Discussion and news about the modern effort to understand the nature of life on Earth, finding planets around other stars, and the search for life elsewhere in the universe

Thursday, March 31, 2011

JWST Launch Brought Forward to 2012

Time for fun. Here on the east coast of the United States the planet has clawed its way into night again, but in a few short hours we'll be entering the Gregorian date of April 1st. Fools day. The wonderful thing about the very best April fools jokes is that as absurd as they are in retrospect, they succeed in tricking us because they sound or appear almost real. It's the same thing that makes that noble institution The Onion so incredibly funny. "Queen To Run Marathon", "Harvesting The Spaghetti Trees of Italy", "No Taxes in 2012". Told with a straight face they can just make us pause for an instant. That is interesting, these jokes are an opportunity to examine just what is ludicrous versus what might actually be a plausible extrapolation.

So, life in the universe, exoplanets, all fair game for April 1st. What would be clearly a hoax headline and what would be on the borders of acceptability?

"Star system found to harbor 18 planets, including 3 in habitable zone." 

"Cassini Mission Spots Cruise Liner on Titan"

"Alien Microbes Found In Cheese: apparently taste 'really nice' "

"Journal of Discombobulation Publishes Theory: scientists baffled but impressed"

"Bacterium That Plays Music"

"Exoplanet Covered in Checkerboard"

"Life in Hydrothermal Vent Carries Gambling Gene"

"New Telescope to Search For Signs of Ruminants"

"Government Files Reveal Canals on Mars Were Real"

"New Horizons Probe Cannot Find Pluto"

"NASA to send astronauts to Neptune"

"Ancient Plants Used Sound to Communicate: fossil records tell story"

"Parallel Universe Detected in Parallel Universe"

"Kepler Mission Discovers Planets Made of Steel"

"Helium Loving Microbes Discovered"

"Europa Cracks Open: it's full of shrimp"

"SETI Hears Alpha Centauri Customer Service Menu"

and the last, best one:

"Over 1,500 Planets Discovered Since 1995: other Earths surely out there"

Monday, March 28, 2011

Carbonaceous Cotton Candy

A typical proto-star is surrounded for a few tens of millions of years by a great disk of nebular material. One percent of the mass of this disk is initially microscopic dust, most likely produced in the atmospheric outflows of earlier generations of elderly stars. The other ninety-nine percent is gas, the same mix of gas we see in the great nebula scattered throughout the galaxy. From this orbiting plate of sauce both the central star grows, and the planets coalesce. While there are many hurdles yet to overcome in our understanding of planet formation, one of the trickiest occurs right at the start of this process.

How exactly the microscopic dust grains and gas-phase matter in a proto-planetary disk go from this state to even a tiny crumb of rocky, icy material is a topic of intense debate. We actually have a bit more confidence in what happens once there are meter-sized chunks of stuff flying around than we do in this earliest stage. Observations of proto-stellar systems and laboratory experiments here on Earth have suggested that the first agglomerations of solid material were probably extremely "fluffy" aggregates of the tiniest particles. Now a recent study of the structures in carbonaceous chondrite meteorites seems to shed further light on this primordial stage in planet building.

A new paper by Bland et al. in Nature Geosciences demonstrates the incredible utility of modern microscopic techniques. In this case the backscatter of electrons reveals previously hidden details about the crystalline texture of the meteorite - otherwise impossible to get at owing to the fragile and complex nature of this class of object. In a nutshell, they examine the alignment of microscopic dust grain particles that are coating what are known as chondrules inside the meteorite. Chondrules are some of the most primitive (i.e. oldest) solids from a young planetary system. Whatever they picked up in their travels, and how they picked it up, provides a unique fossil record of conditions.

The outcome is that the very first solids that formed in our solar system were indeed likely to be extremely "fluffy" or porous, with some 85% of their volume just empty space. The Bland et al. results indicate that the chondrules underwent a large amount of "rolling" and even shocking by pressure waves. In effect a turbulent environment acted to compact the initially fluffy, cotton-candy like materials into denser states. Random rollings and collisions naturally produces closely spherical bodies.

The world beneath our feet may well have begun as sticky cosmic fluff.

[But probably not pink]

Thursday, March 24, 2011

The End is not the End

A couple of weeks ago a slightly provocative, but intriguing paper started doing the rounds. Its title "Transit surveys for Earths in the habitable zones of white dwarfs". The author, Eric Agol, makes a careful and thorough study of the potential characteristics of Earth-type planets orbiting close enough to white dwarf stars to meet the usual rudimentary criteria for habitability (i.e. liquid surface water).

White dwarfs, the remains of the stellar cores of roughly solar-mass stars, are tremendously compact objects supported by electron degeneracy pressure - the direct manifestation of quantum mechanical exclusion, close packed electrons don't like their wave-functions overlapping. As Agol points out, a typical white dwarf is about the same size as the Earth. This would result in a doozy of a planetary transit signature (white dwarf on, white dwarf off). He then goes on to figure out what the orbital configurations would need to be around white dwarfs of varying ages and temperatures for a planet to hit the "habitable" mark.

White dwarfs are low luminosity - they're just very small - so this zone is about 0.005 AU to about 0.02 AU for a range of parameters, and lasts for at least 3 billion years as the dwarfs cool off. Planets this close in to dwarfs will have orbital periods on the order of about 10 hours. So the odds of catching transits, which are going to be extremely deep as the planets block out most of the light, are really good. Rather neatly, since the white dwarfs are so dense, such close planets will be unable to raise a tidal bulge on the star and so their orbits are likely to remain stable over long timescales.

The catch is that these planets may or may not exist, and if they do they may have very uninteresting compositions. On its way to becoming a white dwarf a solar type star will inflate its outer atmosphere all the way out to about 1 AU. This is probably the ultimate fate of the Earth, to be engulfed by the star that has nurtured it for the previous 10 billion years. Even planets outside this puffed up stellar envelope may get destroyed as tidal effects perturb their orbits, some estimates suggest that even 3 AU is not a safe distance. Furthermore, as the star loses as much as 50% of its mass before ending up as a white dwarf the fundamental dynamics of any outer planets is changed. Orbits expand outwards and the mutual Hill radii, or range of influence of planets increases.  This can lead to planet-planet scattering events that rearrange the entire planetary architecture.

Despite all this, as Agol points out, we do know that planetary bodies can exist even around neutron stars - the pulsar planets. Other observations also suggest disks of material, possibly containing planetary sized bodies, around stellar remnants. Just because one batch of planets gets destroyed doesn't mean that material can't get recycled into forming "new" planets. So there may be pathways for nature to rebuild or rearrange planets to put them right in the habitable zone of a white dwarf. Whether they would have compositions that include either water or young radioactive elements (vital for maintaining internal heat and hence geophysical activity) is rather a taller order to satisfy.

Nonetheless, if we've learned anything from exoplanetary science it's that nature is going to surprise us at every turn. Spotting worlds around white dwarfs would be immensely cool, er, temperate, and would undoubtedly yield a host of insights to the nature of planet formation in general - even if these are dry and inert lumps of hand-me-down material.

Monday, March 21, 2011

Multiple intelligence test

This will sound like it's off topic, but it's not. Really. Even if it rambles. Some very intriguing discussion has been taking place recently on the apparent discovery that Neanderthal's were making highly sophisticated use of fire during their heyday some 400,000 to 30,000 years ago. This included a bit of home-spun low-oxygen chemistry in manufacturing sticky pitch to help with building better tools. Given the undeniably spotty nature of the data then it seems plausible that this species had plenty more tricks up its metaphorical sleeve.

There is something extremely spooky about all of this. We know that there was once more than one distinct hominid species walking around on Earth. It seems increasingly likely that they all had good, thinking, brains. Whatever happened to eradicate, or conceivably subsume, a species like Neanderthal we may never know. Nagging suspicions include the distinct possibility that we modern humans, or rather our Cro-Magnon ancestors might have had a hand in it. We're certainly still adept at genocidal behavior.

I think this has special relevance to discussions of 'intelligent' life in the universe. It's possibly of  critical importance. One angle that people take in trying to predict the likelihood of intelligence in the cosmos is the 'Rare Earth' hypothesis. This has cropped up before, so I won't go into detail here. This is really based on the notion that here we are, the sole "intelligent" life on the planet, and many distinct phenomena have to be just-so for that to have happened. A similar argument applies to any physiologically complex life. But let's turn the clock back to 35,000 BC. Now there's a world with at least 2 intelligent, but distinct, species of hominids walking around. It might be wrong to think that this was a freakish moment in Earth history. That would presume that our current status is an end-point, an equilibrium. It's no more so than the world of H. Neanderthal, Cro-Magnon (us), Denisova Hominin, and who knows who else. Yes, you can still make similar Rare Earth arguments for 35,000 BC, but eventually it has to be hard to deny that Earth was generating "intelligent" species with some amount of abandon - it'd be easier to assume that this isn't such a delicate phenomenon after all.

So the question I think this raises is whether we're missing something important about the nature of the rise of "intelligence" (as in technology, tool making, abstract thinking) on a planet. This impacts how we might search for it in the universe (from SETI to sniffing for signs of industry in planetary atmospheres), and whether it's likely to be looking around itself (listening, traveling, building signposts).

One question is: if we had today another intelligent species on Earth would we have the same level of curiosity for finding intelligence in the cosmos? It might just seem that much more mundane. Are intelligent worlds quiet and introspective because they just don't care?

Another, more sinister possibility is that multiple intelligent species can co-exist only for so long. Eventually resources become limited enough to force survival of the fittest and they annihilate each other. You might well say that this can happen for a single species just as readily. But imagine for a moment. This is another species we're talking about. What would you do if it was us or the dolphins, seriously? Whatever morality might exist will be worn pretty thin when it's your species on the line. This could lead to a curious resolution to the Fermi Paradox. The paradox is: given the age of the galaxy then if intelligent life is not incredibly rare should it not have spread enough for us to have already come across it? Perhaps intelligent life does occur in abundance. So much so that it usually crops up in several versions on a single planet, whereupon inter-species conflict wipes it all out again. Paradox solved.

What about us then? Perhaps the awful truth is that while we survived and Neanderthal's didn't, we weren't the smart ones.

Tuesday, March 15, 2011

Springtime on Enceladus

What a difference seven years can make. Before 2004 Saturn's moon Enceladus was just another of the 61 significant natural satellites in this system. Yes, it was exceptionally reflective, its snowy white surface pretty much the highest reflectivity of any body in the solar system. Yes, it appeared to have a particularly youthful, less cratered surface, as seen by Voyager 2's brief incursion. This was an intriguing but incomplete suggestion of geophysical activity. But overall there really wasn't anything that suggested it would be more than another of the beautifully individual large moons around the great ringed world.

Then along comes Cassini. Not only did Enceladus show clear signs of a complex and geophysically active (or is that cryophysically active?) surface but it was spewing what seemed to be geysers of icy water particles out into the cold space of the Saturnian system. Scanning towards its southern polar region revealed that the great 'tiger-stripe' fissures were significantly hotter than their surroundings - although still frigid by our terrestrial standards.

Enceladus is an active, albeit tiny, world. Later flybys and flythroughs of the plumes of water have revealed the presence of salts, ammonia, simple hydrocarbons and even dust. The presence of these things suggests that somewhere inside Enceladus there is liquid water in contact with rock. Whether there is a global subsurface ocean or localized lakes is still unclear. At the southern pole then deep fissures are venting some of this pressurized water out to space. What's keeping the interior of Enceladus warm is unknown. Tidal flexure resulting from interaction with the moon Dione and Saturn's great gravitational field could provide some heating at present, but not enough. The radioactive decay of elements within a rocky core might be a significant heat provider, but the apparent localization towards the southern pole may suggest some internal lopsidedness.

It's incredible that this tiny world, just over 300 miles across and 4.5 billion years old, is still stirring. Now, the latest results from Cassini have put a better limit on just how much cooking Enceladus is doing. It is pumping out about 16 Gigawatts of thermal energy, equivalent to almost three times as much as all of Yellowstone National Park here on Earth. Since present tidal heating could at most only account for 1-2 Gigawatts this is very firm evidence that either Enceladus is still releasing pent-up energy from an earlier epoch where the moon orbits and tides were different, or that unexpectedly high
radiogenic heating is the primary energy source. Either option increases the odds of a substantial subsurface liquid water ocean.

The notion that long-term/short-term variations in moon orbits might be responsible is particularly intriguing. The idea here is that the orbits of Enceladus and its neighbor Dione may experience temporary variations that result in short episodes of intense tidal flexure on Enceladus. The thermal energy then takes time to escape through the icy crust - squeezing out as we see it, through places like the polar tiger stripes. This seems to be supported by the claimed high level of argon gas in the plumes. Argon in a planetary environment comes from radioactive decay of potassium-40. If Enceladus had been venting steadily for more than about 10 million years we would expect it to have already lost its argon. The simplest explanation is that the venting of material is episodic.

What does this mean for Enceladus as a potential harbor for life? It's unclear. If Enceladus freezes up solid in-between heating episodes then that could be a tough deal for organisms that somehow inhabit a subsurface environment. If on the other hand it just simmers down to an extended internal winter before the next summer in a few hundred thousand, or million years, then pockets of water could perhaps sustain hibernating life. Maybe Enceladus is like a perennial bulb, budding and flowering every spring, before withering and overwintering again until woken by gravity's warming embrace.

Monday, March 14, 2011

The Romans go to Jupiter

With so much attention focused on the extraordinary progress being made in exoplanet searches it can be easy to forget that there is still much that we do not know about the planets in our own solar system. A great example is our very own gravity lord, Jupiter.

There is much to learn about Jupiter's internal composition. For example, we don't actually have a very good idea of the water content of its atmosphere. When the Galileo mission dropped its probe into the abyssal gloom of the Jovian clouds for a 7 hour long plunge (for which only the first hour maintained communication, as expected) it found things much drier than anyone had suspected. Although this data barely penetrated 0.3% of the way into Jupiter, the absence of much water was and still is a bit of a puzzle. It is quite likely that the probe simply entered a region with few water vapor clouds, perhaps a product of severe downdrafts in the atmosphere, but it's critically important to understand on a global scale. In essence the water content of Jupiter offers a probe of the formation pathway for the planet. Jupiter should have formed with the same kind of oxygen to hydrogen (and hence water) ratio as was in the proto-planetary disk of material surrounding our young Sun 4.5 Gyr ago. A real deviation from this would indicate either some mechanism of sequestration or something funny about Jupiter's formation history.

Then there is Jupiter's powerful magnetic field. Some 20,000 time stronger at the poles than Earth's own field it profoundly effects the environment within the entire jovian system. Intense particle radiation rains down on moons like Europa, influencing surface chemistry and appearance. Within the polar regions of Jupiter itself then the great aurora make Jupiter glow in the ultraviolet and pump out radio emission. Understanding the geodynamo inside Jupiter as well as its external manifestations are high up on the list for exoplanetary science.

Another visit to Jupiter is long overdue. Quick flybys by missions like New Horizons, on its way to Pluto and the Kuiper Belt, offer tantalizing glimpses of the system but we want to get up close again.

Sitting in a clean room in Denver is humanity's next voyager to the gas giant. Juno - the Roman goddess, wife to Jupiter, among other dodgy attributes - is due to launch in August this year. It's a terrific example of a well focused mission with some very specific goals. After a 5 year journey it will enter into an elliptical polar orbit around Jupiter, complete about 32 of these orbits and then be sent to a gaseous doom within the atmosphere. While it flies from pole to pole it will probe Jupiter with a suite of instruments that include a microwave radiometer to peer deep into the upper atmosphere, optical and infrared imagers, an ultraviolet imager/spectrograph, particle detectors, and a magnetometer. By carefully observing Doppler effects the entire spacecraft will also serve as a gravitational plumb-bob - feeling out the internal mass distribution of the giant planet. To protect against the intense radiation at Jupiter then Juno also hides it's electronics away in a shielded vault - a first for this kind of mission and likely a useful pathfinder for later attempts to explore this environment.

Remarkably this is all being done using solar power. Juno is the first deep-space probe to manage this - sunlight is a good 30 times fainter out around Jupiter than it is at the Earth. Advances in solar cell technology aren't just for humans and Juno's three panels give the craft a great three-winged shape, and total span of over 60 feet.

There's a good chance that Juno will reveal much to us about Jupiter's deep interior structure and atmospheric dynamics. This will serve as an extremely important datum for our models of gas giant planets in general. While every new planet found around a distant star is something to celebrate, our own planetary system has a vast amount to still teach us, and Juno is likely to unearth some surprises.

Sunday, March 6, 2011

There's Something About Meteorites

Yikes. This is a post I wasn't going to write. Claims of microbial fossils in carbonaceous chondrite meteorites in a slightly dodgy feeling journal with a peculiar angle on publicity and the all-to-laughable 'news' reporting of certain media networks really is a sticky package. I can feel my blood pressure rising.

However, a couple of conversations had me thinking about this a little more, and after reading some rather sharp and apparently hurried public criticisms of said work (can people really not be bothered to spell someone's name correctly?) I felt there was perhaps something to discuss and add after all.

The paper ruffling some indignant feathers is "Fossils of Cyanobacteria in CI1 Carbonaceous Meteorites: Implications to Life on Comets, Europa, and Enceladus", by Richard B. Hoover. The bottom line is that Hoover (a long established and respected NASA scientist) is claiming to find evidence for fossil-like remains of microbial life inside carbon-rich, highly friable meteorites, based largely on electron microscopy investigations. He then goes on to speculate that the original organisms were a) extraterrestrial in origin, b) perhaps originally inside comets, and c) these could all be related to species that would find a home in the ice on Europa or Enceladus - right down to exhibiting pigmentation consistent with those locales. Wow. That's a lot to take in.

I'm going to first ignore the rather non-mainstream nature of the 'Journal of Cosmology' that this paper appears in, as well as their odd call for open-source commentary. That's really a whole other discussion that I'll pick up later on. However, as I'll explain below, this work didn't just pop out of a vacuum. The paper itself is chock-a-block in some respects, less so in others. As some of the critiques have pointed out, there are big and serious questions about terrestrial contamination of the meteorite samples (most have been in storage for decades). Also there are the funky compositions Hoover finds for the variety of bizarre looking microscopic structures that are his principle evidence of 'life'. Some of these structures are indeed spooky and intriguing - filamentous threads just a few microns in length, seemingly composed of a core and a sheath. Structural similarities to known microbial forms are certainly suggestive. Elemental compositions are probed, but without extremely clear calibration (again, as pointed out by some of the critiques), and are decidedly odd.

My take on it all requires a little disclosure. About five years ago I was invited to a SPIE meeting in San Diego that Richard Hoover was chairing - a respectable enough venue. I guess I arrived as an interested observer. Over a few days we heard about a variety of research into astrochemistry, terrestrial microbiology and paleo-microbiology, and Hoover's findings in both extreme Earth environments and meteorites. As a skilled microscopist he had some great stuff to show off. Bacteria in permafrost emerging from spore states and yes, the bizarre looking forms from deep inside carbon rich meteorites. There was a lot of discussion about contamination and the like. The off-kilter elemental composition of the microscopic meteorite structures wasn't consistent with contamination, nor was the fact that some of these meteorites utterly disintegrate at the slightest contact with water - suggesting that their storage might not have been so haphazard after all. There was a lot of head scratching.

My problem was the same then as it is now. I had no counterpoint, no idea what the insides of a carbon-rich meteorite should look like at a microscopic level if never touched by living organisms. Heck, for all I knew these weird and fascinating structures were perfectly reasonable consequences of non-biological zero-g chemistry, but there was no calibration for that. And I'm not sure there is any calibration now. Fossils of microbial life on Earth are also pretty tough to find and study, so that isn't a great help in this case. Hoover clearly felt then, as he does now, that he was finding something genuinely important and interesting in the meteorites. Maybe he is. Sure there are flaws in the way the data is presented, and the claims are stretched beyond the comfort zone, but I think it's still worth understanding what's going on. The catch-22 is that until someone from the outside takes this work seriously enough to perform that counter-investigation I don't think anyone is going to pay too much attention. The new tarnish doesn't help.

I feel my ire directed towards the Journal of Cosmology. For those of us trying very hard to develop a still emergent 'inter-discipline' like astrobiology, free from past nonsense and wish-fulfillment speculation, the kind of sensationalist, half-baked, awkward promotional tactics they are employing is poison. This is not how science should get reported, it's based on a fantasy about the nature of discovery. Yes, every so often a study comes along that blows us all away. Game-changers happen. But they almost never, ever happen like this. Talk about shooting yourself in the foot.

It's too bad - meteorites are really, really fascinating.

Saturday, March 5, 2011

The Evolution of Planet Earth

About 425 million years ago something quite extraordinary happened to this small rocky planet. A new type of living structure began to cover the surface of its dry landmasses. For a distant observer then  across the plains of the supercontinent Gondwana a peculiar green pigmentation would have appeared.

This was the dawn of vascular plants. A critical physiological characteristic of these lifeforms are the stomata - the pores on leaves that take in carbon dioxide, push out oxygen, and enable transpiration, the release of water vapor into the atmosphere. Transpiration is key to the uptake of water from the ground and as part of the cooling mechanism for plants.

How many stomata a plant needs is a function of species and growing environment. Some remarkable new research now indicates that we may be witnessing a fundamental shift in this parameter as global carbon-dioxide levels rise, as they are incontrovertibly doing. A pair of papers by Lammertsma and de Boer and colleagues in the Proceedings of the National Academies detail an extensive study of a diversity of plants in Florida. By tracking both changes in plant stomata over the past few decades as well as comparing modern plants to preserved samples from over a century ago, they find a clear trend. Today's plant life in Florida, and potentially elsewhere, have about 34% fewer stomata than they did more than a century in the past.

Cause and effect is tricky to understand. However, these data appear consistent with the rise in global CO2 over a hundred years. Higher CO2 concentration and plants need to breathe less, so they cut back the number of stomata. But this also impacts the rate at which they transpire, profoundly effecting the uptake of surface water and its release into the atmosphere. This process plays a central role in the Earth's hydrological cycle - the conveyor belt of water evaporation, precipitation and movement that links rivers, lakes, and oceans to the atmosphere. So what might happen if plants send less water vapor skywards? Although at first this would increase the reservoir of surface water it would also reduce atmospheric water content. Less water in the atmosphere and less precipitation. Dry regions might get drier. The entire cycle of freshwater in a region would alter. The upshot - adding CO2 to the atmosphere may actually help dry it out.

Plants are both adapting to changing environmental conditions, and effectively adapting the environmental conditions to their modified physiology. The Earth is evolving. Little wonder that debate is continuing on whether or not we are now within an episode of mass extinction - the end of the Holocene. A recent study of species diversity seems to suggest that we may not be quite there yet, at least in comparison to ancient events, but things are not particularly rosy either.

All of this brings me back to a theme that has come up before in these posts. Questions of planetary habitability and biological stability are extremely slippery. While some broad stroke assessments of whether a planet might be in a 'habitable zone' around its parent star can serve a purpose, I'm becoming less and less convinced that this is a very productive avenue of investigation. Witness the hoopla over recent planet detections. Yes, we absolutely want to learn more about how climate operates in different planetary configurations, and how geophysics and chemistry may effect the near surface environment of a world, but the equation that takes us to 'habitability' is a very murky one.

Perhaps ironically the very kinds of changes that are being wrought on the Earth by humans might also offer some vital clues about what we should be sniffing for on other worlds.  The sliding of ecosystems towards some new equilibrium, or even extinction, might actually be far more informative than a situation of perfect balance. Obviously this is looking quite a way into the future, but it could be critical to sort out some of these issues now since they will help determine whether we build instruments and telescopes to operate for decades or just years. The kinds of planetary environments we are so eager to find are also those that may require lifetimes to understand. Shifting the paradigm from discovery to study will require careful planning.