Is there life on Mars?
December 20, 2013 10:11 AM   Subscribe

When scientists seek out life forms on other planets, what kind of methods/ technology are employed (both past and present)? I am especially interested in anything on this topic that would have been going on in 2006, but any information would be helpful about any era.
posted by mermaidcafe to Science & Nature (11 answers total) 3 users marked this as a favorite
Start here and enjoy the endless rabbit hole. For Mars specifically, you might want to read the Wiki on the exploration of Mars, though not all missions were looking for signs of life. You can read up on the Viking missions from the 1970s or the more recent rovers (launched in 2003 but still going in 2006 and partially to the present day) that set out to detect water and to see if the Martian environment might have been friendly to life in the past.
posted by bondcliff at 10:25 AM on December 20, 2013 [1 favorite]

Ok, I will start and someone else can fill in and improve...

Scientists looking for life on Mars are basically looking for the biproducts of life and the conditions that would (or would have in the past) support life.

Biproducts are things like organic molecules that generally do not arise without life creating them like ringed organics, hydrocarbons with repeating side chains, organometals, that sort of thing. Other biproducts can be represented as things in the soil or atmosphere that are out of equilibrium like oxygen, unusual amounts of methane or other things that would not be there without an active process creating them faster than they would be otherwise be created by non-life processes like by sunlight or volcanoes.

Conditions that support life are things like the presence of simple organics, liquid water, a reduced nitrogen source as well as an energy source like light or reduced molecules that can provide the energy for fighting against entropy. There are certainly possibilities for life that use different conditions, but we generally are looking for things that we can describe and understand. The science fiction concepts of strange life that is based on salt gradients or other weird stuff is just too far out there for us to really know how to look for.
posted by BearClaw6 at 10:31 AM on December 20, 2013

Spectroscopy is something you can do at home with a carboard tube and a few cents worth of diffraction grating (or even an old CD out of the trash can), but which can also be done via orbital telescope to detect signs of life on exo-planets orbiting alien suns, to reveal chemicals in the atmosphere which seem either conducive to life, or which are not known to be able to be created by any non-living (ie geological) methods.
posted by anonymisc at 10:35 AM on December 20, 2013

(How to build a spectrascope)
posted by anonymisc at 10:41 AM on December 20, 2013

They look for signs of the most basic building blocks: Water, carbon and other chemicals, and an energy source.
Those things do not mean life exists, but they can create conditions in which life can occur.
posted by Flood at 10:45 AM on December 20, 2013

Gilbert V. Levin designed one of the life science experiments on the Viking lander. His site has details of how he came to design the experiment, and copies of his published papers. He is now pretty certain that there is life on mars, probably similar to lichen.
posted by Sophont at 11:20 AM on December 20, 2013

The dominant form of life on Earth is bacteria. By every possible measure, single-celled organisms are the most successful life forms here. They formed earliest, and they represent the vast majority of the biomass. They are found everywhere there is any other kind of life and they're found a lot of places where there is no other kind of life.

It is presumed that will be the case elsewhere if life exists. So when they seek life elsewhere, what they look for is indications that microorganisms are present.

The Viking landers carried experiments to look for life. They had nutrient mediums and plopped soil samples into them, and kept them warm, and looked for biproducts of micro-organism metabolism.

There were three experiments. Two of them were negative; no biproducts were seen. The third one initially looked like it was positive, but later it was explained as being the result of inorganic catalysts.

That doesn't prove that there is no life on Mars. But if you had done that with a soil sample from nearly anywhere on Earth (even somewhere as desolate as Antarctica) you'd have gotten a positive result.

Other landers since then have carried such experiments, and none of them have found unambiguous positive results, either. So if there is life on Mars, it's isolated and rare.
posted by Chocolate Pickle at 11:50 AM on December 20, 2013 [1 favorite]

And, you know, there may have been life there. But proof of that will be much harder to find, especially if, as Chocolate Pickle's post suggests, said life never got beyond the microbial stage before it went extinct.
posted by Guy_Inamonkeysuit at 2:36 PM on December 20, 2013

My uncle is an astrobiologist and is actively studying life on Mars. One of his experiments involves the collection of rock samples (specific types that are present on Mars) from deep-ocean hydrothermal vents, which are under similar environmental conditions as Mars and other planets (pressure, temperature, chemical composition, etc). In the lab, he places the rock samples in pressure vessels that replicate these environmental conditions, and then introduces various compounds thought/proved to be present (now or in the past) on Mars. Through mass spectroscopy, he's able to determine the chemical breakdown of the resultant environment and look for specific compositions that are known to sustain various forms of life.
posted by mrrisotto at 2:48 PM on December 20, 2013

If life is ever definitively found anywhere else (e.g. Mars, the oceans of Europa) and samples are brought back to earth and cultured, the definitive test will be genetic analysis.

All life on earth uses DNA and RNA for genetics, and there's a standard chart that translates DNA triples into amino acids. The chart is arbitrary, but every life form on earth uses the same one.

It happens that the potential number of charts is a proposterously huge number. If there is a unique second creation of life elsewhere, then even if it is based on DNA and RNA the chance that it is using the same chart as us is negligible. So if it turns out that it is the same chart then it'll either be contamination from earth or the result of panspermia.

But if the chart is radically different, then it means it's not related to us.

Another thing is that all our proteins are made using 21 particular amino acids. There are other amino acids (as well as mirror image versions of most of our 21) which could have been used but were not. If a potential alien life form is analyzed and turns out to use different amino acids than we do, then it is new and unrelated.
posted by Chocolate Pickle at 3:02 PM on December 20, 2013

Three links for you, in increasing academic heaviness:

1. Emily Lakdawalla at The Planetary Society runs a fantastic blog about space exploration that frequently touches on astrobiology, especially since the Mars rover and Cassini mission are very active right now. If you do nothing else, set yourself up to check that blog routinely (here is the RSS feed if you use an RSS reader). This week she posted excellent writeups about the AGU announcements.


3.; look for conferences in particular and crash one near you. One of these happened in my town recently and I found out about it the day after it ended. Doh.

Note, when chemists talk about "organic" compounds, that doesn't mean life. It just means carbon. Now, the fancier carbon-based compounds may very well come from life processes, which is why they are interesting, but by themselves they don't equate to life.
posted by intermod at 8:56 PM on December 20, 2013

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