6 AUSTRALIAN SKY & TELESCOPE February | March 2019
THE BEPICOLOMBO SPACECRAFT
launched late last year from French
Guiana on an Ariane 5 rocket,
beginning a seven-year journey to
Mercury. The voyage began perfectly,
atop towering pillars of flame that lit
up the early morning sky and remained
visible until the side boosters burned
out 2 minutes later, leaving the
steady light of the main rocket stage
visible as a greenish point in the sky.
BepiColombo’s journey will return it to
Earth, past Venus twice, and take it by
Mercury six times before finally settling
in to orbit on December 5, 2025.
Getting to Mercury is difficult — so
difficult that fewer spacecraft have
visited Mercury than have visited Saturn.
NASA has previously sent two spacecraft:
Mariner 10, which flew by three times
in 1974 and 1975, and Messenger, which
orbited the planet from 2011 to 2015.
BepiColombo, a combined effort of
the European Space Agency (ESA) and
the Japan Aerospace Exploration Agency
(JAXA), will bring flagship-class science
to Mercury to answer questions old andMission to
Mercury on its way
new. How can the terrestrial planet
with the biggest iron core have so little
iron in its crust? How can its crust have
so much sulfur when it’s so close to the
Sun? Why is its magnetic field shifted
north of the planet’s centre?
The mission comprises two science
spacecraft (plus a third craft that
provides ion propulsion for most of
the journey). The Mercury Planetary
Orbiter (MPO), built by ESA, will
operate in a nearly circular orbit
close to the planet. The Mercury
Magnetospheric Orbiter (MMO), built
by JAXA, will fly in an elliptical orbit far
from the planet.
Both probes carry magnetometers
to study how Mercury’s magnetic field
responds to buffeting from the Sun.
Both carry instruments to study the
planet’s exosphere, the neutral atoms
and ions knocked off Mercury’s surface
by incoming radiation. MMO also
has a dust counter, something NASA’s
Messenger didn’t have.
MPO has cameras and spectrometers
to take photos and compositionalmeasurements of the surface. From
its nearly circular orbit, MPO will get
much closer to Mercury’s southern
hemisphere and obtain much sharper
images than Messenger could. The
orbiter will try to understand the
composition of Mercury’s crust, the
nature of its volcanic activity, and
the timing of the planet’s apparent
shrinking. Scientists are particularly
interested in seeing Mercury’s south
pole up close for the first time, to
confirm whether it has reservoirs of ices
and organic-rich materials, as the north
pole does.
BepiColombo has a long way to
go, but it has accomplished the most
dangerous part of its mission — the
launch. Orbit insertion in December
2025 should be a piece of cake by
comparison. By the time the spacecraft
completes its sixth flyby of Mercury in
January of that year, it will be traveling
slowly enough to be captured naturally,
by Mercury’s own gravity, the seventh
time the planet and spacecraft meet.
■ EMILY LAKDAWALLAThe BepiColombo
mission to Mercury
launches from Europe’s
spaceport in Kourou,
French Guiana.S. CORVAJA / ESANEWS NOTES