Mars Has Methane—But Does It Have Life

We may be one step closer to cracking the Mars methane mystery.

NASA’s Curiosity rover mission recently determined that background levels of methane in Mars’ atmosphere cycle seasonally, peaking in the northern summer. The six-wheeled robot has also detected two surges to date of the gas inside the Red Planet’s 96-mile-wide (154 kilometers) Gale Crater—once in June 2013, and then again in late 2013 through early 2014.

These finds have intrigued astrobiologists, because methane is a possible biosignature. Though the gas can be produced by a variety of geological processes, the vast majority of methane in Earth’s air is pumped out by microbes and other living creatures.

Some answers may soon be on the horizon, because that June 2013 detection has just been firmed up. Europe’s Mars Express orbiter noted the spike as well from that spacecraft’s perch high above the Red Planet, a new study reports.

“While previous observations, including that of Curiosity, have been debated, this first independent confirmation of a methane spike increases confidence in the detections,” said study lead author Marco Giuranna, of the Istituto Nazionale di Astrofisica in Rome.

And that’s not all. Giuranna and his team also traced the likely source of the June 2013 plume to a geologically complex region about 310 miles (500 kilometers) east of Gale Crater.

The researchers used data gathered by Mars Express’ Planetary Fourier Spectrometer instrument (PFS), which also sniffed out traces of Red Planet methane back in 2004. (The spacecraft has been orbiting Mars since December 2003.)

Giuranna, the PFS principal investigator, had prepared for synergy with the Curiosity team. Soon after the rover’s August 2012 touchdown inside Gale, he decided to monitor the air above the crater over the long term, Giuranna said.

Toffee Planets” Hint at Earth’s Cosmic Rarity

It might not occur to us surface dwellers very often, but rocks can flow—more like the way exceedingly lethargic toothpaste would rather than water. Exposed to the extreme temperatures and pressures that reign in the hellish realms far below our feet, rocks can practically swim—slowly diving down and bobbing up through much of Earth’s subsurface.

For some rocky worlds around other stars, what is true for Earth’s innards may extend right up to the surface. Super Earths—sometimes rocky exoplanets that are bigger than our pale blue dot but smaller than massive ice giants such as Neptune—have comparatively strong gravitational fields. Thanks to this extreme gravity, some scientists suspect, rocks on such worlds would flow far closer to the surface.

This arrangement would mean rocks that snap, fracture and break might only be found in thin veneers on these exoplanets’ crust. If these rocky super Earths have thick, Venus-like atmospheres or are especially close to their parent star, they might exhibit no familiarly brittle geology at their surface at all. Instead, says Paul Byrne, a planetary scientist at North Carolina State University and lead author of a study on the Super Earths, their surface rocks would be strangely malleable over long timescales, flowing a bit like the stretchy, sugary confections on offer in any earthly candy shop.

Byrne and his colleagues’ work hinges on defining the point at which rocks deep below a planet’s surface no longer break in a mechanical way and instead begin to move like hot plastic. This point, known as the brittle-ductile transition (BDT), depends on how the pressure and temperature change with depth. For our own world’s crust, the BDT lies about 15.5 miles below the surface, although it varies quite a bit. But what about on super Earths, where greater gravitational forces would correspondingly increase pressures on rock? At what depths would BDTs emerge on such alien planets?

Taking inspiration from their own 2017 precursor paper, the researchers compiled data from 200 preexisting studies examining the lab-based deformation of basalt and other common rock types over a wide range of pressures and temperatures. They first used these data to calculate the BDT depth for Earth, calibrating their equations until sensible numbers emerged. Then they plugged in the estimated gravitational forces prevailing on five sizable, potentially rocky exoplanets found by NASA’s late, great Kepler space telescope, from the hefty Kepler-36b to the smaller Kepler-406c.