Posts Tagged ‘space’
is there life on enceladus?
a cool place – and note the tiger stripe
The Curiosity landing has been fabulously successful, and it’ll certainly be worth keeping tabs on the rover’s findings. I posted recently on the possibility of life on Mars, not a couple of billion years ago, as many Mars experts think probable, but right now. The Curiosity rover, as we know, will be investigating this possibility further, but meanwhile there are other possibilities of finding extra-terrestrial life in this solar system, and one of the best places to look, I’m reliably informed, is Enceladus, a tiny moon of Saturn.
Enceladus is only about 500 kilometres in diameter, but its surface has intrigued astronomers ever since Voyager 2revealed detailed features in the early eighties, indicating a wide range of terrains of varying ages. Data from the Cassini spacecraft that performed fly-bys in 2005 showed a geologically active surface, with the most spectacular feature being a large volume of material, mostly water vapour, issuing from the southern polar region. This indicated the existence of ice volcanoes, or cryovolcanoes, which have also been observed elsewhere, and were in fact first observed by Voyager 2 on Triton, Neptune’s largest moon. However, on Enceladus what we have are more like geysers spewing out material from an area known by observers as ‘the tiger stripes’, a series of prominent, geologically active ridges. This material is now known to account for much of the outermost E ring of Saturn, within which Enceladus has its orbit, though a certain amount falls back onto the moon as snow.
Finding water on any object in the solar system obviously excites the souls of astrobiologists. A report from a May 2011 conference on Enceladus stated that this moon “is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it”. However, there are plenty of sceptics, or I should say cautious questioners. First, the existence of water vapour spumes doesn’t necessarily entail liquid water below the surface – for, in spite of the thrill of detecting snow in large quantities on the surface, liquid water is generally regarded as essential to finding life. And even if we assume liquid water…
Some analysts argue that the spumes may be a result of sublimation – a change from a solid, icy state to a vapour, missing out on the liquid phase – or of the decomposition of clathrate deposits. A clathrate is a type of ice lattice that traps gas [methane clathrates are found at the polar regions of Earth]. However, the recent discovery of salt in these plumes has made these possibilities less plausible. Salt is more likely to be associated with liquid water, but hydrogen cyanide, also recently found, would have been expected to react with liquid water to form other compounds, not found as yet. In short, the jury is still out on the presence of liquid water.
And assuming there is liquid water, how could we test for life within it? With great difficulty, obviously. Analysts would be searching for biomarkers, ‘chemicals that appear to have biological rather than geophysical origins’ [Cosmos 44, p78]. Photosynthetic production wouldn’t be an option, so other systems are being hypothesised, including a methanogenic system in which methane is synthesised from carbon dioxide, or a system of metabolizing acetylene, which occurs on Earth. Traces of acetylene have been found on Enceladus. Other biomarkers include amino acids with the right chirality – that’s to say a strong chiral preference, one way [as found on Earth] or its opposite. Amino acids with no chiral preference are likely to be abiotic.
To test for such biomarkers would require new instrumentation and another visit to this intriguing moon. Something else to look forward to. What would we do without anticipation?
is there life on mars?
good question, Davie
Back in 1975, NASA sent two space probes to Mars. Their landers touched down on the Martian surface less than a year later. The Viking 1 lander remained operational for more than six years, Viking 2 for three and a half. During this time, biological experiments were conducted upon Martian soil. As far as the general public is concerned, the results of these tests were negative, though for those in the know, it wasn’t quite that simple. Not that there was any great conspiracy or cover-up; the consensus amongst the cognoscenti was that the evidence tilted much more towards no-life than towards life, for the minute samples examined.
It seems, though, that exobiologists have long been intrigued by some of the findings in a particular batch of experiments, known as the Labelled Release experiments. As this Wikipedia article describes, these experiments involved a soil sample being inoculated with a weak aqueous nutrient solution. The nutrients were of the type produced in the famous Miller-Urey experiments of the fifties. Evidence was sought for metabolisation of these nutrients by micro-organisms in the soil, if any, and the first trial of these experiments produced surprisingly positive results. In fact, both the Viking probes produced initially positive results from different soil samples, one with a sample of surface soil exposed to sunlight, the other with a sample from beneath a rock. However, when the tests were repeated later, they produced negative results. Many other different types of biological tests were carried out during this mission, all of them yielding negative results. So it was all very inconclusive and mysterious.
Fast forward to April 2012, when a report was released by an international team of scientists suggesting that, after thorough analysis of the Labelled Release data, ‘extant microbial life on Mars’ may have been detected.
Researchers long ago abandoned the idea of multicellular life currently existing on Mars. Conditions for the maintenance of such life forms may have existed there billions of years ago – the Viking orbiters found evidence of erosion and the possible remains of river valleys – but those conditions have changed, though some have argued that the soil coloration and recent detection of silicate minerals indicates more recent signs of water, vegetation and microbial activity. All of this is highly contentious, but all good fun, and indicates that more research is required.
In 2008, a robotic spacecraft landed on Mars, in the polar region, and remained operational for about six months. The Phoenix lander had two principal objectives, to test for any history of water in the region, and to search for anything organic in the surrounding regolith [the surface layer of broken rock and soil affected by wind or water]. Preliminary data revealed perchlorate, an acid-derived salt, in the soil, which wasn’t a good sign. Perchlorate can act as an ‘anti-freeze’, lowering the freezing point of water. Generally, though, the pH levels of the tested soil, and its salinity, were benign from a biological perspective. CO2 and bound water were also detected.
We’ve only minutely scratched a few surface points of a huge beast, you might say. What we’ve found isn’t too promising, but it’s enough to keep us wanting to investigate further, just to make sure, or to know more. After all, there’s still plenty to learn about the surface of our own planet. Recently, for example, we learned how perchlorates can be formed from soils with highly concentrated salts, in the presence of UV and sun light. Chloride is converted to perchlorate in the process, which has been reproduced in the lab. Only in 2010, soils with high concentrations of perchlorate were discovered over a large section of Antarctica.
Between August 6 and August 20, that’s to say in two or three weeks time, the Mars Science Laboratory [MSL, also known as ‘Curiosity’] will land on Mars and look for further signs, past or present, of biological activity. It’s likely that whatever is discovered, not just in terms of life itself, but in terms of conditions for life, will be hotly debated. This Wikipedia article, covering the whole life-on-Mars search and debate, includes this intriguing para:
The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.
True enough, but even if dead, what a revelation it would be. Extra-terrestrial death means extra-terrestrial life, and so very very close to home in the great vastness of the universe. Another blow to our uniqueness, what terrible fun.