Is there life on Mars? Or Rosetta, Europa, or even Pluto? A dilettante hand-waving exercise follows.
Once upon a time, most of the material that made all of our solar system was gathered from a cloud of gas and dust by gravitational effects, to form our sun and its extensive system of planets, asteroids, comets, fragments and dust. Simple school science gives the impression that we have a neat little system of orbiting planets ending around Pluto (now re-graded as a ‘dwarf planet’). But the material in the nebula that gave rise to the solar system was not mopped up into a few neat packages that we can label. And the solar system doesn’t stop at Pluto; the remnants of our primordial cloud are believed to extend about 3 light years in a spherical bubble of material, named the ‘Oort Cloud’. Our nearest star – Proxima Centauri – is about 4.2 light years away. The ‘clockwork’ solar system we are familiar with formed in a plane from a gravitational accretion disk, resulting in the eight major planets starting with Mercury and terminating with Neptune. And the erstwhile ‘planet’, Pluto, that lies beyond Neptune (some of the time – their orbits cross) marks the inner edge of the icy belt of planet-making material we know as the Kuiper Belt. This material is stuff left over from the earliest days of the solar system, so is of great interest scientifically.
Recently, observers have found other dwarf planets on extraordinary orbits, which has led to a re-modelling of how the solar system came to be the way it is today. (Look up Sedna and Eris for starters). Gravity makes complicated arrangements out of clouds! And the jury is still out on whether there is another large planet out there, hidden in the dark of the boundaries of interstellar space.
OK, I opened this piece with a teaser about life on Mars. So where is this little hand-waving exercise going? I have blogged previously about this – follow the tags if you can bear it. Our solar system came from material left after previous generations of stars died, collapsed, became novae and deposited the heavy atoms that make up the periodic table of elements. Any nucleus bigger than lithium was made inside a star (but these can be modified by us to make ‘exotic’ ones). To gather the material to make our solar system would have taken many stars and billions of years. (See ‘The Cosmic Teapot’ post). We have been gifted with some fertile material to make planets – and life. We recognise that life exists on Earth, but does it exist elsewhere in the solar system? Here, I think it is easy to be glib. Some folk insist on touting probabilities of life forming independently on each world, but perhaps we should think more roundly, more solar systemy, more galactically, about how complex life happens to be on Earth. Life seems to like Sol 3. The earliest life began on the planet once the rocks cooled, not so long after the solar system was created. It has taken four billion years or so to get to humans. We wouldn’t be here without the generations of microbes and slimy things that converted the planet from an inhospitable carbon dioxide dominated atmosphere, and moved biology along, into forms amenable for the development of more complex organisms. Indeed, we couldn’t live as advanced human life forms without the help of millions of bacteria in our guts and on our skin that allow us to digest food and ward off malevolent microbes. Complex life needs a big support team. Cells have changed from simple all-purpose forms to specialist within-organism forms. None of these can live independently of an organism. We see plenty of examples of symbiotic relationships on a simpler level that have bridged the sustainability gap. Nothing works alone. But, clearly, Earth has a lot going for it as far as sustaining abundant life is concerned, but I argue that it is not isolated and that life on this planet should be considered in the wider context of the solar system, maybe beyond that.
Humans are specialised creatures that are acting out the laws of thermodynamics (see ‘Barking Up the Tree of Life’). But getting back to the original question requires stepping off the argument before we even get to life. Chemistry is exciting because you can make pretty colours, crystals, gloopy stuff and explosions. Underneath it, we find the structure of the universe, the behaviour of fundamental particles that allows structure to happen. Structure is a given. There is no escaping it. My hand-waving kitchen sink argument is that where there is fertile ground for complexity, complexity will emerge and we ultimately find interesting dynamic systems that act in the context of thermodynamics. So it would not surprise me to find some interesting chemistry in the dark retreat of the Kuiper Belt, nor indeed on Rosetta. 4.5 billion years of stewing is quite a long time for something to happen, even in the coldest, darkest places. Back to Mars – it is believed Mars once had oceans – there is plenty of geological evidence for abundant water. But Mars has been dry – on the surface – for most of the time there has been life on Earth, and the atmosphere, in the absence of a protective magnetic field, has been scoured off by solar wind. So it is unlikely that complex life had much of a chance. The argument I put is not that we should expect obvious ‘life’ on Mars, Rosetta, or Pluto, with tentacles and green skin, but for some interesting chemistry with maybe some kind of potential for being in the chain of life-forming ingredients. It is hard to define what ‘life’ is and when it begins. It is clear that what we call life emerges from the fundamental structure of the universe, and the way things are set up in energy terms seems to tip us from randomness to a driven process.
It has been suggested that organic carbon compounds could be formed in interstellar space without the risk of destruction from radiation, and perhaps the same applies on comets, and certain icy bodies that contain carbon. We share a gravitational well with all of these components, and bits do get ejected from larger bodies and fall towards the sun. Scientists have found pieces of Mars strewn on the Antarctic ice. Fragments of Earth will be out there somewhere – we are contagious! Material from solar systems can be ejected into interstellar space and dust can be shared. Nothing is truly isolated. Some of the stuff that made life on Earth could have come from another part of the solar system, where conditions seem ideal for it to flourish. But life takes time. And time is patient. Humans are not! A question that bugs me over the kitchen sink, is are we part of an even grander scheme of life? If so, how?
Forgive my glibness, this is intended as a thought exploration, not a science essay. If I say that everything is formed from the underlying structures of the universe – emerging via fundamental structure and thermodynamics to produce the rich universe we are beginning to understand. I say ‘beginning’. I can barely imagine how much more we have to unpick this cosmic yarn to ‘understand’ a substantial amount of what there is to know about why things are as they are and how it can be how it can be. Cosmology has made some giant leaps since my undergraduate days in the seventies. There was no dark matter and energy about then (and neutrinos were tasteless and had no mass) and scientists, bar some prominent dissenters, like Fred Hoyle, believed in the Big Bang, and probably the Big Crunch. Now we have lost that certainty, and have to think about time on a jaw-dropping scale. Observations on the way galaxies behave has thrown a stick in the wheel of time.
Dark matter was conceived when measurements of the radial velocity of galaxies showed they were not behaving as they should if they contained only the matter calculated from their brightness, and measurements of the rate at which distant galaxies are receding has shown that they are accelerating, which requires an unknown force dubbed ‘dark energy’. The mapping of the cosmic microwave background and subsequent fine analysis hint at deeper goings on before the universe sparked into life, and the influence of dark energy pushes models of the universe into the monumentally long timescales orders of magnitude beyond anything we had ever imagined. Maybe in my remaining lifetime I will see some important dots joined between these scales.
Observations of timescales and complexity maybe give some clues – based on the age of the universe, how long it has taken to develop minds capable of fretting over the whichness of the why and so on. This all leans on the concepts of thermodynamics and statistical mechanics, a knotty, Gradgrind of a mathematical subject. (I approached statistical mechanics with all the fear of a rabbit in the headlights of a car, so please don’t rely upon me for coherence.) Very simply, these disciplines tell us how energy and structure behave in relation to time. I direct the reader to many excellent resources freely available in libraries and on the Internet.
Humans have come into being with the support of dying stars, gravity, and the built-in structure of the periodic table, which itself comes out of the balance of fundamental constants that are as they are for even more fundamental reasons that perhaps we’ll understand one day. Deep breath… We, tiny motes of organic matter, inhabit a pond the size of the observable universe and have the temerity to consider what might happen beyond, and also within and without – if you are happy to consider ‘many universe’ ideas. So we begin to realise that physics won’t be complete for a fair old while yet. And I wonder what is the layer of complexity that ‘complex’ life on Earth belongs to – are we part of a supporting hierarchy above us, as microbes and simpler life forms are necessary to support life on this planet? Perhaps that is emergent on a much longer timescale than us. Would we know if such a higher order existed? As microbes surely do not reason as we do, perhaps the higher order manifestation would be impenetrable or meaningless to our understanding. A thermodynamic signature of life is that it dissipates energy – converts high quality energy to lower grade stuff capable of doing less work. Humans and our support team on Earth are good at making infra red. An excess of infra red in a spectral analysis of another planet could lead us to think there were alien cockles and mussels alivo and cooking. What would be the thermodynamic signature of a higher order life form? I am not going to speculate out loud. We struggle to count the beans of the universe – much of it is not perceived by us, other than its influence upon ordinary matter. There are theories for dark matter and dark energy, but evidence for what it could be is elusive. It seems that the universe becomes more puzzling the more we think about it. Is life simply the consequence of thermodynamics, inevitable where conditions are right? Maybe the answer is tied more deeply to the notion of structure – it is arguable that structures, even abstract ones, have a tendency to produce more structures. It’s life, Cap’n but not as we have even dreamed it.
As I finish this excursion, I am delighted to note that New Horizons has successfully completed its fly-past of Pluto. What new science will be revealed in the 16 month long download of data? We should certainly watch this space, but not, perhaps, for little green men. (I put the ‘perhaps’ in to cover my back.)