Universe Today

The ongoing search for the existence of life that doesn't call the Earth 'home' could potentially find that life right here in our own Solar System. There is considerable debate about whether evidence for that life has already been found on Mars, but astronomers might do well to look at other, more exotic locations in our neighborhood.

At the recent meeting of the American Geophysical Union in San Fransisco, Francis Nimmo, who is a professor of Earth and planetary sciences at UC Santa Cruz, said that the conditions on Saturn's moon Enceladus, and Jupiter's moon Europa may be just right to harbor life. Read more…

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Exobiology (same thing as astrobiology) is about life in space (on other planets, and moons; in other solar systems): where it is, what it is, how it started, and how it evolved (all studied scientifically, of course). Because the origin of life right here on Earth, and its early evolution, is essentially unknown, and because of the distinct possibility of similiarities with the origin (and early evolution) of life elsewhere in the universe, exobiology includes research into abiogenesis (and early, and extreme, life on Earth).

Exobiology is very much a multi-disciplinary field, drawing on biology, chemistry, geology (and planetary science), physics, and astronomy.

Because we have a sample of just one – life on Earth – it is difficult to make anything but the most general decisions on what lines of exobiology research are likely to be productive (keep in mind that null results can, of course, be quite productive). Conservatively, looking for planets like Earth in orbit around stars like the Sun (in age as well as mass, metallicity, etc), and looking for clues for fossil life in planetary environments like those found today on Earth (e.g. early Mars) seem better options than investigating possible silicon-based life (to take just one example).

As the number of exosolar (or extrasolar) planetary systems known continues to grow, quickly, discovering the prevalence of Earth-mass planets, in goldilocks orbital zones, seems like a good idea … so today we have the Kepler mission and COROT.

As the early Mars becomes better understood – and the widespread distribution of liquid water then – so today we have plans for the Mars Science Laboratory and ExoMars (the discovery of methane in the Martian atmosphere certainly spurs such developments).

Less conservatively, the discovery of life around black smokers and sites like Lost City (not to mention entire ecosystems within crustal rocks … several km beneath the surface) sparked interest in the possibility of life in Europa, on Titan, even Enceladus (life – albeit rather simple life – we now know does not need to depend, ultimately, on the Sun's (or another star's) radiant energy … think chemolithoautotrophs).

Did you know that NASA has an exobiology branch? Check it out! Duke University's Chemistry Department has an interesting Introduction to Exobiology you might find interesting too.

Universe Today stories on exobiology? Yep, lots; here's a random selection: Martian Explorers Should Be Looking for Fossils, Did Life Arrive Before the Solar System Even Formed?, Extremophile Hunt Begins in Antarctica, Implications for Exobiologists , and New Targets to Search for Life on Europa.

Any Astronomy Cast episodes on exobiology? Yep … but it's called Astrobiology.

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Instead of life originating here on Earth (abiogenesis), perhaps it came from somewhere else, either in our solar system, or from beyond it? Panspermia is the name for that idea.

Panspermia is a very old idea, dating back to at least the ancient Greeks. Perhaps its most famous, recent, proponents are Fred Hoyle and Chandra Wickramasinghe.

That life could have originated somewhere in our solar system and then spread to Earth is not particularly controversial, today.

For a start, there's pretty good evidence that at least some kinds of bacteria and archaea – and perhaps simple eukaryotes too, a protist for example – could survive a journey between Mars and Earth, inside a rock blasted off by a meteorite impact. After all, there are a number of meteorites, found here on Earth, which came from Mars (and some from the Moon too), and their interplanetary journeys could have been as brief as a century (or less), which lots of prokaryotes could survive in a state of suspended animation (and some species have extremely high radiation tolerance too). While the acceleration of blast-off would likely kill most multicellular organisms, a great many single celled species could survive such a high-g event.

Then there's the overwhelming evidence that conditions on Mars in its early years would have been favorable to life – liquid water, clement temperatures, … More: indirect evidence of life on Earth is as old as the oldest rocks, so perhaps life seeded Earth as soon as the molten oceans solidified (Mars may have had a somewhat more favorable, and stable, environment, for longer, than that of the Hadean Earth).

Less is known about conditions on Venus, the Galilean moons (Io, Europa, Ganymede, Callisto), and Titan – other solar system bodies where life may have begun – during the first ~500 million years or so of their history, so the possibility of any of these seeding life on Earth is more speculative.

The possibility of life originating in other than early-Earth-like environments – such as active iceballs like Enceladus, or comets – is quite speculative, but research over the next decade or three may show it to be quite likely … and the case for panspermia strengthened accordingly.

An interstellar source of seeded life – an older planetary system perhaps – seems quite unlikely, because survival of the seeding life is thought to be zero; the travel times are too long (millions of years), and the possibility of a suitable life-bearing vessel (a cm-sized rock, say) arriving intact in as short a time as 500 million years or so also zero (while a considerable quantity of interstellar grains arrives in the solar system every year, nothing as large as even a sand grain has yet been observed among the arrivals).

Panspermia is popular! Look at all these Universe Today stories on it: Panspermia Flower Power, Life on Ceres: Could the Dwarf Planet be the Root of Panspermia?, An Experiment to Test Panspermia, Did Life Arrive Before the Solar System Even Formed?, If Life Exists on Venus, Could it be Blown to Earth? … and that's just a sample!

Astronomy Cast has a special episode on this topic, Panspermia; well worth a listen.

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