Imagining Alien Ecospheres

A Europan Scenario

Between living dirigibles on gas giants and potential organisms under the ice, we’ve had quite a week in terms of exotic life-forms. I didn’t have space in yesterday’s review of Unmasking Europa to talk about the book’s chapter on biology, but here’s an interesting glimpse of a not implausible biosphere on that moon, as presented by physicist Richard Greenberg:

Brisk tidal water sweeps over creatures clawed into the ice, bearing a fleet of jellyfish and other floaters to the source of their nourishment. As the water reaches the limits of its flow, it picks oxygen up from the pores of the ice, oxygen formed by the breakdown of frozen H2O and by tiny plants that breath it out as they extract energy from the sun. The floating creatures absorb the ocygen and graze on the plants for a few hours.

The water cools quickly, but before more than a thin layer can freeze, the ebbing tide drags the animals deep down through cracks in the ice to the warmer ocean below. Most of the creatures survive the trip, but some become frozen to the walls of the water channels, and others are grabbed and eaten by anchored creatures waiting for them to drift past. The daily cycle goes on, with plants, herbivores, and carnivores playing out their roles.

Into Jovian Skies

One can only wonder what a rich environment we’ll eventually uncover on this water world. As to Jupiter itself, Larry Klaes’ story on Edwin E. Salpeter and the ‘gasbags of Jupiter’ elicited plenty of interest. Larry passed along this clip from the Cosmos series, containing the relevant comments by Sagan and discussing the development of these ideas:

A world “…in which organic molecules might be falling from the sky like manna from heaven, like the products of the Miller/Urey experiment” is not inconceivable as an abode of life. Sagan and Salpeter’s ‘sinkers,’ ‘floaters’ and ‘hunters’ seize the imagination, but I like the broader frame Sagan places them in: “Biology is more like history than it is like physics. You have to know the past to understand the present. There is no predictive theory of biology just as there is no predictive theory of history. The reason is the same — both subjects are still too complicated for us…”

Understanding how to frame a complex issue is what communication is all about, a fact that’s seldom so gracefully exemplified as in Cosmos.

The Wrong Schaller

If you’ve gone back to look at Larry’s post on Sagan and Salpeter’s Jovians, you’ll have noticed that I changed the artwork. Larry wrote shortly after I posted the story that I had chosen the wrong image — the one from Cosmos, as viewable in the video above, is the one now embedded in the text. As to the other, a Schaller image that I reinsert below, it was used as the cover of the artist’s book Extraterrestrials: A Field Guide for Earthlings (Camden House, 1994). And if memory serves, it also ran as a magazine cover — I suspect on an issue of Analog from the 1970s, but if anyone knows for sure, drop me a note.


Unmasking Europa: Of Ice and Controversy

You wouldn’t think the thickness of ice on a distant moon of Jupiter could emerge as something of a political hot-button, but that seems to be what has happened in the ongoing investigation of Europa. Thick ice or thin? The question is more complicated than it looks, because by ‘thin’ ice we don’t mean just a few inches, but perhaps ten kilometers, perhaps five. The key question is not a specific measurement, but whether the ice is thin enough to allow the surface and the global ocean beneath to be connected, in the form of occasional cracks, melt-throughs or other events.


Much hinges on the answer. As Richard Greenberg shows in Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon (Springer, 2008), the small world quickly fell under the scrutiny of scientists with a geological bent after first Voyager and then Galileo imagery became available. The latter was a problem, for the failure of the spacecraft’s high-gain antenna meant the total number of images was sharply reduced, and many questions that might have been resolved by now continue to be controversial due to lack of data. What we do have from Europa is on the order of 1,000 images, a small enough selection that, as Greenberg recently told me, it fits on a single CD.

The upcoming Europa Jupiter System Mission should remedy the lack. But that mission won’t get us back to Jupiter before 2026, and in the meantime, there is much analysis that can still be done on older datasets. And if you read Unmasking Europa, with its painstaking analysis of numerous Europa images, you’ll come away with the sense that the geological model is on extremely thin ice here. Yes, solids can often mimic the flow of liquids, as can be shown right here on Earth, but take a look at an area of so-called ‘chaotic terrain’ on Europa and the visible evidence for melt-through of the ice, followed by reformation in a new configuration, seems palpable.


Image: Conamara Chaos region imaged during the Galileo spacecraft’s E6 orbit . Resolution is 180 m/pixel. Credit: NASA/JPL/University of Arizona Lunar and Planetary Laboratory.

We’re looking at chunks of crust that have undergone significant disruption, the re-frozen result of movement over the ocean beneath, following some kind of melting event. At least, that’s an interpretation that seems consistent with every image of such chaotic terrain that Greenberg shows, and he goes on to demonstrate that you can clip images of such terrain in order to ‘reassemble’ the features that had been there before the ‘rafts’ of individual material — often including distinctive ridges — broke away and floated into new positions.

I mentioned earlier the curiosity of the thickness of ice becoming a political issue, but in the highly-charged world of planetary science, that is exactly what happened. The debate has favored the thick ice model from the outset, but the fact that the new mission (Greenberg is on the design team for it, as are many proponents of the thick ice model) will have as a major goal to determine the thickness of the ice shows that Greenberg’s battle for a much thinner ice coating has had its effect.

The issue, of course, is critical for future study. An ice sheet a hundred kilometers thick makes investigation through some kind of ‘melt-through’ probe and submarine exploration that much harder, and diminishes the chances for life. But Greenberg, a celestial mechanician, demonstrated how powerful are the tidal forces acting on the Jovian satellites, particularly Io and Europa, and how much heat they may produce. Thin ice is a model that seems well supported by Greenberg’s evidence, and one that makes the possibilities of detecting life considerably more likely.

We discussed this by phone the other day in terms of the early study of these matters and how it explained what Voyager first found at Jupiter:

“When it was first proposed by Stan Peale and people at NASA Ames that you would have enough heat to do a lot at Io and even keep the H2O melted at Europa, that was such an outrageous idea that its proponents had to be extremely conservative. To make that case you had to say that even with a modest amount of heat, the water can remain liquid. If they’d said that a lot of heat could keep almost all the water liquid, then that would have been radical and hard to sell. But as time has gone on it has become apparent there is no problem having lots more heat. The amount of tidal heating of Io is way beyond what they had estimated, and the same is true of Europa.”

Yes, and what a surprise Voyager scientists had after Peale and team’s prescient call, just weeks before the flyby, that both Europa and Io should be very lively places on the basis of tidal effects alone! Greenberg recalls slapping his hand to his forehead when discussing the idea with Peale, realizing that the numbers pointed inexorably to the outcome that Voyager actually found — volcanic activity on a tortured Io, and growing evidence for substantial amounts of water inside Europa.

So much rides on this debate. For if there is demonstrated interaction between the global ocean and Europa’s ice sheet, we may not have to use submarines or drilling apparatus at all. A probe won’t last long in Europa’s radiation-bathed environs, but it could be shielded to last long enough to land near a Europan ridge where cracked ice may have exposed indigenous life forms to quick re-freezing. Moreover, not just tidal effects but underwater volcanic activity could be keeping this pattern of ice disruption alive and enhancing the likelihood of life.

This is a peppery, fascinating account that spares no detail in analyzing the varied topography of Jupiter’s ocean moon, but also offers a look inside the science of major space missions and how they are managed. It is filled with insights into the problems of observational bias in analyzing images and the all too human failing of seeing what we want to see. Can a geological model, of necessity assuming a thick ice mantle, explain the numerous features Greenberg analyzes here? It is hard to see how, for the model doesn’t adapt well to this non-Terran environment, even if it will take another mission to nail down the case once and for all.

HD 80606b Transit Bagged

An email from Greg Laughlin confirms that the planet HD 80606b has indeed been caught in a transit, a roughly 15 percent probability now turned into hard data. Laughlin (UCSC) and team recently wrote up their Spitzer infrared observations of this mutable gas giant, a world with an orbit so eccentric that it almost mimics a comet, swinging out to 0.85 AU from its star, then rushing in to a breathtaking 0.03 AU for a brief, searing encounter. The possibility of a transit has been on his mind ever since.

“If you could float above the clouds of this planet, you’d see its sun growing larger and larger at faster and faster rates, increasing in brightness by almost a factor of 1,000,” Laughlin said at the end of January in this JPL news release. His team captured what happens on this world as its atmosphere heats rapidly and produces 5 kilometer per second winds that create vast storm systems, gradually easing as the planet moves away from its star. I’ve already run the resultant image (which also became the cover of the late January issue of Nature that the paper ran in), but let’s see it again. After all, we’re looking at the most realistic image yet made of an exoplanet.


Image: The planet HD80606b glows orange from its own heat in this computer-generated image. A massive storm has formed in response to the pulse of heat delivered during the planet’s close swing past its star. The blue crescent is reflected light from the star. Credit: D. Kasen, J. Langton, and G. Laughlin (UCSC).

Of course, HD 80606b isn’t your normal exoplanet, not even by the exotic standards of the many ‘hot Jupiters’ we’ve found. Most of these — gas giants orbiting tightly around their parent stars — are assumed to be in tidal lock, with one side always facing the star. HD 80606b, on the other hand, is spinning, which gave the scientists the chance to collect data showing how its atmosphere responds to the changing temperatures.

From a recent systemic story:

Our interpretation of the light curve is that we’re seeing the planet heat up rapidly, from a temperature of roughly 800K to a temperature of about 1500K over a time period lasting roughly five or six hours. This indicates that the starlight is being absorbed at quite a high level in the atmosphere, where the air is thin and the heat capacity is low.

Who would have thought the storm systems of Jupiter were trivial? But compared to HD 80606b’s activity in the less than a day it takes to move through periastron, Jupiter dishes up little more than a tropical breeze. Observers worldwide went to work on the mid-February transit opportunity, covered by regular updates on Laughlin’s systemic site, even as they battled weather issues in eastern Europe and Scandinavia. The transit discovery paper notes that only five of the known transiting planets have a period of more than five days, with HD 80606b becoming the sixth and having much the longest period, a full 111.4 days.

All this has me wondering how anyone with an interest in astronomy could fail to be drawn to the exoplanet hunt in this remarkable period of discovery. Congratulations to Greg, whose tireless work on this sizzling world called the attention of astronomers to the transit possibility, and provided a continuing forum for discussion. It was fine work all around, and let’s hope Greg’s team wins approval on its recent request for more Spitzer time later this year and in 2010 to again study HD 80606b.

The discovery paper is Moutou et al., “Photometric and spectroscopic detection of the primary transit of the 111-day-period planet HD 80606 b,” submitted to Astronomy & Astrophysics (abstract). The Nature paper is Laughlin et al., “Rapid heating of the atmosphere of an extrasolar planet,” Nature 457 (29 January 2009), pp. 562-564 (abstract).

Addendum: David Kipping (whose work on exomoons we have examined previously in these pages) reports that he also detected the HD 80606b transit at the University Observatory of London. More on that catch in his team’s paper, “Detection of the transit by the planetary companion to HD 80606,” available here. Writes Kipping, “We are all very pleased here to have detected such a challenging target from the city limits of London. Due to the very long transit duration we are able to pin down the system parameters to a very high precision despite only using ground based telescopes. It really is a truly bizarre world, as Greg pointed out in his quotes in your article!” Nice catch!

Edwin Salpeter and the Gasbags of Jupiter

By Larry Klaes

‘The Gasbags of Jupiter’ sounds for all the world like the title of an early 1930s novel that would have run in a venue like Science Wonder Stories. In fact, as Larry Klaes tells us below, the idea grew out of Carl Sagan’s speculations about free-floating life-forms that might populate the atmospheres of gas giant planets like Jupiter. Cornell physicist Edwin Salpeter had much to do with the evolution of that concept, helping Sagan produce a paper that was a classic of informed imagination (and one that led to numerous science fiction treatments as the idea gained currency). Larry’s celebration of Salpeter’s life gives a nod to that paper but also notes his deep involvement in the study of the most distant celestial objects.

On March 14, the Department of Astronomy at Cornell University will commemorate the life of one of their most prestigious faculty members: Edwin E. Salpeter, the James Gilbert White Distinguished Professor of Physical Sciences Emeritus. Salpeter died of leukemia last November 26 at his home in Ithaca, just before his 84th birthday.

At the Heart of the Quasar

The biographies on Salpeter, who came to Cornell in 1948, primarily mention his work in the astrophysics of distant cosmic objects. As just one example, Salpeter was among the first scientists to come up with the current explanation for the enormous energies from quasars, which is short for QUAsi-StellAr Radio sources. The cores of these very distant galaxies contain supermassive black holes which collect vast amounts of debris that are pulled into fast-spinning accretion disks around these gravitational wells.


So much debris falls onto these black holes that it is often ejected back into deep space in relatively tight beams known as relativistic jets, which shoot out across intergalactic space for many thousands of light years. Quasars are some of the most luminous objects in the Universe and thanks to Salpeter’s work on understanding their nature, astronomers have a much better idea how these distant bodies are such powerhouses.

Image: The physicist Edwin Salpeter, photographed in 1978. Credit: Cornell University.

But perhaps the most recognized work of Salpeter is, ironically, one that many probably do not know he was involved with, or that his collaborator was one of the most recognized names and faces in science: The late Cornell astronomer Carl Sagan, who died in December of 1996 from myelodysplasia, a rare form of leukemia.

Pushing Habitability to New Extremes

Among Sagan’s many and varied interests, perhaps his favorite was extraterrestrial life. Sagan was one of the pioneers who brought about the acceptance by the mainstream science community of the possibility that beings of all kinds existed beyond our planet Earth. He would often speculate on alien life on worlds and in realms few had considered at the time.

One of Sagan’s truly revolutionary ideas about aliens was the concept of creatures that dwelled not on or in the surface of some Earthlike planet but spent their entire lives floating in the atmosphere of giant gaseous worlds such as Jupiter, which could hold over one thousand Earths. Unlike the inner terrestrial worlds such as Venus and Mars, Jupiter and its fellow giants are made up primarily of atmospheric gases, though the incredible pressures in these worlds’ lower layers of air turns the hydrogen in them into a metal.

Sagan thought that since the upper atmosphere of Jupiter was relatively friendlier by comparison and contained many complex organic molecules, they may have had time in the five billion years since the formation of the Solar System to turn out some type of life, an aerial form of creature that never touched or knew a planetary surface.

To determine just how scientifically plausible such aliens might be, Sagan asked his colleague Salpeter to help him produce a paper on the subject which was titled “Particles, Environments, and Possible Ecologies in the Jovian Atmosphere.” The paper first appeared in the prestigious The Astrophysical Journal Supplement Series in late 1975.

A Jovian Taxonomy

Sagan and Salpeter envisioned three main types of Jovian creatures. There were sinkers, small organisms which were constantly falling towards the deadly deep, dense, and hot layers of the planet but always managed to survive long enough to produce offspring that would stay up in the more habitable air layers to repeat their cycle of life. The other aerial residents of Jupiter were known as floaters, which Sagan would later describe as being “kilometers across, enormously larger than the greatest whale that ever was, beings the size of cities.” Floaters were seen as drifting across the vast alien sky in great herds, looking like a collection of immense balloons, which in essence there were, using the lighter elements of Jupiter’s atmosphere to stay aloft.


Image: Salpeter and Sagan’s Jovian aerialists, as imagined by the artist Adolf Schaller.

As with life on Earth, the Jovian ecosystem would also have its share of predators which Sagan and Salpeter named, appropriately, hunters. The hunters were envisioned as being fast and able to maneuver, preying on the floaters “for their organic molecules and for their stores of pure hydrogen.”

Love and Death Among the Gasbags

As author William Poundstone stated in his 1999 biography Carl Sagan: A Life in the Cosmos about this paper and its authors, “they produced one of the more singular scientific articles of the time, a quantitative analysis (with sixty equations) of life, love, and death in the air of Jupiter.” Poundstone was especially amused about Sagan and Salpeter’s speculations on how such Jovian natives might reproduce, highlighting the paper’s statement that “the distinction between hunting and mating under these conditions is not sharp.”

The paper also noted that the two Voyager space probes scheduled to make flybys of Jupiter in 1979 had cameras powerful enough to just resolve the floaters if such beings existed at that world and were high up enough to be spotted. Whether the images of Jupiter’s swirling, colorful face that were later returned by the twin robot explorers were ever scrutinized for any floaters remains unknown.

Landmark as this paper was, it was the appearance by the Jovian aerial beings in Sagan’s equally landmark television series Cosmos that brought this concept to the general public. In the second episode of the thirteen-part PBS series first shown in 1980, the Jovians were briefly introduced in a magnificent painting made by artist Adolf Schaller. Sagan also mentioned his colleague by name as the person who helped to bring these strange beings to life in both the episode and in the companion book to the series. The Cornell scientist noted that even if sinkers, floaters, and hunters did not actually live on Jupiter, they might still dwell on some other worlds in the Milky Way galaxy.

More information on the Cornell commemoration of Edwin E. Salpeter, which takes place on March 14 at Barnes Hall, can be found here. The classic Salpeter and Sagan paper is “Particles, Environments and Possible Ecologies in the Jovian Atmosphere,” Astrophysical Journal Supplement Series, vol. 32, Dec. 1976, pp. 737-755 (available online).

Gamma-Ray Burst Exceeds All Others

Adam Goldstein must be living right. Here’s a grad student (University of Alabama, Huntsville) who’s on his first day on the job working with the Fermi Gamma-ray Space Telescope. He’s given the task of monitoring the Gamma-ray Burst Monitor (GBM) instrument, which routinely detects bursts, about one a day. This time, though, when the phone rings, it is to flag a burst like no other, 700 times longer in duration than the average.


We already knew that GRBs were exotic events. Many astronomers believe that they occur when, out of its nuclear fuel, a massive star collapses into a black hole, creating jets of material that interact with gaseous debris previously shed by the star. But this one, detected in mid-September last year, was a true behemoth, with a red shift pegging its point of origin as twelve billion light years from Earth, in the constellation Carina. GRB 080916C turns out to be the most powerful gamma-ray event ever detected.

Image: GRB 080916C’s X-ray afterglow appears orange and yellow in this view that merges images from Swift’s UltraViolet/Optical and X-ray telescopes. Credit: NASA/Swift/Stefan Immler.

Valerie Connaughton (UAH), a member of the GBM team, says this about the burst:

“This is the most spectacular burst ever seen at high energy. If the event that caused this blew out in every direction instead of being a focused beam, it would be equivalent to 4.9 times the mass of the sun being converted to gamma rays in a matter of minutes.”

But it’s not just the power of the burst that is worth noting. GRB 080916C lasted for 23 minutes, implying (at the specified distance) that the actual event was four minutes in duration when it occurred. What processes produce this kind of gamma-ray activity? Moreover, rather than starting with high-energy gamma rays, the early detection here was on the low-energy side, with the high-energy gamma rays not showing up until five seconds into the event. The cooler gamma rays faded out early on but the high-energy rays persisted for an additional twenty minutes. Why?

“This one burst raises all sorts of questions,” says Peter Michelson (Stanford). “In a few years, we’ll have a fairly good sample of bursts, and may have some answers.”

Those answers could give us insights into the environment around gamma-ray bursts, which includes stellar debris, a black hole and massive amounts of radiation. They might also give us a read on theories of quantum gravity that suggest empty space is actually a froth of quantum foam, one that would allow lighter, lower-energy gamma rays to move more quickly than their higher-energy cousins. Future observations to study unusual time lags like these should help us pin down a plausible explanation.

The paper is Abdo et al., “Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C,” Science Express February 19, 2009 (abstract). A news release from the SLAC National Accelerator Laboratory is also available.