People want one thing from space more than anything else: neighbors. Astronomers have cobbled together rough equations to help guess how likely or unlikely neighbors are. Telescopes scan the heavens for deliberate signals beamed in from far away. Many of these potential neighbors already have names, such as “Venusians,” “Romulans,” or plain-old "extra-terrestrials.”
Today the European Space Agency and Roscosmos, its Russian counterpart, launched their ExoMars mission, which is designed to figure out if Earth has, or once had, neighbors on Mars.
The ExoMars mission is carrying two projects to the Red Planet. An Orbiter will circle the planet and analyze gases that make up a small part of its weak atmosphere. NASA’s Curiosity rover detected methane on Mars in 2014, a discovery that has since kindled hopes that some kind of living organism is producing it. On Earth, living things can produce methane as a metabolic by-product, most famously, of soil microbes, cows, and teenage boys.
Methane is the simplest hydrocarbon, which on Earth also makes it a terrific fuel. Natural gas is mostly methane, or a molecule of four hydrogen atoms pinned to one carbon atom.
But living things aren’t the only source of methane. Scientists have simulated in labs how high heat and pressure such as that of the Earth's interior can forge methane, which then leaks up to the surface. Besides, Saturn’s hydrocarbon moon, Titan, has entire lakes of liquid methane, and no one’s suggesting excessive bovine activity there.
The ExoMars orbiter will help scientists understand if Mars’s methane is geological or biological in origin.
The second project ExoMars is carrying is called the Schiaparelli module, named for Giovanni Schiaparelli, a 19thcentury Italian astronomer who studied the Martian surface. This module is a test for entering the Mars atmosphere, descending safely, and landing in one piece. It’s a practice run for a second ExoMars mission, to be launched in 2018, which will deliver a life- and fossil-detecting rover.
Even if no current or past evidence of life on Mars is ever found, the better we get at going to Mars, the easier it may be eventually to send people there—making sure the planet has neighbors even if we have to place them there ourselves.