Our resident guest columnist, professional astronomer Claude Plymate of NSO at Kitt Peak takes up more Big Questions. This week : Life in the Universe, Part I ~ Are We Martians?
One of the foremost questions in science as well as theology has always been “are we alone in the cosmos?” For the first time we are actually making real headway into answering this fundamental question. Recent results in biology have shown that life is far more tenacious than we ever could have imagined. At the same time, astronomers are demonstrating that planets are rather common companions to stars. Current estimates are that between 30 – 60% of stars include planetary systems. That would indicate that there are something like 30 to 60 billion planetary systems in our galaxy alone! That’s 5 – 10 planetary systems for each individual living on Earth. And if you assume our solar system is somewhat typical, each planetary system likely includes several planets. These overwhelmingly huge numbers makes it very easy to assume that Earth cannot be so special as to be the only place in our Universe where life has taken hold.
Observations of Mars from telescopes atop Mauna Kea, Hawaii have found evidence of methane in its thin atmosphere. This methane could be the result of geologic processes but could just as well be a side effect of life – living, farting organisms! What would if mean for the commonality of life throughout the Universe if we were to find it growing right now on our next door planet? Well, it depends. If it was found that life had spontaneously and independently sprang into existence on at least two distinct planets in our solar system, the implication would be that life is easy to get started and that life is likely to be found just about anywhere that the proper conditions exist. If however there is or ever was life on Mars, it is highly likely that it is directly related to life here on Earth and that its origin was not independent.
It is well known that throughout the history of our solar system a significant amount of asteroidal material has been flung back-and-forth between the Earth & Mars. The Martian meteorite ALH84001 made quite a media splash back in the 1996 when a team of NASA researches announced that structures imbedded in the rock appeared to show fossilized evidence of microbes. The controversy continues about the origin and meaning of these structures but it does clearly show that material from Mars occasionally does make the trek to Earth. Presumably, although not nearly as common, rocks that have been blasted off of the Earth by asteroid impacts should also occasionally find their way to Mars. (Mars’ weaker gravity and thinner atmosphere makes it easier to eject material off that planet than from the Earth. At the same time, more meteors will get pulled into Earth’s deeper gravity well.) It’s been shown that many types of microbes can easily survive inside a rock catapulted off of a planet and in the harsh conditions of interplanetary space for the time required for travel between Mars and Earth. This cross-contamination between the two planets would seem to make it highly likely that any life there is directly related to life here. The concept of life on a planet being seeded by life from elsewhere goes by the name panspermia. Panspermia makes it quite possible that we are all Martians!
As cool as it may seem to think that we might have or had microbial relatives living on Mars, it would tell us nothing about how likely or how often life gets started in the first place. Mars, however, is far from our last possible place to look for extraterrestrial life inside our solar system. Several of the moons around Jupiter and Saturn are believed to have liquid water oceans below frozen ice mantles. Any of these sub-surface oceans might make comfortable ecospheres for extraterrestrial critters. And it is rather unlikely that Earth or Martian bugs could have made the journey that far out in the solar system. Any life out there is quite unlikely to be related to us. If any other life that is truly unrelated to life here on Earth is found within our solar system, the odds are overwhelming that life must be pervasive throughout the Universe.
This leaves us at this the moment without knowing how easy it is for life to get itself started. What is clear is that once life does get going, it quickly adapts to a very wide range of conditions; I think the quote from Jurassic Park was “life finds a way.” Even if we find that life is difficult and takes a long time to get started, there are so many planets that have been around for such a very long time that the odds seem good that life – at least microbial life – is common across the galaxy.
National Solar Observatory ry