Ok, it’s time for an editorial intervention here. Centring upon what scientists think about the possibility of life on bodies other than Earth.
First of all, let’s get out of the way, the silly cartoon little green men with anal probes. This is beneath deserving of a point of view.
Instead, let’s start from some basic facts, and work on from there. The first basic fact being that molecules implicated in life as we know it on Earth, have been found in meteorites (the Murchison meteorite alone yielded 70 amino acids), and in ininterstellar gas and dust clouds containing cometary ices. Indeed, I’ve covered in the past, some of the experiments demonstrating that molecules such as glycine and tryptophan can be synthesised in cometary ices via ultraviolet photolysis. Very recently, I also encountered this extremely interesting paper, in which a variety of nucleobases were synthesised in the laboratory, under conditions present in interstellar gas clouds[/url] (high vacuum and 10 kelvin temperature). Since the paper is a free download from the journal, I’ll let interested parties peruse the paper directly.
Then, of course, we have the research conducted in the field of prebiotic chemistry, about which I’ve posted voluminous posts in various threads here in the past, and the diligent won’t take long to track them down. Indeed, one of those posts covers much of the state of the art in prebiotic chemistry, and the steps from simple molecules to self-replicating RNAs, leading to much more recent research on synthetic model protocells. But I digress.
Since it has been established that molecules relevant to life on Earth are pretty much ubiquitous in both the Solar System and interstellar space (if memory serves, one paper even discusses the presence of polyaromatic hydrocarbons in the outermost envelopes of cool stars), it’s not unreasonable for scientists to hypothesise that life could well be present on bodies other than Earth. Though usually, the discussion centres upon single celled life forms of the sort that were inhabiting the Earth’s oceans 3.5 billion years ago.
Of course, thre’s also the matter of which bodies are likely to provide us with direct evidence of this. Exoplanets tens or hundreds of light years away are, of coursse, unavailable for direct close observation, and while interesting spectroscopic data may indirectly point to the presence of at least a primitive biosphere on some of those eoxoplanets, that’s the best that these bodies will provide for the foreseeable future.
On the other hand, there are two bodies that are within reach of space probes in reasonable time, and which possess interesting features rendering them worthy of investigation. Namely the Jovian moon Europa, and the Saturnian moon Enceladus. both of which possess substantial subsurface oceans under their icy crusts. Flybys through the ejecta from Enceladus has already provided tantalising hints that some sort of life may be present there, but tantalising hints they currently remain, until we send a mission constructed from the outset to detect life there properly. Likewise, Europa may offer some tantalising hints, but we’ll have to wait for a properly cnostructed space mission to answer the requisite questions centred upojn that body.
Needless to say, scientists are not expecting to find anything as advanced as, say, crustaceans or fish in those subsurface oceans. Again, they’re interested in finding possible single celled life forms, akin to bacteria or protists. Though if a future space mission to either body does find macroscopic, multicellular life forms (possibly reembling the wackiness that is the Ediacaran fossil Halucigenia, perchance?), then you can bet a lot of champagne corks will be popped!
Even hard evidence of primitive single cells will set the champagne corks popping in many quarters, of course, because we will have, for the first time if such evidence emerges, a definitive answer to the question of whether life is possible on a body other than Earth. Though obtaining that evidence is going to present formidable technical challenges. Take Europa for example. The icy crust is possibly as much as 30 km thick. Even the uppermost layers of any liquid water ocean under that crust will be under tremendous pressure, not to mention the deep parts of that ocean, which may be as much as 100 km deep. The uppermost ocean layers, under 30 km of ice, will be at a pressure of several thousand atmospheres, and direct exploration of that water via a submersible type probe, will require that probe to be built to hitherto unparalleled levels of compressive strength. Then of course, there’s the matter of penetrating that 30 km ice crust to launch the submersible.
Enceladus presents similar challenges to a mission of the sort I’ve just described above. Although the ocean of Enceladus is “only” 31 km deep, it’s under a 40 km ice crust. Again, direct exploration with a submersible, while possible in principle, will be hideously expensive to realise. Building a submersible to resist several thousand atmospheres of pressure is not a trivial task.
And, of course, once any such submersible is launched, enabling it to communicate with the surface will pose yet more extremely expensive technical challenges. Punching a radio signal through 30 or 40 kilometres of dense ice is going to need a lot of power, even if it’s found to be possible, and means that our submersible will have to be, in effect, a full-blown nuclear submarine flown the hundreds of millions of miles to its destination prior to launch. This would require constructing an operational nuclear submarine in space, one packing several thouand tons of mass for its pressure hull even without the need for life support (the scientific instruments will need protecting from the crushing pressures).
Consequently, the best we can hope for, is capturing ejecta from the two bodies, storing it safely once captured, then subjecting it to the attentions of a full-blown histology lab aboard the probe. A mission that’s “doable”, but which is going to cost a colossal sum of money regardless.
But, let’s assume that the pre-requisites are in place - the funding, the technical know-how, and the will to press ahead and build the requisite space probe and launch it. We’ll still have to wait three or four years for the probe to arrive at its destination. In the case of Europa, we’ll have to plan the mission so that the probe is exposed as infrequently as possible to the hostile radiation environment in the moon’s vicinity - a whopping 540 rems per day. Possibly we’ll need a two part probe - a “collector” that darts in close to Europa to collect ejecta, before zooming out on a highly elliptical orbit to a much safer radiation environment, where the main analysis probe will be waiting. Which will then have to dock with the main analysis probe and transfer its contents. More complicated technical issues to solve, all adding to the expense.
But, the point is, both Europa and Enceladus are within our reach, even though actual missions will cost a king’s ransom.
However, in my case, I’ll be popping the champagne cork not upon finding actual single celled life on one of these bodies, but a fully functioning RNA world instead. The prebiotic chemists will have a special reason to celebrate this,. of course. 