Somewhere in a shady corner of this chaotic landscape on comet 67P/Churyumov–Gerasimenko, the tiny lander Philae has received enough sunlight to send signals to earth, breaking seven months of silence.
The most likely resting place for Philae is the object circled in the photo above. The Rosetta team found this bright dot in images taken on different days in December last year, but not in images of the same area taken by the main spacecraft after it first reached 67P last August and before the Philae lander was released on November 12.
Preliminary examinations of the packets of data received at its mission control centre in the European Space Agency say Philae has been sending earlier messages that had not been heard.
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The breakthrough transmission means there is a chance Philae will do something it was never intended to do: provide a close-up view of a comet after it has become highly active, emitting clouds of gases and dust as it plunges toward its closest encounter with the heat (and high energy particles) being emitted by the sun.
Philae successfully descended from its mother ship, the Rosetta probe, to the surface of 67P on November 12 last year, but it bounced several times after a feather light touch down on the comet’s surface, where the gravitational field of the 4300-metre-wide body is so light that the intention was to secure it with a harpoon-like anchor and screws.
This didn’t work as intended, and the comet’s surface, far from being the cliched snowball of lazy science reporting, proved as hard as granite in places.
The original program called for Philae to use solar power to extend the life of its instruments and cameras but because it came to rest in a shaded rocky zone, it ran out of battery power after several Earth days.
The solar panels were expected to keep it alive for the best part of a month, and the lander was then expected to fail because of internal overheating as the short-term periodical comet drew closer to its closest approach to the sun, which it will reach mid-August.
According to early reports, the temperature in Philae is -35C, raising hopes it will not overheat too quickly. However the surface of 67P is now releasing increasingly high-volume streamers of gases and dust, and the mother ship, Rosetta, which has continued to fly alongside the comet, has retreated several hundred kilometres away from the action to avoid being damaged by the debris forming a typical set of cometary tails.
Some thousands of years ago 67P is believed to have become a shorter period comet orbiting the sun once every 6.75 years after its longer-term orbit took it close to Jupiter, robbing the comet of sufficient momentum to return to the outer reaches of the solar system.
Its orbit now brings it closest to the sun at a point between the orbits of Mars and the Earth and sends it as far out as a point beyond Jupiter’s orbit. 67P rotates on its axis about twice every earth day, and the comet’s dynamics are affected by repeated losses of mass as each visit to the inner solar system strips off the material in response to increased solar heating.