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getting mildly excited about water

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Icy Enceladus with a yummy green centre
Icy Enceladus with a yummy green centre

I’ve generally thought that the extraordinary volume of water on our planet’s surface was a problem, scientifically speaking, but I’m probably wrong. I used to think that the idea that water came to Earth in meteor showers (haha) couldn’t be right, because the days of Earth’s heavy bombardment came early in the planet’s history when everything was molten hot and the water or ice from meteors would’ve just boiled away. But what would I know? And why would meteors, or planetesimals, be so full of water?

As the astronomers are constantly telling me, water in solid, liquid and gaseous form is commonplace in our solar system, our galaxy, our universe. In the habitable zones of our universe it can exist in all three forms close together, and that’s what presumably makes those regions habitable. On Earth we have a hydrological cycle – evaporation and transpiration, condensation, and precipitation – involving the three forms of this precious stuff, more or less. Recently, some fuss was made about water found in the atmosphere of a not-so-distant exoplanet, and the female interviewer was seemingly excited about – hey, water, and maybe life!!! – but the scientist was much more impressed by the detection abilities we’ve developed for working out the chemical signature coming from distant bodies (this one was about 100 light years away – our galaxy is many thousands of light years across). Water in the atmosphere and even on the surface of these bodies is unsurprising, apparently. 

When you (I mean I) consider that hydrogen is the simplest and most abundant element in the universe, and oxygen is also a relatively simple and abundant molecule, we shouldn’t be surprised that water is commonplace. As the above-mentioned scientist pointed out, water is found in the interstellar medium between star systems, amongst gas clouds, and within our solar system, especially in the material of the Kuiper Belt and in the ‘ice giants’, Neptune and Uranus. More excitingly for the possibilities of life, liquid, flowing water has been found on Mars – albeit highly salinated and mineral-rich. There’s still a possibility, though, that less ‘contaminated’ water may be found nearer the Martian poles. It’s also seen as a sign that Mars is drying up, water-wise, that it was once a much more watery world, and for a long time. Could it have seeded life on Earth?

Water worlds are being found elsewhere in the solar system too. The Cassini spacecraft has made major discoveries about Enceladus, a tiny, very bright moon of Saturn. Jets of water vapour, ice and surprisingly large quantities of organic chemicals burst out from below the moon’s icy crust at tremendous velocity. Some of the material is added to Saturn’s particulate ring system. The E ring’s particles, where the Enceladus material ends up, have been examined by Cassini, and in short, the examination suggests that there are hydrothermal vents beneath the icy shell of the moon, similar to those underneath the Pacific Ocean. Cassini’s analysis has also strongly indicated an ocean with a depth of around 10 kilometres underneath the thick ice (30-40 kms) at the southern polar region.

There are other promising watery discoveries too, and a relatively new theory about water on Earth, which I’ll leave for another post.

References

NASA discovers a water world in our solar system (mashable video)

https://imagine.gsfc.nasa.gov/features/cosmic/milkyway_info.html

https://solarsystem.nasa.gov/missions/cassini/science/enceladus/

How did Earth get its water?

Written by stewart henderson

December 24, 2019 at 2:15 pm

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.

References

http://www.abc.net.au/news/science/2018-07-26/vast-liquid-lake-found-under-mars-south-polar-ice-cap/10030264

https://theconversation.com/discovered-a-huge-liquid-water-lake-beneath-the-southern-pole-of-mars-100523

http://www.abc.net.au/news/science/2018-07-26/mars-life-evidence-organic-carbon-methane-liquid-water/10038324

https://www.bbc.com/news/science-environment-44952710

 

Written by stewart henderson

August 11, 2018 at 10:38 pm