The Chase

The plan, hatched way back in 1993, was ambitious almost to the point of being audacious:  send a spacecraft to rendezvous with a comet traveling at 84,000 miles per hour (135,000 km/h) and, just for a little additional challenge, land a probe on its surface.  Landing an object on a comet had never been attempted, but scientists at the European Space Agency (ESA) thought they could get the job done.  And they did.

Named after the Rosetta Stone, the Rosetta spacecraft was launched from the Guiana Space Center, in 2004, and traveled a whopping 4 billion miles (6.4 billion kilometers) during its 10-year chase to reach Comet 67P/Churyumov-Gerasimenko.  Rosetta required four planetary gravitational assists to get up to the required velocity, and it flew by two asteroids (2867 Steins and 21 Lutetia) on its way to 67P.  Its primary objective:  to understand better the origin and evolution of the Solar System.

Comet 67P/C-G was discovered by and named after two Soviet astronomers, in 1969.

Mysterious Traveler

Approximately 4.6 billion years ago, the Sun and planets of our system began to form from a “pre-solar nebula.”  Among the first objects to coalesce were comets such as 67P that, in their composition, are representative of the ingredients that were available in that nebula for stellar and planetary formation.



Rosetta’s OSIRIS wide-angle camera captured an outburst from the Atum region on Comet 67P (Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

Comets are also believed to have been instrumental in the development of planets and to have provided substantial quantities of water in frequent impacts with the larger bodies, such as Earth.  So, to the Rosetta mission planners, a fast-moving mysterious traveler like 67P presented an unparalleled opportunity to study an example of one of the primordial objects that helped to sculpt the Solar System.

Success Tempered by Disappointment

Rosetta carried with it a probe called Philae.  After catching up with Comet 67P and entering a low orbit around it, Rosetta released Philae, which landed on the surface almost two years ago.  The feat was an unprecedented success, and the astronomers and engineers at ESA’s Mission Control were jubilant.

Comet 67P/Churyumov-Gerasimenko has 19 distinct regions, each named after an ancient Egyptian deity.

Comet 67P’s jagged topography presented extraordinary challenges for landing the Philae probe. (Image credit: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0)

Unfortunately, the Rosetta team’s joy was short-lived.  Philae was situated in the shadow of cliff, thus depriving it of crucial solar power.  Using batteries, it transmitted data consistently for only two days (and then intermittently a few months later) and was unable to attempt a significant portion of its planned scientific research.  Still, there was much to be learned from Rosetta, which continued to orbit 67P at an altitude of only about 19 miles (30 kilometers), and the overall mission proceeded.

The Mission Comes to an End

Last week, there were two especially significant items of news from the Rosetta mission:  (1) Eagle-eyed analysts spotted the unlucky Philae lander, nestled among boulders in the shadow of a ledge; and (2) mission controllers announced that Rosetta itself would end its mission, later this month, with a slow-motion crash into the surface of the now somewhat less mysterious traveler.

The Philae probe was deprived of necessary solar power when it landed in the shadow of a cliff ledge. (Image credit: Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/ NavCam – CC BY-SA IGO 3.0)
Rosetta will “crash” into a target called Ma’at (red circle). (Image credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0)

What began with a fiery launch from the Guiana Space Center, a dozen years ago, will end in a gentle descent to the surface of Comet 67P/Churyumov-Gerasimenko.  The target will be an area the Rosetta team has named Ma’at, which harbors active pits from which dust jets shoot out from the comet.  On its way down, the controllers of the Rosetta spacecraft will instruct it to snap some final high-resolution photos to send home.  Then it will go quiet, its remains carried on the comet as it loops for eons around the Sun between the orbits of Jupiter and Earth.