On Thursday, comet 67P/Churyumov-Gerasimenko has reached the point closest to the sun on its long journey through space. More ice evaporates than ever before. The big question: will lander Philae make himself heard?
The chief of the European Space Agency ESA's satellite mission control was relieved: "everything went well," Paolo Ferri told dpa early on Thursday morning in Darmstadt: "The fly-by was not very spectacular."
Before reaching the point, closest to the sun, comet Chury (67P/Churyumov-Gerasimenko) has come a long way. It traveled all the way from the Kuiper Belt in the outlying areas of our solar system. It will get closer and closer to the sun and eventually disintegrate, but that's still a long way away.
When it flew by the sun this Thursday morning, Chury still kept a safe distance of about 185 million kilometers (114 million miles) from the sun, traveling in an elliptical orbit. From now on it will fly back into darkness - only to return to the sun's vicinity in more than six years.
During the fly-by, the distance between Chury and the sun was greater than the distance between the sun and our Earth, which is 150 million kilometers (93 Million miles).
Never before has a robot got this close
The scientists are exited: never before has a robot been in a position as good as this one to observe the process of comet-evaporation. Space craft Rosetta has been orbiting Chury for almost a year, constantly recording any change. Then, Rosetta caught up with the comet after a more than ten-year journey through deep space. At that point the distance to the sun was still 500 million kilometers (310 million miles).
Since then, Rosetta has started to observe the process of the comet heating up and more ice evaporating by the day. On Chury, the surface is already hotter than on Earth because there is no atmosphere shielding the comet from sunrays. Surface temperatures reach 80 degree Celsius (176 degree Fahrenheit), enough to turn Hydrocarbon-compounds, or even water, into steam under circumstances of very low pressure.
Rosetta, meanwhile, is collecting large amounts of data with its spectrometers, cameras and other instruments. Especially the chemical makeup of the coma - the gas-shell surrounding the comet - is of interest to the researchers.
Ample hydrogen sulfides, methane and dust
Rosettas ROSINA instrument - a special spectrometer for analyzing ions, operated by the University of Bern - registered some noticeable changes in the days leading up to the approach to the sun. Chury has started emitting almost twice as much carbondioxide, four times the amount of methane and seven times the amount of hydrogen sulfide compared to the weeks before. Only the amount of water vapor has remained stable.
The amount of measurable dust has also increased. The instruments measured about ten times more than at the beginning of July. And the researchers expect the increased values to continue for some more weeks: "We are expecting more explosions and dust-emissions into September," Ferri said.
Philae does not speak - but does it listen?
Nobody knows what's up with tiny landing robot Philae, which Rosetta released onto the comet at the end of last year. The experts who are in charge of Philae at the German National Aeronautics and Space Research Center (DLR) were last in touch with the lander on July 9th.
Since then, all attempts to establish a data connection to the robot have failed. And the approach to the sun has not made it easier for mission control: Because of the increasing activity of the comet, Rosetta has to keep a safe distance and maintain a higher orbit.
Nevertheless, the scientists are far away from giving up hope: They have sent telemetry commands to Philae in the hope that the robot hears and understands them and starts using its instruments. They hope that at a later point, when Chury is less active, Rosetta will be able to find a better orbit, close in on the comet, establish a connection to the lander and hopefully retrieve the collected data.