My first Magazine Sky & Telescope - 02.2019 | Page 12

NEWS NOTES
The BepiColombo
mission to Mercury
launches from Europe’s
spaceport in Kourou,
French Guiana.
MISSIONS
Mission to Mercury
Launches
THE BEPICOLOMBO SPACECRAFT
launched October 19th from French
Guiana on an Ariane 5 rocket, begin-
ning a seven-year journey to Mercury.
The voyage began perfectly, atop tower-
ing pillars of fl ame 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
fi nally settling in to orbit on December
5th, 2025 (S&T: Nov. 2018, p. 22).
Getting to Mercury is diffi cult — so
diffi cult that fewer spacecraft have vis-
ited Mercury than have visited Saturn.
NASA has previously sent two spacecraft:
Mariner 10, which fl ew by three times
in 1974 and 1975, and Messenger, which
orbited the planet from 2011 to 2015.
BepiColombo, a combined effort of
10
FE B RUA RY 2 019 • SK Y & TELESCOPE
the European Space Agency (ESA) and
the Japan Aerospace Exploration Agency
(JAXA), will bring fl agship-class science
to Mercury to answer questions old and
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 fi eld shifted
north of the planet’s center?
The mission comprises two sci-
ence spacecraft (plus a third craft that
provides ion propulsion for most of
the journey). The Mercury Planetary
Orbiter (MPO), built by ESA, will oper-
ate in a nearly circular orbit close to the
planet. The Mercury Magnetospheric
Orbiter (MMO), built by JAXA, will fl y
in an elliptical orbit far from the planet.
Both probes carry magnetometers,
to study how Mercury’s magnetic fi eld
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 Mes-
senger didn’t have.
MPO has cameras and spectrom-
eters to take photos and compositional
measurements 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 shrink-
ing. Scientists are particularly interested
in seeing Mercury’s south pole up close
for the fi rst time, to confi rm 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 Decem-
ber 2025 should be a piece of cake by
comparison. By the time the spacecraft
completes its sixth fl yby 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 LAKDAWALLA
For an infographic of the jour-
ney and video of the launch,
see https://is.gd/bepilaunch.