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

Monday, May 31, 2010


A couple of weeks ago I talked to Robert Krulwich of National Public Radio (NPR) about a number of things. Amongst these was the so-called 'Wow!' signal. This was a narrow-band radio signal (possibly a 'burst', possibly the tail-end of a longer period of emission) picked up by the Big Ear radio telescope in Ohio in August 1977. Big Ear was engaged in a scan of part of the sky for the Search for Extraterrestrial Intelligence (SETI) - looking for anything that appeared artificial but not terrestrial. The 'Wow!' signal remains one of the most intriguing examples of transient radio emission probably not of terrestrial origin.

The whole story is given at the NPR site, and you can listen to the program, which is a nicely constructed piece. I voiced what I think is the general opinion of many scientists, a lot of skepticism but also an acknowledgement that it's probably good that SETI carries on. Like all these interviews, what got broadcast is trimmed down from perhaps an hour of conversation, maybe someday you'll hear further pearls of attempted wisdom that ended up in the edit buffer.

Monday, May 24, 2010

Artificial Life: some assembly required

Inoculated as we are against surprise, a dubious gift of the internet and our information overloaded age, there are still things that are best heard sitting down with a stiff drink. The announcement last week by Gibson et al. and the J. Craig Venter Institute of the creation of 'artificial life' was indeed best heard this way.

The 'Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome' is a landmark work. So what did these guys do ? Put simply, they built complete genomes - stretches of circularly linked DNA of about 1.08 million nucleic acid base-pairs - according to the known blueprint of a real organism, the bacterium Mycoplasma mycoides. They then stuffed these genomes into the cells of another bacterium, that had been scraped clean of native DNA, and managed to get these new artificial-synthetic-hybrid organisms to multiply and function as if they were natural.

A number of things stand out as remarkable (apart from the estimated $40M price tag, which may make these the most valuable bacteria ever). The first is deceptively mundane. In publishing this result they also released a pretty complete 'read these instructions before attempting assembly' paper. Running to 29 pages it's a wee bit more complex than your typical flat-pack from IKEA, and probably a bit more frustrating, but here it is, a step-by-step guide to how to glue one thousand pre-made base sequences of 1080 base-pairs length together to make an organism. At first one's reaction is 'cool', then as it sinks in the questions begin.

What strikes me is how this is surely the ultimate nail in the coffin of the idea of 'vitalism'. That is the notion, harking back a couple of thousand years, that life is somehow imbued with a vital spark, is something more than the sum of the parts, is special. This experiment, to my mind, is saying nope, it's really quite ordinary. Stick the right molecules together in the right order, provide the right environment, and let it go. Now of course the blueprint was taken from nature, not designed (apart from the cheeky base-pair watermarks quoting James Joyce and providing email addresses,  distinguishing the new bacteria). I think it'd be hard to argue though that there is something 'vital' about the design - a printable list of 1.08 million A's, T's, C's and G's. Of course life is still a remarkable phenomenon, and by the time you get to complex organisms like us it's increasingly difficult to peel away the layers to say that we're not 'special'. But this is an amazing and complex universe, apparently capable of assembling such intricate structures - given time and the right conditions. To paraphrase Arthur C. Clarke; any sufficiently complex phenomenon is indistinguishable from magic.

Thursday, May 20, 2010

A calcium rich diet

There are often a bewildering array of new things to talk about, percolating up through the scientific press. The amazing thing is how many new discoveries or ideas are relevant to the quest for an understanding of the origins of life in the universe. Perhaps this isn't surprising though. In terms of physics and chemistry the phenomenon of life (at least the terrestrial version) is linked through just about every level, from quantum mechanics to the particular cosmic time we find ourselves in.

A nice paper showed up in Nature this week by Perets et al. that details a picture of a new type of supernova, based on observations of a system that went 'pop' in a distant galaxy some 110 million years ago. As the photons from this distant cataclysm showed up on Earth in 2005 it was apparent that this stellar explosion belonged to a new category of 'calcium rich' supernova. Perets et al. argue that a low-mass white dwarf (an old stellar core) in a close binary configuration with another star was stealing helium from its companion, until it could gorge no more and gravity caused a catastrophic thermonuclear reaction. Boom. It's by no means certain that this is precisely what happened. Indeed, another paper in Nature presents an alternative model - but if these offbeat supernova are reasonably common then they could be the culprits behind the decent helping of calcium floating around in not just that distant galaxy, but our own as well.

Calcium, forged in these events and spewed out into interstellar space, eventually ends up incorporated into  subsequent generations of stars, and planets. Calcium isn't just good for your bones, it plays a critical role in  cellular processes as a signaling mechanism that helps keep enzymes and proteins in check. On the Earth its also a major part of our lithosphere, in carbonate rocks and dissolved in the oceans. Without calcium the carbon-silicate cycle that keeps our terrestrial climate under control over hundreds of thousands of years would not operate since calcium ions help 'scrub' carbon-dioxide from the atmosphere.

So, we probably owe a couple of major and critical pieces of our happy existence to a particular class of greedy little white dwarfs. Why do these guys go pop ? Well, before they overeat they are prevented from collapsing under their own weight by quantum mechanical degeneracy pressure - a wonderful consequence of the Pauli exclusion principle. When this fails to support the dwarf it's all over. Perets et al. argue for a slightly less complete failure, with runaway helium fusion at the dwarf's surface, but that only happens because the stage is set by degeneracy pressure keeping such a massive, dense, object alive.

Quantum mechanics and gravity, enjoy that milkshake.

Monday, May 17, 2010

Intelligence and life

It really must be in the water, or perhaps it's the 50th anniversary of SETI. Yet again I've found myself in recent days trying to answer questions about whether or not there's intelligent life elsewhere in the universe.  Yet again I find myself in the role of sourpuss, or is that sceptic? One item that actually helped focus this for me was another question on how aliens might show up brandishing their weapons and licking their lip-like-features, before squishing humanity.

Let's just go through this. Do I think there's life - recognizably familiar, reproducing, information carrying arrangements of molecules - elsewhere in the universe? I think there's an awfully good chance. Do I think any of it's 'intelligent', like wot we are? Well, I think the odds are far worse, but given the size of the universe then sure, it just may be tucked away somewhere we'll never, ever, know about. So, on the face of it this kind of kills the notion of the mother-ship arriving over suburbia and hordes of iPhone wielding creatures texting us into submission. Except...well, except that there's another way to look at things.

I'll start by saying that I know this is not an original idea. Let's take the history of life on Earth. Intelligence - in the form of machine creating, modeling, mathematically fixated organisms - has not played a big role over the past 4 billion years. Dinosaurs were fabulously successful as a type of life, a hundred million years of romping (plus all the chickens running around today), extraordinary adaptations and variations...but not a wheel, differential equation, or moon shot in sight. Humans, by really all measures, are freakish - an extraordinary and wonderful oddity. This doesn't even begin to address the issue of the microbes, ancient and incredible terraformers and survivors, but no intelligence in the way we define it.

Given all of that, I think in-the-incredibly-unlikely-event that aliens show up on our doorstep they will be no smarter than your average jellyfish. They will not have built spaceships, at least not the way we think about spaceships, with flush toilets. They might have built some kind of structure to carry them through space, much in the same way that ants build a nest, or hermit crabs snag a nice shell, but they won't be doing this as an outcome of design review, they'll be doing it instinctively. These will be organisms that have evolved to treat space much like we treat the oceans. Sailing, drifting, or zooming, when they find a useful resource (if they need such things) they make planetfall and set to work, maybe like locusts, or maybe less destructively.

Is this crazy? Maybe, but less so than the other options. There are still significant physics problems. Assuming any such life originated on a planet, then climbing out of that gravity well is always going to be tough. Perhaps this filters out all but the tiniest organisms, lofted up to the exosphere, evaporated out into space. Or perhaps it filters out all but the oddities....

Obviously I should stop drinking the water.

Sunday, May 16, 2010

The fountains of Earth

The Earth is wet. Not only does it have substantial surface oceans, the outer part of the planet - the lithosphere - also contains a healthy amount of water and other volatile compounds. Exactly where all this water came from during the planet's assembly some 4 billion years ago has long been debated. Although objects like comets - prone to smack into the Earth every so often - can carry a lot of water, it's not quite the right flavor to match the stuff sloshing around in your bathtub. Comets carry more deuterium (heavy hydrogen) in their water molecules than the terrestrial version. One solution is that another family of celestial objects; asteroids or meteorites, are the culprits. Formed at warmer, less distant places in the young solar system, some of these rocky bodies carry just about the right deuterium mix.

There's another issue though. Did the water get 'painted' into the surface of the young Earth in a veneer, or was it implanted earlier on, as a more integral part of the planet's composition? A new paper in Science this past week seems to shed some light on the question. By studying isotopic ratios of silver, as well as some other elements, the authors were able to demonstrate similarities between the composition of rocks from the Earth's mantle and some types of so-called primitive meteorites. But they hit a snag - one set of measurements suggests that the Earth's inner core formed very quickly, in a mere 10 million years, the other suggests a much more leisurely process, taking up to 100 million years. The neat solution that they offer up is that as the Earth assembled from lumps of material agglomerating due to gravity, the composition of the lumps changed over time. The starter mix was much drier than the later stuff.

They also point out that the addition of water-rich material could have pretty much all happened when the Earth was hit by a Mars-sized proto-planet, long hypothesized as responsible for the formation of the Moon, 4.53 billion years ago. Here's the bit that I find most interesting. Based on their model this proto-planet would have actually had a very similar composition to that of the young Mars. Picture our baby solar system, with another substantial, terrestrial-like, planet forming in a similar orbit to the Earth. Although gravitational dynamics probably sealed its fate early on, I cannot help but wonder if a few small nudges could have set things off along a very different track, to a dry Earth and an additional, significant, wet world...

Wednesday, May 12, 2010

Universal Common Grandma

A profoundly interesting and important question is whether or not all of the life we see on Earth today has one common ancestor - we'll call that organism 'Grandma' - or whether the great domains of bacteria, archaea, and eukarya (such as ourselves) have a number of deep, ancient, and unrelated ancestors. This is a big question from the point of view of understanding the history of life on this planet, and also possibly for understanding more about the origins of life - at what point did recognizable things arise? A brand new study, delving deeply into the statistical relationships of key bits of genetic code seen across modern organisms, seems to point to a single 'Grandma'.

This work, hot off the presses at Nature is by Douglas Theobald, together with a nice opinion piece by Steel and Penny, is quite a tour-de-force of advanced statistics incorporating Bayesian methods to look at correlations in amino acid sequences between different species. The bottom line is that a single 'Grandma' is about 100,000 times more likely than multiple grandmas. The author and commentators point out that this is not really anything terribly shocking, the received wisdom has long been that all modern life has a common 'Grandma' ancestor. It is however a very nice piece of quantitative analysis that breaks through some significant  hurdles - such as the horizontal transfer of microbial genes that hugely complicates this type of detective work.

Does this mean that life only arose once on the Earth? Well, as Steel and Penny discuss, no it doesn't. It only means there's a high probability that the three great domains that we see today have the same 'Grandma'. If there were other, genuinely distinct branches of early life then their genetic imprint may be gone forever. What I find remarkable, in retrospect, is that the incredible diversity of species we see today could indeed come from just one, with a few billion years of natural selection thrown into the mix. So much for life being prone to evolutionary bottlenecks....

Monday, May 10, 2010

The YouTube Universe

A year or so ago I gave a public lecture to a very general audience called 'Protons to Planets to Penguins'. It was a very brief, and somewhat simplified, overview of how the chemistry of life is something that we see out in the cosmos - carbon molecules and the like. By way of an experiment I decided to make a narrated slide show and upload it to YouTube. If you're feeling like killing 5 minutes of time, or have some other masochistic inclination then take a peek. I've resisted the urge to embed the video here for aesthetic reasons...honestly.

Sunday, May 9, 2010

Into the core

I've been putting the finishing touches on a paper that describes an investigation into whether planets that orbit very close to their parent stars can visibly alter or disturb the radiation output of those stars. Actually, `visible' is a bit of a misnomer, since the study looks into the X-ray photons pouring out from the million degree plasma surrounding stars, known as the corona. This tenuous, super hot, mix of raw nuclei, electrons and ions is the result of as-of-yet not fully understood energy transfer from the much cooler (a mere few thousand degrees) visible surface of stars. Magnetic fields almost certainly play a big role in this heating, and a star like the Sun has a doozy of a magnetic field. So too do gas giant planets. Jupiter has a roughly averaged magnetic field strength more than ten times that of the Earth, in certain regions it can be thousands of times stronger. Put a gas giant planet, like a hot Jupiter, in close proximity to a star - say where it orbits every couple of days, and you might expect the two magnetic fields to get into some interesting tangles.

What does this have to do with life and worlds like the Earth ? Our magnetic field makes a big difference; apart from providing some amount of protection for surface life from cosmic radiation streaming in (by deflecting particles with electrical charge) it has - over the lifetime of the planet - helped slow the rate at which our atmosphere leaks out into the cosmos. This deflecting power decreases the impact of high energy cosmic particles that would otherwise smack into the upper atmosphere and gradually erode it. However, we don't completely understand the details of the massive circulations, or dynamos, deep in the Earth that generate the magnetic field.

For terrestrial-type exoplanets it'd be incredibly useful to either be able to measure magnetic fields (and put another pin on the map to see if they're more or less Earth-like), or to make believable predictions about what their magnetic fields might be.

Which gets back to the study of X-rays from stellar coronas. After some careful analysis it looks like there is a surprisingly strong relationship between the amount of energy pouring out and the size of the hot Jupiters whizzing around the closest to their stars. There could be all sorts of nasty hidden biases and effects that are really responsible, but in the best tradition of sticking ones scientific neck out I explore what the implications are if we're actually witnessing the clash of planetary and stellar magnetic fields. Lo and behold, the effect seen is remarkably similar to what might be expected if the deep dynamos of these planets obey a set of rules that seem to work well for planets in our own solar system.

So...there may indeed be some universal laws governing how strong planetary magnetic fields are, and we might be able to probe the deep circulations in planetary cores that generate these fields by exploiting the fact that some planets are causing a ruckus in their star's hairy outer reaches. It's early days, but studying the interiors of exoplanets may not be impossible.

Thursday, May 6, 2010

Guest post at Discover Magazine site

I'm super happy to be a guest at the Cosmic Variance blog on the Discover Magazine web site. Check out Cosmic Variance, and my guest post. It's entitled 'Oddly Familiar' and is really an opinion piece about the latest commentary that seems to be going on around the media with regard to various colorful, intriguing, but also probably rather distracting ideas about life in the universe - in particular the 'shadow biosphere'. This also follows on from my post here a little while back. Thanks to Sean Carroll for graciously putting this online at CV.

Monday, May 3, 2010

Active Venus

Venus is by any terrestrial standards a pretty rotten place for life. With a massive greenhouse atmosphere pushing the surface temperature up to over 800 F, and a crushing pressure 92 times that on the Earth's surface, it has long been held up as a poster child for an terrestrial-type planet gone awry. Of course that's a great simplification and probably the wrong way to characterize it. Nonetheless, it has certainly seemed that Venusian geophysics do not give rise to the kind of long-term regulatory processes that we seem to have on Earth - such as the carbon-cycle. Indeed, the common lore has been that Venus exhibits none of the volcanic activity that we see here on Earth, and that it is locked into a fundamentally different state whereby only rare and catastrophic upheaval resurfaces the planet (almost literally turning the crust inside out).

This situation would predict a certain release and cycling of gas components into the atmosphere, and control various aspects of long-term climate. Now a new study by Smrekar et al, using visible and infrared imaging data from Europe's Venus Express orbiter has indicated that this received wisdom may be wrong. Combining the better topographical measurements with spectral analyses of composition seems to have robustly identified a number of geophysical 'hotspots' on Venus, with vast areas of 'flow' or younger material, perhaps only a few tens of meters thick and likely only a few tens or hundreds of thousands of years old.

In a nutshell, Venus may be geologically active today, and with a near surface structure of hot plumes of rock not at all dissimilar to those of the Earth. So perhaps our sister planet is not as different as we suspected....