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Posts Tagged ‘astrobiology

is there life on Mars? – encore

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Don’t worry Davey, we’ll find out

The recent announcement about a large lake of water beneath the ice near the south pole of Mars has naturally engendered great excitement among those desperate to find life ‘elsewhere’, and with good reason. Mars, our closest planet, has long been a haven of hope for this sort of thing, but it has also engendered the ‘too good to be true’ response. It’s almost been seen as a lazy conjecture, as if we should expect to work really hard, and over unimaginably long distances, to find this precious and surely extremely rare stuff called life. But in recent decades we’ve managed to discover life surviving and even thriving under the most extreme circumstances in odd nooks and crannies of our own planet, which has widened our view of life’s diversity and tenacity. And the fact that we’ve been discovering new life on our own planet, is a testament to our developing skills and technology in the search for life – because, of course, the life we’re discovering isn’t new at all, what’s new is our technology and our deeper awareness of life’s range and possibilities.

And what we know about life on Earth is all about water. We’re full of the stuff, as are the plants and animals around us, and we now know that our ancestors emerged from the stuff, and we’ve never stopped being dependent on it. So it’s not surprising that the question about life on Mars is also all about water.

In previous centuries it was much speculated that water lay on the surface of Mars, in what appeared to be canals or waterways of some kind. Nowadays what we’ve learned about the atmosphere at Mars’ surface – low temperature and pressure – has rendered the possibility of liquid water increasingly unlikely. However, water below the surface is another matter. Lake Vostok, four kilometres below the surface in Eastern Antarctica, is just the largest of a number of subsurface lakes – at least 400 found under that continent – and they support thousands of living species.

So for some time there’s been a search for subsurface water on Mars. A radar instrument called MARSIS, orbiting the planet on the European Space Agency’s Mars Express, and purpose-built to search for underground water, has been sending out radio waves which are reflective to liquid water but not to ice or rock. A particularly reflective patch near the south pole appears to reveal a layer of water about 1.5 kilometres below the surface. However, MARSIS is limited in the data it can provide. The depth of the water, and what other material is mixed in with it, are not known – though we know that it’s about 20 kilometres across, and the the Italian research team that has published the findings estimates the water to be at least a metre deep, indicating a genuine lake rather than meltwater. It’s expected that the water will contain salts, which lower the freezing point of water, as would pressure from the material above the lake.

There are still many unknowns here, but the various Mars rovers and orbiters are building evidence, for example that Mars was once warmer and wetter, and that even now liquid water can still be found at periods on the surface. What we haven’t found so far is evidence of life. So how can we get this evidence? First, we need to look for life ‘as we know it’, carbon-based life, because that’s very likely the kind of life we’ll find on our nearest neighbour, and because we have no way of knowing how to look for completely alien life.

Mars’ Curiosity rover has already found organic molecules, specifically methane, which may or may not be produced by biological activity beneath the surface. The rover has been sampling the atmosphere and has found methane at varying levels as the seasons have changed. However, it’s generally believed that the thin atmosphere at Mars’ surface would be insufficient to deflect life-harming radiation. The discovery of a specific and more or less substantial body of water below the surface, perhaps sufficiently protected from radiation, provides a target for future researchers to aim at.

The next step would be to obtain samples from the lake, which is easier said than done. It would require some sort of robotic drill to be sent out there and operated remotely, a task beyond current capabilities. Meanwhile, a Chinese probe is set to be flown to Mars in 2020. It will have radar instrumentation similar to MARSIS, but operating at a slightly different frequency. It may confirm the MARSIS findings or discover other underground bodies of water, further piquing our interest in the very real possibility of life on the red planet.

Is it an underground lake? We can’t be entirely sure.



Written by stewart henderson

August 11, 2018 at 10:38 pm

is there life on enceladus?

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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?

Written by stewart henderson

August 29, 2012 at 7:07 pm