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5 Best Places To Look For Life Outside Earth

5 Best Places To Look For Life Outside Earth

Possible alien life in our own solar system.

A tally of the worlds in our Solar System where most of the ingredients for life have been found, and thus stand a good chance of harbouring life that evolved completely separate from Earth.

1. Marsmars

From Viking to Phoenix, with each passing mission to it, the robotic study of the Red Planet has only further piqued our interest in it, with respect to its ability to support, or to have once supported, life on its now harsh, rusty surface.

An article by Christopher P. McKay goes through all the goodies, including the evidence for the presence of water, mainly of ancient geological features that are undeniably fluvial (created by flowing water) in origin, and even getting into how to possibly determine if any (microbial) life found there could be of a ‘second genesis’ with respect to Earthly life, mainly of looking at the bug’s organic molecules, like amino acids and genetic material for subtle differences that would scream of an alien origin.

The author also goes into the possibility of some microbial life (the only form of life that would be able to survive, in suspended animation, in Martian permafrost) perhaps originating from Earth.  The hypothesis is that, since Martian meteorites have been found on Earth, rocks blasted from the Earth could have made it to Mars – though he notes that Earth-to-Mars travel for a space rock is more unlikely than vice versa.  But the possibility is there.

Which could make for an interesting model, which would involve both worlds.  In my mind, it could be possible to find purely Martian microbes as well as Earthly ones that had evolved a separate lineage on Mars before it deteriorated.  That would certainly make for an interesting three-way comparison – life on Earth, life from Earth on Mars, and life on Mars.

europa2. Europa

Europa is a nearly Moon-sized moon of Jupiter – one of the four Galilean Moons (because they were first discovered by Galileo), Jupiter’s four largest moons.  The blue layer in the cut-away image of the moon, above, is the really, potentially, exciting part about Europa.

A paper by Khurana et al. discusses in depth about this layer, which has been postulated as being anything from more a more ductile, though equally solid, layer of ice, to actual liquid water (which obviously is the more exciting option).

But generally, since its solid surface is of water-ice, it is postulated that the layer indicated in blue is also some form of water; either in solid or liquid form.  If the layer is indeed liquid water, then chances are, far greater than for Mars, any life we do end up finding on Europa will certainly be alien – unless an Earthly asteroid was able to reach Europa, too.

3. Ganymedeganymede

Like Europa, Ganymede is one of Jupiter’s Galilean Moons, and also like Europa, Ganymede has been evidenced as having a good likelihood that a layer of liquid water could exist just below its thick icy surface.

That is, according to Steve Vance of NASA, who recently put out an article on the matter. In it, he proposes, with evidence in the form of advanced computer modelling of Ganymede’s rotation and surface structure – much like with Europa, that Ganymede’s interior resembles a ‘Dagwood sandwich’ of Blondie cartoon fame; layers of ice interspaced with layers of liquid water of varying salinities.

But again, as with Europa, the only definitive way to prove the existence of this water is to plant seismic probes on the surface, for starters, to seismically gauge the nature of the layers of interest, and ultimately try to send a submarine down there to actually check the layers out.

And if all the right data comes in, then potentially we could have two worlds that would likely have spawned life separately from each other; just around Jupiter alone.

enceladus4. Enceladus

Enceladus, a moon of Saturn, is only a few hundred kilometers across, but since the Cassini probe reached Saturn and began investigating, this one particular icy little moon has increasingly shot up through the ranks to become one of the most promising worlds within our System to potentially harbour life.

The main reason for this is the geysers that have been seen spewing out from the moon’s south pole.  The probe flew by the area in 2005, and sampled the ejected material and found compounds like nitrogen, carbon dioxide, and most importantly, water.

Another fly-by in 2008 revealed that even more exciting data about the plumes – that they contained traces of simple organic compounds.  NASA documents the find in its mission news.

These geysers infer that some amount of liquid water is most definitely sitting somewhere near the surface, at the moon’s south pole.

Between 2010 and 2012, Cassini made gravity measurements of the moon, and its results seem to conclusively indicate that an extensive body of liquid water sits trapped under the south-polar ice (more specifically, a negative-mass anomaly – ie, less dense than the compressed solid ice above it, implying a liquid).

All this evidence could prove Enceladus to be the most promising alien world in our Solar System yet.

5. TitanTitan

Second only to Ganymede in moon size, Titan is the only moon in the Solar System that has a noticeable atmosphere.  And again, thanks to Cassini, even this moon can be considered as potentially life-giving – though in this case we’d have to stretch our concepts on life a bit.

This paper of Jonathan I Lunine outlines the aspects of Titan recently discovered that make it a candidate for life in our Solar System – as well as touching on the exciting aspects of many of the other worlds mentioned in this post of mine.

Undoubtedly, Titan is most Earth-like in terms of surficial processes, if one simply replaces water with methane.  There are lakes, rivers, seas, storms, even a hydrological-type cycle.  Basically, methane acts on Titan like water does on Earth, and that similarity could even extend to allowing life to come about and evolve.

And as the paper notes, if there are lifeforms inhabiting the liquid methane bodies on the moon, then pretty-much by default, since it would likely have to be wildly different from water-based life, that life would be uniquely Titanic.

But the paper also raises an interesting possibility: that of a liquid water layer hidden deep under its largely water-ice surface, that could also harbour life.  And that would definitely be a first – two independently originating biota on one world.

Looks like we got our work cut out for us, here on Earth!

References:
McKay, C. (2010). An Origin of Life on Mars Cold Spring Harbor Perspectives in Biology, 2 (4) DOI: 10.1101/cshperspect.a003509

Khurana KK, Kivelson MG, & Russell CT (2002). Searching for liquid water in Europa by using surface observatories. Astrobiology, 2 (1), 93-103 PMID: 12449858

Vance, S., Bouffard, M., Choukroun, M., & Sotin, C. (2014). Ganymede׳s internal structure including thermodynamics of magnesium sulfate oceans in contact with ice Planetary and Space Science, 96, 62-70 DOI: 10.1016/j.pss.2014.03.011

Waite JH Jr, Combi MR, Ip WH, Cravens TE, McNutt RL Jr, Kasprzak W, Yelle R, Luhmann J, Niemann H, Gell D, Magee B, Fletcher G, Lunine J, & Tseng WL (2006). Cassini ion and neutral mass spectrometer: Enceladus plume composition and structure. Science (New York, N.Y.), 311 (5766), 1419-22 PMID: 16527970

Iess L, Stevenson DJ, Parisi M, Hemingway D, Jacobson RA, Lunine JI, Nimmo F, Armstrong JW, Asmar SW, Ducci M, & Tortora P (2014). The gravity field and interior structure of Enceladus. Science (New York, N.Y.), 344 (6179), 78-80 PMID: 24700854

Lunine, Jonathan (2009). Saturn’s Titan: A Strict Test for Life’s Cosmic Ubiquity. Proceedings of the American Philosophical Society

Image Credit:  By Ryan Wick (https://www.flickr.com/photos/ryanwick/3461850112) [CC BY 2.0], via Wikimedia Commons

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Jeffrey Daniels
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