Ever since astronomer Giovanni Sciaparelli observed in 1877 what he described as channels on the surface of Mars, humanity has been fascinated with the possibility of life on our red neighbour.
Mars, however, has never been a great candidate for life, at least not current life.
There are good candidates in the neighbourhood, though, specifically several moons of Jupiter and Saturn.
Life, at least as we know it, requires three basic things, liquid water, an energy source and organic compounds, i.e., carbon-containing molecules.
Since we now know all the bodies in the solar system are basically made up of the same stuff, whether these basic building blocks are present on other celestial bodies is not only plausible but quite likely.
But how likely is it that these molecules, even in the presence of an energy source and liquid water would evolve?
We tend to, or at least like to, think Earth is special; that if there is life out there in the universe, it is a rare occurrence.
But what if the opposite is true. What if the evolution of life is virtually inevitable where favourable conditions exist?
And what if favourable conditions are much more abundant than we ever thought they were.
A lot of research has focussed on what scientists refer to as the “goldilocks zone,” that area of a solar system where a planet is not so close to its sun that it is too hot or too far away so it is too cold.
In our system, that means Earth and Mars. If Mars had an atmosphere like ours, its climate would not be dissimilar.
But exploration of the outer planets, coupled with startling discoveries of bizarre lifeforms on this planet in places we never expected to find them are starting to turn even that idea on its head.
There are at least five moons orbiting Jupiter and Saturn that likely have large subsurface oceans of liquid water. Despite their distance from the sun, this is possible because of gravity. Because their orbits are elliptical, the pull of their giant planets causes an effect called “tidal squeezing,” which causes friction, which in turn creates heat, which keeps the water liquid under the moons’ frigid surface.
We see this on Earth to a much smaller degree. Our tides are caused by the gravity of the moon tugging at the planet as it orbits.
We still need an energy source, however, and that could be the moon itself. One of the most exciting finds of the 20th century was the discovery of life living around hydrothermal vents in Earth’s deep ocean trenches far from where the energy source we most associate with life, the sun, can penetrate.
Perhaps the best candidate in the solar system is Jupiter’s moon Europa. Scientists are fairly certain, based on the moon’s magnetic field likely caused by the circulation of salt water and evidence of water leaking up through the icy surface that there is an ocean on Europa that could contain as much as three times the amount of water as all of Earth’s oceans.
NASA is so excited by Europa it plans to send a probe to the moon to be launched in 2025.
If we were to discover life on another object so close to home, the implication is astounding, although perhaps not really. One thing we know about the universe is that it is governed by the laws of nature.
What if one of those laws is water plus energy plus organics equals life all the time?
Very exciting indeed.
