largest solar panel so that as 67P neared the Sun in mid-2015, the
added illumination would revive the probe.
The effort paid off. On June 13, Philae phoned home. The craft
had survived its seven-month hibernation in great shape despite
temperatures that dropped to around –240° F (–150° C). As this
issue went to press in late June, Philae remained awake and alert,
though it had yet to resume science activities.
The view from above
While Philae rested, Rosetta did not stand idly by. The spacecraft
— the first to orbit a comet — continues to reveal 67P in extraordi-
nary detail. Mission controllers have adjusted its f light path many
times to give both global and close-up views of the comet. The
initial orbits had it about 60 miles (100km) from the comet. Later
in 2014, Rosetta spent time in circular orbits 18 miles (29km), 11.6
miles (18.6km), and 6.1 miles (9.8km) from 67P’s center.
Afterward, Rosetta embarked on a series of close f lybys, some
dipping to within 4 miles (6km) of the surface. But in the months
before 67P’s August 13 perihelion — the comet’s closest approach
to the Sun in its 6.44-year orbit — Rosetta had to back off.
Like all comets, 67P grows more active as it nears the Sun. Our
star’s light heats ices on or just below the surface, causing them to
turn directly from solids into gases in a process known as subli-
mation. As the gases escape in powerful jets, they carry with them
dust particles and larger bits of rock embedded in the ice. These
liberated substances form a tenuous atmosphere, or coma, as well
as gas and dust tails.
It all proved a bit too much during Rosetta’s close f lyby in late
March. The spacecraft uses “star trackers” to navigate and orient
itself, but 67P’s dust production grew so high that the trackers
started mistaking cometary debris for stars. Hundreds of false stars
confused the star trackers enough that Rosetta went into a “safe
mode,” switching off its science instruments and awaiting help
from Earth. Mission controllers recovered the spacecraft within
24 hours but quickly moved it into a safer, more distant orbit.
Rosetta’s first 10 months at 67P delivered exquisitely detailed
information. The comet is a contact binary shaped like a “rubber
ducky” with one large lobe (the “body”) joined to a smaller lobe (theAshBasetHathorBabiAtenKhepryAkerImhotepApisSethRosetta captured this view of Comet 67P/Churyumov-Gerasimenko
from a distance of 12.4 miles (19.9 kilometers) March 28. The two-
image mosaic shows part of the comet’s Imhotep region at a resolu-
tion of 5.6 feet (1.7 meters) per pixel. ESA/ROSETTA/NAVCAMRosetta scientists have identified 19 different regions on Comet
67P/Churyumov-Gerasimenko, 10 of which show up in this view
looking from the comet’s “body” toward its “head.” In keeping
with the ancient Egyptian theme used for both the Rosetta and
Philae spacecraft, the regions are named for Egyptian deities.
ESA/ROSETTA/MPS/OSIRIS TEAM