Sky & Telescope - February 2019 - 10

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, 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
5th, 2025 (S&T: Nov. 2018, p. 22).
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
10

FE B RUA RY 2 019 * SK Y & TELESCOPE

the European Space Agency (ESA) and
the Japan Aerospace Exploration Agency
(JAXA), will bring ﬂagship-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 ﬁeld shifted
north of the planet's center?
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 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 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 LAKDAWALLA

S. CORVA JA / ESA

For an infographic of the journey and video of the launch,
see https://is.gd/bepilaunch.
https://www.is.gd/bepilaunch
Sky & Telescope - February 2019

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