, it might be a bit more habitable, but not to this point,” Ferreira says. “It’s really surprising that the temperatures at the poles are still habitable.”


Image: A water world at Earth’s distance from the Sun, assuming a deep enough ocean, could maintain habitable temperatures year-round even if its obliquity is high. Credit: Christine Daniloff/MIT.

It’s also a fragile situation, to judge from these results. A ten-meter deep global ocean would not be deep enough. The world would experience a runaway effect in which the first ice that formed would spread quickly onto the dark side. The eventual emergence of the dark side into light would not help, for by this point, the massive ice sheets that had formed would reflect sunlight efficiently enough to allow the ice to continue to spread, until the world became completely encased in ice. With this kind of high obliquity world in an Earth-like orbit — Ferreira and Seager call it an ‘aquaplanet’ — you’re either facing a warm ocean and benign temperatures or a global snowball.

But the potential is there for an all-water planet at high obliquity, one with a sufficiently deep ocean, to offer conditions in which life might develop. Adds Ferreira:

“The expectation was that such a planet would not be habitable: It would basically boil, and freeze, which would be really tough for life. We found that the ocean stores heat during summer and gives it back in winter, so the climate is still pretty mild, even in the heart of the cold polar night. So in the search for habitable exoplanets, we’re saying, don’t discount high-obliquity ones as unsuitable for life.”

The paper is Ferreira et al., “Climate at high-obliquity,” Icarus Vol. 243 (15 November 2014), pp. 236-248 (abstract). An MIT news release is available.



Voyager: Shock Waves in Deep Space

by Paul Gilster on December 17, 2014

What exactly is the shock wave that Voyager 1 encountered earlier this year, a wave that is still propagating outward, according to new data from the craft? Researchers at the Jet Propulsion Laboratory refer to it as a ‘tsunami wave,’ a simile that reminds us of the devastating effects of roiled water as it encounters land following an earthquake or an impact in the ocean.

But in this case the cause is a coronal mass ejection (CME), in which the Sun heaves out a magnetic cloud of plasma from its surface, generating a pressure wave. As this JPL news release explains, the outgoing wave runs into charged particles in deep space — interstellar plasma — creating the disturbance. In all, Voyager 1 has experienced three of these shock waves, with the most recent first being observed in February of 2014 and still continuing.

The new data were presented on December 15 at the American Geophysical Union meeting in San Francisco by Don Gurnett (University of Iowa), who is quoted as saying “Most people would have thought the interstellar medium would have been smooth and quiet. But these shock waves seem to be more common than we thought.” Project scientist Ed Stone (Caltech) said the shock wave was causing the ionized interstellar gas to “‘sing’ or vibrate like a bell.”

“The density of the plasma is higher the farther Voyager goes,” Stone added. “Is that because the interstellar medium is denser as Voyager moves away from the heliosphere, or is it from the shock wave itself? We don’t know yet.”

You can hear the ‘singing’ that Stone describes in this JPL video, which includes a color-coded graph showing the frequency of the waves — this indicates the density of the plasma. Detection of the wave came through the spacecraft’s plasma instrument. Previous instances of the phenomenon occurred from October to November of 2012 and April to May of 2013. In fact, it was the shock wave in 2013 that helped scientists determine that Voyager 1 had left the heliosphere, the ‘bubble’ created by the solar wind that extends well past the outer planets. The plasma the spacecraft encountered then was forty times denser than any previously measured.


Image: The graphic above shows the frequency of the waves, an indication of the density of the plasma. Colors correspond to the intensity of the wave, with red being the loudest and blue the weakest. Credit: NASA/JPL.

Just how far out should these ‘tsunami waves’ be encountered? Gurnett, who is principal investigator for the plasma instrument on Voyager, thinks the waves may propagate out to twice the distance currently separating Voyager and the Sun. If that’s the case, we’ll be dealing with interesting plasma data as long as the Voyagers stay with us. Somewhere around 2025 is the likely endpoint of communications as the two probes run out of the power needed to transmit.

Ponder this: If it were not for loss of consumables, as seen in Voyager’s diminishing hydrazine and power levels, we could probably continue to track the craft for another century. As of this morning, Voyager 1 is 129.92 AU from the Sun, for a round-trip light time of over 36 hours.



The Virtues of Oddly Shaped Planets

by Paul Gilster on December 16, 2014

A new paper out of George Mason University tackles the subject of planets deformed by tidal effects in close proximity to their star. It’s a useful study for reasons I’ll explain in a moment, but first a digression: I once had the chance to talk physics with the late Sheridan Simon, who besides being a popular lecturer on astrophysics at Guilford College (Greensboro, NC) also had a cottage industry designing planets for science fiction writers. Simon loved oddly shaped planets and because the Super Bowl was coming up, he had taken it upon himself to design a planet in the shape of a football, just to see what would happen if a place like this actually existed.

“And you know what? It works,” the bearded, exuberant Simon said with a grin. “But when you model what it looks like from space, the atmosphere is a problem. It looks plaid!”


Simon played around with planets of every description, and if you’d like to see him at work on a planetary system around Tau Ceti, check what he developed back in 1992 for James K. Hoffman. I don’t know if he ever worked with Robert Forward, but of course the ultimate deformed planet in science fiction would be Rocheworld, from the novel of the same name (in an early version, Flight of the Dragonfly), where Forward envisions two worlds close enough to each other that they are deformed into egg-shapes and actually share an atmosphere.

Deformed planets in the realm of hot Jupiters have been studied for some time, for some of these worlds are close enough to their star to experience significant distortion in shape. One that Prabal Saxena and his George Mason University team mention in their paper is WASP-12b, which has been shown in earlier studies to have ellipsoidal variations in its transit depth that suggest a 3:2 ratio between the planet’s longest and its shortest axes. It’s an important effect because misunderstanding the distortion in shape caused by rotational and tidal effects can lead to mistakes in calculating the radius of the planet, and thus parameters such as density.

What Saxena and team are interested in is how rocky worlds orbiting red dwarf stars may experience stresses that can change their shape. Saxena comments:

“Imagine taking a planet like the Earth or Mars, placing it near a cool red star and stretching it out. Analysing the new shape alone will tell us a lot about the otherwise impossible to see internal structure of the planet and how it changes over time.”


Image: An artist’s impression of a stretched rocky planet in orbit around a red dwarf star. So close to the star, there is a difference in the strength of the gravitational field on each side of the planet, stretching it significantly. Credit: Shivam Sikroria.

The paper, which appears in Monthly Notices of the Royal Astronomical Society, goes to work on how to take both tidal and rotational forces into account. The French astronomer Édouard Roche (1820-1883) was the first to calculate the distance within which an orbiting body will disintegrate because of the tidal forces induced by its primary. Inside what we now call the Roche limit, material in orbit will become dispersed into rings, while outside the limit, it can coalesce. The process varies depending on the innate rigidity of the body in question. A more fluid world deforms gradually, a process that compounds the tidal forces that will destroy it, while a more rigid planet may hold its shape until being broken apart by these same forces.

All of this could be useful as we try to learn more about the planet’s characteristics. From the paper:

The variation of rigidity of a planet may produce a small but detectable signal in the cases that were tested as one gets very close to the fluid Roche limit, and again it is important to remember planets have also been detected interior to the fluid Roche limit (the inner distance bound). Merely the constraining of tidal bulge amplitude along with Roche limit considerations may put meaningful limits on interior structure. The ability to directly constrain the shape of a planet would provide clues towards tidal theory, the orbital configuration of the system and bulk properties of the planet.

Not many M-dwarf planetary systems are likely to show the signature of worlds near the Roche limit, but the paper argues that the general physical principles in play here may also help us interpret the signatures of planets in particular orbital resonances or other configurations. Several dozen ‘hot Jupiters’ have been found that should, by virtue of their proximity to the Roche limit, show observable effects. For solid planets, the large transit depth may make red dwarf planets near the Roche limit an excellent realm for further study as we learn to interpret what any planetary deformations can tell us about their internal characteristics.

The paper is Saxena et al., “The observational effects and signatures of tidally distorted solid exoplanets,” published online by Monthly Notices of the Royal Astronomical Society 14 December 2014 (abstract / preprint).



Tightening the Focus on Near Earth Asteroids

by Paul Gilster on December 15, 2014

The impact at Tunguska, Siberia on June 30,1908, evidently a small asteroid, devastated 1300 square kilometers, which works out to be the equivalent of a large metropolitan area. June 30, 2015 is thus an appropriate date to launch Asteroid Day, a global awareness campaign to put the issue of dangerous impacts in front of as many people as possible. An early December press conference at the London Science Museum, hosted by Lord Martin Rees, UK Royal Astronomer, announced the campaign and released a declaration of needed action:

  • Employ the available technology to detect and track near-Earth asteroids that threaten human populations
  • A rapid hundred-fold (100x) acceleration of the discovery and tracking of NEOs
  • Global adoption of Asteroid Day on June 30, 2015, to heighten awareness of the asteroid hazard and our efforts to prevent future impacts

The list of scientists, business leaders and artists behind the 100x Declaration, as it’s being called, is an impressive one that includes Jill Tarter, Kip Thorne, Stewart Brand, Richard Dawkins, Google’s Peter Norvig, astrophysicist and guitarist Brian May, Alexei Leonov, Jim Lovell and Rusty Schweickart, a group numerous and diverse enough that I’ll send you to the list of signatories available on the Asteroid Day website for more. Founding partners of the event include The Planetary Society, Astronomy Magazine, the Association of Space Explorers (ASE), and the California Academy of Sciences. ASE chairman Tom Jones explains:

“Finding hazardous asteroids early through an accelerated search program is the key to preventing future destructive impacts. The 100x Declaration will focus space policymakers on that important goal. ASE called last year for a stepped-up, global search effort; this can lead within a decade to an international deflection demonstration mission to show we know how to nudge an asteroid. Once we know what’s coming, we can design an effective space deflection campaign against dangerous objects we find.”

Visualizing Asteroid Data

In November, NASA’s Near Earth Object Program released a map showing a visualization of data gathered between 1994 and 2013. Atmospheric impacts large enough to produce a fireball occurred on 556 occasions during this period, with almost all the small asteroids disintegrating before they reached the ground. The most prominent exception is the Chelyabinsk event in 2013, the largest asteroid to cause surface damage during this period. We learn that asteroids no larger than a meter in diameter hit the atmosphere and break apart about every other week. The Chelyabinsk event was caused by the explosion in the atmosphere of an asteroid thought to be about 20 meters in size.


Image: This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth’s atmosphere to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”. Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size. Credit: Planetary Science.

The good news is that the Earth’s atmosphere screens small asteroids from the surface quite effectively, but Lindley Johnson (NASA NEO Observations Program) says that data like these will help us figure out how often asteroids large enough to cause ground damage do get through. According to this JPL news release, the NEO Observations Program has identified 96 percent of the estimated population of one-kilometer or larger asteroids, with a goal of finding 90 percent of NEO’s larger than 140 meters in diameter. These are estimated to be as much as 25 times more numerous than the one kilometer asteroids. The NEO Observations Program finds and tracks asteroids whose orbits bring them within 50 million kilometers of Earth’s orbit.

Two other notes: A 2013 paper from Peter Brown and team reports that existing telescopic surveys have discovered about 500 near-Earth asteroids that are 10-20 meters in diameter — that’s Chelyabinsk size — out of an estimated near-Earth asteroid population of roughly 20 million, “… implying that a significant impactor population at these sizes could be present but not yet cataloged in the discovered near-Earth asteroid population.” All of which gives the 100x Declaration some punch and underscores how much we still have to do.

And in a paper just released on the arXiv site, Clemens Rumpf (University of Southampton, UK) unveils ARMOR, the Asteroid Risk Mitigation Optimization and Research tool currently being developed at the university. The tool calculates the impact location and probability distribution on Earth’s surface (the so-called ‘risk corridor’), using (in this paper) a sample size of ten asteroids. Future iterations of ARMOR may prove useful in assessing the risk of individual asteroids.

The Brown paper is “The flux of small near-Earth objects colliding with the Earth,” Nature, Vol. 420 (21 Nov. 2002), pp. 294-296 (abstract). The Rumpf paper (thanks to Ashley Baldwin for the tip) is “Global Asteroid Risk Analysis” (abstract).



Of an Archive on the Moon

by Paul Gilster on December 12, 2014

Lunar Mission One is an interesting private attempt to put a payload on the lunar surface, a crowdsourced project aimed at doing good science and deepening public participation in spaceflight. Remembering the Apollo days, I’m always interested in seeing what can be done to renew interest in space, and having the chance to make a contribution toward such a self-starting space mission is undeniably attractive. As witness Lunar Mission One’s pitch on Kickstarter, which has aimed for an ambitious £600,000 and has already raised £520,341.

That figure is as of this morning, with five days to go in the attempt, and it’s clear enough that £600,000 won’t buy a lunar mission of considerable complexity, as this one is. But it’s enough to take an effort that has been seven years in the building to the next level, which means establishment of working management teams and the beginning of procurement planning and risk assessment. That turns what has been a part-time volunteer project into a full-time effort.

Writing about a lunar mission is a bit out of the norm for Centauri Dreams, where I decided from the beginning to adopt a focus on the outer planets and beyond, meaning deep space technologies that could lead to an eventual interstellar effort and all that entails. But what caught my eye about Lunar Mission One is that there is a ‘deep time’ aspect to the whole thing, one that looks past short-term results to think about the future of the species and how we can connect to it. The connection grows out of Lunar Mission One’s ambitious science agenda.


Going Deep at the Pole

To explain that, let me discuss the larger plan: The Lunar Mission One probe will land at the lunar south pole. Aboard it will be a 2-meter drill connected by cable to the spacecraft, with which controllers will remotely drill a 5-centimeter borehole. The plan here is to retrieve cylindrical rock cores for analysis by instrumentation aboard the craft, and the drilling time is envisioned as lengthy — three to four months — until a target depth of 20 meters has been achieved, although the planners speculate that the drill might reach depths up to 100 meters.

This sets up some interesting science, for even the nominal 20 meter goal takes us into unexplored terrain — I believe the deepest we’ve reached from any spacecraft on the Moon is no more than a couple of meters. Enormously useful geological measurements could result and may help us better understand elements of the early Solar System’s history, including the late heavy bombardment period. Moreover, Lunar Mission One should be able to study the surrounding surface at the pole, analyzing any local materials that might aid a future human base.

But it’s what happens when the drilling is done that particularly interests me. When I spoke of ‘deep time,’ I was referring to the plan to use the borehole — after the science goals have been achieved — to lower a publicly assembled archive of life on Earth, the history of our species and a database stuffed with information about our biosphere, deep below the lunar surface. The substantial protection provided by tens of meters of lunar regolith should make this an unusually long-lasting capsule, one the planners believe can remain intact for perhaps a billion years.

Lunar Mission One also has a private archive, what it describes as millions of individual ‘memory boxes’ to which contributors to the project will be able to upload data. Longer-term funding for the mission, it is hoped, will grow out of what will become a ten-year opportunity to sell these memory boxes, which could contain photos, video, audio or any other digital information. The plan is to store tens of terabytes of such material within the private archive, with larger contributions to the project allowing the donor to buy larger amounts of storage.

To boost donations, individual memory boxes might do the trick, but my interest is in the development of the public archive, which forces decisions about how we view ourselves, what our priorities are, and what we choose to be preserved for an unknowable future generation to find. The assembly of that kind of content is a fascinating process, one that Centauri Dreams regular Heath Rezabek has devoted himself to developing through his Vessels project, which you can read about in posts like Deep Time: The Nature of Existential Risk.

The term ‘deep time’ invokes Gregory Benford’s 1999 book of that name (Deep Time: How Humanity Communicates Across Millennia), which in turn harkens back to a 1992 paper in which Benford discussed a program of freezing and preserving species in threatened ecospheres as a response to the loss of biodiversity in our era. What can we do, Benford asked, to create such a ‘Library of Life,’ and how should we assemble the samples? All this is discussed in the later book within the context of how humans communicate with each other across historical eras, questions raised by the great monuments of history, and by engineering projects like storage sites for radioactive materials that must long outlive their makers.

Lunar Mission One is exploring this terrain with its announced purpose of creating an archive that, if I read its Kickstarter page correctly, will be assembled using its core crowdsourcing methods. In my judgement, assembling a representation of our species is a highly productive exercise. Think of the Voyager Golden Record, or the ongoing private attempt to craft an archive that will be uploaded to New Horizons after its outer system mission is complete, if NASA signs off on the plan. We question our basic priorities when we look long-term, gaining perspective on the values that count, and perhaps learning where our strongest efforts need to be re-focused.

Long-haul archives, in other words, are not only about the future, but about our ability to make course corrections as we back off to view ourselves in the context of history and of nature.

So good luck to Lunar Mission One. We need projects that look at these matters. We need not only single ‘time capsule’ archives but a host of archival sites that are designed, like the Long Now Foundation’s 10,000 Year Clock, to last into a deep future against which our own lifetimes are acted out on the smallest of scales. If selling personal memory boxes is what it takes to get a serious public archive buried deep within the Moon, then let’s hope this one of many possible archives can be completed as planned, a gesture to the future from its myriad creators.



Rosetta: New Findings on Cometary Water

by Paul Gilster on December 11, 2014

Where did the water in Earth’s oceans come from? It’s an open question, but new data from the Rosetta mission, in particular its ROSINA instrument (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) indicate that terrestrial water probably did not come from comets like 67P/Churyumov-Gerasimenko, around which Rosetta has been orbiting since August. There is little doubt that water reached Earth through bombardment from small bodies early in the planet’s history, but the Rosetta findings sharpen the question of where these objects came from.


Image: This composite is a mosaic comprising four individual NAVCAM images taken from 19 miles (31 kilometers) from the center of comet 67P/Churyumov-Gerasimenko on Nov. 20, 2014. The image resolution is 10 feet (3 meters) per pixel. Credit: ESA.

At work here is analysis of the ratio between hydrogen and deuterium, a heavy form of hydrogen with one proton and one neutron in the nucleus (common hydrogen lacks the neutron). This D/H ratio on 67P/Churyumov-Gerasimenko turns out to be over three times the terrestrial value, among the highest values yet measured in the Solar System, making it unlikely that comets like these supplied Earth’s oceans. Back in 1986, the European Giotto mission to comet Halley found a D/H ratio twice that of Earth’s, seeming to rule out Oort Cloud comets as the source.

67P/Churyumov-Gerasimenko and Halley are two different kinds of comet, so let’s explore this. Cometary origins are complex because of interactions in the early Solar System. Long-period comets that swing into the inner system from the distant Oort Cloud are thought to have formed originally somewhere beyond the snowline in the region where Uranus and Neptune now orbit, to be scattered by subsequent gravitational interactions with the large outer planets. 67P/Churyumov-Gerasimenko is a Jupiter-family comet, a class whose origins are believed to lie beyond Neptune in the Kuiper Belt. Comets like these sometimes have their orbits disrupted so that they fall under the gravitational influence of Jupiter, hence their designation.

In contrast to 67P/Churyumov-Gerasimenko, comet Hartley 2, which was examined by the European Space Agency’s Herschel spacecraft in 2011, turned out to have a deuterium/hydrogen ratio similar to Earth’s. The discrepancy is surprising because Hartley 2 is also a Jupiter-family comet, and models of the early Solar System produce a D/H ratio for these comets more like 67P/Churyumov-Gerasimenko, even higher than their Oort Cloud cousins.

The disparity may indicate that we know less about Jupiter-family comets and their origins than we realized. The new Rosetta data tell us that this family of comets is hardly uniform, and thus nudge us away from them and toward asteroids as the primary water delivery mechanism. Kathrin Altwegg (University of Bern) is principal investigator for the ROSINA instrument and lead author of the paper on this work, which has just appeared in Science:

“This surprising finding could indicate a diverse origin for the Jupiter-family comets – perhaps they formed over a wider range of distances in the young Solar System than we previously thought. Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.”

The measurements in question were made in the first month after Rosetta’s arrival at 67P/Churyumov-Gerasimenko. With the Rosetta data, we now have D/H information about eleven comets, finding that only Hartley 2 shows a ratio matching the composition of Earth’s water. We also know that meteorites with an origin in the asteroid belt show a good fit with Earth’s D/H ratio. Although the overall water content of asteroids is lower than we find in comets, a large number of asteroid impacts could account for the primary delivery mechanism.

Meanwhile, the mission continues, and will for some time. Rosetta has now been at 67P/Churyumov-Gerasimenko for 127 days. Perihelion is 244 days away.

The paper is Altwegg et al., “67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio,” published online in Science 10 December 2014 (abstract). This ESA news release is helpful.



Why Interstellar Matters

by Paul Gilster on December 10, 2014

My friend Frank Taylor was in town over the Thanksgiving holiday, having flown in from South Africa. With his wife Karen, Frank has spent the years since 2009 circumnavigating the globe aboard a 50-foot catamaran called Tahina, an adventure chronicled with spectacular photography on the Tahina Expedition blog. I highly recommend the site for anyone interested in travel and the sea, not to mention how high tech has transformed the ancient art of sailing. But when we spoke recently just before Frank returned to Africa, he had another kind of high tech in mind. Specifically, what had I thought about the film Interstellar?

I haven’t delayed my comments on the movie intentionally, but I was slow in getting to see it, missing the opportunity at the end of the Tennessee Valley Interstellar Workshop and then getting involved in recent activities including the One Earth New Horizons Message workshop at Stanford. I also wanted to read Kip Thorne’s The Science of Interstellar (Norton, 2014) and give the movie a second viewing. All that behind me, it’s time to explain why I was surprised by Interstellar. My expectations for Hollywood science fiction are always low, as I’ve found that today’s filmmaking wizardry all too often masks serious flaws in plot and character.

I can find problems in Interstellar as well, as many reviewers have, but I think this is an important movie whose mistakes aren’t significant compared to what it accomplishes. Interstellar is a movie that will baffle a large part of its audience, the movie-going public far more comfortable with battles in space and sleek starships like the Enterprise. This is not an audience that will easily follow the twists and turns through time and space that Christopher Nolan has created. But Nolan’s attention to detail, his partnership with Thorne, and his insistence on scientific plausibility wherever possible will get through to an important subset.


I’m talking about younger people with an interest in science for whom the movie’s stunning visuals will impel them to learn how to untangle the plot. For the intellectually curious, Interstellar is a tandem creation, a movie/book duality where each plays off the other — the motivated minority will want to immerse themselves in both. The film’s plot is demanding and operates at various degrees of believability, but there is a science puzzle to be untangled here, one to which Thorne’s book offers the key. When I was researching Centauri Dreams back in 2002-2004, I was surprised at how many scientists and aerospace engineers told me they had chosen their fields because of science fiction novels like Poul Anderson’s Tau Zero. This movie will have the same effect. In fact, I can think of no movie that is so likely to create careers in the sciences, particularly physics, than this one.

Let’s talk about why. Here I get into details and suppose I should say that there may be spoilers below for those who haven’t yet seen Interstellar, so proceed with caution. I could focus on various issues, from a worldwide blight to passage through a wormhole, but the film’s treatment of black holes is what I’ll use as my working material. The wormhole itself, out near Saturn’s orbit and an apparent way out for a desperate humanity, is richly described in Thorne’s chapters, especially with regard to the special effects that bring it to life.

Our protagonist, Cooper, must learn which of three planets in an unusual system dominated by an enormous black hole called Gargantua is most suited for humans. When he and his team need to get to one of these, Miller’s Planet, from their parking orbit near the black hole, they have to produce huge velocity changes in the range of 100,000 kilometers per second. Thorne goes through the physics of this, including the bizarre time distortion on a world so close to a black hole. The upshot is that a gravitational slingshot maneuver must be performed. The movie skims over the matter quickly, but Cooper does discuss how this must have been done later, when he talks about using a neutron star to decelerate. The neutron star is a bit of a fudge — it turns out it wouldn’t be big enough to force the needed maneuver, but an intermediate-mass black hole would do the trick. Thorne made this case to Nolan but the director stuck with the neutron star.

That’s a scientific error forced by Hollywood values. Thorne relates his objections to Nolan during the re-writing of the screenplay and goes on to explain what happened:

…he [Nolan] didn’t want to confuse his mass audience by having more than one black hole in the movie. One black hole, one wormhole, and also a neutron star, along with Interstellar’s other rich science, all to be absorbed in a fast-paced two hour film; that was all Chris thought he could get away with. Recognizing that strong gravitational slingshots are needed to navigate near Gargantua, Chris included one slingshot in Cooper’s dialog, at the price of using a scientifically implausible deflector: the neutron star instead of a black hole.

Interstellar is closer to three hours than two (Thorne was writing before the film was finalized), but does anything else about this bother you? I’m going to argue that the combination of Nolan’s movie and Thorne’s book — and the fruitful collaboration the two engaged in throughout — induces the kind of puzzle-solving ethos that will prompt many a young mind to dig deeper into the movie’s physics. Nolan made a choice with a mass audience in mind, but the framework of that choice is laid bare in Thorne’s book, which goes on to explain how careful Nolan was to stick to scientific plausibility where he felt that he could. Filmmaking is always a matter of compromise, but Nolan was surprisingly tough. Finding where Interstellar works and where it stretches science out of shape is itself a lesson in problem solving.

The point is, the director was thinking about these things within a framework that, in terms of its spectacular visuals, is meticulous about getting the larger details right. Think about the accretion disk around the black hole Gargantua. Here we’re seeing a magnetic field in the process of converting gravitational energy into heat and then light — the field, explains Thorne, provides the friction that slows the circumferential motion of gas in the disk even as the black hole’s gravity tries to speed up the infalling material, with kinetic energy being converted into heat and light along the way. But go to the projections of black hole accretion disks you’ll find on the Net or in technical publications and you’ll find Nolan’s depiction is far more spectacular. Another Hollywood-enforced choice?

No. What Nolan and Thorne added was the gravitational lensing of the disk by its own black hole, an effect explored through computer code developed for the film. While you would expect that portion of the disk behind the black hole to be out of sight, gravitational lensing produces two images of it, one above and the other below Gargantua. This is special effects wizard Eugénie van Tunzelmann’s work, carefully wrought to produce the nested effect Thorne describes:

Inside these primary images, we see thin secondary images of the disk, wrapping over and under the shadow, near the shadow’s edge. And if the picture were made much larger, you would see tertiary and higher-order images, closer and closer to the shadow.


Moreover, Gargantua’s distortion of spacetime distorts the disk images, pushing the perceived disk away from the shadow on one side and toward the shadow on the other, creating an effect that appears lopsided. Here again Nolan intervened in an attempt to avoid confusion, especially as the audience tried to work out the reason for the lopsidedness of the disk and the star patterns created near its edge. So for the purposes of the imagery, he slowed the spin of Gargantua to reduce the effect, just as van Tunzelmann removed the Doppler shift created by the disk’s motion, which would have created an even more lopsided and confusing effect.

What pleases me here is that these changes and their rationale are thoroughly explored in Kip Thorne’s book, which likewise offers those intrigued with such visualizations the opportunity to explore how they could be fine-tuned and rendered with greater accuracy. Given the Hollywood culture in which he operates, I think that Christopher Nolan produced a movie with as much scientific accuracy as he could get past his producers, given the imperative for ratings and box office sales.

Most people are going to be wowed by the visuals; some will be dismayed by the all but supernatural intervention of beings from a higher dimension who may be our descendants. But a few, the ones I’m focused on, are going to use the high points of this movie — its unapologetic call for exploration, its entanglement with science as a form of quest — to choose to learn more, and there is no more engaging a guide than Kip Thorne to show them the way. Thorne says he was moved by the underlying message of Interstellar that the universe can be viewed optimistically because our species is capable of choosing its future:

But doing so, controlling our own fate, requires that a large fraction of us understand and appreciate science: How it operates. What it teaches us about the universe, the Earth, and life. What it can achieve. What its limitations are, due to inadequate knowledge or technology. How those limitations may be overcome. How we transition from speculation to educated guess to truth. How extremely rare are revolutions in which our perceived truth changes, yet how very important.

Thirty years from now there will be working scientists who explain to interviewers how Interstellar, a movie flawed by occasional mawkishness (think of Amelia Brand’s regrettable lines about love being the fifth dimension), weighed down by what may be the ultimate deus ex machina (in the form of Cooper operating through the tesseract), and reactive to Hollywood’s relentless popular ethos, nonetheless captured their imagination so that they read a book (Thorne’s) that helped to launch them down a path whose end they could not imagine. I call that a fine result, and reiterate my surprise in finding a Hollywood blockbuster I can seriously recommend.



Deep Space: Moving Toward Encounter Mode

by Paul Gilster on December 9, 2014

No spacecraft has ever traveled further to reach its primary target than New Horizons, now inbound to Pluto/Charon. From 4.6 billion kilometers from Earth (four hours, 26 minutes light travel time), the spacecraft has sent confirmation that its much anticipated wake-up call from ground controllers was a success. Since December 6, New Horizons has been in active mode, a state whose significance principal investigator Alan Stern explains:

“This is a watershed event that signals the end of New Horizons crossing of a vast ocean of space to the very frontier of our solar system, and the beginning of the mission’s primary objective: the exploration of Pluto and its many moons in 2015.”


Image: Pluto and Charon, in imagery taken by New Horizons in July of 2014. Covering almost one full rotation of Charon around Pluto, the 12 images that make up the movie were taken with the spacecraft’s best telescopic camera – the Long Range Reconnaissance Imager (LORRI) – at distances ranging from about 429 million to 422 million kilometers. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

Not that hibernation is an unusual event for the spacecraft. We’ve followed several cycles here on Centauri Dreams, but it’s startling to realize that New Horizons has gone through eighteen hibernation periods, with two-thirds of its flight time in that state. A weekly beacon stayed alive during these periods, as did the onboard flight computer that broadcast its status tone, but much of the spacecraft was powered down to protect system components. For this special awakening, English tenor Russell Watson recorded a special version of ‘Where My Heart Will Take Me,’ which was played in New Horizons mission operations upon wake-up confirmation.

Pluto observations begin on January 15, with closest approach on July 14, and by mid-May, we will begin receiving views of Pluto and its moons that are higher in quality than anything the Hubble Space Telescope has yet given us. More on the awakening of New Horizons on this JHU/APL page. Meanwhile, the private effort to upload a message from Earth to New Horizons following the end of its science mission continues. If NASA gives the go-ahead, Jon Lomberg’s team will crowdsource content for the One Earth New Horizons Message. A workshop discussing message methods and content just concluded last week at Stanford.

The View from the Asteroid Belt

Speaking of images better than Hubble, we’ve certainly managed that with the Dawn mission, which brought us spectacular vistas from Vesta during its fourteen months in orbit around the asteroid. Now we can look forward to topping Hubble’s views of Ceres, the spacecraft’s next target. Below is an image that, while not yet better than Hubble can manage, does give us an idea of the spherical shape of the asteroid (click to enlarge). Dawn is now 1.2 million kilometers out, about three times the Earth-Moon distance from its target.


Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Dawn will be captured into orbit around Ceres in March, but by early 2015, we’ll be seeing images at higher resolution than Hubble has yet provided. The approach phase begins on December 26, with the nine-pixel-wide image just released serving as a final calibration of the spacecraft’s science camera. With both missions, we are pushing into unknown territory, about to see things in greater detail than our best telescopes can offer. A bit of the old Voyager and Pioneer feeling has me in its grip, a confirmation of our human need to explore and a validation of all the hard work that got us here.


At left is Ceres in the best photo we currently have, a color Hubble image. These observations were made in both visible and ultraviolet light between December 2003 and January 2004, showing brighter and darker regions that may be impact features or simply different types of surface material. 950 kilometers across, Ceres may have an interior differentiated between an inner core, an ice mantle, and a relatively thin outer crust.

Every time I see this image I remember Alfred Bester’s The Stars My Destination, a 1956 novel in which protagonist Gulliver Foyle takes the pseudonym Fourmyle of Ceres as part of the unfolding of his ingenious plan for revenge. The asteroid pops up in many science fiction tales (Larry Niven’s ‘Known Space’ stories come particularly to mind), but perhaps none as compelling as the one Dawn is about to tell us.