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n November 12, 2014, the European
Space Agency’s (ESA) Rosetta space-
craft jettisoned some of its most pre-
cious cargo. Rosetta, which had been
orbiting Comet 67P/Churyumov-
Gerasimenko (“67P” for short) for three months,
released the Philae lander from an altitude of
14 miles (22.5 kilometers).
The washing machine-sized probe fell toward the
comet for seven hours before touching the surface.
Unfortunately, it didn’t stick around. Philae was sup-
posed to land on its three legs and then secure itself by
shooting two harpoons into the comet, but they failed
to fire. The probe was off to explore new frontiers.
Philae bounced off the surface at a speed of 15
inches (38 centimeters) per second, a significant frac-
tion of the comet’s escape velocity. But gravity won
out, and the probe started to descend again. Data
returned by the Rosetta Lander Magnetometer and
Plasma Monitor (ROMAP) show that it hit the
ground again about 45 minutes later. “We think that
Philae probably touched a surface with one leg only
— perhaps grazing a crater rim — and after that the
lander was tumbling,” said ROMAP co-principal
investigator Hans-Ulrich Auster from the Technische
Universität in Braunschweig, Germany, in November.
Philae embarked on another excursion, this one
lasting 65 minutes and reaching an altitude of about
0.6 mile (1km). After hitting the surface a third time,
the lander bounced several feet and then came to aAs Comet 67P/Churyumov-
Gerasimenko heads closer
to the Sun and grows more
active, the Rosetta and
Philae spacecraft scrutinize
its complex behavior.
by Richard Talcott
stop. Unfortunately, it ended up in an awkward posi-
tion — tipped on its side and in the shadow of a cliff.No time to waste
The cliff created a sense of urgency back on Earth.
Mission planners designed Philae’s battery to oper-
ate for about 60 hours. This pioneer comet lander’s
solar panels would recharge the battery continuously
when they were in sunlight, however, allowing Philae
to operate for several weeks or months.
But the deep shadows would not cooperate. The
craft received only 1.5 hours of sunlight during each
12.4-hour day. It survived 57 hours on its battery
power, during which it accomplished roughly 80
percent of what scientists had planned.
The probe’s cameras photographed its surround-
ings. Some instruments sniffed 67P’s atmosphere,
finding molecules containing hydrogen and carbon.
Others examined the comet’s surface, which turned
out to be as hard as ice in contrast to the “soft and
f luffy” consistency scientists expected. But the shut-
ters on one instrument failed to open and a drill on
another could not penetrate the surface to deliver
samples for onboard analysis.
As Philae neared its final hours November 14,
controllers on Earth raised the craft 1.6 inches (4cm)
and rotated it 35°. They hoped this would orient theRichard Talcott is an Astronomy senior editor and author of
Teach Yourself Visually Astronomy (Wiley Publishing, 2008).Comet activity was starting to ramp up nicely by early
May, when Rosetta took this side-on view from a dis-
tance of 84 miles (135 kilometers). ESA/ROSETTA/NAVCAMA LARGE CRACK
(part of which crosses
the center of this
image) runs across
the comet’s neck.
ESA/ROSETTA/MPS/OSIRIS TEAMTHIS HIGH CLIFF
FACE at the edge of
the Hathor region
reaches 330 feet
(100 meters) high.
ESA/ROSETTA/MPS/OSIRIS TEAM