Exoplanetary Thoughts for 2010

Several stories stick in my mind as we approach the New Year, presented here in no particular order, but merely as material for musing. The detection (by the MEarth Project) of a transiting ‘super-Earth’ this past month opens up interesting areas for speculation. Gliese 1214b is roughly 6.5 times as massive as Earth, orbiting an M-dwarf some forty light years from our Solar System. You’ll recall we discussed this one in terms of possible study of its atmosphere.

Abundant Small Worlds

On the always interesting systemic site, Greg Laughlin notes that the orbital period of this planet is a mere 1.58 days. In fact, the planet is separated from the system barycenter by 0.014 AU, which turns out to be the smallest separation yet measured for any planet. What stands out here is the density of the red dwarf. Says Laughlin: “Gliese 1214 is more than twice as dense as lead. The density of the Sun, on the other hand, is bubblegum by comparison.”

The result: a planet/star separation that isn’t quite as tight as it seems, a reminder of just how tiny M-dwarfs really are. Here’s Greg’s diagram of the system:

But what I want to focus on is what Gliese 1214b implies. In the recent post, Greg goes on to say:

Gliese 1214b lies at enough stellar radii from Gliese 1214 that its a-priori transit probability was only about 7%. The Mearth survey currently covers only ~2000 stars, and so the fact that the discovery was made so quickly was probably not luck, but rather points to the existence of a very large number of low-mass planets orbiting small stars.

Indeed, and recent trends tell us we’ll be learning a good deal more about such worlds. The MEarth Project reminds us of the viability of continuing transit surveys that will look for true Earth analogs around low-mass M-dwarfs. Is 2010 the year we’ll find such a world? The potential is there, but it’s also true that in addition to transits, our radial-velocity capabilities are being sharpened all the time. And then, of course, we have space-based missions like Kepler and CoRoT, the results of which should enliven the coming year.

Charting Nearby Brown Dwarfs

More musings: The recently launched WISE (Wide-Field Infrared Survey Explorer) satellite has jettisoned its protective cover. Up next for the 40-centimeter telescope and four infrared detector arrays is the adjustment of the spacecraft to match the rate of the onboard scanning mirror, which allows WISE to counteract the spacecraft’s motion to take ‘freeze-frame’ snapshots of the sky every eleven seconds, totaling some 7500 images per day.

Image: This is the central region of the Milky Way Galaxy as viewed in infrared light. The image is a composite of mid-infrared imagery from the MSX satellite and near-infrared imagery from the 2MASS survey. WISE images will be similar in quality. Credit: WISE/MSX/2MASS.

WISE begins its infrared survey in mid-January, and we’ll see ‘first-light’ images released to the public in about a month, after the telescope has been fully calibrated. Again we think in terms of significant discoveries within the next year, for in addition to WISE’s detection of asteroids and distant, dusty galaxies, the spacecraft has the ability to detect nearby brown dwarfs in numbers beyond anything we’ve been able to achieve before. WISE has a primary mission lasting nine months, ending when its coolant evaporates, but it’s possible that may be long enough to spot a brown dwarf closer than Alpha Centauri. At any rate, our brown dwarf catalog should be beefed up considerably.

Planetary Formation from Another Epoch

Further afield, New Scientist offers a brief comment on the work of Erin Mentuch (University of Toronto), whose analysis of the light from 88 remote galaxies, emitted when the universe was between a quarter and a half of its current age, shows what appears to be the signature of circumstellar disks. From the article:

The galaxies’ light output peaks at two distinct wavelengths. One represents the combined light of a galaxy’s stars; the other, at longer wavelengths, comes from the glow of its interstellar dust.

In each case, Mentuch noticed a faint third component between the two peaks. Whatever produces this light is too cold to be stars and too warm to be dust. The most likely source is circumstellar discs – embryonic solar systems around young stars. “It’s the most surprising result I’ve ever worked on,” says Roberto Abraham, who collaborated with Mentuch.

Perhaps not as surprising as all that, given that it fits our current model of abundant planetary formation, but useful in that it may help us get a handle on planet formation in an earlier stage of the universe’s existence. Whatever that result, we enter 2010 with great anticipation of data that may change our map of nearby space and add substantially to our catalog of exoplanets, some of which may well be similar to the Earth. From Kepler, CoRoT and WISE to sharpened detection methods here on Earth, the golden age of planetary detection continues and, if we’re lucky, 2010 may just be the year we find a planet around Centauri A or B. Plenty to muse upon in all this, and plenty of excitement building for the New Year.


Voyagers Look at the Edge of the Solar System

We always cite the Mars rovers as examples of missions that perform far beyond their expected lifetimes, but the two Voyager spacecraft are reminding us once again that we have instrumentation at the edge of the Solar System that is still functioning after all these years. Both Voyagers are now in the heliosheath, the outermost layer of the magnetic bubble we call the heliosphere. With Voyager 1 crossing into the heliosheath in late 2004 and Voyager 2 in the summer of 2007, we get an estimate of the size of the heliosphere, a useful finding because it tells us something about what lies beyond.

What’s out there has been known for some time. Indeed, the interstellar medium (ISM) houses some ten percent of the visible matter in the Milky Way, mostly in the form of hydrogen gas. The ISM is patchy, enough so that astronomers have been able to isolate a Local Interstellar Cloud through which our Solar System is moving, a cloud flowing outward from the Scorpius-Centaurus Association, a region of star formation. About thirty light years wide, this cloud is colloquially called the ‘Local Fluff.’

Image: An artist’s concept of the Local Interstellar Cloud, also known as the “Local Fluff.” Credit: Linda Huff (American Scientist) and Priscilla Frisch (University of Chicago).

The Voyagers have yet to reach the cloud, but they’re closing in on it, and therein hangs a tale. For what determines the size of the heliosphere appears to be the balance between the inflation of the ‘bubble’ by the solar wind and the compressive forces of the Local Interstellar Cloud. In a new paper in Nature, Merav Opher (George Mason University) uses Voyager data to study this balance. Some of the pressure exerted by the cloud is magnetic, and Opher’s measurements of the magnetic field help us to understand how the cloud continues to exist despite forces that should tear it apart.

The problem is that the ‘Local Fluff’ should have been dissipated by the effects of nearby supernovae that exploded some ten million years ago. These hot gases would break up the cloud were it not for its strong magnetic field, argues Opher, who goes on to phrase the issue starkly:

“Using data from Voyager, we have discovered a strong magnetic field just outside the solar system. This magnetic field holds the interstellar cloud together and solves the long-standing puzzle of how it can exist at all.”

The Local Interstellar Cloud is thirty light years across and, given its temperature and density, should not be able to resist the effects of the supernova gases around it. Opher’s finding is that the cloud is much more strongly magnetized than had been previously thought, between 4 and 5 microgauss. This is roughly twice previous estimates. “This magnetic field,” adds Opher, “can provide the extra pressure required to resist destruction.”

: Voyager flies through the outer bounds of the heliosphere en route to interstellar space. A strong magnetic field reported by Opher et al in the Dec. 24, 2009, issue of Nature is delineated in yellow. Image copyright 2009, The American Museum of Natural History.

The field is found to be tilted between 20 and 30 degrees from the interstellar medium flow direction (determined by the Sun’s motion), and is at an angle of 30 degrees from the galactic plane. The conclusion: The interstellar medium is turbulent, at least in the vicinity of our Solar System. If other nearby clouds are similarly magnetized, the heliosphere should vary in size as the Sun moves through them (on a timescale of hundreds of thousands of years), varying the protection the heliosphere offers the inner system against galactic cosmic rays.

The paper is Opher et al., “A strong, highly-tilted interstellar magnetic field near the Solar System,” Nature 462 (24 December 2009), pp. 1036-1038 (abstract).


Decelerating at Alpha Centauri

As we await results from ongoing observations of the Alpha Centauri stars, let’s summarize for a moment what we currently know. While the subject is still up for debate, a number of studies have suggested that terrestrial planets can form around either Centauri A or B, with planetary systems extending as far out as 2.5 AU. And while planets have been discovered in binary systems not dissimilar to the Centauri stars, current estimates are that Centauri B has the greater chance of having a planet within the habitable zone. A warm blue and green world with oceans and continents, not so different from Earth, perhaps, could yet be found around Centauri B.

Supposing this scenario is proven correct, Greg Matloff (CUNY) has gone to work on how we might use Centauri A, even if it turns out to be without planets, to help us explore Centauri B. He’s thinking, of course, in terms of solar sails and the need to decelerate upon arrival in the destination system. Centauri A, a G2V star, is larger and brighter than Centauri B, a K1V. And as Matloff notes in a paper authored for the International Astronautical Congress in Daejeon, Korea this past October, the high luminosity of Centauri A improves solar sail deceleration for a future interstellar mission.

This leads to some interesting scenarios. Centauri A is better at decelerating a solar sail starship than the Sun would be at accelerating it in the first place. Suppose, then, we start thinking in terms of getting the most out of both stars. From the paper:

One possibility is a two-stage starship. A solar sail could first be used to accelerate a starship leaving the solar system. Since α Centauri A could decelerate a faster craft, a second stage (fusion pulse, beamed energy or antimatter) could be used after the sail has concluded solar acceleration.

Matloff is clearly thinking here about an initial acceleration based on solar photons alone, in which case the sail has done most of its work by the time it has passed, roughly, the orbit of Jupiter. We could extend the idea even further by coupling beamed sail concepts with the two-stage approach, using laser or microwave beaming to provide enhanced acceleration for a much longer period before a second-stage using any of the technologies Matloff mentions kicks in.

A second prospect conjures up a well-known science fiction novel:

Another approach is to utilize both the α Centauri suns to decelerate a solar-sail starship. The spacecraft would first approach one of these stars, decelerate and perform a gravity-assist maneuver to approach the second star to complete the deceleration process. This is the reverse of the acceleration maneuver of the fictional residents of the α Centauri system described by Apollo 11 astronaut Buzz Aldrin and John Barnes in their novel Encounter with Tiber (Warner, NY, 1996).

Matloff examines several scenarios that put these ideas in context, including the case of a spacecraft that uses a solar sail at Centauri A to decelerate to rest relative to the star. Here he looks at various values for sail reflectivity and areal mass thickness, showing the maximum velocity (i.e., the initial spacecraft velocity at the start of deceleration) possible for each of these conditions to bring the sail safely to rest at 0.066 AU from the star. Even in the best case scenario, we are talking about velocities less than .004c, or roughly 1150 kilometers per second. Quite a step up from current technologies (such as New Horizon’s current heliocentric velocity of 16.49 kilometers per second), but a long 1100 year haul to Centauri space.

The paper is Matloff, “Solar Photon Sail Deceleration at Alpha Centauri A.” Many thanks to Dr. Matloff for passing along a copy of this paper.


The Problem with Warp Drive

Paul Titze, who somehow finds time to write the excellent Captain InterStellar blog when not preoccupied with his maritime duties in Sydney, passed along a 2009 paper on warp drives yesterday that I want to be sure to consider before the year is over. Warp drives as in Miguel Alcubierre’s notion of a method of reaching speeds that are faster than light. The Star Trek echo in the choice of names was playful and intentional on Alcubierre’s part, and the physicist kicked off a cottage industry in exotic spacetimes and their geometries when he used it in a 1994 paper on superluminal flight.

Specifically, Alcubierre noted that although nothing can move faster than the speed of light through spacetime, spacetime itself has no such restriction. That notion is more or less built into the theory of inflation, which demands a vast expansion of the infant cosmos that would have far outstripped any lightspeed restriction. And Alcubierre saw that if spacetime could be made to contract in front of a vehicle while being expanded behind it, the craft would remain within a conventional spacetime ‘bubble’ while being carried to its destination at speeds that would allow fast human transport among the stars.

There’s always a catch, of course, and the first to be noticed was the huge demand for negative energy to support the warp drive. While that issue has been kicked around in the literature for some time (and various solutions introduced to lower the requirements), it is also necessary to take quantum effects into account, which is what Stefano Finazzi (International School for Advanced Studies, Trieste) and colleagues have done in their paper. In particular, Finazzi’s team finds that the quantum field known as the renormalized stress-energy tensor (RSET) becomes a problem. From the paper:

…it was noticed that to an observer within the warp-drive bubble, the backward and forward walls (along the direction of motion) look, respectively, like the horizon of a black hole and of a white hole. By imposing over the spacetime a quantum state which is vacuum at the null infinities… it was found that the renormalized stress-energy tensor (RSET) diverges at the horizons. Independently of the availability of exotic matter to build the warp drive in the first place, the existence of a divergence of the RSET at the horizons would be telling us that it is not possible to create a warp-drive geometry within the context of semiclassical GR: Semiclassical effects would destroy any superluminal warp drive.

The ‘bubble’ housing our starship, in other words, becomes unstable under these conditions. But this is hardly the last of our problems. Assuming that this instability could be avoided by some kind of external action on the warp drive bubble, Finazzi’s team argues that Hawking radiation at the center of the bubble will burn the occupants to a crisp with temperatures in the area of 1032 K. If this highly detailed argument is correct, the Alcubierre warp drive will remain what it has been up to this point, a useful way to study general relativity and quantum field theory in curved spacetimes, with little possibility of being translated into technology.

Is there any hope for warp drive? Perhaps, says Finazzi, though not on the level of Star Trek-style vessels making interstellar journeys in mere days:

…we think that this work is casting strong doubts about the semiclassical stability of superluminal warp drives. Of course, all the aforementioned problems disappear when the bubble remains subluminal. In that case no horizons form, no Hawking radiation is created, and neither strong temperature nor white horizon instability is found. The only remaining problem is that one would still need the presence of some amount of exotic matter to maintain the subluminal drive.

A subluminal warp drive may not sound quite the exotic note of the classic Alcubierre drive, but in any other circumstances attaining a substantial percentage of the speed of light would seize the imagination. So perhaps a subluminal warp drive will continue to play a role in interstellar thinking, even if its energy demands remain hugely problematic. The paper is Finazzi et al., “Semiclassical instability of dynamical warp drives,” Physical Review D 79, 124017 (2009). Abstract and preprint available.


Avatar: Plausibility and Implications

by Larry Klaes

We continue Larry Klaes’ look at the James Cameron film Avatar, noting the technology with interest, but also examining the people involved and the always relevant question of how we deal with other cultures. How plausible are the creatures depicted in the film, and what sort of artistic choices forced Cameron’s hand? On a broader level, what sort of a future will humans make for themselves if and when they develop interstellar flight?

The starship that transported our hero, a Marine named Jake Sully, to Pandora made only a brief appearance at the beginning of the film. While nothing much was really said about this vessel, it did at least bear a resemblance to a craft that might actually operate in space at least during the next few centuries. This is in opposition to the starships of Star Trek and Star Wars, which often tend to be ‘sexy’, sleek to the point of being needlessly aerodynamic in the near vacuum of space. I do not recall the type of propulsion used by the starship in Avatar, but apparently it could attain high relativistic velocities, as the crew was in suspended animation for just over five years, which would be just about right for traveling from Earth to the Alpha Centauri system. Now whether we will have such a starcraft or any kind of manned starship by the year 2154 when the film takes place is another matter.

Now about the humans in Avatar: It seems that 150 years in the future people haven’t changed all that much, even though they do have some expectedly neat technology. But the people themselves don’t seem all that transformed by it, either physically or socially. This future society does have the means to repair major injuries, apparently – if the one injured can afford the care – and they do have the Avatar Program which allows people to place their minds in a genetically formed body of a Na’vi. But otherwise they seem to be a lot like us, which will probably remain true if we don’t do anything radical to ourselves over the next few centuries. Plus, just as with the aliens in Avatar, I realize the filmmakers didn’t want either party too different from their human audiences of 2009, for otherwise they would risk causing viewers to become unable to relate to the characters, even though ironically they have attended this film knowing they will be transported to what is supposed to be an alien world.

The Plausibility of Aliens

This brings up another point: Just how possible are the Na’vi and their environment? Will we find other alien intelligences who are even humanoids, to say nothing of having thought processes similar to ours? Or will evolving in similar environments bring about similar physiologies? Note how there are many different types of creatures in the oceans of Earth, but their liquid ecosystem brings about similar physical features across a wide spectrum. Perhaps we might expect to find similar looking organisms swimming in the global ocean of Jupiter’s icy moon Europa. I must admit, however, that once I got past the exoticness of being introduced to Pandora in 3-D, I was a bit disappointed at how familiar many creatures seemed, such as the animals the Na’vi rode: They bore more than a little resemblance to Earthly horses, just as those doglike creatures which attacked Jake early on resembled wolves or hyenas. I still have to wonder how anything complex could live on Pandora so long as that moon remains so close to its huge parent planet. By all rights the little moon should be suffering massive quakes and eruptions of lava, but I saw no evidence of such activity.

The ‘goddess’ Eywa, the complex biological organism every creature on Pandora seems to be a part of, had potential to be more interesting as a type of serious Gaia concept. However, much of the biology of Eywa was lost in the spiritual and New Age aspects the film emphasized. While it is certainly understandable that beings like the Na’vi might only see Eywa as a deity, I found it a shame that the concept and entity could not be further explored in a more scientific manner, but then I suppose that would turn Avatar into some kind of nature documentary, albeit fictional.

A Realistic Human Future?

My next point is the motives for humans being on Pandora. While the need for resources and land and the removal of any group that happens to be occupying the place where those resources are by a stronger group is an unfortunate but age-old reality on this planet, how plausible will it be once our civilization expands into the galaxy?

I was disappointed that Cameron made it seem that most of humanity occupied one planet, the one it came from, when it was obvious that the society of 2154 was a spacefaring one. The presence of manned starships would presume a serious colonization of the Sol system, yet we are told that Earth (meaning human society) is in trouble if it doesn’t get its hands on a mineral called unobtanium, which costs ten million per kilogram. Well, that price is understandable if one needs to haul a precious mineral across 25 trillion miles of deep space! It also seems fairly ridiculous for a society that should be occupying much of an entire solar system, where there are plenty of planetoids and moons and certain planets whose resources can be exploited.

I know the whole premise of Avatar is to teach present humanity about taking care of Earth’s environment and respecting other species of all intelligence levels, but as both a long time space buff and science fiction fan, having Earth remain the focus of humanity to the point where if things go wrong there all of humanity is doomed while at the same time the race possesses the ability to explore and colonize other star systems seems incredibly narrow-minded to me. However, I have to keep in mind that Avatar is designed to appeal to a wide common denominator. Folks like me who nitpick may be acknowledged at best, but in the end the most relatable story rules the day. Again, this is why those who care about the public comprehending real science need to latch on to the themes in Avatar and utilize them to explain how certain things really work in our world.

Motives for the Great Voyage

So this leads us to the ultimate question: By the time we are ready to explore the stars and colonize alien worlds, will we actually do so? Will it be necessary to spread out into the galaxy? I think so, but I also have to wonder if the ones who do such actual interstellar exploring and colonizing will be very different from us, certainly much more different that the humans in Avatar. Will this mean that such encounters as depicted in the film will not happen, because the beings that do leave Earth will not be much like us, if at all? And the aliens we come across may not resemble much at all certain native peoples of our planet’s past and present.

The point that is often missed in plans for interstellar exploration and colonization is this: Whether we go into the galaxy with peaceful intentions or for reasons of empire, the odds seem good that the intelligent species out there may have serious difficulties in relating to us in any meaningful way, and we may have similar issues. Will it eventually lead to new understandings on certain levels, or will we ignore each other, or actually try to destroy one another either from fear or a lack of awareness of the intelligence of the other?

It will be very interesting to see what really takes us to the stars. We hope it will be for science and expanding humanity’s frontiers of knowledge, but just as with Apollo, science may have to hitch a ride with the plans of politicians and corporations which have other agendas than advancing human understanding. This may explain why we have yet to find others in the Milky Way galaxy, either nearby or far away.

One thing is certain: The Universe itself has its own agenda, consciously or otherwise. We may hope not to act as the company did in Avatar when it comes to other less advanced species, but at the same time we should consider the possibility that someone out there sees us as potential prey. Or random non-biological acts such as supernovae may threaten us with their arbitrary methods of destruction. We need to be ready as a society and a species to truly wake up to the fact that we live in a massively large Cosmos that perhaps has not destroyed us yet by the mere fact that we got lucky when it comes to rolling dice with reality. Hopefully one of the goals from our cosmic awareness is to respect other species no matter different they may be from us.

Avatar might just be another popcorn flick with more expensive special effects. Or perhaps it might be the film that inspires members of its audience to turn the dream of interstellar travel into reality. As with so many things in our existence, that choice is up to us.