The American space agency's InSight lander appears to have
detected its first seismic event on Mars.
The faint rumble was
picked up by the probe's sensors on 6 April - the 128th Martian day, or sol, of
the mission.
It is the first
seismic signal detected on the surface of a planetary body other than the Earth
and its Moon.
Scientists say the
source for this "Marsquake" could either be movement in a crack
inside the planet or the shaking from a meteorite impact.
Nasa's
InSight probe touched down on the Red Planet in November last year.
It aims to identify
multiple quakes, to help build a clearer picture of Mars' interior structure.
Researchers can then
compare this with Earth's internal rock layering, to learn something new about
the different ways in which these two worlds have evolved.
Interestingly,
InSight's scientists say the character of the rumble reminds them very much of
the type of data the Apollo sensors gathered on the lunar surface.
Astronauts installed
five seismometers that measured thousands of quakes while operating on the Moon
between 1969 and 1977.
InSight's
seismometer system incorporates French (low-frequency) and British
(high-frequency) sensors. Known as the Seismic Experiment for Interior
Structure (SEIS), this instrument was lifted on to the Martian surface by the
probe's robotic arm on 20 December.
Both parts of the
system observed the 6 April signal, although it wasn't possible to extract any
information to make a more definitive statement about the likely source or the
distance from the probe to the event.
"It's probably
only a Magnitude 1 to 2 event, perhaps within 100km or so. There are a lot of
uncertainties on that, but that's what it's looking like," said Prof Tom
Pike, who leads the British side of the seismometer package.
On Earth, very few
people would notice a Magnitude 1 to 2 event.
The team is
investigating three other signals picked up only by the low-frequency sensors -
on 14 March (Sol 105), 10 April (Sol 132) and 11 April (Sol 133). However,
these were even smaller than the Sol 128 event, and the InSight scientists do
not have the confidence yet to claim them as real seismic events.
The probe's prime
mission is set to run for two Earth years - a little more than one Martian
year.
Given the time taken
to make this first detection, it might suggest InSight should record another
dozen or so seismic signals in the initial operating period, explained Prof
Pike.
"When you've
got one, you don't know whether you were just lucky, but when we see two or
three we will have a better idea.
"Of course, if
the other three are confirmed then we could be looking at quite a large number
of detections over the next two years," the Imperial College London
researcher said.