More sounds from Mars have been revealed and, while some are likely to be marsquakes, the others are a mystery.
NASA’s InSight lander arrived on the red planet last November and recorded its first seismic rumbling in April, described by NASA as “quiet but distinct shaking”.
The audio samples released on Tuesday cover more than 100 events detected by InSight’s seismometer.
Only 21 were likely to have been marsquakes.
The others could be. Or they could be something else…
Among the other sounds were the Martian wind, mechanical movements by the seismometer’s arm and other noises described by the NASA team as “dinks and donks”.
The “dinks and donks” are thought to be parts of the seismometer expanding and contracting and the ticking sound could be due to heat loss – similar to the sound a car engine makes after it is turned off and begins cooling.
Constantinos Charalambous, from Imperial College London, who worked on the audio recordings, said: “It has been exciting, especially in the beginning, hearing the first vibrations from the lander.
“You’re imagining what’s really happening on Mars as InSight sits on the open landscape.”
It is hoped that, by studying the marsquakes, scientists can learn more about how rocky planets – such as the Earth -were formed.
So far, the team has learned that the Martian crust is like a combination of the Earth’s and the Moon’s.
On Earth, cracks in the crust seal as water fills them with minerals, meaning sound waves continue uninterrupted as they pass through old fractures.
On the Moon, the crusts do not seal, meaning sound waves are scattered for many minutes.
Mars, with its cratered surface, is slightly more Moon-like, with seismic waves ringing for a minute or so, whereas earthquakes can come and go much more quickly.
They also found that evenings were best for clear recordings because there was more wind interference during the day.
Meanwhile, NASA’s other task on Mars is not going quite as well.
A German-made driller was meant to dig 16ft (almost five metres) below the surface but has managed barely 1ft (30cm) – not enough to fulfil its purpose: measuring the planet’s internal temperature.
It is not yet clear how the digger got stuck but scientists think the sand does not have enough friction for digging, meaning the “mole” has dug a pit around itself rather than digging deeper.