Information and Cosmic Evolution

by Paul Gilster on February 16, 2015

Keeping information viable is something that has to be on the mind of a culture that continually changes its data formats. After all, preserving information is a fundamental part of what we do as a species — it’s what gives us our history. We’ve managed to preserve the accounts of battles and migrations and changes in culture through a wide range of media, from clay tablets to compact disks, but the last century has seen swift changes in everyday products like the things we use to encode music and video. How can we keep all this readable by future generations?

The question is challenging enough when we consider the short term, needing to read, for example, data tapes for our Pioneer spacecraft when we’ve all but lost the equipment needed to manage the task. But think, as we like to do in these pages, of the long-term future. You’ll recall Nick Nielsen’s recent essay Who Will Read the Encyclopedia Galactica, which looks at a future so remote that we have left the ‘stelliferous’ era itself, going beyond the time of stars collected into galaxies, which is itself, Nick points out, only a small sliver of the universe’s history.


Can we create what Isaac Asimov called an Encyclopedia Galactica? If you go back and read Asimov’s Foundation books, you’ll find that the Encyclopedia Galactica appears frequently, often quoted as the author introduced new chapters. From its beginnings in a short story called “Foundation” (Astounding Science Fiction, May 1942), the Encyclopedia Galactica was seen as the entirety of knowledge throughout a widespread galactic empire. Carl Sagan introduced the idea to a new audience in his video series Cosmos as a cache of all information and knowledge.

Image: The May, 1942 issue of Astounding Science Fiction, containing the first of the short stories that would eventually be incorporated into the Foundation novels.

Now we have an interesting new paper from Stefano Mancini and Roberto Pierini (University of Camerino, Italy) and Mark Wilde (Louisiana State University) that looks at the question of information viability. An Encyclopedia Galactica is going to need to survive in whatever medium it is published in, which means preserving the information against noise or disruption. The paper, published in the New Journal of Physics, argues that even if we find a technology that allows for the perfect encoding of information, there are limitations that grow out of the evolution of the universe itself that cause information to become degraded.

Remember, we’re talking long-term here, and while an Encyclopedia Galactica might serve a galactic population robustly for millions, perhaps billions of years, what happens as we study the fate of information from the beginning to the end of time? Mancini and team looked at the question with relation to what is called a Robertson-Walker spacetime, which as Mark Wilde explains in this video abstract of the work, is a solution of Einstein’s field equations of general relativity that describes a homogeneous, isotropic, expanding or contracting universe.

In addition to Wilde’s video, let me point you to The Cosmological Limits of Information Storage, a recent entry on the Long Now Foundation’s blog. As for the team’s method using the Robertson-Walker spacetime as the background for its development of communication theory models, it is explained this way in the paper:

… we can consider any quantum state of the matter field before the expansion of the universe begins and define, without ambiguity, its particle content. We then let the universe expand and check how the state looks once the expansion is over. The overall picture can be thought of as a noisy channel into which some quantum state is fed. Once we have defined the quantum channel emerging from the physical model, we will be looking at the usual communication task as information transmission over the channel. Since we are interested in the preservation of any kind of information, we shall consider the trade-off between the different resources of classical and quantum information.

In other words, encoded information is modeled against an expanding universe to see what happens to it. The result challenges the idea that there is any such thing as perfectly stored information, for the paper finds that over time, as the universe expands and evolves, a transformation inevitably occurs in the quantum space in which it is encoded. Noise is the result, what the authors refer to as an ‘amplitude damping channel.’ Information that is encoded into a storage medium is inevitably corrupted by changes to the quantum state of the medium.

Cosmology comes into play here because the paper argues that faster expansion of the cosmos creates more noise. We can encode our information in the form of bits or we can use information stored and encoded by the quantum state of particular particles, but in both cases noise continues to mount as the universe continues to expand. Collecting all the material for our Encyclopedia Galactica may, then, be a smaller challenge than preserving it in the face of cosmic evolution. On the time scales envisioned in Nick Nielsen’s essay (and studied at length in Fred Adams’ and Greg Laughlin’s book The Five Ages of the Universe: Inside the Physics of Eternity, the keepers of the encyclopedia have their work cut out for them.

Preserving the Encyclopedia Galactica will demand, it seems, continual fixes and long-term vigilance. But consider the researchers’ thoughts on the direction for future work:

…one could also cope with the degradation of the stored information by intervening from time to time and actively correcting the contents of the memory during the evolution of the universe. In this direction, channel capacities taking into account this possibility have been introduced… In another direction, and much more speculatively, one might attempt to find a meaningful notion for entanglement assisted communication in our physical scenario by considering Einstein-Rosen bridges… or entanglement between different universe’s eras, related to dark energy.

Now we’re getting speculative indeed! I’ve left out the references to papers on each of the possibilities within that quotation — see the paper, which is available on arXiv, for more. Mark Wilde notes in the video referenced above that another step forward would be to look at more general models of the universe in which information could be encoded in such exotic scenarios as the spacetime near a black hole. The latter is an interesting thought, and my guess is that we’ll have new work from these researchers delving into such models in the near future, a time close enough to our own that the data should still be viable.

The paper is Mancini et al., “Preserving Information from the beginning to the end of time in a Robertson-Walker spacetime,” New Journal of Physics 16 (2014), 123049 (abstract / full text).



A Full Day at Pluto/Charon

by Paul Gilster on February 13, 2015

Have a look at the latest imagery from the New Horizons spacecraft to get an idea of how center of mass — barycenter — works in astronomy. When two objects orbit each other, the barycenter is the point where they are in balance. A planet orbiting a star may look as if it orbits without influencing the much larger object, but in actuality both bodies orbit around a point that is offset from the center of the larger body. A good thing, too, because this is one of the ways we can spot exoplanets, by the observed ‘wobble’ in the stars they orbit.

The phenomenon is really evident in what the New Horizons team describes as the ‘Pluto-Charon dance.’ Here we have a case where the two objects are close enough in size — unlike planet and star, or the Moon and the Earth — so that the barycenter actually falls outside both of them. The time-lapse frames in the movie below show Pluto and Charon orbiting a barycenter above Pluto’s surface, where Pluto and Charon’s gravity effectively cancel each other. Each frame here has an exposure time of one-tenth of a second.


Charon is about one-eighth as massive as Pluto. The images in play here come from New Horizons’ Long-Range Reconnaissance Imager (LORRI), being made between January 25th and 31st of this year. The New Horizons team is in the midst of an optical navigation (Opnav) campaign to nail down the locations of Pluto and Charon as preparations continue for the July 14th flyby. None of the other four moons of Pluto are visible here because of the short exposure times, but focus in on Charon. We’re looking at an object about the size of Texas.

Now take a look at Pluto/Charon back in 1978 when James Christy, an astronomer at the U.S. Naval Observatory, could see it using the 1.55-m (61-inch) Kaj Strand Astrometric Reflector at the USNO Flagstaff Station in Arizona. Christy was studying what was then considered to be a solitary ‘planet’ (since demoted) when he noticed that in a number of the images, Pluto seemed to be elongated, a distortion in shape that varied with respect to background stars over time. The discovery of a moon was formally announced in early July of that year by the International Astronomical Union. Charon received its official name in 1985.


Image: What Pluto/Charon looked like to James Christy in 1978. Credit: U.S. Naval Observatory.

The New Horizons time-lapse movie shows an entire rotation of each body, the first of the images being taken when the spacecraft was 203 million kilometers from Pluto. The last frame, six and a half days later, was taken when New Horizons was 8 million kilometers closer. Alan Stern (Southwest Research Institute), principal investigator for New Horizons, notes the significance of the latest imagery:

“These images allow the New Horizons navigators to refine the positions of Pluto and Charon, and they have the additional benefit of allowing the mission scientists to study the variations in brightness of Pluto and Charon as they rotate, providing a preview of what to expect during the close encounter in July.”

That’s an encounter that will close an early chapter in space exploration — all nine of the objects formerly designated planets will have had close-up examination — but of course it opens up yet another, as New Horizons looks toward an encounter with a Kuiper Belt object as it moves ever outward. Just as our Voyagers are still communicating long after Voyager 2 left Neptune, New Horizons gives us much to look forward to.



What Comets Are Made Of

by Paul Gilster on February 12, 2015

When the Rosetta spacecraft’s Philae lander bounced while landing on comet 67P/Churyumov-Gerasimenko last November, it was a reminder that comets have a hard outer shell, a black coating of organic molecules and dust that previous missions, like Deep Impact, have also observed. What we’d like to learn is what that crust is made of, and just as interesting, what is inside it. A study out of JPL is now suggesting possible answers.

Antti Lignell is lead author on a recent paper, which reports on the team’s use of a cryostat device called Himalaya that was used to flash freeze material much like that found in comets. The procedure was to flash freeze water vapor molecules at temperatures in the area of 30 Kelvin (minus 243 degrees Celsius). What results is something called ‘amorphous ice,’ as explained in this JPL news release. Proposed as a key ingredient not only of comets but of icy moons, amorphous ice preserves the mix of water with organics along with pockets of space.

JPL’s Murthy Gudipati, a co-author of the paper on this work, compares amorphous ice to cotton candy, while pointing out that on places with much more moderate temperatures, like the Earth, all ice is in crystalline form. But comets, as we know, can change drastically as they approach the Sun. To mimic this scenario, the researchers used their cryostat instrument to gradually warm the amorphous ice they had created to 150 Kelvin (minus 123 degrees Celsius).

What happened next involved the kind of organics called polycyclic aromatic hydrocarbons (PAHs) common in deep space. These had been infused in the ice mixture that Lignell and Gudipati created. Lignell describes the result:

“The PAHs stuck together and were expelled from the ice host as it crystallized. This may be the first observation of molecules clustering together due to a phase transition of ice, and this certainly has many important consequences for the chemistry and physics of ice.”

Expelling the PAHs meant that the water molecules could then form the tighter structures of crystalline ice. The lab had produced, in other words, a ‘comet’ nucleus of its own, similar to what we have observed so far in space. Gudipati likens the lab’s ‘comet’ to deep fried ice cream — an extremely cold interior marked by porous, amorphous ice with a crystalline crust on top that is laced with organics. What we could use next, he notes, is a mission to bring back cold samples from comets to compare to these results.


Image: Rosetta NAVCAM image of Comet 67P/C-G taken on 6 February from a distance of 124 km to the comet centre. In this orientation, the small comet lobe is to the left of the image and the large lobe is to the right. The image has been processed to bring out the details of the comet’s activity. The exposure time of the image is 6 seconds. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

Meanwhile, we have the spectacular imagery above from Rosetta at comet 67P/Churyumov-Gerasimenko. What the European Space Agency refers to as ‘a nebulous glow of activity’ emanates from all over the sunlit surface, but note in particular the jets coming out of the neck region and extending toward the upper right. In this year of celestial marvels (Ceres, Pluto/Charon, and Rosetta at 67P/Churyumov-Gerasimenko), we’re seeing what happens to a comet as it warms and begins to vent gases from all over its surface. We’re now going to be able to follow Rosetta as it studies the comet from a range of distances, a view that until this year was solely in the domain of science fiction writers. What a spectacle lies ahead!

The paper is Lignell and Gudipati, “Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature,” published online by the Journal of Physical Chemistry on Oct0ber 10, 2014 (abstract).



Overcoming Tidal Lock around Lower Mass Stars

by Paul Gilster on February 11, 2015

One of the big arguments against habitable planets around low mass stars like red dwarfs is the likelihood of tidal effects. An Earth-sized planet close enough to a red dwarf to be in its habitable zone should. the thinking goes, become tidally locked, so that it keeps one face toward its star at all times. The question then becomes, what kind of mechanisms might keep such a planet habitable at least on its day side, and could these negate the effects of a thick dark-side ice pack? Various solutions have been proposed, but the question remains open.

A new paper from Jérémy Leconte (Canadian Institute for Theoretical Astrophysics, University of Toronto) and colleagues now suggests that tidal effects may not be the game-changer we assumed them to be. In fact, by developing a three-dimensional climate model that predicts the effects of a planet’s atmosphere on the speed of its rotation, the authors now argue that the very presence of an atmosphere can overcome tidal effects to create a cycle of day and night.

The paper, titled “Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars,” was published in early February in Science. The authors note that the thermal inertia of the ground and atmosphere causes the atmosphere as a whole to lag behind the motion of the star. This is seen easily on Earth, when the normal changes we expect from night changing to day do not track precisely with the position of the Sun in the sky. Thus the hottest time of the day is not when the Sun is directly overhead but a few hours after this.

From the paper:

Because of this asymmetry in the atmospheric mass redistribution with respect to the subsolar point, the gravitational pull exerted by the Sun on the atmosphere has a nonzero net torque that tends to accelerate or decelerate its rotation, depending on the direction of the solar motion. Because the atmosphere and the surface are usually well coupled by friction in the atmospheric boundary layer, the angular momentum transferred from the orbit to the atmosphere is then transferred to the bulk of the planet, modifying its spin.

This effect is relatively minor on Earth thanks to our distance from the Sun, but is more pronounced on Venus, where the tug of tidal friction that tries to spin the planet down into synchronous rotation is overcome by the ‘thermal tides’ caused by this atmospheric torque. But Venus’ retrograde rotation has been attributed to its particularly massive atmosphere. The question becomes whether these atmospheric effects can drive planets in the habitable zone of low mass stars out of synchronous rotation even if their atmosphere is relatively thin.

Pressure units in a planetary atmosphere are measured in bars — the average atmospheric pressure at Earth’s surface is approximately 1 bar (contrast this with the pressure on Venus of 93 bars). The paper offers a way to assess the efficiency of thermal tides for different atmospheric masses, with results that make us look anew at tidal lock. For the atmospheric tide model that emerges shows that habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar masses could overcome the effects of tidal synchronization. It’s a powerful finding, for the effects studied here should be widespread:

Atmospheres as massive as 1 bar are a reasonable expectation value given existing models and solar system examples. This is especially true in the outer habitable zone, where planets are expected to build massive atmospheres with several bars of CO2. So, our results demonstrate that asynchronism mediated by thermal tides should affect an important fraction of planets in the habitable zone of lower-mass stars.

Here is the graph from the paper that illustrates the results:


Image: Spin state of planets in the habitable zone.The blue region depicts the habitable zone, and gray dots are detected and candidate exoplanets. Each solid black line marks the critical orbital distance (ac) separating synchronous (left, red arrow) from asynchronous planets (right, blue arrow) for ps = 1 and 10 bar (the extrapolation outside the habitable zone is shown with dotted lines). Objects in the gray area are not spun down by tides. The error bar illustrates how limits would shift when varying the dissipation inside the planet (Q ~ 100) within an order of magnitude. Credit: Jérémy Leconte et al.

The result suggests that we may find planets in the habitable zone of lower-mass stars that are more Earth-like than expected. Do away with the permanent, frozen ice pack on what had been assumed to be the ‘dark side’ and water is no longer trapped, making it free to circulate. The implications for habitability seem positive, with a day-night cycle of weeks or months distributing temperatures, but Leconte remains cautious: “Whether this new understanding of exoplanets’ climate increases the ability of these planets to develop life remains an open question.”

The paper is Leconte et al., “Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars,” Science Vol. 347, Issue 6222 (6 February 2015). Abstract / preprint available. Thanks to Ashley Baldwin for a pointer to and discussion of this paper.



Twinkle: Studying Exoplanet Atmospheres

by Paul Gilster on February 10, 2015

A small satellite designed to study and characterize exoplanet atmospheres is being developed by University College London (UCL) and Surrey Satellite Technology Ltd (SSTL) in the UK. Given the engaging name Twinkle, the satellite is to be launched within four years into a polar low-Earth orbit for three years of observations, with the potential for an extended mission of another five years. SSTL, based in Guildford, Surrey and an experienced hand in satellite development, is to build the spacecraft, with scientific instrumentation in the hands of UCL.

The method here is transmission spectroscopy, which can be employed when planets transit in front of their star as seen from Earth. Starlight passing through the atmosphere of the transiting world as it moves in front of and then behind the star offers a spectrum that can carry the signatures of the various molecules there, a method that has been used on a variety of worlds like the Neptune-class HAT-P-11b and the hot Jupiter HD 189733b. The goal of the Twinkle mission is to analyze at least 100 planets ranging from super-Earths to hot Jupiters, producing temperatures and even cloud maps.

Hot Neptune

Image: This artist’s impression depicts a Neptune-class world grazing the limb of its star as seen from our vantage point. Analyzing starlight as transiting worlds pass in front of and then behind their star can tell us much about the constituents of the planet’s atmosphere. Credit: NASA/JPL-Caltech.

Giovanna Tinetti (UCL), lead scientist for the mission, describes it as the first mission dedicated to analyzing exoplanet atmospheres, adding that understanding the chemical composition of an atmosphere serves as a key to the planet’s background. Distance from the parent star, notes this UCL news release, affects the chemistry and physical processes driving an atmosphere, and the atmospheres of small, terrestrial-class worlds, like that of our own Earth, can evolve substantially from their initial state through impacts with other bodies, loss of light molecules, volcanic activity or the effect of life. The atmosphere, then, can help us trace a planet’s history as we learn whether it was born in its current orbit or migrated from another part of the system..

I should mention that Tinetti was deeply involved in the discovery of water and methane in the atmosphere of HD 189733b. From Tinetti’s website at University College London:

A key observable for planets is the chemical composition and state of their atmosphere. Knowing what atmospheres are made of is essential to clarify, for instance, whether a planet was born in the orbit it is observed in or whether it has migrated a long way; it is also critical to understand the role of stellar radiation on escape processes, chemical evolution and climate. The atmospheric composition is the only indicator able to discriminate an habitable/inhabited planet from a sterile one.

Twinkle was presented several days ago at an open meeting of the Royal Astronomical Society. Interestingly, the mission is being developed with a mixture of private and public sources, at a total cost of about £50 million, including launch. That number seems strikingly low to me, with mission designers claiming that Twinkle is a factor of ten times cheaper to build and operate than other spacecraft developed through international space agency programs. The low cost is being attributed to the use of off-the-shelf components and growing expertise in small mission development. These numbers will be worth remembering if Twinkle performs as expected.



We Have Fed Our Sea

by Paul Gilster on February 9, 2015

One of the reasons I do what I do is that when I was a boy, I read Poul Anderson’s The Enemy Stars. Published as a novel in 1959, the work made its original appearance the previous year in John Campbell’s Astounding Science Fiction as a two-part serial titled “We Have Fed Our Sea.” The reference is to Kipling’s poem “The Song of the Dead,” from which we read:

We have fed our sea for a thousand years
And she calls us, still unfed.
Though there’s never a wave of all her waves
But marks our English dead…

Space was, for Anderson, the new sea, one whose imperatives justify the sacrifices we make to conquer her, and “We Have Fed Our Sea” is a far better title for this work than its book version. Kipling writes:

We were dreamers, dreaming greatly, in the man-stifled town;
We yearned beyond the sky-line where the strange roads go down.
Came the Whisper, came the Vision, came the Power with the Need…

Enemy Stars

I bought The Enemy Stars at the Kroch’s and Brentano’s bookstore on S. Wabash Avenue in Chicago (this was the flagship store of the chain, and what an astonishing place it was for a book-dazzled boy like me to wander about in). I still have that paperback, and I can remember picking it up because of what was on the back cover:

They built a ship called the Southern Cross and launched her to Alpha Crucis. Centuries passed, civilisations rose and fell, the very races of mankind changed, and still the ship fell on her headlong journey toward the distant star. After ten generations the Southern Cross was the farthest thing from Earth of any human work – but she was still not halfway to her goal…

That was my first encounter with the idea that we might go to the stars in multi-generational ways. But Poul Anderson was always ahead of his time, and this is not a generation ship in the model of, say, Heinlein’s Orphans of the Sky. People do not live out their lives aboard the Southern Cross and hand on the great imperative of the mission to their descendants. Instead, crews in the Solar System are regularly teleported out to the ship.

It’s a wonderful story, and that Kipling reference will put a chill up your spine when you see what Anderson does with it. Baen Books incorporated a later novella called “The Ways Of Love” into its edition of The Enemy Stars in 1987, but I much prefer the unadorned core story. I went back to it this past weekend after writing On the Role of Humans in Starflight on Thursday, having thought for several days about the different ways we approach doing long-term things. Probably if I had read Nelson Bridwell’s just published essay To Be or Not to Be? Mankind’s Exodus to the Stars a day earlier, I would have incorporated it into the Thursday post.

But today will do just as well, for Bridwell’s themes are much to the point, reminding me of generation ships in all their manifestations, as well as generation-spanning projects. Described as a ‘senior machine vision engineer working in manufacturing automation,’ the author sees interstellar flight as a natural and necessary outcome of our space efforts, one that will take millennia and will not require violations of physical law. It is an effort, though, that should not be delayed. Writes Bridwell:

Because starships will not be ready to go for many centuries and interstellar voyages may last for thousands of years, we will want to get started sooner rather than later, initially allocating a small but steady fraction of the space budget to identify the most promising engineering approaches and performing early proof-of-concept experiments when affordable. The first application of this technology will be for unmanned interstellar probes that will conduct close-up reconnaissance of nearby solar systems.

Taken to its outer limit, a long-term perspective on Earthly life tells us that the planet will eventually meet its doom, if in no other way, through the gradual swelling of our parent star. But as Bridwell points out, we’re a long way from not just starflight but even a sustained human presence off this planet. It’s prudent, then, to do whatever we can to minimize the existential risk of something happening in the interim to destroy our species. That might involve accelerating the search for near-Earth asteroids and comets to provide plenty of time to change the trajectories of those in dangerous orbits. It also might involve a heightened awareness of and countermeasures for the kind of pandemic that could cut the population in half, if not worse.

In terms of space, bringing the long-term focus of interstellar thinking into play involves continuing the search for promising nearby solar systems where humans may eventually travel even as we develop the kind of closed-loop life support technologies that would sustain human crews over the duration of long voyages. The latter aspect receives far less attention than it should, but it is as key a driver as propulsion for figuring out how to make star journeys.

I think Bridwell has it right that an interstellar effort grows directly out of sustained development here in our own Solar System. We will learn the essentials of closed-loop life support by experimenting in places much closer to home than even the nearest star:

Because it is not at all likely that a warm, moist, green, oxygen-rich twin of Earth will be within our reach, the third goal must be learning how to live under less-ideal conditions, such as on the Moon. We should establish manned outposts on the Moon and Mars where we can develop the expertise to efficiently manufacture everything that we need from local planetary materials. Over the course of hundreds of years, as these outposts grow, they will become second homes within this solar system for humanity.

I see this in terms of O’Neill-class colonies that gradually grow in size and sophistication, as well as bases on planetary surfaces. The immediate need is to develop our skills at living in nearby space so that if something does happen to our planet — nuclear war, perhaps, or biological catastrophe — enough colonies will exist to perpetuate the species. Over the course of the next few centuries, creating such self-sustaining populations in space should be within our technological powers, and these will inevitably spread outward as we explore our system’s resources. I find this prospect encouraging because it assumes nothing the laws of physics do not allow.

Bridwell wonders whether our reluctance to think beyond the current moment is not itself a passing phenomenon, perhaps ‘a madness left over from the Cold War.’ I do think it is a cultural phenomenon, though I have no opinions about its origins in 20th Century geopolitics. We make our own values by choosing what to build, what to believe in, and what goals to pursue. A positive perspective is one that protects the home world first while ensuring that unexpected catastrophe cannot destroy our species. It then begins the long process of exploration and settlement that may spread as far as the outer planets, or perhaps the Oort Cloud, or if we have the determination to make it happen, the distant stars Poul Anderson saw as our destiny.



New Views of Ceres, Pluto/Charon

by Paul Gilster on February 6, 2015

Watching Ceres gradually take on focus and definition is going to be one of the great pleasures of February. The latest imagery comes from February 4, with the spacecraft having closed to about 145,000 kilometers. Here we’re looking at a resolution of 14 kilometers per pixel, the best to date, but only a foretaste of what’s to come. For perspective, keep in mind that while Ceres is the largest object in the main asteroid belt, its diameter is a scant 950 kilometers. Is there an ocean under this surface?


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

Meanwhile, a good deal further out in the system, a small vial of Clyde Tombaugh’s ashes continues its remarkable trek, with new imagery from New Horizons, the spacecraft carrying it, being released on the same day the Ceres images were taken, February 4, which happens to be Tombaugh’s birthday. Born in 1906, Tombaugh’s long life ended in 1997, and he has stayed very much in the thoughts of New Horizons principal investigator Alan Stern, who commented:

“This is our birthday tribute to Professor Tombaugh and the Tombaugh family, in honor of his discovery and life achievements — which truly became a harbinger of 21st century planetary astronomy. These images of Pluto, clearly brighter and closer than those New Horizons took last July from twice as far away, represent our first steps at turning the pinpoint of light Clyde saw in the telescopes at Lowell Observatory 85 years ago, into a planet before the eyes of the world this summer.”


As with Ceres, we’ll be watching a distant speck turn into an actual place with features we’ll need to name as this year moves forward. The image at left, taken at a distance of over 200 million kilometers, come from New Horizons’ telescopic Long-Range Reconnaissance Imager (LORRI), an animation assembled from separate images taken on January 25 and January 27, which makes them the first acquired during the approach phase of the mission. The spacecraft’s flyby of Pluto/Charon takes place on July 14.

Image: A long distance look from LORRI: Pluto and Charon, the largest of Pluto’s five known moons, seen Jan. 25 and 27, 2015, through the telescopic Long-Range Reconnaissance Imager (LORRI) on NASA’s New Horizons spacecraft. New Horizons was about 203 million kilometers from Pluto when the frames to make the first image were taken; about 2.5 million kilometers closer for the second set. These images are the first acquired during the spacecraft’s 2015 approach to the Pluto system, which culminates with a close flyby of Pluto and its moons on July 14. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

So now New Horizons is giving us Pluto at the 2-pixel level, with Charon subtending 1 pixel as seen by LORRI, which JHU/APL describes as “ essentially a digital camera with a large telephoto telescope.” The exposure time here is one-tenth of a second, too short to make any of Pluto’s other moons, much smaller than Charon, visible. We’ll have the satisfaction of watching this system grow in our field of view over the coming months. Along the way, New Horizons will take many images of Pluto against background stars to refine distance estimates and plan course corrections needed for the flyby.


Image: Six Months of Separation: A comparison of images of Pluto and its large moon Charon, taken in July 2014 and January 2015. Between takes, New Horizons had more than halved its distance to Pluto, from about 425 million kilometers to 203 million kilometers. Pluto and Charon are four times brighter than and twice as large as in July, and Charon clearly appears more separated from Pluto. These two images are displayed using the same intensity scales. In LORRI’s current view, Pluto and Charon subtend just 2 pixels and 1 pixel, respectively, compared to 1 pixel and 0.5 pixels last July. The images were magnified four times to make Pluto and Charon more visible. Both images were rotated to show the celestial north pole at the top. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

As to Clyde Tombaugh, whenever I think of him, I think of Michael Byers’ splendid portrait in his novel Percival’s Planet (Henry Holt, 2010), although to be sure, Byers focuses not just on Tombaugh but on the entire enterprise of planet-finding and the nature of obsession (the latter being Percival Lowell’s fixation on ‘Planet X’ as well as the private demons of his subordinates). My earlier review of Percival’s Planet is here. Tombaugh was a Kansas farmboy who could grind lenses like no one else, a self-educated master craftsman whose eye for detail would change our view of the Solar System. What a pleasure to hear the words of his daughter in this New Horizons news release:

“My dad would be thrilled with New Horizons,” said Annette Tombaugh, Clyde Tombaugh’s daughter, of Las Cruces, New Mexico. “To actually see the planet that he had discovered and find out more about it, to get to see the moons of Pluto … he would have been astounded. I’m sure it would have meant so much to him if he were still alive today.”


My favorite photograph of Tombaugh has always been the one above (from the collection at New Mexico State University). Look at the sheer determination in that face! This is a man who knows what he is about — I wish I had known him.



On the Role of Humans in Starflight

by Paul Gilster on February 5, 2015

What does it take to imagine a human future among the stars? Donald Goldsmith asks the question in a recent op-ed for called Does Humanity’s Destiny Lie in Interstellar Space Travel, playing off the tension between successful robotic exploration that has taken us beyond the heliosphere and the human impulse for personal experience of space. Along the way he looks at options for star travel both fast (wormholes) and slow (nuclear pulse, or Orion).

A fine science writer who worked with Neil deGrasse Tyson on Origins: Fourteen Billion Years of Cosmic Evolution, Goldsmith nails several key issues. The successes of robotic exploration are obvious, and we’re in the midst of several more energizing episodes — the arrival of Dawn at Ceres and the approach of New Horizons to Pluto/Charon, as well as the recent cometary exploits of Rosetta. We have much to look forward to and, as mentioned yesterday, new impetus has arisen for the Europa Clipper mission, which would constitute a fine tandem operation with the ESA’s Jupiter Icy Moons Explorer.

Freeman Dyson, in fact, thinks the success of robotics is so marked that the real work will necessarily be done by machines, with human travel in space in the category of entertainment rather than science. But Goldsmith finds this unsatisfying, and I think he speaks for quite a few people when he says a human presence on places like Mars speaks to our deepest impulses:

Just about everyone welcomes new information about the solar system, but what many really — really — want is for humanity to plant its boots on new soil, as Earth-bound explorers have done for many centuries. Lonely humans in space speak directly to our emotions, but pioneering spacecraft far less so. (Even an apparent exception, such as the hero of the movie “WALL-E,” connects with us through its seeming humanity, a fact that won’t surprise anyone who reflects for a moment on how storytelling works.)

Machines get more powerful at a mind-numbing pace, while the evolutionary changes that help us adapt to new environments move with far slower rhythms. Hybrids of human and machine may one day be feasible, or some kind of mind-uploading (a prospect I still think unworkable, as it tries to fit a consciousness that is the result of evolution in a physical body into an alien matrix). There is also the prospect of artificial intelligence achieving human-like capabilities, as witness the poetic, deeply introspective star-probe of Greg Bear’s novel Queen of Angels.

But for those who insist upon human bodies aboard a starship, these options aren’t enough, which leads us to the confrontation with the reality of distance, the nearest star, Proxima Centauri, being approximately 260,000 times the distance from the Earth to the Sun. Goldsmith takes a look at the Project Orion study in which Dyson played such a major role, envisioning a spacecraft that would be driven by a series of nuclear explosions behind the craft, their energies extracted by a pusher plate and a crew-saving system of enormous shock absorbers.


Image: An early conception of Orion as an interplanetary vehicle, one that would eventually be reworked into Freeman Dyson’s interstellar design. Credit: Adrian Mann.

Dyson’s 1968 paper on the ultimate Orion, a starship capable of reaching the nearest stars in 140 years, gave us what Goldsmith calls ‘the gold standard for visions of interstellar travel,’ in that Orion used technologies not impossibly far from what was currently available. But it’s telling that Dyson still sees the key requirement for interstellar flight as a society that can think in terms of centuries and work with long-term planning and execution of generational projects. Orion ran afoul of test ban treaties and the ever-controversial issue of radiation, but in any case it’s hard to see a culture with such short time-horizons as ours building such a vessel.

I’m glad to see Goldsmith referring to Steve Kilston’s ideas on slow expansion, which throws out the false dichotomy between fast results or none at all. Kilston’s idea is best described as a worldship, one we’ve looked at before in these pages. An astronomer and something of a philosopher, Kilston believes that within 500 years we will be able to build a vast structure capable of carrying a million people on a journey at a small fraction of the speed of light. It’s a generation ship, and one that banks on serious changes in the human outlook. Says Goldsmith:

Kilston’s “Plausible Path,” like any other low-velocity journey, requires that generations upon generations of spacefarers pass their entire lives short of their goal. Today, this plan would attract few volunteers. But if human society came to feel sure of its long-term viability, so that our time horizon stretched beyond the current limits of (at most) our grandchildren’s lifetimes, the situation would become quite different. Perhaps the wisest aspect of Kilston’s plan lies in its final pre-launch phase: a 100-year cruise through the solar system to demonstrate the full feasibility of the spacecraft and the willingness of its crew to pass their lives in space.

You can read more about Kilston’s ‘plausible path’ in The Ultimate Project, a presentation the scientist made at the Jet Propulsion Laboratory back in 2006. What he is arguing is that starflight will not become a reasonable expectation unless we reach a point where at least some people think that travel times of thousands of years are acceptable given the goal to be accomplished. Here I want to quote Kilston himself, from a comment he wrote on this site in 2013, responding to a suggestion that there may be reasons for interstellar flight that are irrational:

I’m not sure there is such a thing as an “irrational reason” — explanations and motivations certainly should pay attention to emotional factors. The pursuit of long-term goals and dreams is as vital for our mental and societal health as a concern and empathy for other humans is.

Children respond with wonder and enthusiasm when they hear about a grand project like interstellar travel. It can continue to magnificently inspire them long after we initiate it. As Pierre Teilhard de Chardin wrote, “The future belongs to those who give the next generation reason for hope.”

Goldsmith himself seems to be in this camp. And I think he’s practical enough to acknowledge that the outcome is very much up to us. There is no certainty that our species will ever attain interstellar flight, but if we are to make it happen, we’ll have to learn how to live off the Earth long-term. That would in my view involve ever increasing colonization within the Solar System to master the technologies needed for starflight and the human issues of survival in deep space.

At that point, I see no reason why space habitats on the scale of what Steve Kilston has long studied could not be built, either as explicit starships or as O’Neill-style colony worlds. Would generations accustomed to living in constructed habitats like these eventually decide to take one of their vessels all the way to another star? We have trouble imagining people who would be willing to live this way, but several centuries of technological development and experience in space could make the prospect far less onerous. I agree with Kilston that it’s a plausible path, and whether it happens or not, we still have rapidly advancing artificial intelligence to fall back on. In one form or another, I think human efforts will indeed result in interstellar journeys.



On to Europa?

by Paul Gilster on February 4, 2015

With the 2016 budget cycle beginning, it’s heartening to see that Europa factors in as a target amidst a White House budget request for NASA of $18.5 billion, higher than any such request in the last four years, and half a billion dollars more than the agency received in the 2015 budget. This follows Congress’ NASA budget increase of last year. Casey Dreier, who follows space policy issues for The Planetary Society, cites what he calls a ‘new commitment to Europa’, as seen in a request for $30 million to start the mission planning process. Dreier adds:

At its most basic level, it means that NASA can pursue the development process to create a mission to explore Europa. That’s new, and that’s important. Europa has moved from “mission concept” to “mission,” with details to figure out, plans to draw, teams to assemble, and hardware to build (eventually). It’s a step that Congress could not force NASA to take (NASA being an executive branch agency and all) no matter how much money it gave to them. The White House and NASA deserve credit for deciding to pursue this mission. In fact, I believe that this budget will occupy a small place in history as document that officially began the exploration of Europa.

I leave you to Dreier’s analysis for details about other budget components so we can focus this morning on Europa. But do keep in mind that while we’re only at the beginning of a budget debate, documents like these are nonetheless critical in setting the terms under discussion and keeping key mission ideas current. While we’ve seen huge changes in direction and mission targets over the past fifteen years, the persistence of Europa as a focus for robotic exploration is heartening, and it’s a focus buttressed by the outstanding results from Cassini at Saturn.

The Europa Clipper mission that may emerge from all this bears in its projected operations a certain similarity to Cassini, in that over the years since the latter began orbiting Saturn, we’ve learned a huge amount about Saturn’s moons from flybys. Just as Cassini has opened up detailed study of Titan, Europa Clipper would be an orbiter that would make forty to fifty flybys of Europa’s surface during its primary mission. This will demand a highly elliptical orbit aimed at minimizing radiation damage and a spacecraft heavily shielded against dangerous particles.


Image: Concept to achieve “global-regional coverage” of Europa during successive flybys. Credit: NASA/JPL-Caltech.

So no landing on Europa — not at this stage of the game — but a series of close Europa flybys at altitudes ranging from 2700 kilometers down to 25 kilometers would give us priceless information. If the moon really does have geysers that vent water from the presumed deep ocean below the ice, a spacecraft this close to the surface could take samples, in addition to giving us close-up views of the reddish veins that so distinctively mark the crust, possibly containing organic compounds that may be involved in cycling between surface and sea.

Also positive is the news that the current budget request will contain funding for the instruments NASA intends to contribute to the European Space Agency’s Jupiter Icy Moons Explorer mission (JUICE), which is to launch in 2022 (see Jupiter Icy Moons Explorer). Arriving in Jupiter space in 2030, the mission is to spend several years studying not just Europa but Ganymede and Callisto as well, all three being candidates for subsurface oceans. After flybys of Europa and Callisto, (including measurements of the thickness of Europa’s crust), the spacecraft will enter orbit around Ganymede to study the surface and structure of the only Solar System moon known to generate its own magnetic field.

This JPL page on Europa Clipper notes that it too would make flybys of Ganymede and Callisto, but only for the sake of orbital adjustments, the primary mission being Europa. There, the campaign would consist of four segments designed to produce maximum coverage of the surface under consistent lighting conditions. From the document:

During each flyby, a preset sequence of science observations would be executed. On approach the spacecraft would perform low-resolution global scans with its IR spectrometer (“nodding” the spacecraft’s field of view back and forth across the moon, much like the Cassini spacecraft does during its moon flybys), followed by high-resolution scans with that instrument. At 1,000 km the ice-penetrating radar, topographic imager and ion and neutral mass spectrometer (INMS) would power up. The radar pass would occur from 250 miles (400-km) inbound altitude to 250 miles (400-km) outbound altitude, during which stereo imaging and INMS data are acquired continuously. During departure, the IR spectrometer would conduct additional high- and low-resolution scans as the spacecraft moves away from Europa.

And apropos of yesterday’s discussion of CubeSats, I want to note that NASA is looking at proposals from ten universities for CubeSat concepts to enhance Europa Clipper, an announcement that was made last October. The idea here is to carry small probes as auxiliary payloads that would be released in the Jovian system for further measurements of Europa. According to the agency, the science objectives for potential CubeSat probes include reconnaissance for future landing sites, gravity fields, magnetic fields, atmospheric and plume science, and radiation measurements. The latter may be a showstopper, in my view, given the radiation environment in which these diminutive spacecraft would be forced to operate.

So the outer planet news is at least momentarily positive, and as Phil Plait reminds us in NASA Has Its Sights Set on Europa, the Europa Clipper mission has a strong champion in Congress in Rep. John Culberson (R-Texas), whose support has been useful to NASA in past debates. With a launch in the early 2020s and a 6.5-year journey to Jupiter that includes gravity assists around Venus and (twice) the Earth, Europa Clipper could open up the next phase of outer planet exploration, followed shortly thereafter by the arrival of JUICE. That would make the years around 2030 a golden era for our understanding of Jupiter’s provocative moons.



Looking Ahead to LightSail

by Paul Gilster on February 3, 2015

The news that The Planetary Society is readying the first of its Lightsail spacecraft for a May launch stirs memories of Cordwainer Smith (Paul Linebarger) and mainframe computers. Smith wrote his haunting science fiction in the days when computers filled entire rooms, and the pilot who flies a solar sail thousands of kilometers wide in “The Lady Who Sailed the Soul” is there because, as a technician tells her, “…a sailor takes a lot less weight than a machine. There is no all-purpose computer built that weighs as little as a hundred and fifty pounds. You do. You go simply because you are expendable.”

Despite the anachronisms, Smith’s short stories (collected in The Rediscovery of Man) are as mesmerizing as ever. As computers were big in those days, so have been our sail designs, from Smith’s behemoth (towing 26,000 adiabatic pods containing frozen human settlers) to Robert Forward’s beamed-laser sails. Given the need for harnessing the momentum of photons, all this makes sense, but we’re learning how many interesting things we can do with much smaller sails, like NASA’s NanoSail-D, an experiment in sail deployment and de-orbiting payloads that was a scant 10-meters square. LightSail, in sail terms, is still quite small, with a combined area of 32 square meters.

Both NanoSail-D and LightSail take advantage of the wild card technology of recent times, the CubeSat, which allows sails to be packed into containers no larger than a loaf of bread. Each of the mylar sails aboard the LightSail mission — there are four of them — is about 4.5 microns thick, deploying from four metallic booms that gradually unwind to unfold the triangular sail panels. The craft will use three electromagnetic torque rods to interact with the Earth’s magnetic field to maintain proper orientation. After sail deployment, ground-based lasers will measure the solar photon effect.


Image: LightSail-1 fully deployed. The mission is a precursor to a later LightSail mission to test true solar sailing in a much higher orbit. Credit: Josh Spradling/The Planetary Society.

The Planetary Society is calling this mission a ‘shakedown cruise,’ one that will allow scientists to test out the basic functions of the mission in preparation for the launch of a second LightSail in 2016 aboard a SpaceX Falcon Heavy. A four-week checkout period will be followed by sail deployment, after which, because of its low orbit, the craft will be pulled within days back into the atmosphere. Even so, we should get interesting views of the deployment through LightSail’s two inward-facing cameras, offering time-lapse imagery of the sail’s brief period of operations.

In Jason Davis’ recent article on LightSail, he notes a fact that many of us vividly recall. It will be ten years this June since the Russian Volna rocket carrying The Planetary Society’s Cosmos 1 failed in its attempt to lift the sail to orbit. That left the Japanese space agency JAXA to win the honor of achieving the world’s first operational solar sail when it launched IKAROS in 2010. But interest in small sail technology remains intense, with NASA planning both NEA Scout and Lunar Flashlight for launch in 2018. Both are CubeSat-based, though with larger sails than LightSail. For more on sail projects now in development, see A Near-Term Sail Niche. Note as well that The Planetary Society has created a new website for the two LightSail missions.

But even 85-square meter sails like NEA Scout and Lunar Flashlight are tiny compared to the 1000-kilometer lightsail Robert Forward envisioned for a manned mission to Epsilon Eridani. Can we really do worthwhile science with sails this small? The answer is a resounding yes. By reducing payload mass and maximizing the power of miniaturization, CubeSats give us options like ‘swarm’ missions to the outer Solar System that could be enabled by sail technologies. This could be a low-cost approach to deepening our knowledge of places we’ve only seen in flybys.

So as we continue work on larger designs, let’s see what we can learn from small sails close to home. When LightSail deploys, I’ll probably go back and re-read “The Lady Who Sailed the Soul,” where Cordwainer Smith describes “…the great sails, tissue-metal wings with which the bodies of people finally fluttered out among the stars.” Our CubeSat sails are early steps along the road to the great ships of Smith, Robert Forward and all the researchers who have seen the promise of sunlight and beamed energy as ways to push our payloads into the cosmos.