NASA’s InSight lander has picked up a range of strange rumbling sounds from below the surface of Mars.
The robotic spacecraft, which landed on the Red Planet last November, comes equipped with an extremely sensitive seismometer called the Seismic Experiment for Interior Structure (SEIS).
This device can pick up vibrations as subtle as a breeze, and was designed to listen for marsquakes.
NASA claims that studying how the seismic waves of these quakes move through the planet’s interior could reveal the deep inner structure of Mars for the first time.
Since being placed on the Martian surface on 19 December 2018, it has detected around 100 events – 21 of which are strongly considered to be quakes.
The remainder could be quakes as well, according to NASA, but the science team hasn’t ruled out other causes.
The rumblings that have detected so far suggest that the Martian crust is like a mix of the Earth’s crust and the Moon’s.
Cracks in Earth’s crust seal over time as water fills them with new minerals. This enables sound waves to continue uninterrupted as they pass through old fractures.
Drier crusts like the Moon’s remain fractured after impacts, scattering sound waves for tens of minutes rather than allowing them to travel in a straight line.
Mars, with its cratered surface, is slightly more Moon-like, with seismic waves ringing for a minute or so, whereas quakes on Earth can come and go in seconds, according to NASA.
SEIS has no trouble identifying quiet quakes, but its sensitive “ear” means scientists have lots of other noises to filter out.
These include wind gusts, noises from the camera on InSight’s robotic arm, and even “dinks and donks” from the seismomenter itself as its internal parts expand and contract.
“It’s been exciting hearing the first vibrations from the lander,” said Constantinos Charalambous, an InSight science team member at Imperial College London who works with the SP sensors.
“You’re imagining what’s really happening on Mars as InSight sits on the open landscape.”
Last month, InSight detected strange magnetic pulses in Mars’ magnetic field, starting at around midnight local time, and sometimes lasting as long as two hours.
The pulses puzzled scientists because, on Earth, these types of pulses tend to happen at higher latitudes, but InSight is currently positioned near Mars’ equator.
One theory is that the pulses are caused by the shape of Mars’ magnetic bubble, which is created as solar winds interact with its thin atmosphere.
This bubble is “compressed by the solar wind’s magnetic field, causing part of the bubble to take on a tail-like shape,” National Geographic explains.
“At midnight, InSight’s spot on Mars is aligned with this tail, and as it passes through, the tail may be plucking the surface magnetic field like a guitar string.”