[b][/b] The American space agency Nasa has launched
its latest mission to Mars.
InSight will be the first probe to focus its
investigations predominantly on the interior of
the Red Planet.
The lander - due to touch down in November -
will put seismometers on the surface to feel for
"Marsquakes".
These tremors should reveal how the
underground rock is layered - data that can be
compared with Earth to shed further light on the
formation of the planets 4.6 billion years ago.
"As seismic waves travel through [Mars] they
pick up information along the way; as they travel
through different rocks," explained Dr Bruce
Banerdt, InSight's principal investigator. "And all
those wiggles you see on seismograms -
scientists understand how to pull that
information out. After we've gotten many, many
Marsquakes from different directions, we can
put together a three dimensional view of the
inside of Mars."
Thick fog did not affect the launch on an Atlas
rocket from the Vandenberg Air Force Base in
California at 04:05 local time (12:05 BST) on
Saturday.
Nasa last sent seismometers to the Red Planet
on the Viking landers in the 1970s. But these
missions failed to detect ground vibrations
because the instruments were positioned on the
body of the probes.
All they recorded was the landers' shaking as
the wind whistled by. InSight, by contrast, is
going to place its seismometers directly in the
Martian dirt.
How many quakes will be detected over the
course of a year is uncertain, but estimates
suggest perhaps a couple of dozen. They are
likely to be small - probably well less than a
Magnitude 3, which many people on Earth would
sleep through.
However, even these gentler signals will carry
sufficient information about the subsurface to
allow scientists to construct a model of Mars'
depths and composition.
The planet should have a metal core, a dense
mantle and a lighter crust - but where precisely
the boundaries lie is speculative.
The seismometer experiment is French-led. The
European nation has provided the broadband
sensors that will detect low-frequency vibrations
of the ground, while the UK has contributed a
trio of microseismometers, about the size of a
pound coin, that will go after the higher
frequencies.
A good source of these short period vibrations is
likely to be meteorite impacts.
The Franco-British systems should be able to
locate the origin of quakes to within a few
hundred km. "The pattern of Marsquakes is
going to be very important," said Prof Tom Pike
from Imperial College London.
"On Earth, earthquakes are very much aligned
with the edge of tectonic plates.
"We don't think that plate tectonics is active on
Mars but we fundamentally don't know at the
moment, and so just seeing the pattern of
seismicity that comes in - that's going to be just
a critical bit of information in and of itself."
Researchers believe Mars once had a liquid core,
as evidenced by the magnetism this generated
and which is still retained in many of the
planet's rocks. Whether any of that ancient fluid
persists is something InSight will test by using
radio equipment to observe how Mars shifts on
its axis of rotation.
"If you take a raw egg and a cooked egg and you
spin them, they wobble differently because of
the distribution of liquid in the interior," explained
InSight's deputy project scientist, Dr Suzanne
Smrekar.
"So by tracking our spacecraft very precisely,
we're able to see how Mars wobbles and that
really tells us a lot of information about the core
of Mars."
For those who recall the ill-fated Beagle Mars
lander from 2003, there will be interest in the
heat probe InSight plans to deploy. This
incorporates a hammer to dig itself up to 5m
into the ground.
The technology, from Germany, has heritage in
the "mole" designed for Beagle. InSight's heat
probe will provide information on how much
energy inside Mars is available to drive changes
at the surface.
The mission has a few weeks to get off Earth
before Mars' movement in its orbit around the
Sun makes a journey between the planets start
to become impractically long. But assuming
InSight gets up and away cleanly, it will have a
six-month cruise before landing on 26 November.
As ever, getting down in one piece will not be
easy. Like all surface missions before it, InSight
will have to endure the "seven minutes of terror"
- the time it takes for a spacecraft entering the
top of Mars' atmosphere at 6km/s to slow itself
to a standstill at the touchdown point.

Artist's rendering of the InSight lander

Phoenix landing art, similar to InSight InSight will have to endure the "seven minutes of terror" - the time it takes for a spacecraft entering the top of Mars' atmosphere at 6km/s to slow itself to a standstill at the touchdown point.

6km/s...