Looking forward

As our planet, a slowly crystallizing 6,300 kilometer radius ball of silicates and carbonates with a healthy dose of metals, comes streaking up on the same orbital patch it passed 12 months ago, it seems appropriate to ponder some of what might be heading our way in the future. Perhaps not by the next time we're this side of the Sun, but in the orbits to come.

There are undoubtedly many goodies on the near horizon for the study of exoplanets. A far better grasp on the number of Earth-sized worlds out there in the galaxy is on its way, thanks to both the Kepler mission and the ongoing efforts of other surveys using radial velocity, transit, and gravitational microlensing measurements. Thus far everything points towards a universe positively filled with small rocky worlds, and undoubtedly many will fulfill several of the basic, albeit biased, requirements for Earth-style climates and surface environments. On the tail of this will be the possibility of rudimentary measurements of atmospheric composition for a few select worlds, most likely orbiting low-mass stars in our neighborhood.

All is good, but these are items that have been written about ad nauseam, in these pages as well as elsewhere. Surely barreling towards our orbital solstice at 30 kilometers a second we can afford a little more reach?

In the next decade or so we should see the advent of the largest optical telescopes ever built by humans. With mirror diameters in the range of 30 meters and advanced adaptive optics, calming and helping eliminate the distortions of the Earth's atmosphere, these goliaths will not only open up exoplanetary studies but also the study of our own solar system. For the first time ever we will be able to make daily (if not by the minute) observations of places like Jupiter's icy Europa with spatial resolution of just a few tens of kilometers, combined with exquisite optical and infra-red spectroscopy. With spatial fidelity more than ten times better than the Hubble Space Telescope and the James Webb Space Telescope these monumental observatories will allow us a god-like reach across our solar system. It is impossible to know exactly what we will see. Seasonal changes on Titan will be visible - and followed across decades - as will surface changes on Io, Europa, Ganymede, and even Enceladus around Saturn. Maybe we will witness rare but revealing phenomena. Perhaps one day Europa will crack, a chasm ten kilometers deep forming as the immense stresses of the Jovian gravitational tide wins out, and a watery soup will spill forth. As it sublimates and freezes, shutting this tear like all those scars before it, perhaps we will see not just the chemical signatures of a deep biosphere but strange organisms themselves, flopping to the surface in waves. Each freezing out but giving up their latent heat to the next, all reaching for photons and oxygen ions, favorite foods from the last harvest a thousand years before.

If Enceladus is indeed the rebuilt child of Saturn's rings, themselves the product of a long-since shredded moon, perhaps we will watch as it continues to twist and crack, shaking itself to some new equilibrium, at the same time providing a warm oasis for life far from the Sun. Even the cold dark Uranian and Neptunian systems will be far more accessible to us, and perhaps cryo-volcanically active places like Triton have unexpected goodies yet to be revealed.

Eventually Mars' daily globe will adorn our screensavers, a view not afforded by orbiting instruments, their cameras designed to probe only tiny patches. We will watch as yet another sandstorm rises and engulfs the planet, and marvel at the ephemeral delicacy of the icy environment. Perhaps here too we will enjoy watching the overlays that depict the migrations and flows of a newly discovered subsurface martian biosphere, probed and followed by fleets of wandering robotic avatars.

As comets venture through their perihelion, lighting our Earthly skies, these giant instruments will yield views previously the exclusive province of high-octane spacecraft flybys. The pocked and crumbly nuclei, some wet and spewing sublimated gases into space, others discrete but laden with rich organic chemistry, will all be routinely charted and examined for critical clues to the nature of solar system assembly and possibly the chemical mix that our planet started with some 4 billion years ago.

If there is one future wish, as we tumble into another stellar orbit, then it would be for such fidelity of cosmic vision, as well as the fidelity of terrestrial vision to recognize our common humanity. As the very stuff of stars, alive in an immense and ancient universe it would be a dreadful tragedy if we squander our moment in blindness.

The ten most important questions for astrobiology: Number 6

This next question for astrobiology has a fairly long history, going back at least 1500 years or so, with occasional flurries of interest over the past two hundred years. Interestingly, for every controversial idea put forward to address it there are also many sober and reasonable ideas. Question number 6 is:

Can life spread through space itself?

Like the other questions this one requires some further qualification. The typical context is the idea that life originates, or is incubated, on or in planetary bodies. Subsequent events lead to the transport of viable organisms, or at the very least viable biochemical 'seeds', across the gulf of space - either within a single planetary system or between distinct stellar systems. The term most generally used is 'panspermia', coined by the ancient Greeks and meaning 'all seed', more modern studies often refer to 'lithopanspermia', meaning the transport of life-containing material from planetary lithospheres.

It is a very interesting idea. Remarkably, the more we learn about the resilience of life here on Earth, from super-tough microbes to multi-cellular organisms like tartigrades, the more plausible it seems that organisms could in principle survive long-term exposure to interplanetary, and just possibly interstellar, space. This is especially true if they are tucked away inside big chunks of rock or ice, shielded from disruptive electromagnetic and particle radiation. The rub, and there always is one, is that the physical processes that might loft life away from a cozy planetary surface or enable their descent onto a new planetary body are pretty awfully violent - from asteroid impact induced spallation of lithospheric material (big collison=ejected planetary rocks), to hyper-velocity re-entry through a planetary atmosphere. This is such a make-or-break problem that tests have been undertaken, both in the lab and with space-born experiments to scope out how extreme pressures and temperatures weed out organisms. So far nothing suggests that the violent circumstances initiating or ending panspermia are complete deal-breakers.

Then there are issues of actual transportation within a planetary system, how long does it take and how often can a piece of planet A arrive on planet B? Detailed gravitational simulacra of our own solar system provide some insight. Earth-Mars/Mars-Earth exchange (as we know from meteoritic evidence) occurs, and can be on reasonably 'quick' timescales of a few years to a few tens of thousands of years. Even channels that carry material from, for example Earth to Europa, exist - but the efficiency is very low. Out of roughly 100 million bits of ejecta from suitable asteroid impacts on the Earth perhaps only 100 might eventually intersect Europa. So the orbital architecture of a planetary system plays a dual role - determining the rate of ejecta-producing impacts on planetary bodies, and determining the transport efficiencies of these lumps between worlds.

Then there is interstellar panspermia. Solar winds may be able to both accelerate and decelerate tiny crumbs of dust or ices carrying microbial organisms, or at least DNA fragments. A speck is propelled from one star and then if it intersects the stellar wind of another may be slowed down to drift inwards to the planetary zone. Microscopic material can sink down into a planetary atmosphere, as we see here on Earth with high-altitude interplanetary dust particles. The biggest challenge is for anything of any remote biological function to survive the interstellar environment for the huge lengths of time required.

Which gets to the last, and most speculative and abused piece of this. If life, in varied and splendid forms, is common in the universe then wouldn't at least some of it have evolved to exploit the greater terrain offered by migrating through space? Not by building machinery, but either by natural selection or just sheer biological grit. Given the apparent propensity for lithospheric material to get exchanged between planets in our solar system and the potential diversity of planetary systems out there, then it seems plausible that somewhere is a place that could be analogous to one of our terrestrial archipelagos. This Indonesia of planets could offer the kind of back and forth that would, over time, select for organisms best suited to space travel - a little evolutionary honing before they set off into the galaxy.

So the answer to Number 6 remains 'possibly', and by exploring our own solar system there is both a chance of finding our relatives and finding the misplaced chunks of planets that might give us some more clues.

Voyager to the stars

Thirty-three years ago Voyager 1 was launched from Cape Canaveral. It now appears to have crossed into the true interface between the particle radiation from our Sun and that of the great gulf of interstellar space - as it travels through the heliosheath. In this region, 10.8 billion miles or 16 light hours from us, the solar wind is being turned sideways, blowing against the as-of-yet unsampled interstellar medium as we orbit around the galaxy. Eventually Voyager will cross the absolute edge of this zone of balance, through the heliopause and out into the galaxy proper.

Despite its age, Voyager is true to its name. Most of its monitoring instruments still function. It senses the ambient particle environment by registering the impact of charged particles. As their energy appears to decrease we can tell that their forward velocity is dropping, the Sun's influence now too weak to punch any further. Its 3.7 meter diameter radio dish still picks up instructions at about 16 bits/second, and relays back microwave telemetry at a typical 160 bits/second, boosting to 1.4 kilobits/second for plasma-wave data. It is overseen by 3 doubly redundant processors (6 total) that by today's standards are barely recognizable as such. These are wonderfully tough relics, ancestors with 16 and 18 bits compared to the 64-bit architectures of today's most modest laptop. The three radioisotope thermoelectric generators now generate only about 270 watts of power, compared to 470 watts in 1977 when their plutonium-238 contents were freshly minted - possibly the only rational purpose for an advanced civilization to dabble in such toxic and dangerous materials. It is a brilliantly conceived and engineered machine, something for humans to be proud of.

Together with Voyager 2 (traveling at a slower rate, still a mere 8.8 billion miles from Earth), and Pioneers 10 and 11, these amazing craft represent our first tiny steps into the interstellar void. These small specks of cosmically rare elements are for now the only outward physical sign of our presence in the universe. It is quite possible that long after we humans have become extinct, or evolved to something new, or just simply moved on, these devices will continue to serve as monuments to our curiosity and eagerness to join with the cosmos. The odds of their intersecting anything else in the universe are extremely small, it is a fair bet that they will still drift through space long after all the stars have gone out, in about 100 trillion years time. It is a sobering and fantastic thought that despite our all-to-human problems, our daily lack of perspective, we have nonetheless found on occasion the clarity to produce evidence of our existence that may live forever.

The ten most important questions for astrobiology: Number 5

The next question relates, as they all do, to previous questions. It may not represent where cutting edge progress is being made in astrobiology, whether it be in microbiology or exoplanetary science, but it's a perennial query. I've lost count of how many times it's been raised after a few drinks and left hanging there casting a slightly embarrassing shadow over the conversation, so here's Number 5:

Could there be life in the universe operating on entirely different principles?

So what exactly does this mean? Typically the definition of 'life' here is pretty broad and a bit fuzzy. It ranges from stuff we'd recognize by its actions (that rock just ate my sister!) to stuff we'd have to kick ourselves about later (that cloud not only looks like a rabbit...). As for 'principles', well this too has a broad range of meaning.

At the simplest end we're talking about fiddling with terrestrial-style biochemistry. But to operate with different principles there have to be some fairly radical alterations - more than just substituting arsenic for phosphorus or silicon for carbon, assuming any of that can work. A key factor has to be the capacity to store information in a way that is both robust and yet readily accessible. Our biochemistry uses complex polymers and a great array of support structures and molecules, from histone spools to enzymes. Various array-like, or quasi-periodic molecular forms occur in other parts of nature, in clay lattices and crystals. The read-write issue is a tough one though, to read out something like DNA, to convert that information into function, requires unzipping the molecule - a dangerous exercise. Equally, the process of writing to that storage device can be both very subtle (the filter of natural selection over short to long timescales) or quite brutal (viral RNA insertion). As we look at the enormous complexity of our own biochemistry it becomes increasingly hard to blithely suggest a plausible alternative - which is not to say there couldn't be one, but it seems like an almost insurmountable challenge to invent one with just theory. The closest we can get may well be our own version of artificial life, the push and pull of electrons in semiconductors.

But what if the different principle is really different? Here we firmly enter the realm of science fiction where 'beings of pure energy' serves as a useful scriptwriter cop-out. All that we have in this case is speculation. For example, is something like a galaxy alive? They involve mutual interactions of smaller structures (stars, molecular clouds, globular clusters), large scale connective processes (density waves, magnetic fields), they have speciation, they avoid reproduction as we know it by simply being eternal, they feed off smaller structures and on occasion each other, they call out to their brethren like leviathans in the deep - their booming voices carried across the cosmos as waves of gravity. They are also full of microbial life, most stellar cells carrying a swarm of simple chemoautotrophs, little spherical bodies of rock or gas processing atoms into complex molecules - fed by the mitochondrial-like warmth of nucleosynthesis.

It makes for a good story, but therein lies the problem with this type of speculation. The story is far more compelling than anything we might realistically stand to test or learn from even if it were true.

So the answer to question 5 at the moment seems to be 'possibly, but we really have no good idea what it would be'.

Catching the rays

It's sometimes very hard to choose between topics - from spectrally featureless super-Earth atmospheric light transmission suggesting a possible water vapor composition, to electrically signaling bacteria crossing the line to inter species cooperation. Then along comes an item that just scuppers even those wonderful stories.

Harvesting solar photons for direct bio-chemical processes has been the province of microbial life for at least 3.5 billion years - since sticky colonies of organisms like cyanobacteria sat in the shallow waters of Archaean Earth. Later endosymbiosis allowed plant life to pick up the trick, and make use of the hundred and seventy petawatts of solar energy flooding the planet. Now it appears that at least one species of insect has perhaps also learned to capture photons as a key resource.

This remarkable talent belongs to the Oriental hornet - Vespa orientalis. It had been known that this insect generated electric currents through various structures in its body, and it had been speculated that this related to thermal regulation. Now a new study by Plotkin et al. has shown that on the hornet's abdomen is a remarkable optical 'trap' - an arrangement of skin cuticle ridges about the size of the wavelengths of ultra-violet to optical light that serves to trap incoming photons. Light is repeatedly reflected within layers which increases the odds of it intersecting a special yellow pigment xanthopterin - tuned to selectively absorb photons. In doing so it can generate minute electrical currents within the cells - which could then power bio-chemistry. Plotkin and colleagues have gone as far as constructing a rudimentary organic solar cell in the lab, using xanthopterin, to generate electricity with about a 0.34% efficiency (compared to about 10% for the best artificial solar cells).

The full chain of the process has not yet been disentangled, however the hornet's activity is strongly correlated with the intensity of ambient ultraviolet light, and it seems that there is most metabolic activity within these optically-tuned pigmented parts of their bodies. It may still be that thermal regulation is the driving force behind the evolution of this capacity, however many things point towards Orientalis as being a genuinely solar-augmented organism.

This raises a number of intriguing points. Hybrid energy production is a useful talent, allowing greater efficiency and flexibility. Solar radiation is also the bulk energy resource on the planet - offering many orders of magnitude more power than chemical or thermal geophysical sources. So why don't we all do it? Obviously in an indirect fashion we do. Humans for example can produce vitamin-D by absorbing UV photons in our skin. Reptiles can do the same but they mainly need the direct thermal energy of sunlight to help maintain their internal temperatures. But actually generating fundamental power - electrical voltages that can be exploited for biochemistry - is another matter. There is probably a down-side, whether in terms of the biological expense of the necessary structures and chemistry, or in terms of the lifestyle that could make best use of a little solar electrical jolt - however that is all rather specific to terrestrial environments and the history of life here.

One wonders whether life elsewhere, in different circumstances, might have found better reason to walk around with a photon capturing carapace, opening up a whole range of interesting possibilities...
 

The ten most important questions for astrobiology: Number 4

Another big question, but this one is at the core of astrobiology. It also follows on quite nicely from the hubbub of bacteria seemingly utilizing arsenic rather than phosphorus (emphasis on seemingly).
As with the other questions there are some qualifications for Number 4:

How does life originate?


Strictly speaking the slightly modified version of this question that is really under the microscope is: How did life originate on Earth? However astrobiology has to set its sights high because the origin of life here may or may not represent the same type of origin as life out there. It's also true that one of the biggest scientific motivations for astrobiology is that in order to understand our own origins we desperately need a proper context. One planet with life, even if hugely complex and with a 3-4 billion year history, is still just one sample of a phenomenon. Seeing how this phenomenon operates  elsewhere in the universe would help answer all those nagging issues of probability, bio-chemical uniqueness, convergent evolution, and so on.

All signs point towards the existence of microbial life on Earth somewhere in the time-slot of 3.5 to 3.8 billion years ago - mainly from the fingerprints of ancient stromatolite rock structures, products of bacteria and archaea colonies. We really don't know how far back it all goes, owing to the dearth of unaltered continental crust from these times. We especially don't really know what was going on during and before the Late Heavy Bombardment - a period of massive pounding by asteroidal and cometary material about 4.1 to 3.8 billion years ago. It probably also doesn't make sense to be seeking a single 'moment' at which life sprung up and started tweeting. As a phenomenon of self-organizing, information carrying, reproducing, eating, pooping stuff, life in truth represents many interleaved networks and systems.

The bottom line is that right now we have no single clean answer to this question. Many, many hypotheses exist. These range from having life delivered pre-formed from other planets or star systems (panspermia) - which rather avoids the question - to an array of so-called 'pre-biotic' chemical scenarios that lead to the basic biotic molecules that we see today, or at least variants thereof. These include origins in atmospheric chemistry, deep sea vents, clay lattices,  and polycyclic aromatic hydrocarbons to name but a few. Then there are ideas that seek to tackle a possible transition from molecules to real, recognizable bio-structures - like cell membranes and catalyzing molecules. Coming from the other direction people have studied the potential ancestral forms of modern DNA. Since RNA molecules can serve as both information storage and enzymes (a role generally taken by proteins in modern biochemistry) then perhaps there was an 'RNA-world' before there was a DNA-world, a simpler, much more fluid and information-loose biology that eventually hit upon the more robust 'hard-drive' data storage offered by the DNA molecular structure.

In short - it's a tough problem. No one suggestion has yet had the ring of completeness, and it may be that there simply is no single mechanism, but rather a parallel series of critical steps and components that have to have a few tens of millions of years to cook the right pie. The environment of the kitchen probably plays a big role. Small rocky planets, with a nice rich chemical wash, and both stellar and geophysical energy input may well provide one of the most conducive environments in the universe...as far as we can tell.

An intriguing avenue of investigation may be coming around the horizon with the advent of artificial biological organisms - this type of reverse-engineering might just provide some unexpected clues. Similarly, as we better understand microbial and viral ecology there may be pointers to fundamental rules that haven't quite come into focus yet. In truth, it sure would be handy to have another biosphere to compare against...

Arsenic and old lace

Arsenic is an insidious element. With 5 outer valence electrons the arsenic atom is chemically similar to the biologically critical element phosphorus, but only in crude terms. Life depends extensively on phosphorus - it helps form the molecular backbone of DNA, it is part of molecules like Adenosine triphosphate (ATP) that serves as a vital rechargeable chemical battery within all living cells, as well as many other biologically vital roles. Arsenic on the other hand can weasel its way in, waving its valence electrons in a come-hither fashion, and getting the best seat in the house. The problem is that once an organism takes in arsenic, replacing some of its phosphorus, it typically begins to malfunction - arsenic is is a fatter atom and biochemistry is a sensitive thing. There is good reason why arsenic has long been a poison of choice for nefarious human dealings.

As is often the case though, microbial life has an exception to the rule. There was a flurry of buzz earlier this week about an astrobiology press-release, rumors of alien organisms were rife. Now the embargo is lifted we can reveal what the fuss was about. Wolfe-Simon and colleagues in a paper in Science this week present some remarkable discoveries made by tinkering with a particularly hardy strain of bacterium (actually a proteobacterium, part of a very diverse group). The bacterium Halomonadaceae GFAJ-1 is a halophile (salt-lover), found in the alkaline and hyper-saline Mono Lake in California. Many such bacteria are known to be highly tolerant of toxins, such as arsenic, but now it turns out this one is far more than merely tolerant.

While carefully culturing organisms from Mono Lake in the lab Wolfe-Simon et al. gradually removed phosphates from the food supply, replacing them with arsenic compounds tagged with radio-isotopes to enable them to be tracked into the bacterial cells. One bacterium, GFAJ-1 grew faster than anyone else. Not only did GFAJ-1 survive it swapped out its phosphorus for arsenic - in cell structures, and most remarkably, in DNA itself. It appears to be nature's own Transformer. It's pretty amazing. How does this organism keep a viable bio-chemical system running with the same molecular structures but with the fat arsenic atoms replacing phosphorus? It remains to be seen whether strict one-to-one replacement is really occurring, it's also the case that phosphates are still required by this organism, albeit in small amounts.

The notion that life might use arsenic instead of phosphorus has cropped up before. In particular its been wafted around as a plausible case of 'shadow life', a parallel type of life with a separate but contemporaneous origin to phosphorus using life. That's certainly an intriguing idea, although how and why GFAJ-1 would have switched over to phosphorus yet still retained the capacity to use arsenic is unclear.

For astrobiology it definitely offers encouragement that some of the seemingly hostile chemical environments in our solar system - Martian perchlorates for tea anyone? - may be ok for some very specialized 'niche' lifestyles. However in the broader context I think there's a hitch for talk of arsenic based life on other planets. Phosphorus itself is made by hefty stars over about 15 solar masses and in terms of cosmic abundance it is relatively scarce compared to other major bio-chemically important elements. It is roughly 1000 times less abundant than carbon. Nonetheless, in terrestrial life it is much more concentrated, only a factor of 30 or so less abundant than the carbon in your ham sandwich. So there is a bit of a bottleneck for life in terms of having enough phosphorus around - it wouldn't take much of a deficit of phosphorus in a forming planetary system to leave things barren. Now, if we wanted to postulate planets of arsenic-based life the problem is even more acute since arsenic is 1000 times less abundant than phosphorus - it's really a trace by comparison. Despite some of the breathless discussions already going on; the chances of arsenic-based planet-wide biospheres....slim to nonexistent.

The ten most important questions for astrobiology: Number 3

It would be easy to argue that the next question is too big, to broad, and too unanswerable to be in the list. Nonetheless it's a question that keeps cropping up and is also representative of the bigger and deeper issues that astrobiology must ultimately tackle. So, question number 3:

Is this universe particularly suited for the phenomenon of life?

Because this is a bit ambiguous there are some necessary qualifications. First, implicit in the way I've phrased this question is the idea that 'this universe' is either one of many or that it represents an instance of a phenomenon that somehow reoccurs. Second, and this is really just an expansion of the question, it suggests that life requires a particular range of physical laws and/or 'contents' in a universe to happen. Third, this question hits the button to sound the anthropic principle klaxon, opening a Pandora's box of weak and strong arguments about the timing of life, its privileged position and even its necessity for the existence of the universe in the first place.

It can be quite a morass, so I'll try to stick to the easy bits. The second item above can also be rephrased as a question about what the minimum requirements are for life to show up at some point, and whether some physical laws are more or less important. If we stick with carbon-based life then there's a ready laundry list, not least of which is the need for carbon in the first place. Carbon comes from the triple-alpha process in stellar nucleosynthesis. Intriguingly this set of nuclear reactions hinges critically on resonances between nuclear energy levels, allowing beryllium and helium nuclei to gracefully flop into forming a new carbon-12 nuclei. Without that coincidence then carbon would be little abundant in the universe, rather than the 4th most abundant element in the universe - after hydrogen, helium and oxygen. This resonance hinges in turn on the value of the fine-structure constant, describing the universal strength of electromagnetic interaction. Change this constant by a few percent and among the consequences you can kiss carbon goodbye.

Even if you feel you can do without carbon - preferring some alternative life chemistry - then a different fine structure constant also messes up things like covalent bonds in molecules, at least compared to the way they are around us. Before even getting to details like this if the universe had a different overall composition, or differing gravitational constant, or differing CP violation, then it could be radically different from the outset - perhaps never making any structures beyond individual atoms. In brief, there are a lot of things that seem to have to fall into place for something like us to come along.

Because we feel (rightly) incredibly uncomfortable with any notion we might be special to the universe (the universe clearly being special to us) then things get sticky, and answering question 3 hits a wall....unless we get to the first qualification I give above: the universe is one of many, whether contemporaneous (multiverses) or one of an endless succession (cyclical). An infinite number of universes, or quantum realities, are like the infinite number of monkeys with typewriters - somewhere amongst them will be the ones that can produce life like us. Much like the realization that carbon production requires something special - and indeed how Fred Hoyle came up with the physics for it - it may be that a version of the anthropic principle is actually telling us that there must be multiple universes, or else things are even more bizarre.

Astrobiology can't answer 3 yet, at least not in any satisfactory way. But finding out more about life in the universe, carbon-based or otherwise, could just possibly nudge us in the right direction.

The ten most important questions for astrobiology: Number 2

Question number 2 is close to home: Is there life elsewhere in our solar system?

For all the talk of exoplanets and habitable worlds out amongst the stars, our own humble solar system probably remains the most likely place for us to find the first convincing evidence for non-terrestrial organisms. Not only are there plausible environments for life to survive, they're close enough that we might hope to gather in-situ data. Mars is a great example, and for a mix of historical and practical reasons is still our main target for exobiological investigation. Evidence for past and present aqueous environments, as well as ongoing atmospheric chemical skulduggery - albeit contested and curiously correlated with some funky geophysical locations -  reinforce Mars as a critical target for astrobiology. The extraordinary high-def mapping of the martian surface by recent missions is key to helping us home in on places that might offer the best clues, and provide targets for upcoming missions like Curiosity, nee Mars Science Laboratory.

A sub-question that Mars raises, with its likely diverse climate history, is whether we're looking for fossils or living breathing organisms. In that context the real question at hand is perhaps better stated as whether there has ever been life elsewhere in the solar system. This opens up a whole slew of intriguing environments (while not excluding the possibility of extant life in any of them). The list includes: comet nuclei, big asteroids or dwarf planets, and moons like Europa, Ganymede, Titan, and Enceladus.

Cometary nuclei are more diverse than expected, the recent Hartley 2 flyby providing spectacular evidence of this. We already knew these bodies to be rich in organic chemistry and while finding signs of life within them may be pushing it a bit, they actually hit all the buttons for 'follow the water' and 'follow the chemistry' type strategies. As we move further out in the solar system then the typical volatile content (water and hydrocarbons) of bodies tends to increase - a characteristic left from  the proto-planetary disk temperature structure 4 billion years ago. The great moons of Jupiter and Saturn offer an extraordinary range of environments, from potentially vast subsurface oceans of liquid water (albeit likely full of noxious solubles) within Europa or Ganymede, to possible 'micro-environments' in Enceladus, to the novel and little probed cryo-chemistry of Titan's surface. A long way from the Sun these potential habitats can have a major energy input from phenomena like tidal heating, itself ultimately derived from nothing other than angular momentum.

Then there are nooks and crannies, some not so small, that may surprise us. The upper atmosphere of Venus can be positively temperate at the right altitude, and here on Earth it's increasingly apparent that microbial life among the clouds may be significant and substantial. Venus might not be a place to overlook after all.

The rub, and there is always one, is that getting to these places is tough. Then getting to the right spot, whether in a chasm on Mars or beneath ten kilometers of ice on Europa, is even tougher. Then there is the thorny issue of finding evidence of life if it's sparse. There are no magical CSI-like probes that conveniently produce the answers, and the problem of forward-contamination is ever-present. Nonetheless, question number 2 remains both very important and very much within our grasp, especially if we get past our space-exploration hangovers and recognize the critical role that our great wilderness in the sky can play in humanity's future.

The ten most important questions for astrobiology: Number 1

As our year approaches its end, with the planet slithering ever closer to where it was 12 months ago and towards its closest approach to the Sun on January 3rd, it seems like a good time to indulge in a highly biased and incomplete bit of rumination. There have been many tremendous discoveries and advances this past year, each inching us closer to tackling some of the core questions about life in the universe. Nonetheless, lots of big and important questions remain. Some approach the philosophical, some are quite narrow, but they're all interesting, and many overlap greatly. I thought I'd do a series of posts on the ones I particularly like, you may agree or disagree with the choices - a reasonable and necessary part of the process - but hopefully they will stimulate.

Number 1 is relatively non-challenging: Are there other planets like the Earth?

We're much, much closer to answering this than we were a year ago. As surveys for exoplanets increase in sensitivity, sample size, and sampling time it appears that small rocky worlds are essentially ubiquitous. With statistical estimates that at least 1 in 4 Sun like stars harbor Earth-sized planets within their habitable zones (extrapolating from shorter period objects) there is good reason to believe that Earth mass planets in comparable orbits are definitely out there. Kepler will help nail the rates to the wall. It will remain a tough question to tackle at a deeper level though. 'Like the Earth' is a bit ambiguous. Mass and orbit are one small piece. How many of these worlds have comparable chemistry, geophysics and climate? A good bet is that there are numerous cousin planets, recognizable but nonetheless a bit alien. That may of course be just fine. We're awfully biased about ourselves, often without recognizing the fact. One of my favorite mantras is that the modern Earth is not typical of our homeworld throughout its history. The suitability of the Earth today for life is a poor template to use.

So, if we treat 'like' as a broad qualification then the answer is almost certainly yes, and in another 12 months we'll have even better evidence supporting this.

Our leaky galaxy

A while back I wrote about the leakiness of our solar system - how significant amounts of material in the outer regions around the Sun could have really come from other stellar systems. Then I got on a bit of a jag about planets in other galaxies and the impending collision (well, one has to take a long-term view) with the Andromeda galaxy. Then lo and behold, like a fabulous new ice-cream flavor, someone turns up a new planet in the Milkyway that almost certainly came from another galaxy.

HIP 13044b is a giant world a little more massive than Jupiter orbiting a red giant star every 16 days, reported by Setiawan et al. in Science. Detected via the tell-tale velocity wobble of its host planet it might not garner much attention except for the fact that this system is part of the so-called Helmi star stream, some 2000 light years from us. The Helmi stream is the remnant of a dwarf galaxy that dove into the Milkyway sometime between 6 and 9 billion years ago, becoming shredded by galactic tidal forces.

Clearly the original host galaxy for this system was pretty puny, and one might argue that it was never truly distinct from the Milkyway - merely a part of its halo entourage, like some loose hair or slightly wayward limbs that would inevitably get subsumed. Nonetheless, it has some quite striking implications. The host star has an extremely low heavy element content - about a hundredth that of the Sun. This is the least element rich star yet found to host any type of planet. So the fact that it has at least one chunky world orbiting it is very interesting since lower heavy element abundance in stars correlates with a lower probability of giant planets. It's also an old and doddery star, well past its prime and has swollen in size as a result - possibly engulfing even shorter orbit planets, and possibly shedding some element-rich outer atmosphere.

Taken altogether it's another tick mark for planet formation being both a universal phenomenon and apparently a quite efficient one. As we learn more about the stellar populations in our galaxy we see just how messy they really are. Satellite galaxies can dive through the galactic plane, not just shedding their stars but also pulling out bona-fide Milkyway residents in their gravitational wakes. There may well be stars and planets that formed snug in our galactic disk that are now arcing over us, dragged tens of thousands of light years away from home. Remarkably, the opportunity to study planets with truly extragalactic origins may be all around.

The grains of Mars

We know that something is afoot on Mars. Apart from the surprising and intriguing measurements of atmospheric methane plumes there is clearly something funky about the chemistry of the Martian atmosphere that cleanses it of this organic gas in very short order. Various ideas have been put forward, including the possibility that there is some important effect of the dust that is often lofted skywards in the great Martian duststorms.

Now a new work here on Earth suggests that both our planet and Mars may share something in dusty atmospheric chemistry. Shaheen et al. report in the Proceedings of the National Academy of Sciences that they have painstakingly identified a set of chemical reactions that occur between ozone, water, and carbon dioxide on an incredibly thin layer on the surface of atmospheric dust. The smoking gun is an enhancement of the oxygen 17 isotope in carbonate material on the dust grains compared to other natural carbonate sources. Isotopic fractionation points towards a different chemical history, involving the formation of hydrogen peroxide on the dust grain surfaces.

Remarkably, a similar isotopic excess was known to lurk in one of the famed Martian meteorites from the Allan Hills finds in Antarctica. While this doesn't necessarily prove a common chemical mechanism it is very suggestive that the type of grain surface chemistry that occurs in the Earth's atmosphere may happen on Mars too. Dust-grain surfaces offer a fast way for chemistry to occur by capturing reactants into a solid/liquid layer. As Shaheen et al. point out, the unusual carbonate deposits in this meteorite that have provoked so much intrigue as potential micro-fossils could possibly just be aerosol produced carbonates - we just didn't know about this mechanism for their formation.

Dust grain chemistry is not just confined to planetary atmospheres. Interstellar and interplanetary dust (admittedly far more microscopic than most terrestrial or Martian dust) plays a critical role in astrochemistry - accelerating reactions that might otherwise take an eternity, and engaging in all manner of cycles for molecular chemistry in the relatively warm and wet environment of protoplanetary disks. Given that it's perhaps not so surprising that it should play an important role in the soupy airways of rocky planets. Interesting questions remain - does this chemistry offer clues to Mars' ability to scrub itself clean of methane, and can it provide another window into paleo-climate both on Mars and the Earth?

From Andromeda with Love

The galactic theme in the context of planets and life is an interesting one. Take our own particular circumstances. As unappealingly non-Copernican as it is there is no doubt that the Milkyway galaxy today is 'special'. This should not be confused with any notion that special galaxy=special humans, since it's really totally unclear that the astrophysical specialness of the galaxy has significant bearing on the likelihood of us sitting here picking our teeth. Nonetheless, the scientific method being what it is we need to pay attention to any and all observations with as little bias as possible - so asking the question of what a 'special' galaxy might mean for life is ok, just don't get too carried away.

First of all the Milkyway galaxy is big. As spiral galaxies go it's in the upper echelons of diameter and mass. In the relatively nearby universe it and our nearest big galaxy Andromeda are the sumo's in the room. This immediately makes it somewhat unusual, the great majority of galaxies in the observable universe are smaller. The relationship to Andromeda is also very particular. In effect the Milkyway and Andromeda are a binary pair, our mutual distortion of spacetime is resulting in us barreling together at about 80 miles a second. In about 3 billion years these two galaxies will begin a ponderous collision lasting for perhaps 100 million years or so. It will be a soft type of collision - individual stars are so tiny compared to the distances between them that they themselves are unlikely to collide, but the great masses of gas and dust in the two galaxies will smack together - triggering the formation of new stars and planetary systems.

Some dynamical models suggest that our solar system could be flung further away from the center of the merging galaxies, others indicate it could end up thrown towards the newly forming stellar core of a future Goliath galaxy. Does any of this matter for life? For us the answer may be moot. In about only 1 billion years the Sun will have grown luminous enough that the temperate climate we enjoy on the Earth may be long gone. In 3 billion years it may be luminous enough that Mars, if not utterly dried out and devoid of atmosphere by then, could sustain 'habitable' temperatures. Depending on where the vagaries of gravitational dynamics take the solar system as Andromeda comes lumbering through we might end up surrounded by the pop and crackle of supernova as the collision-induced formation of new massive stars gets underway. All in all it doesn't look too good. But for other places, solar systems that we see forming today, it could be a very different story.

Imagine a terrestrial world just beginning to form right now. By the time Andromeda is ploughing through our galaxy in 3-4 billion years, merging and settling, there could be a species sitting there writing a blog about what a 'special' time and place they exist in. They might marvel at how fortuitous it was for their sun to be thrown further out from the new galactic center - away from all those nasty supernova. They might stare in awe at the myriad new planetary systems being formed as the gas from these cousin galaxies collides, a golden era for new worlds. They would doubtless write papers on how galactic mergers might be signposts to highly habitable regions of the universe - unlike all those boring isolated galaxies out there. It sounds like they're getting carried away, but really they're not doing anything we don't already. Getting perspective is one of the most difficult things to do, especially from our tiny mote of existence.

The Galaxy is Not Enough

Megalomania can sometimes be good. Well, with a lot of emphasis on the 'sometimes'. Here we are as a species, scooping up detections of planets around other stars at a ferocious rate. Our galaxy is however a big place, and we're going to be sifting through its two hundred billion or so stars for a very, very long time. Eventually though, presuming that we remain aware of the deeper meanings of the word civilization, we might find ourselves not content to be just parochially curious. We talk about life in the universe but the Milkyway is merely one of a couple hundred billion galaxies in the observable cosmos. Can we seek out planets in other galaxies?

Even now the answer is a surprising 'almost'. A paper by Ingrosso et al. about a year ago in the Monthly Notices of the Royal Astronomical Society, discusses in detail the possibility of seeing evidence for planetary mass objects in gravitational microlensing events occurring in the Andromeda galaxy (M31) - a mere 2.5 million light years away across our backyard. As with lensing detection of planets in our own galaxy the mechanism is that a foreground star with planets (in this case within Andromeda) acts as a gravitational lens on the light from a background star (also in Andromeda), dramatically magnifying it as the two systems drift into close alignment from our point-of-view. At the distance of Andromeda the best we can do is see 'pixel-lensing', which is a variation in the number of photons coming from individual pixels in our digital cameras, each of which contains the light from many indistinguishable stars - too close together on the sky to be separated. During magnification the tiny lensing effect of planets can also be greatly enhanced, adding characteristic spikes and wiggles to the way the light varies during the alignment.

By carefully modeling what one might expect to see, Ingrosso et al. demonstrate that there is a pretty good chance that in a few percent of Andromeda lensing events you should find the signs of Jupiter-scale planets if they are there. They even go so far as to offer support for the detection of a 6 Jupiter mass planet in a rather funky lensing event seen in Andromeda by An et al. with the gripping name of PA-99-N2. As with all micro-lensing studies there are huge challenges owing to the amount of data needed to spot events and to fully characterize them as they play out over days to weeks. The pay-off is an incredible statistical cleanliness and sensitivity.

Probing for planets in Andromeda may therefore be fruitful. What of further afield? There's the rub. The same technique might be applied to more distant galaxies, but it will require bigger telescopes, capable of fitting more pixels across the faces of these stellar swarms. It could be worth it though. Suppose we were able to evaluate the planetary populations (albeit statistically) in a representative chunk of intergalactic space. That would be an incredibly interesting set of numbers. It would tell us what galaxy types - elliptical to spiral - are most fertile grounds for other worlds, and take us closer to answering the question of the true capacity of this universe for life.

Necropanspermia

It's a fitting title for a few days past Halloween. Sugar withdrawal and the odor of gently scorching pumpkin fresh in our minds. This term - necropanspermia - is a new one to me, and comes from a thorough and carefully put together paper that popped up this morning from Paul Wesson. Although it is ostensibly a review of the ideas of panspermia (and a nice balanced one at that), it also gets to some rather interesting points.

The transfer of planetary - potentially life-carrying - material between stellar systems seems only likely for tiny particles. Dust grains of a few to a few tens of microns across are the ultimate solar sailors. The radiation pressure of photons from one star accelerates these minute pieces across interstellar space. Routes that lead into new solar systems result in the gentle deceleration of the dust as it plunges into the photon cloud of a star, and the possibility exists of being swept into the atmosphere of any handy planets - just as happens here on Earth. The question is what, if any, viable organisms can hold up over millions of years of interstellar transport - subject to cosmic rays and high-energy photons - to re-plant on a new world?

Wesson's discussion takes a rather interesting direction. He argues both that viral material may be prevalent, and that this type of fragmented DNA/RNA may be quite sufficient to help 'seed' life in new environments. One motivation for suggesting this is the conclusion that most transferred organisms are dead-on-arrival, there just doesn't seem to be a way that intact DNA and/or cells are going to survive their trans-galactic journeys. Another motivation is simple physics - a microscopic dust grain might barely have space for one poorly protected bacterium, but it could easily harbor a hundred much smaller viruses.

The hypothesis that there was an ancient 'viral world' here on the Earth - complete with unique viral genes that help replication - has been around for a while. While even viruses might not arrive intact after interstellar transit, this might be far less of a problem, since they play fast and loose with their molecules in the first place. It's an interesting twist to the long and checkered history of the idea of panspermia - perhaps we should be rushing cosmic dust particles from high in our atmosphere off to the labs for some quick looks for viral DNA?

1 in 4

Having sweated over my previous post I'm hesitant to knock it off the top slot, but this is too good to pass up. Appearing in the 29th October issue of Science is a wonderful paper by Howard et al. The bottom line is that they have made as careful a statistical study of Doppler detected planets as seems practical at this time. The results of monitoring 166 relatively nearby normal stars for five years indicates that an astonishing 1 in 4 such stars may harbor small Earth-mass planets on close orbits.

It's important to be very clear, the planets actually detected in this survey are rocky objects a few times the mass of the Earth, and they are emphatically not in the classically defined habitable zone of these stars - orbiting within 0.25 AU (a quarter of the distance of the Earth from the Sun). However, the extrapolation to true Earth-mass objects is pretty likely to be robust. It'd better be, this claim is effectively saying that there are tens of billions of such planets in our galaxy and that they outnumber giant worlds in close orbits.

This presents a big challenge to certain aspects of how we think planets form. Most current models suggest that there should in fact be a deficit in small rocky worlds in these close-in orbits, since the processes of orbital migration or runaway planet growth tend to thin this population drastically. Something is afoot - and it may also indicate that those holy grail worlds - the Earths in the habitable zone - are far more numerous than we had dared to hope. Indeed, the authors of this paper suggest that Earth-mass planets orbiting at 1AU could be more numerous than their close-orbit cousins.

Howard et al. end their paper by evaluating the implications for Kepler results. It's awfully promising - as many as 260 Earth sized (1 to 2 times Earth radius) planets with 50 day or less orbital periods should be coming our way, and who knows what in the habitable zone of Kepler stars...

Megavirus vs Bicosoecid

It would make an excellent B-movie (if that's not an oxymoron). Giant virus attacks! Come see the battle for supremacy in technicolor 3D-surround sound!

Viruses lurk at the hairy edge of what we generally consider to be 'living' things. Small infectious structures, they replicate only by digging into a host's intracellular environment and hitching a ride. The smallest are barely 10 nanometers across - the size of a wavelength of ultraviolet light - and coded for by only a few thousand nucleotide base-pairs (compared to the more than 3 billion that code a human). Vast numbers of viruses exist in nature. In marine environments there can be 250 million individuals per milliliter of water, most of them so-called bacteriophages - targeting microbial hosts. Viruses play fast and loose with genetic material, clipping, swapping, dropping and incorporating at a mind-boggling rate. There is no doubt that they have played a critical role in the molecular evolution of life on Earth over the past 4 billion or so years. Our human genome contains millions of fragments of viral DNA - accumulated by our distant, distant ancestors and ourselves. Viruses bring into question even the very notion of 'species', we are all molecular ragdolls, a button sewn on here, a piece of thread incorporated there.

A newly discovered virus steps up the ante (and adds to the zoo of such things). Infecting a single-celled marine organism known as Cafeteria roenbergensis (good name, apparently it's a voracious eater) this virus is a monster. Its genetic makeup is 730,000 base-pairs, with 500 regions that look like bona-fide genes, many likely involved in making protein structures - something most viruses don't bother with. Like all viruses it's not a cellular organism, but here it is doing much of what regular living things do. It not only seems to have genes that could help make cell membranes, it even seems to have stolen genes directly from bacteria.

The line between this remarkable structure and 'life' is thin indeed and I think makes it very clear that there is more of a continuum than any dramatic 'jump' between complex molecules and what we clearly recognize as organisms. We have barely scratched the surface in our understanding of the relentless activity of the microscopic world. Intriguingly this Megavirus infects one of the major predators of the marine microbial environment. In that context it's hitching a ride with an organism that hoovers up both bacteria and viruses as food. What an excellent smorgasbord of genetic material it must see, one cannot help but wonder if that opportunity has helped it build its own massive library.

In the quest for life in the cosmos, and particularly as we continue to poke around in our own solar system, we need to think carefully about what we are looking for. Fragments of DNA from a formerly aqueous environment on Mars - should they ever be found - would likely offer a window into this borderworld  between molecules and self-contained organisms. It's going to be messy.

Scale-free mobility

Some ideas feel like an itch that you can't quite scratch because it's hard to pin down, but you really want to. A recent paper by Young et al. in Nature Physics (and available here), along with a commentary by Brockmann feels a little bit like that - at least when seen through the soupy goggles of astrobiology. On the surface this paper appears pretty innocent. It studies the nature of human mobility. With the rise of data-logging; from global positioning, cell-phone records, and the colossal airline databases of 3 billion annual travelers there is unprecedented material for studying exactly how we move around the planet. Not surprisingly we exhibit particular statistical patterns. For both distances traveled and 'rest times' (how long we linger over a cup of coffee or beneath the umbrella of some tropical beach) the distributions are inverse power laws. In plain language this means that we are more likely to travel short distances and to spend little time in any one place during travel.

There's nothing that sounds particularly revolutionary about that. But it gets more interesting. As Young et al. discuss, the particular shape of the statistics appears to be modeled rather well with a form of 'preferential return'. In other words although we may explore - making new journeys - we are more likely to travel to locations that we already know.  Not only that but the more locations that we already know the less likely we are to explore new ones at all. This naturally produces a so-called scale-free distribution - if you go out to any particular pub then there will be another pub that you are twice as likely to visit, and another one that is half as likely to have your patronage. The Young et al. model boils down to assigning a probability for any given 'step' in an individual's travels that results in exploration (a new location). They give this as the number of prior travel steps to the inverse-power of....0.2.

Why 0.2 ? Nobody knows, but this describes the way human populations explore the world - individuals will deviate from this pattern, but en-masse this is what we do. It's a deceptively simple, but extremely provocative result. Does this same kind of probabilistic scaling apply to other species? Do other species have a different power law value than 0.2? What are the implications for the occupation of niches by organisms on a planetary scale and throughout the history of life? This implicit tendency for exploration to slow down in favor of re-visiting known locations makes me wonder about a recent discovery on the global East-West divide in marine microbial genetics. While environmental differences are the most obvious root bio-physical cause (particularly the differing soluble phosphorus amounts in the Atlantic vs. Pacific oceans), does this give rise to a similar 'preferential return' scaling?

Then, to return to a popular theme - is there something to be learnt from this model for the questions of life exploring the cosmos beyond a planetary homeworld? On the face of it the more you explore the more likely you are to slow down and just keep circulating amongst the places you know. Clearly the present data represents humans who are not, we presume, exploring for survival or vital resources - lattes don't count. Nonetheless it is reasonable to hypothesize that humans behave this way because there is some circumstantial evolutionary advantage to it. The hard-to-pin-down-itch is that one suspects there is something deeper - perhaps universal -  in all this, waiting to be ferreted out.

Blowing hot and cold

Understanding the structure, dynamics, and chemistry of planetary atmospheres is key to exoplanetary science. It's sobering then that as of now it is still an enormous challenge to even model the atmospheres of planets in our own solar system. Despite great advances a variety of trickery has to be employed to simulate something like the Jovian atmosphere, such as pretending that it has a very different soupiness and energy transport in order to overcome computational demands. Modeling the atmospheres of gas giant exoplanets is even more in its infancy. An intriguing result in the past week has come from Crossfield et al. and their study of how we see the infrared light varying in the planetary system of Upsilon Andromedae. Their Spitzer space telescope phase photometry on Ups And reveals the glow emitted by the innermost, roughly Jupiter sized, planet around this F dwarf star (about 1.3 times the mass of the Sun).

The planet orbits very tightly, every 4.6 days, and is expected to have been evolved by tidal interaction with the star to a state of spin-orbit-synchronicity - in other words, in the simplest case, its day will equal its year and there will be permanent day/night sides. This sets the planet up for an extreme case of thermal disparity. We'd expect hot atmosphere from the dayside to flow to the cold night half of the planet - in doing so there might be great jet-stream like structures, and the hottest point of the planet might get shifted along in the direction of these winds. Something like this seems to be happening on Ups And b, but to an extent that is truly puzzling. As it zips around in its orbit the glow of its hot atmosphere betrays the temperature distribution and is seen in the varying number of infrared photons collected by Spitzer. It's not in synch with the planet orbit - or more specifically it is systematically offset or phase shifted by almost 90 degrees. In other words the hottest side of the planet is almost at right angles to the direction of the star. On the Earth this would be a bit like saying the hottest time of day is at sunset instead of noon.

It's a puzzle. Some amount of offset might be expected, driven by the strong hot to cold winds, but this is extreme. There are various possibilities - maybe the stellar heating is reaching to greater depths in the planetary atmosphere than expected and altering the fundamental dynamics. Perhaps the winds are so strong that they are going supersonic, forming great shock waves that pile energy up on this side of the planet. It's a tough call - even models of these hot Jupiter-like planets disagree on such things, and none of them predict exactly what we see on Ups And b. The good thing about this result is that it challenges the modelers to really sort out what works and what doesn't - advances will be made.

Crossfield et al. also end their paper with an interesting fact. This system of Ups And is actually too bright for the upcoming James Webb Space Telescope (JWST) to observe at shorter wavelengths - its sensitive instruments would simply be saturated with photons. They further point out that a small space telescope dedicated to studying the phase curves of nearby hot-Jupiter systems might just provide the data needed to crack the problems of these extraordinary regimes of planetary atmospherics. This is a sentiment that could also apply to the hunt for terrestrial-type exoplanets - especially those that transit stars much closer than the distant Kepler objects - we need a dedicated all-sky survey to find the targets for powerhouse instruments like JWST.

Cosmic minds

In recent months there has been more discussion around about the idea that 'advanced' life in the universe might employ artificial intelligences to do the dirty work of exploring. Indeed, AI might just push off on its own accord and could, it is presumed, be made effectively immortal. These patient devices could then withstand the enormous times and extreme environments involved in crossing interstellar, or even intergalactic, space. In part these ideas are an attempt to narrow the search parameters for our efforts to spot signs of intelligent life in the universe - as nicely discussed by Paul Gilster. There is something intriguing about these notions, but they also raise some other questions. I thought I'd try to stir things up a bit.

Without getting too deeply into the meaning of AI (Turing tests and the like), it's interesting to consider the history of attempts to build such things here on Earth. In the late 1950's there was a huge push to construct an AI, everyone felt it was only a decade or so away, governments dumped money into research - to little obvious avail except for general advances in computing. In the early 1980's there was another bout of enthusiasm and billions of dollars got funneled into AI work. Most of the focus was on the idea of expert systems - the idea that much of intelligence stems from the ability to assimilate and utilize large amounts of data; knowledge was the fuel for AI. Another bubble has happened more recently with the notion that true AI cannot be some disembodied piece of code, it needs a robotic avatar in the real world. Incredible things have been done in the name of AI. The fundamentals of modern programming have to some extent been reshaped by this thinking, and we indeed now experience the rudiments of AI every time Amazon or Netflix gleefully present us with 'suggestions' for what we might want to spend our money on. However, the true AI that we all imagine is nowhere yet to be seen.

Indeed, there are even deeper questions and doubts about the whole idea of a physical machine that can mimic a living mind. Roger Penrose in his dense but fascinating 480 page argument - The Emperor's New Mind - made a pretty sobering case that quantum mechanical processes are central to our type of intelligence. Of course this was written prior to gains in quantum computation, but its thesis has not yet been disproved.

So where am I going with all this? I think there are two important, although speculative, points that come from our baby-steps in AI. The first is the idea that if we keep working at it then one day an AI will 'appear', like a new iPad or model of car. What if that conceit is just wrong? It certainly appears incorrect so far.  It may be that AI is something that emerges very, very gradually. So gradually in fact that we barely realize it's happening, just like the processes of natural selection and evolution. As we upload more and more of ourselves - our knowledge - onto Google or Facebook we may actually be pushing the process along, but we could have a thousand years or more to go. The second point is related. What if Penrose is correct, and only quantum processes have access to the right amount and type of computing power for intelligence? True AI may well be indistinguishable from biology.

What this could mean is that there will never be AIs in the universe that can be distinguished from their biological parents (I know, shades of Battlestar Galactica, but fiction is often prescient). There could be 'dumb' AI explorers - complex machines of limited flexibility - but there will never be true AI exploration, because those AI would likely be subject to the same problems that we have with interstellar distances and timescales. Thus,  if we want to try to define a more targeted set of search criteria for 'intelligent' life in the universe (which is certainly not a bad idea), there are probably two options. One set of life is going to be just like us - whether it's AI or not. The other is going to be extremely machine-like, not super-Turing-test-smart, but well programmed and equipped with a big knowledge base. So the question is, what would exo-Google be doing out there in the universe?....

Through the halo

The technology for detecting planets continues to advance. A new paper by Sascha and colleagues contains the first direct imaging data of a planet obtained with an emerging optical technology called an apodized phase plate. Interestingly this builds on a set of ideas that have also been kicking around for a while in microscopy - the techniques for peering into the infinitesimal can also help us peer into the infinite.

The classic difficulty in looking directly at exoplanets is that they always appear extraordinarily close to their parent stars on the sky. Stars are millions to billions of times brighter than planets (depending on the precise wavelength of observation), and the wave nature of light always results in the blurring, or diffraction, of light as it passes through any kind of optical instrument. So the starlight ends up swamping out the feeble emission or reflection from any orbiting planets. Getting rid of the starlight is an entire field of research unto itself. Methods such as coronagraphy, and the rather ominous sounding nulling interferometry all seek to remove or suppress the light of the star, leaving behind the glimmer of any planets. It's been likened to trying to spot fireflies in the glare of a searchlight when you're thousands of miles away - that's not a bad analogy.

The apodized phase plate is a nifty bit of trickery. An earlier paper in 2007 by Kenworthy et al. describes the application to astronomy. In a nutshell the plate (combined with a coronagraph - a disk directly blocking some of the light of the star in the image) is a transparent chunk of material - in this case zinc selenide which is highly transparent in infrared wavelengths - that is modified to introduce a complex spatial pattern of phase changes to incoming light. Ok, so that's not so much a nutshell as a mouthful of walnut. Imagine a watery surface with light reflecting from it. You've undoubtedly seen this happen - wonderfully varied patterns of light and dark occur in the reflected light, the stuff of a summers day, shimmering on the hulls of boats, or off the dirty dishes in a kitchen sink. What you're observing are the phase shifts in the light - tiny time delays because a watery surface is not perfectly flat. If the phase shifts are out of sync light cancels out, if they're in sync it adds together - and we see dark and light regions in the reflected images.

The phase plate exploits the same physics, but in a careful, mathematically controlled way. Its 'rippled' surface adds time delays in pre-determined locations across the beam of light from a distant stellar system. These are cleverly designed so that on one side of the final image the light of the star gets blanked out (nulled), but the light of any planets remains. It's a tough challenge to get this to work. You also have to remove as much of the other sources of blurriness - like that induced by Earth's own atmosphere - as possible. Sascha et al. seem to have accomplished this, re-detecting a giant planet around the young star beta Pictoris, on an orbit of a mere 7 astronomical units (that's between Jupiter and Saturn if it were our solar system).

It's a terrific step. There are certainly many side effects of such trickery - a narrow waveband, imagery of only one side of the star, calibration challenges - but together with many other emerging techniques it does seem that we're well on our way to doing even richer exoplanetary science.

We salute you...

Bacteria. Asexual lords and masters of the planet. An extraordinary and fascinating piece of work has popped up that indicates a form of bacterial networking that inches this sentiment even further along from the figurative to the literal. In a study of the bacterium S. oneidensis (an organism capable of actually reducing, or 'breathing', heavy metals) El-Naggar and colleagues find that when stressed these microscopic lifeforms can grow so-called bacterial nano-wires. These incredibly thin protrusions - really stalks of protein - exhibit electrical conductivity. This work builds on earlier studies that also hinted as this property.
They're no piece of copper when it comes to transporting electrons, but they seem to be on a par with semi-conductor materials.

The experimental work is quite wonderful, and shows that colonies of S. oneidensis may actually link themselves together in a remarkable type of electrical grid. Why do they do this, are they just engaged in some form of microbial Facebook? The answer may be one of survival. The respiration of S. oneidensis is acutely dependent on the ability to off-load unwanted electrons - performing chemical reduction on anything able to accept the electrons. If a single individual can't dump its electrons it dies. So, if you can send out nano-wires and make an electrical connection with someone else you can pass off your particles - and if that individual can't accept them it can simply re-route the current further along the network, until eventually it gets slurped up. It's an incredible ability, the colony comes to the rescue of the few, and nobody has to get out of their armchair.

As the researchers point out, beyond enabling the group to respire and survive, bacterial nano-wires open up a whole new avenue of fast communication - much speedier than chemical signaling. One cannot help but see a parallel between this situation and the web of neurons and electrical synapses lurking between our own ears. The more we learn about life on Earth, the more blurred the line becomes between 'simple' and 'complex' life, and the more archaic that classification appears.