Life In The Solar System

Introduction to Life in the Solar System: Humans and our associated kin on the third rock out from the Sun are lords of life forms in the solar system. Other abodes in the solar system, most probably Mars, Jupiter, Europa, and Saturn are anywhere from possible to probable habitable abodes to simple microbial life forms; perhaps something slightly above and beyond that. Bacteria survived on the surface of the Moon - on Surveyor Three. Astronauts from the Apollo 12 mission brought back to Earth parts of the unmanned Surveyor Three Lunar Lander. Terrestrial bacteria on those parts survived the lunar vacuum, solar radiations (UV, etc.), the massive temperature extremes, and lack of water and nutrients. Microbes are easy to transport. Translated, I firmly expect that the universe (including our solar system) is teaming with microbial life in all sorts of places. On Earth, microbes rule, OK? If fact, there are millions of microbes living inside you - most beneficial. Microbes have another decided advantage over more complex life forms, like plants. Solar energy (photosynthesis) isn't the only kind of energy available to organisms. No sun; no life. All life ultimately depended on photosynthetic plants which in turn couldn't exist without sunlight. From terrestrial environments to those of outer space and our solar system is but perhaps a small step for microbes. Mercury: The planet Mercury, closest planet to our Sun, unfortunately lacks any atmosphere to speak of, and broils on the side facing the Sun and freezes on the side facing away - much like our Moon, and is in fact is similarly heavily cratered. Venus: The planet Venus had long been thought of as Earth's twin sister. It also has an atmosphere. No life here!

In the upper atmosphere, the temperature and pressure of Venus drops to more terrestrial surface conditions. There can't be surface life-as-we-know-it on that planet, but what about simple, say microbial life existing in the upper atmosphere?

Earth (Terra): Home! The Moon (Luna): Like Mercury, our Moon is airless and subject to extremes in temperature depending on whether the Moon is facing towards or away from the Sun. While hardly indigenous Lunar life forms, they give credibility (as if any were needed) that microbes are composed of the right stuff to survive the rigours of outer space.

Mars (The Red Planet): Microbial life on the red planet Mars is just about a sure fire a thing as death and taxes, albeit it's probably spread very thinly.

The concept of there being not only life but intelligent life on the red planet Mars has been a part of the imagination of astronomers and the general public for the better part of a century. Even the two tiny Martian moons were seriously suspected of being artificial.

Several independent discoveries have all but proved that life, albeit simple life, probably exists, currently exists, on Mars.

There are those scientists involved with those Viking experiments who still maintain that microbial life was detected on Mars in 1976. Recall there was four separate and independent reasons for coming to the conclusion that the meteorite contained fossil microbial life forms from Mars. Thirdly, spacecraft orbiting Mars have detected methane in the Martian atmosphere. A major source of methane on Earth is from micro-organisms. Fourthly, there's no longer any question about Mars once having had extensive water. Where's there water, there's the probability of life.

Since microbial life exists on Earth, some of it would have been transported throughout geological history to Mars. It's quite possible that Mars seeded Earth as well, maybe even initially. The atmosphere is so thin that liquid water can't exist on the surface because the atmospheric pressure is so low. Jupiter (The Giant Planet): Jupiter is the largest planet in our solar system, but composed mainly of gas. In fact, Jupiter has been insulted by being compared to our Sun, but a failed Sun. Important point number one: Jupiter has its own internal energy source.

Important point's number two, three and four: Secondly, Jupiter's atmosphere is composed of the right sorts of chemicals that one identifies with origin of life events - hydrogen, methane, ammonia, water vapour, etc. Fourthly, the atmospheric bands of Jupiter are highly coloured, an indication that there's lots of complex chemistry, including organic chemistry going on within.

The upshot of all of this is that it is not implausible that within the upper reaches of Jupiter's atmosphere, as per the case of Venus, simple life forms couldn't exist, survive and thrive. Europa (A Satellite of Jupiter): Europa is, apart from Mars, the current darling of the exobiology (astrobiology) set. There is evidence that Europa has a liquid water ocean underneath a thick ice cap that is kept from freezing solid by the flexing action imposed on the moon by its parent planet, Jupiter. If you have liquid water, an energy source, you therefore have possible life, or so goes the thinking. The ice cap is thick enough so that any energy source available for life won't be solar. That is however not a death blow as not all critters on Earth rely on solar energy. All chemicals that would sustain such life would have to be efficiently recycled. Saturn (The Ringed Planet): Saturn is a quasi twin of Jupiter. Although slightly smaller and farther away from the Sun than Jupiter, the same general arguments that apply to Jupiter apply to Saturn. Titan (A Satellite of Saturn): The satellite of Saturn, Titan, is one of the largest moons in the solar system, and in fact, if it existed all by its lonesome, could be considered a planet in its own right. Titan has, fairly unique among satellites, a dense atmosphere. Were Titan the same distance from the Sun that Earth is, well, you could have a real twin of Earth, unlike our false twin, Venus.

Unfortunately, Titan is way, way, way - far away - from the solar energy source that makes Earth such a relative paradise. Thus, Titan is Earth, but an Earth in slow motion because Titan is so cold compared to Earth. If you think of Earth as liquid water at the equator, Titan is molasses at the poles!

Uranus: Uranus is a poor cousin compared to the likes of Jupiter and Saturn. Although farther out, Neptune, like Jupiter and Saturn, radiates out excess energy. It's solar independent, at least as far as any life forms might describe their environment and energy supply.

It's cold. Again, Pluto is too cold to allow for the high temperature chemistry we associate with life-as-we-know-it. If you're looking for life in our solar system, Pluto wouldn't be your first port of call.

Comets, Asteroids/Planetoids, Meteors: These relative tiny bodies can't really qualify as habitable abodes to life, except, there's evidence that not only can some of the above be rich in the sorts of chemicals associated with life (water, carbon compounds and organic chemistry), they could indeed be environments that could house dormant life forms or fossil life forms of a unicellular kind. Too hot, complex organic molecules rapidly break down. My favourite solar system locations for (probably) tough-as-nails microbial life, Mars apart, are the upper atmospheres of the Jovian (gas giant) planets (Jupiter and Saturn; maybe Uranus and Neptune). Their atmospheres are rich in organics and no doubt water vapour. The gas giants, Uranus excepted, radiate more heat energy than they receive from the Sun. There will be regions in their upper atmospheres that have Earth-like temperatures; there will be a lot of atmospheric mixing (useful for bringing different chemicals together); and of course these planets will also have been seeded with organics and water from space via comets, meteors, cosmic dust, etc., if not in fact seeded directly with microbial life forms via panspermia.