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Life on Mars? Why Not?
Guillaume Filion writes "IEEE spectrum has an interesting article about a new probe sent to Mars searching for life: 'Recent missions to Mars have focused on the search for water, past or present, as a surrogate for life itself. But now a British-led team is working to renew the search for life directly, fueled by doubts about the equipment that prompted NASA to declare Mars a dead world some 26 years ago.'"
...were known to be flawed, before the rockets were ever launched. Many of the tests that would have been conclusive (such as those produced by Dr Carl Sagan) were abandoned, due to budget constraints, political concerns (finding life would have made it much harder for Congress to keep slashing NASA's budget) and the greater need to impress the mass media than the scientific community.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
I read a book by Stuart Kauffman (hope I spelt that right). He said he was asked by NASA to help design probes to send to Mars to look for life. He told them not to bother, and his reasoning was:
All life takes in energy and matter from the environment, extracts energy, and produces waste. This process causes chemical imbalences in the atmosphere. Therefore to test for the presence of life, you only need to determine whether the atmosphere is in chemical equilibrium. Mars' atmosphere is, and has been for many millions of years.
Apparently this line of reasoning upset NASA, because they wanted to go to Mars, so they made their probes without his help, and when they arrived on Mars, found no traces of current life.
If they send more probes, they could very well find evidence of past life, but there is nothing going on there at the moment.
However I remember reading a story a while ago on Slashdot about how the atmosphere of Venus is operating far from chemical equilibrium, and that there may be some primitive life in the 400 degree acid in the atmosphere. Maybe someone should pay more attention to Venus...
- Water is highly polar, and therefore has the ability to dissolve ions. Without ions, complex chemistry could not take place.
- Water is liquid at a "reasonable" temperature, meaning water in liquid form is not hot enough to destroy most complex molecules.
- The density of ice is slightly less than that of water, so ice floats on top of water. This is vital, because it allows bodies of water to form a frozen cover which protects against further freezing. This is not common among substances.
- Water blocks ultraviolet light, which would otherwise destroy fragile molecules and organisms.
- Water has a very high specific heat, making it ideal for carrying out chemical reactions -- exothermic reactions can dump their heat into the water, and endothermic reactions can draw their heat from the water. This allows energetic reactions to occur without raising the temperature too high.
Basically, water is a very unusual substance with many favorable properties, and it's likely that life will take advantage of water, if it is present.That's not to say that life cannot exist without water, but it certainly makes life much more plausible.
As for non-carbon-based lifeforms, people have been pondering that for decades. Carbon is interesting because it can bond with itself pretty much ad infinitum, forming complicated structures. It also combines readily with oxygen, nitrogen, hydrogen, sulfur, the halogens, and a host of other elements. Complex life based on some non-carbon element would have to have the ability to form long chains of atoms, branching structures, and structured which curl up into specific shapes (i.e. proteins and enzymes). A carbon-silicon combo might work.
How about a BBC article
The fungi that did the damage, Novikova said, included members of the genera Aspergillus, Penicillium, and Cladesporium - all very common on Earth.
Davak
On the one hand, I agree with you totally. The earliest life on earth was not photosynthetic; even if Martian life is photosynthetic, there is no reason to expect that it would use chlorophyll to capture photons (carotenoids, for example, also work; any aromatic compound of about the same size could do in a pinch.)
On the other hand, your nomenclature is a bit confused.
Viruses are neither cells nor creatures. Furthermore, although they are not complex, they require fairly complex hosts in order to thrive. Martian cellular life might have useless or parasitic DNA, but I rate it unlikely that this DNA kills the hosts (which must be rare,) or packages itself into particles in order to spread. In any case, the viruses would have to be more difficult to detect than their hosts.
Amoeba are not simple, either. They are single celled, but they can sense and react to their environment in amazingly complex ways - early life almost certainly could not. They are, in fact, among the most complicated single-celled lifeforms on this planet.
Modern bacteria are turning out to have complex features, such as the ability to communicate with one another, which we had not suspected.
Nevertheless, ancient bacteria, or proto-bacteria, very ancient life on earth; things similar to that might be found on Mars.
Depending on how old you think such life or proto-life is (estimates vary from 2.5 to 5 billion years) it is conceivable that some sort of nasty event could have deposited some on another planet or vice versa - but I think this is highly unlikely, to say the least.
So, what should we be looking for? Nucleic acids, particularly RNA.
This is based on the RNA-world hypothesis. Basically, it says that before modern life evolved, which is characterised by the fundamental theorem of molecular biology:
DNA makes RNA makes Protein
There was life that used only RNA. In this life, or proto-life, RNA served as both the store of genetic information (we use DNA for this) and as the catalytic workhorse of life (we use Protein for this). RNA has unique chemistry which may make it the only chemical, in the universe, capable of originating life - RNA can catalyze it's own synthesis, so it can reproduce all by itself.
So, this Martian life is probably descendended from RNA molecules, like we are, and probably still contains RNA, just like we do.
On the other hand, this argument is premised on the concept that any life we find must have a chemical origin similar to our own. Unfortunately, I think this is probably the case (so no aliens made of Quartz, sorry,) but maybe not. If it ISN'T the case, we have NO IDEA what to look for, so back to square one.
If RNA is the sole origin of life, then, basically, you need water to have life (RNA only has these desirable properties when dissolved in water.) This leads us back to the rather pedestrian xenobiology of trying to find evidence of liquid water in Mars' past.
On a final note, I think Io is probably a better bet to find extra-terran life. There is definitely liquid water, and it is rich in complex organic molecules (including RNA, I believe) it has a temperature comparable to that of the early earth, and it has rich sources of the sulfur and nitrogen compounds that early life probably used as food.
This raises a significant risk, however. There are living organisms on earth that could probably survive being transplanted to Io (the same is not true, by the way, of Mars.) So, we'd have to be extremely careful not to contaminate the place.
The good and new comes from no quarter where it is looked for, and is always something different from what is expected.