Professor David Rothery
BepiColombo isshooting forMercury. Professor DavidRothery, a key
member of thescience team,reveals what’sin thepipleline and what we’ve
got to look forward to ahead of its rendezvouswith theswift planetin 2025MERCURY MISSION:
“I’M GLAD WE’RE
GOING BACK!”
What will you be doing in preparation ahead of
BepiColombo’s arrival at Mercury in 2025?
My role on the MIXS team is to help prepare to
make the best observations that we can. MIXS’
role towards understanding Mercury’s surface and
composition is to map all the chemical elements it
can, and there are some targets which MIXS will try
to stare at, making sure it’s collecting observations
when it’s over these critical targets where we think
the composition is unusual. MIXS will map the
whole planet, but some small areas need special
attention – places where there have been volcanic
explosions, or regions called ‘hollows’, which is
where the surface is dissipating away to space. At
the present day we think the surface is rotting away.
We have very limited compositional measurements
of these features from the previous mission,
MESSENGER. [BepiColombo] will get much better
spatial resolution with the X-ray spectrometer then
we’ve achieved before. We’re going to make sure we
know in advance where these are and build them
into the data-collection schedule for arrival to be
sure that it’s collecting data when it’s over the right
targets. I’m making sure that MIXS will collect data
over the most important regions. I’m also concerned
with making sure that we understand the context
of the observations we make.What is the surface of Mercury like?
Mercury is covered in craters, volcanic planes and
holes ripped in the ground by violent volcanic
explosions, violent events and more passive
processes where the surface is just dissipating away
somehow. We need to get this mapped. Half the
planet was mapped in the late-1970s by the Mariner
10 mission, but we’ve got something that looksReportedbyLeeCavendishbetter than black-and-white imagery. We’ve now got
a whole planet as seen by NASA’s MESSENGER. But
the MESSENGER team didn’t undertake the job of
making new geological maps of the planet. With our
mission coming up, we’re using the MESSENGER
data to make geological maps because we want to
understand the context of all our observations.What do these maps look like?
There are geological maps, or what we call a
‘morphostratigraphy map’. The pale-brown areas
indicate the smoothest plains, and they’re smooth
because they’re young and there hasn’t been time
for many craters to accumulate. The mid-brown
and the dark brown are progressively older classes
of surface. The older they are, the rougher they are,
because more craters have occurred. Then you map
the individual craters more than 20 kilometres (12
miles) in size and distinguish them by age. The
youngest craters sometimes have rays comingout from them and the ejecta is very prominent;
you can see the burying of the old terrain and
the craters look very fresh. The older craters are
partly buried by younger events and they’re more
degraded with age. We’ve also broken it down to
five degradation classes to try and work out the
age relationships.
There have been topographic maps that have
just come out from the stereo imaging or the laser
altimetry that’s been done. But here [at the OU]
we’re interpreting it as a geologist and identifying
different surfaces and then saying which is older
than which – let’s get the layering worked out or
the sequence of events worked out. When you
have a geological map like that with the relative
ages of surfaces, and then you get a new mission
there and it says, “Hey! Over this area here it’s high
sulphur and low calcium, but over there it’s the
other way around,” we can go straight to the map
and say, “Wow! So that’s the oldest stuff that’s highRight: This
colourful view
of Mercury,
taken by
MESSENGER,
flaunts its
chemical
and mineral
composition © NASA