I am curious, now that water has been discovered on the Moon, why has there been no effort to send a mission to grab a test tube of the stuff and see whats in it? We seem to be focusing on water vapor shooting out of a moon of Saturn without even checking out our own back yard first? If life has the ability to jump from planet to planet, shouldn’t the very first step be to see if it could jump to our own moon first? We want to send people to Mars yet I’ve never heard of anyone discussing this option.
Life generally requires liquid water. To the best of my knowledge, the moon has never had liquid water for any extended period, making it very unlikely life could develop or survive there.
Back in 09…
Bob, not true, NASA estimates there is 600 million metric tons of water on the Moon. It appears there is a lot of it at the bottom of craters in real ice form. From Discovery “NASAs mini-SAR team found 40 craters each containing water ice at least 2 meters deep” http://news.discovery.com/space/just-because-it-has-water-good-enough-reason-for-a-moon-mission-no.htm
The water is frozen in the bottom of the coldest craters, at the poles where they are eternally shaded from the sun.
Life as we know it requires some amount of a liquid phase and some kind of energy input. Some life on earth manages to survive when frozen solid, but AFAIK it’s only metabolically active when it’s living in a liquid phase. That can be found on the surfaces of ice, in pockets of brine, or under the surface of frozen seas.
In, say, Shackleton Crater, where the temperature is 90k, there’s really no possibility of a liquid phase of water. There’s no sunlight, so no energy input. AFAIK there’s no obvious chemical potential energy available in lunar regolith, so there’s no possibility of life that gains energy from lunar minerals.
Just because something is shaded by the sun now doesnt mean that this was the case 50,000 years ago. Im not suggesting that there is active life there now, but why couldn’t sunlight have hit one of those craters many years ago and created a petri dish? Its my understanding the chemical composition of the Moon is identical to that of the Earth, so i see no reason that can’t be energy gleaned from the minerals in the Moon in the same way. Certainly a test tube of the stuff would show evidence of such life, even if it no longer existed now?
As I understand it, the existence of water in these craters is only possible because they’ve been in shadows for geologic time scales (millions of years? Hundreds of millions?)
Even then, if frozen craters were exposed to sunlight and warmed up, the ice would directly sublimate. Liquid water just isn’t possible in the near-vacuum of the lunar atmosphere.
Chemically, minerals on the moon are reduced and there isn’t any available oxidizer, so none of the known lithotrophs that life on Earth would be able to extract energy from Lunar regolith.
If water can be on the surface, then it could certainly be 5 feet deep or 10 or 20 right? Why couldn’t the soil warm water below the surface and still prevent it from sublimating into the vacuum?
How would the soil warm the water?
It isn’t precisely water that’s the pre-requisite, it’s more that liquid water is a marker of the right conditions. The problem with building living systems is they necessarily depend on the constant motion and rearrangement of some molecules – to grow, burn fuel, move, reproduce, et cetera – while other molecules (the “structure” of the living system) can be counted upon not to move or rearrange at all.
Generally, it’s very difficult to arrange temperature and pressure conditions such that one class of chemical reactions is relatively easy but another is almost impossible. But there is one very important exception: the class of molecular rearrangements mediated by hydrogen-bonding. In a fairly broad band of temperature and pressure conditions, hydrogen bonds are stable enough to be counted upon for keeping things organized – they won’t just fall apart and rearrange because of random thermal fluctuations – but because they are significantly weaker than covalent bonds they are also reasonably easy to break and rearrange under conditions mild enough not to disturb any scaffolding or guiding molecules held together by covalent bonds.
That’s the trick, for us. Our DNA and proteins are held together in the right shape essentially by hydrogen bonds. (In the case of proteins, it’s actually the H-bonds in the surrounding water that do the trick, via an indirect interaction called the “hydrophobic” force.) These are strong enough to keep the DNA and proteins doing their job (which depends critically on their shape, or more precisely in the case of DNA on the “accessibility” of the right genes), but weak enough that they can be easily pulled apart and rearranged without disturbing the covalent bonds holding the pulling-apart and rearranging molecules. Now, it is certainly true that there is a fair amount of ordinary chemical reactions going on in living cells – involving the breaking and making of covalent bonds. But of course these must be very carefully controlled, so they don’t destroy the system. For example, you “burn” glucose for energy, but obviously that needs to be done very carefully, lest the combustion get out of control. How is that done? With the tremendous precise guidance that carefully shaped protein catalysts can give to chemical reactions. But the ability to shape protein catalysts in exactly the right way depends on, supra, having available the H-bonding force that is strong enough to hold them together, but weak enough to allow precise and easy shaping.
We know of no other intermolecular force that occupies this lucky middle ground, much stronger than classical van der Waals forces (the forces that make ordinary materials like nitrogen or CO2 liquefy), but much weaker than covalent bonding forces. So, as far as we know, life using information-storage molecules like DNA and shaped catalysts like proteins only works when you are in the temperature and pressure regime corresponding to the typical energy of hydrogen bonds. That is, of course, the temperature and pressure regime of liquid water. And if you’re in that regime, stably, long enough for evolution to do its thing, you would very likely have liquid water around, since water is about the third most common neutral molecule in the universe, what with all the H and O lying around. There is enormous amounts of water in the universe. But most of it is more or less just a different type of rock, at exceedingly low temperatures, and has no known capacity for fostering life. That’s why we get all excited at the possibility of liquid water, when we find it.
It may be useful to discuss the function of liquid water with respect to life. Water, being a slightly polar molecule, acts as both a mild solvent and a medium capable of suspending electrolytes which allows electrochemical reactions and polar bonding to occur. Water also has the neat property of expanding from about 4 °C to below the freezing temperature, which ensures that a solid crust can form over a body of liquid water which serves to both insulate it and that the cold water at the bottom of a body of water will rise, mixing up sediments that primitive live can use as nutrients. the high heat capacity of water serves to moderate temperature swings as well. Water may also contain a useful amount of dissolved diatomic oxygen, carbon monoxide, and carbon dioxide, which is beneficial to organisms which use a respiration metabolism (i.e. all complex multicellular life). However, all of this requires standing bodies of liquid water which cannot exist for any significant duration in a vacuum environment of the Lunar surface (aside from the almost unmeasureably tenuous noble gas and charged dust ‘atmosphere’ of the Moon).
In essence, there is no way for the Moon to support anything like the carbon/nitrogen-based, water-intensive, electrochemical life as we know it. If there is any form of life on the Moon, it will not look anything like what we think of as life, and we’ve seen no signs of the kind of modification of the lunar surface from a stable, unmodified state that we would expect some form of life to perform. Similarly, despite the vague indications of simple organic compounds that have been intermittently spotted on Mars (e.g. methane) there is no wide scale adaptation of the environment to suit the needs of any indigenous life, and no proposed mechanism by which organisms could extract useful energy in subsurface regimes (e.g. no tectonic, geothermal, or significant radiological activity), so any life that might exist on Mars will either be in fossil form or very simple and slow compared even with anaerobic life on Earth.
The best candidates to search for life as we might recognize it are in the large Jovian and Saturnian moons (Europa, Ganymede, Io, Titan, Enceladeus) which have liquid in some form, some hydrocarbons, and most importantly, energy sources for living systems to mediate and extract useful work from (primarily tidal energy, also possibly radioactive decay). Between Europa and Titan I would give almost even odds of finding some kind of self-organizing chemical system organized along some kind of cellular construction that we might consider ‘alive’, although whether it will appear in discrete organisms or look and behave anything like life as we would readily identify it is purely speculative.
Stranger
The moon is filled with underground lava tubes who’s caves are no colder then the coldest caves on Earth according to How the Universe Works narrated by Mike Rowe. Is it possible liquid water could exist in these conditions?
The ambient pressure is the problem, not the temperature. At very low pressure, liquid water cannot exist - ice evaporates directly without ever becoming liquid.
I guess there could be a sealed cave deep underground where gas pressure could build up to permit the formation of liquid water, but closed systems can’t sustain life indefinitely.
Are there active lunar lava tubes, or are they all left over from an earlier era? My understanding was that the Moon was pretty much geologically inactive (thus craters).
They are dead, but interestingly enough they are huge in comparison to Earth lava tubes and perfect for human colonization. Underground tunnels effectively protect from the cosmic rays, the temperatures are manageable and it would be a relatively easy procedure to airlock the tunnels.