Space is the place: did life begin in the cosmic void?

A few weeks' ago I was watching a television documentary about the search for intelligence aliens and featuring the usual SETI experts Jill Tarter and Seth Shostak when I realised that we rarely see any crossover with research into non-intelligent extra-terrestrial life. Whereas the former is often seen by outsiders as pie-in-the-sky work by idealistic dreamers, the latter has more of a down-to-Earth feel about it, even though it has at times also suffered from a lack of credibility.

Based on current thinking, it seems far more probable that life in the universe will mostly be very small and entirely lacking consciousness, in other words, microbial. After all, life on Earth arose pretty much as soon as the environment was stable enough, around 3.7 billion years ago or even earlier. In contrast, lifeforms large enough to be visible without a microscope evolved around 1 billion or so years ago (for photosynthetic plants) and only about 580 million years ago for complex marine animals.

The recent publicity surrounding the seasonal variations in methane on Mars has provided ever more tantalising hints that microbial life may survive in ultraviolet-free shelters near the Martian surface, although it will be some years before a robot mission sophisticated enough to visit sink holes or canyon walls can investigate likely habitats. (As for the oft-talked about but yet to be planned crewed mission, see this post from 2015.)

Therefore it seems that it is worth concentrating on finding biological or pre-biological compounds in extra-terrestrial objects as much as listening for radio signals. The search can be via remote sensing (e.g. of molecular clouds, comets and asteroids) as well as investigating meteorites - bearing in mind that the Earth receives up to one million kilogrammes of material per day, although less than one percent is large enough to be identified as such.

The problem is that this area of research has at times had a fairly poor reputation due to the occasional premature claim of success. Stories then become widespread via non-specialist media in such a way that the resulting hype frequently bears little relation to the initial scientific report. In addition, if further evidence reverses that conclusion, the public's lack of understanding of the error-correcting methods of science leads to disillusion at best and apathy at worst.

One key hypothesis that has received more than its fair share of negative publicity has been that of panspermia, which suggests not just the chemicals of biology but life itself has been brought to Earth by cosmic impactors. The best known advocates are Fred Hoyle and Chandra Wickramasinghe, but their outspoken championing of an hypothesis severely lacking in evidence has done little to promote the idea. For while it is feasible - especially with the ongoing discovery of extremophiles everywhere from deep ocean vents to the coolant ponds of nuclear reactors - to envisage microbial life reaching Earth from cometary or asteroid material, the notion that these extra-terrestrials have been responsible for various epidemics seems to be a step too far.

It's long been known that comets contain vast amounts of water; indeed, simulations suggest that until the Late Heavy Bombardment around four billion years ago there may have been far less water on Earth than subsequently. Considering the volumes of water ice now being discovered on Mars and the Moon, the probability of life-sustaining environments off the Earth has gained a respectable boost.

It isn't just water, either: organic compounds that are precursors to biological material have been found in vast quantities in interstellar space; and now they are being found in the inner solar system too. That's not to say that this research has been without controversy as well. Since the early 1960s, Bartholomew Nagy has stirred debate by announcing the discovery of sophisticated pre-biological material in impactors such as the Orgueil meteorite. Examination by other teams has found that contamination has skewed the results, implying that Nagy's conclusions were based on inadequate research. Although more recent investigation of meteorites and spectrophotometry of carbonaceous chondrite asteroids have supplied genuine positives, the earlier mistakes have sullied the field.

Luckily, thorough examination of the Australian Murchison meteorite has promoted the discipline again, with numerous amino acids being confirmed as of non-terrestrial origin. The RNA nucleobase uracil has also been found in the Murchison meteorite, with ultraviolet radiation in the outer space vacuum being deemed responsible for the construction of these complex compounds.

Not that there haven't been other examples of premature results leading to unwarranted hype. Perhaps the best known example of this was the 1996 announcement of minute bacteria-like forms in the Martian ALH84001 meteorite. The international headlines soon waned when a potential non-biological origin was found.

In addition to examination of these objects, experiments are increasingly being performed to test the resilience of life forms in either vacuum chambers or real outer space, courtesy of the International Space Station. After all, if terrestrial life can survive in such a hostile environment, the higher the likelihood that alien microbiology could arrive on Earth via meteorite impact or cometary tail (and at least one amino acid, glycine, has been found on several comets).

Unmanned probes are now replicating these findings, with the European Space Agency's Rosetta spacecraft finding glycine in the dust cloud around Comet 67P/Churyumov-Gerasimenko in 2016. Although these extra-terrestrial objects may lack the energy source required to kick-start life itself, some are clearly harbouring many of the complex molecules used in life on Earth.

It has now been proven beyond any doubt that organic and pre-biological material is common in space. The much higher frequency of impacts in the early solar system suggests that key components of Earth's surface chemistry - and its water - were delivered via meteorites and comets. Unfortunately, the unwary publication of provisional results, when combined with the general public's feeble grasp of scientific methodology, has hindered support for what is surely one of the most exciting areas in contemporary science. A multi-faceted approach may in time supply the answers to the ultimate questions surrounding the origin of life and its precursor material. This really is a case of watch (this) space!

Life on Mars? How accumulated evidence slowly leads to scientific advances

Although the history of science is often presented as a series of eureka moments, with a single scientist's brainstorm paving the way for a paradigm-shifting theory, the truth is usually rather less dramatic. A good example of the latter is the formulation of plate tectonics, with the meteorologist Alfred Wegener's continental drift being rejected by the geological orthodoxy for over thirty years. It was only with the accumulation of data from late 1950's onward that the mobility of Earth's crust slowly gained acceptance, thanks to the multiple strands of new evidence that supported it.

One topic that looks likely to increase in popularity amongst both public and biologists is the search for life on Mars. Last month's announcement of a lake deep beneath the southern polar ice cap is the latest piece of observational data that Mars might still have environments suitable for microbial life. This is just the latest in an increasing body of evidence that conditions may be still be capable of supporting life, long after the planet's biota-friendly heyday. However, the data hasn't always been so positive, having fluctuated in both directions over the past century or so. So what is the correspondence between positive results and the levels of research for life on Mars?

The planet's polar ice caps were first discovered in the late Seventeenth Century, which combined with the Earth-like duration of the Martian day implied the planet might be fairly similar to our own. This was followed a century later by observation of what appeared to be seasonal changes to surface features, leading to the understandable conclusion of Mars as a temperate, hospitable world covered with vegetation. Then another century on, an early use of spectroscopy erroneously described abundant water on Mars; although the mistake was later corrected, the near contemporary reporting of non-existent Martian canals led to soaring public interest and intense speculation. The French astronomer Camille Flammarion helped popularise Mars as a potentially inhabited world, paving the way for H.G. Wells' War of the Worlds and Edgar Rice Burroughs' John Carter series.

As astronomical technology improved and the planet's true environment became known (low temperatures, thin atmosphere and no canals), Mars' popularity waned. By the time of Mariner 4's 1965 fly-by, the arid, cratered and radiation-smothered surface it revealed only served to reinforce the notion of a lifeless desert; the geologically inactive world was long past its prime and any life still existing there probably wouldn't be visible without a microscope.

Despite this disappointing turnabout, NASA somehow managed to gain the funding to incorporate four biological experiments on the two Viking landers that arrived on Mars in 1976. Three of the experiments gave negative results while the fourth was inconclusive, most researchers hypothesising a geochemical rather than biological explanation for the outcome. After a decade and a half of continuous missions to Mars, this lack of positive results - accompanied by experimental cost overruns - probably contributed to a sixteen-year hiatus (excluding two Soviet attempts at missions to the Martian moons). Clearly, Mars' geology by itself was not enough to excite the interplanetary probe funding czars.

In the meantime, it was some distinctly Earth-bound research that reignited interested in Mars as a plausible source of life. The 1996 report that Martian meteorite ALH84001 contained features resembling fossilised (if extremely small) bacteria gained worldwide attention, even though the eventual conclusion repudiated this. Analysis of three other meteorites originating from Mars showed that complex organic chemistry, lava flows and moving water were common features of the planet's past, although they offered no more than tantalising hints that microbial life may have flourished, possibly billions of years ago.

Back on Mars, NASA's 1997 Pathfinder lander delivered the Sojourner rover. Although it appeared to be little more than a very expensive toy, managing a total distance in its operational lifetime of just one hundred metres, the proof of concept led to much larger and more sophisticated vehicles culminating in today’s Curiosity rover.

The plethora of Mars missions over the past two decades has delivered immense amounts of data, including that the planet used to have near-ideal conditions for microbial life - and still has a few types of environment that may be able to support miniscule extremophiles.

Together with research undertaken in Earth-bound simulators, the numerous Mars projects of the Twenty-first Century have to date swung the pendulum back in favour of a Martian biota. Here are a few prominent examples:

• 2003 - atmospheric methane is discovered (the lack of active geology implying a biological rather than geochemical origin)
• 2005 - atmospheric formaldehyde is detected (it could be a by-product of methane oxidation)
• 2007 - silica-rich rocks, similar to hot springs, are found
• 2010 - giant sinkholes are found (suitable as radiation-proof habitats)
• 2011 - flowing brines and gypsum deposits discovered
• 2012 - lichen survived for a month in the Mars Simulation Laboratory
• 2013 - proof of ancient freshwater lakes and complex organic molecules, along with a long-lost magnetic field
• 2014 - large-scale seasonal variation in methane, greater than usual if of geochemical origin
• 2015 - Earth-based research successfully incubates methane-producing bacteria under Mars-like conditions
• 2018 - a 20 kilometre across brine lake is found under the southern polar ice sheet

Although these facts accumulate into an impressive package in favour of Martian microbes, they should probably be treated as independent points, not as one combined argument. For as well as finding factors supporting microbial life, other research has produced opposing ones. For example, last year NASA found that a solar storm had temporarily doubled surface radiation levels, meaning that even dormant microbes would have to live over seven metres down in order to survive. We should also bear in mind that for some of each orbit, Mars veers outside our solar system's Goldilocks Zone and as such any native life would have its work cut out for it at aphelion.

A fleet of orbiters, landers, rovers and even a robotic helicopter are planned for further exploration in the next decade, so clearly the search for life on Mars is still deemed a worthwhile effort. Indeed, five more missions are scheduled for the next three years alone. Whether any will provide definitive proof is the big question, but conversely, how much of the surface - and sub-surface - would need to be thoroughly searched before concluding that Mars has either never had microscopic life or that it has long since become extinct?

What is apparent from all this is that the quantity of Mars-based missions has fluctuated according to confidence in the hypothesis. In other words, the more that data supports the existence of suitable habitats for microbes, the greater the amount of research to find them. In a world of limited resources, even such profoundly interesting questions as extra-terrestrial life appear to gain funding based on the probability of near-future success. If the next generation of missions fails to find traces of even extinct life, my bet would be a rapid and severe curtailing of probes to the red planet.

There is a caricature of the stages that scientific hypotheses go through, which can ironically best be described using religious terminology: they start as heresy; proceed to acceptance; and are then carved into stone as orthodoxy. Of course, unlike with religions, the vast majority of practitioners accept the new working theory once the data has passed a certain probability threshold, even if it totally negates an earlier one. During the first stage - and as the evidence starts to be favourable - more researchers may join the bandwagon, hoping to be the first to achieve success.

In this particular case, the expense and sophistication of the technology prohibits entries from all except a few key players such as NASA and ESA. It might seem obvious that in expensive, high-tech fields, there has to be a correlation between hypothesis-supporting facts and the amount of research. But this suggests a stumbling block for out-of-the-box thinking, as revolutionary hypotheses fail to gain funding without at least some supporting evidence.

Therefore does the cutting-edge, at least in areas that require expensive experimental confirmation, start life as a chicken-and-egg situation? Until data providentially appears, is it often the case that the powers-that-be have little enticement for funding left-field projects? That certainly seems to have been true for meteorologist Alfred Wegener and his continental drift hypothesis, since it took several research streams to codify plate tectonics as the revolutionary solution. 

Back to Martian microbes. Having now read in greater depth about seasonal methane, it appears that the periodicity could be due to temperature-related atmospheric changes. This only leaves the scale of variation as support for a biological rather than geochemical origin. Having said that, the joint ESA/Roscosmos ExoMars Trace Gas Orbiter may find a definitive answer as to its source in the next year or so, although even a negative result is unlikely to close the matter for some time to come. Surely this has got to be one of the great what-ifs of our time? Happy hunting, Mars mission teams!