Shaken, stirred, shaken, stirred

Water never ceases to amaze. Two protons, one oxygen nucleus, 10 electrons. A simple molecular configuration, two sides of a triangle, an obtuse angle of 104.45 degrees and a tendency for the electrons to huddle close to the oxygen by about a factor of ten - leading to an electrical dipole. As basic as this structure is it lends itself to an incredible array of situations. From a physical building block of planets to an extraordinarily solvent to an integral piece of terrestrial biochemistry, there is excellent reason why many astrobiologists extoll the virtues of 'following the water' in the search for life in the universe. Despite this, our deeper understanding of exactly what it is that makes water so very, very special is still surprisingly limited.

An intriguing new study by Rao, Garrett-Roe & Hamm in the Journal of Physical Chemistry (B), appears to offer a clue or two. By applying modeling techniques usually reserved for the study of complex and dynamic systems, they investigated what might be going on in liquid water on a moment-by-moment basis. The dipolar nature of water molecules means that weak electrostatic bonds (hydrogen bonds) are readily made and broken between structures. So in a crowd of water molecules all manner of temporary arrangements can be made as they jostle around. This new study indicates that there may be two main flavors of these arrangements - one a rather 'blobby' mass of several molecules, and the other a more regular, crystalline arrangement. These structures are exceedingly fleeting - breaking up and re-assembling many times a second at room temperature. The result is, and this is a very crude phrasing, a bit like a 3D piece of velcro that is constantly morphing into different shapes.

So, all jolly nice, but why do we care? Imagine throwing some other molecules into this sticky nest. Perhaps some carbonates, some amino acids, even some proteins. The shape-shifting water structures can provide the perfect chemical incubator - from catalyzing reactions to determining structural forms of complex organic molecules.  This cuts to the heart of one of the long running discussions that crops up in the search for life. Why couldn't you have biology that uses something other than water? Why not methane, or hydrogen peroxide, or ammonia?

The answer may now be clearer - as far as anyone knows these other solvent-like molecules do not exhibit this same type of behavior - so it may be that they offer far fewer, if any, pathways for complex chemistry. Water may be far more intertwined in the processes of life than we had suspected.

Voyagers

Overcoming preconceptions and received wisdom is central to making progress in science, and to be quite honest in pretty much anything else as well. I was reminded of this after a somewhat doleful conversation following last week's burst of exoplanetary adrenaline. It went along the lines of 'even if GL 581g was full of intelligent and occasionally amusing aliens, we're just not a spacefaring race and we'll never get to meet them'. Most of this statement is certainly true, but I was struck by the glum expression of certitude about our Earth-bound nature.

A while ago National Geographic published one of their terrific graphic illustrations that summarized 50 years of human space exploration. I can't do it justice here, so go take a look. The incredible thing is just how much space exploration we've actually tried (and often succeeded at). One target is particularly evocative, and that is Mars. I think it's fair to say that going to Mars has always been far less about politics than some other destinations. Mars looms big in our imaginations, the red planet, awfully familiar, yet awfully different. There is incredible poignancy in the list of missions to Mars. A majority have been failures, years of effort and extraordinary technological know-how thrown to the sacrificial plinth of the void. Yet those that succeeded have genuinely transformed both our understanding of this other world, and transformed our relationship to space exploration.

Here's the list, starting in 1960: Marsnik 1 (failed), Marsnik 2 (failed), Sputnik 22 (failed), Mars 1 (failed), Sputnik 24 (failed), Mariner  3 (failed), Mariner 4 (flyby), Zond 2 (failed), Mariner 6 (flyby), Mariner 7 (flyby), Mars 1969A (failed), Mars 1969B (failed), Mariner 8 (failed), Cosmos 419 (failed), Mariner 9 (orbit), Mars 2 (orbit), Mars 3 (lander), Mars 4 (failed), Mars 5 (orbit), Mars 6 (failed), Mars 7 (failed), Viking 1 (orbit/lander), Viking 2 (orbit/lander), Phobos 1 (failed), Phobos 2 (failed), Mars Observer (failed), Mars Global Surveyor (orbit), Mars 96 (failed), Mars Pathfinder (rover), Nozomi (failed), Mars Climate Orbiter (failed), Mars Polar Lander (failed), 2001 Mars Odyssey (orbit), Mars Express (orbit), Beagle 2 (failed), Spirit (rover), Opportunity (rover), Mars Reconnaissance Orbiter (orbit), Phoenix (lander).

Each of these launches, each chunk of alloy and package of electronics, was made to reach across interplanetary space. There was nothing glum about this. Bottles cast into the currents full of tentative human optimism and love and care. All the hallmarks of a space faring species negotiating its first steps. All for a minuscule fraction of resources across the years compared to wars, financial crises, pharmaceuticals, and political shenanigans. To my mind we are already a space faring species, we just haven't quite realized it yet.

This has a direct bearing on our search for life in the universe . Even as the next generations of giant telescopes and advanced optics are being built on terra firma,  the ultimate goal has to be placing instruments in space - away from atmosphere, unstable environments, and with room to stretch out. Whether it's an occulting optic on a 200,000 mile virtual optical bench, or an array of interferometric mirrors, the high mountaintop of space remains where we need to go if we ever want to truly study, even map, another Earth-type planet or a related species. 

A distant cousin

It seems worth following up on the previous post with a little more on the planet GL 581g. With media attention temporarily swirling around this announcement and numerous opinions being offered it can be a little difficult to locate the core truths. Now that Vogt et al.'s actual scientific report is live we can see the basis for their public commentary. It's a very nice piece of work. It's also a remarkably, and refreshingly, chatty report - not something that scientific papers are particularly known for. The incredibly tricky and slippery nature of extracting planet detections from radial velocity (or Doppler 'wobble') data on the star is nicely laid out. Boy did they have to work hard on this. 11 years of data, including some from a 2nd instrument. Although there were over 200 discrete measurements of the star's motion these were, of course, spaced across a decade in time. This kind of sparse sampling - a necessary evil given the nature of telescope time allocation, weather, and competition - presents many challenges when you're looking for numerous overlaid time-varying signals.

Nonetheless, they pulled out the best solutions they could, checking against gravitational simulations of the system to make sure these answers resulted in a real, stable, system of planets and observing the star for signs of luminosity variation - sunspots and the like - that could dupe us into seeing things. All seems good. It is interesting too that they present an age for the system of 4.3 billion years, based on spectral analysis of the star - rather younger than the 7-12 billion years previous measurements had given, and the basis of some of my previous comments. Dating stars is tricky, so I'll pause on any extrapolations from that.

All of which brings us back to asking whether this really is Earth 2.0 as so many headlines have been suggesting. It's not, is the simple answer. Two big tick boxes get filled in - close to Earth mass and in the 'habitable' zone of a normal star. This alone does not make for tropical islands, lush forests, or highway systems.  The real reason for being excited about this planet is that despite being extraordinarily alien, it nonetheless exhibits characteristics that place it firmly as a distant cousin. Imagine you were a hugely pampered but not overly prejudiced western explorer in the 1500's, and that no one from your neck of the woods had ever set foot beyond Lisbon. Setting off across the oceans you arrive at Papua New Guinea. You would immediately recognize other humans, however they would be engaged in complex and utterly alien work and social customs, like nothing you'd seen or experienced before. Their completely different lifestyle would confound you - but it would be obvious that you shared essential biology and characteristics. I think that's a fair analogy here. GL 581g and Earth are distant relatives, products of a universal set of mechanisms that build planets. The key is that GL 581g is the least distant relative we've come across so far.

A habitable planet

So much for predictions. Now the press embargo is lifted we can take a look at what's going on around a small, nondescript, red dwarf star 20 light years away in the constellation of Libra. This star, Gliese 581 had been known to harbor 4 planets, including a couple of super-earths (less than 10 Earth masses) lurking at the very edges of the so-called orbital 'habitable zone'. Now the Lick-Carnegie Exoplanet Survey has crunched through 11 years of radial velocity spectroscopy or 'wobble' data on this star, and are announcing 2 additional planets, including a 3-4 Earth mass world smack bang in the middle of the habitable zone - GL 581 g.

This is the first world that clearly ticks off two key boxes in the laundry list for habitable planets - it's very close in mass to the Earth, and sits at a perfect distance from its parent star to stand a chance of having a temperate surface. It's a wonderful and thrilling discovery, and I'll confess to going out and staring in the direction of Libra last night - although sadly Gliese 581 is too faint to see directly with our beady human eyes. The relative ease (relative being the operative word, it took the might of the Keck observatory to pin this down) of finding this world and its sisters is a potent indicator that planets like this are quite common.

With a 37 day orbit (putting it about 0.15 AU from the 1/3rd solar mass star) there's a good chance that GL 581 g is tidally locked - with a permanent day and night side, although it's by no means clear that tidal locking is inevitable. This poses significant questions about any climate on the planetary surface - something astronomers and planetary scientists have been worrying about for a while for this kind of scenario. A thick enough atmosphere and thermal transport could help even out the drastic day/night temperature difference and keep things stable.

It's a long way from being Earth-2.0 though. The star is small, an M-dwarf, about 100 times less luminous than our Sun and strongly skewed to emitting photons in the infrared. This is also an ancient system, somewhere between 7 and 12 billion years old. GL 581 g is an old, old world bathed in red light. Although larger rocky planets than the Earth should have a more vigorous geophysical history - and the attendant chemical cycling that seems so critical for life - they too cool off with age and eventually suffer from stagnation. Whether GL 581 g has a significant water component or not is also something that we'll have to wait patiently to find out - one, or two generations of astronomical instrumentation in the future.

It's an alien place for sure. But to even be able to discuss these issues in the context of an actual, real, planet only 20 light years away is only a hairs breadth away from revolutionary - welcome to the coming age of exoplanetary science!

Jovian attraction

A beautifully bright object has been hanging in the sky the past few nights. Big enough to distinguish itself from the stars by not twinkling, the planet Jupiter is closer to the Earth at the moment than it has been since the 1960's. This past Friday I found myself peering up through the canyons of Manhattan, and there it was, brilliant enough to outshine the up-lit urban canopy, muscling aside the landing lights of jetliners and helicopters, second only to the post-harvest Moon. There was something enthralling about it. This tiny disk was so distinctly alien. In my mind's eye I superimposed the great gas giant, king of worlds, two and half times as massive as all the other planets in our system put together. Its vast jet streams and storms, its incredible family of 63 moons, the potent magnetic field, the great plasma torus as Io burrows through a tight orbit. There it was, a place in the sky, a tiny condensed blob of mass. It struck me just how vivid this perspective was on the yawning gulf of interplanetary terrain. Gravity does an incredible job at packing matter down to a small volume, our solar system is indeed mostly empty void, but for these extraordinary cusps of curved space.

The scientist's curse is that any semblance of poetry often gives way to curiosity about numbers. As far and as small as Jupiter appeared in the sky it was surely doing more than just bouncing photons into my eyes. All that mass, now a mere 592 million kilometers away, shouldn't I be able to feel the Jovian lure?

It turns out not by much. If Jupiter was at the zenith then it pulls at us with a gravitational acceleration a few hundred millionths that of the Earth. At first I was disappointed, it had felt so much more out there on the street. It's all a matter of relating though. The Empire State Building is a 365 thousand ton chunk of rock and steel, that's about 730 million pounds. When Jupiter sweeps close, and rises into the night, it reaches out and makes this iconic tower weigh about 26 pounds less than normal. That's not much, but 26 pounds is something I can envisage - it's a chunk of cornerstone, maybe a small floodlight. Not so much that anyone would notice, but there nonetheless.

Of course, the lunar and solar tides sweep across us all the time and do far more - but they lack the charisma of King Jove, our planetary gravity lord. If some distant race were to be monitoring our Sun, seeking the tell-tale dips and wobbles as it is pulled at by the planets, then they too would most likely first see the presence of this gas giant. In their catalog of exoplanets Sol b would be the entry. If anyone bothered with this nondescript system it might eventually gain a Sol c, another gas giant orbiting a little further out. Would anything compel them to keep looking, to seek those small inner worlds that might, or might not, be there? Looking in from the outside is very different from looking out from the inside at a bright object in the September sky.

 

The Martian Methane Chronicles

Since the firm detection of methane in Mars' atmosphere announced in 2009 (confirming earlier, more ambiguous results) it's been tough waiting for the next steps, impatience abounds. Methane is one of those compounds that has a predominantly biological origin on the Earth. Both here and on Mars, simple models of atmospheric chemistry suggest that methane molecules shouldn't last for very long - so if you see them then something is actively putting them into the air. Originally the models indicated that on Mars methane might last for as much as a couple hundred Earth years. The big shocker was that it was getting wiped out in less than one Earth year - showing large seasonal dependency.

We still don't understand either this result, or what's producing the methane (future measurements of isotopic compositions - heavy vs. light carbon and hydrogen - may indicate if biology is involved, since life  usually prefers light nuclei). Some beautiful new results by Fonti & Marzo, using Mars Global Surveyor data, add much needed detail, but also add further layers to the mystery.

Their extraordinary map (click on the image) shows the atmospheric distribution of methane during the Martian fall, three Martian (6 Earth) years ago. Where does the methane hover over? It lurks around both regions sculpted by past volcanism (Tharsis and Elysium) and - rather provocatively - around a region where we know there are large amounts of subsurface water ice (Arabia). This is wonderful news - there's definitely a connection with the most recently active geophysical sites, the same sort of places that could produce the kind of warm, chemically rich, subsurface environments loved by the types of microbial life we are familiar with. Whether the methane itself is geophysically produced, or comes from extinct or extant life, we now know that there are places on Mars where conditions have been pretty juicy.

The hitch is that by the end of Martian winter most of this methane vanishes. Something is very efficiently scrubbing the atmosphere on Mars. Prime candidates are wind driven particulates and tough oxidizers like perchlorates (which are good for making fireworks, no, honestly) that may sweep through the skies. But come the relative warmth of spring and summer, the methane reappears, either released from frozen deposits or, just possibly, maybe, tantalizingly, the result of ongoing biological activity - the blooms of Mars. Are we witnessing the first signs of a very alien ecological system? If biology is responsible then what does this cleaning system imply for the lifestyle of organisms? In effect the methane excreta is tidied up before it can pollute, like some efficient recycling program. Is there anything equivalent here on Earth?

Pushing up daisies

Life is opportunistic. About a 150 million years ago flowering plants did not exist on the Earth, today we are positively tripping over the things, so what happened? While there are many factors involved, a particularly interesting one has come up for recent discussion - and relates to a previous post on these pages.

A couple of weeks ago Bond & Scott published a paper in the rather wonderfully named scientific journal 'New Phytologist' that discusses how flowering planets, or angiosperms, spread during the Cretaceous some 65 to 145 million years ago. The novel aspect to this work is the suggestion that critically during this period, because of an elevated atmospheric oxygen level compared to today - perhaps to 25% rather than our paltry 21% by volume, surface fires were much more pervasive. I talked about this general phenomenon a while back.

So, the picture goes like this. Wildfires (well, I guess every fire was 'wild' during the Cretaceous) would have been significantly more frequent with higher atmospheric oxygen. This would have posed a significant challenge to surface plant life. Long-lived and slow growing species, like larger conifer trees - which have an ancient lineage - would have a hard time regenerating their populations fast enough. Imagine a cosy little spot, a fire rips through, everything burnt to a crisp. Seeds arrive, new plants grow, but sure enough another fire comes tearing across the land. Only those plants that had grown fast enough to mature and dump out the next round of seeds (carried off by wind and newly minted mammals and birds) would stand a chance at producing another generation. It's a vicious cycle, the fast growing angiosperms (one presumes helped along by insect and animal pollination) not only outrun the fire cycle, but they quickly produce the next round of fuel.

The upshot is that flowering plants don't get as much competition for resources from the previously dominant types of vegetation - in essence the weedy daisies win the day. The evidence for all this combustible carnage lurks in the remarkable charcoal deposits, and charcoal fossils from this geological period.

It's another example of the incredibly intertwined nature of life on a planet, and another great example of the constant 'what ifs' of evolution. Would an Earth that had always kept a low oxygen level have ended up with flowering plants - and the particular effect this implies on continental albedo and biosignatures?