THE WOODLANDS, TEXAS – After months of maneuvering, NASA's InSight Lander has placed its hyper-sensitive seismometer on the surface of Mars. The instrument is intended to solve puzzles about the interior of the planet by discovering the roaring thunder of "Marsquakes". But after just a few weeks, the lager in the size of a car has already heard something else: the tiny trembling that constantly shakes our red neighbor. When Marsquakes are the percussion solo, these microseisms, as they are called, represent the bass line.
The signal first appeared in early February as soon as the lander attached a shield over the seismometer, Philippe Lognonné said. A planetary seismologist at the University of Paris Diderot, who leads the team running the instrument, in a presentation here at the annual Lunar and Planetary Science Conference. "We believe that these signals are waves coming from Mars." This is the first time that such microseisms have been discovered on another planet.
On Earth, microseisms are omnipresent, caused in large part by the sloshing of the sea during storms and tides. Despite the dreams of science fiction writers, Mars has no ocean today. Instead, this newly discovered noise is likely caused by low-frequency pressure waves from atmospheric winds that rattle the surface and produce flat, longer-period waves called Rayleigh waves, Lognonné said.
Even though InSight has not done so yet, when a Marsquake was discovered, the microseisms are an important indicator that the lander's seismometer works as hoped. In recent decades, seismologists have begun to regard micro-organisms on Earth not only as a nuisance, but as a valuable tool to understand the characteristics of the subsurface. According to Lognonné, this noise will be equally valuable on Mars, allowing the team's seismologists to study the rigid surface crust in the immediate vicinity of the lander.
The seismometer, however, has not had much time to listen. While the sand-filled crater in which InSight landed was called "Homestead Hollow", making placement difficult by large boulders, the mission still took a month longer than planned, thanks to two delicate tasks. First, the scientists had to carefully adjust the electrical webbing that connects the seismometer to the lander to reduce the lander's noise. Then they had to put a wind and heat shield over the instrument.
Since then, InSight has spent a lot of time troubleshooting its second instrument, a heat sensor that can dig up to 5 meters below the surface. The robotic arm placed this instrument in mid-February. Shortly after the probe had hammered into the surface, her 40-centimeter-long "mole" stuck to only 30 centimeters on a rock or other block. Now mission scientists have stopped hammering while they wait for agency engineers to evaluate their options. It will continue for a few more weeks, said Bruce Banerdt, lead investigator for InSight and a geophysicist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
While micro seismology is coming, all those who work on InSight are waiting for the main event: their first Marsquake. "There's no need to panic, not see," said Banerdt. "Before we get nervous … [the mission is] right where we expected." The team expects to spot about one Marsquake a month, but they are likely to appear in groups that are not perfectly distributed. Banerdt, who has been preparing for this mission for decades, could be patient, he said. "The wait is not over yet."