Rosetta is nearing the culmination of years of cosmic expedition. This fall, a unique spacecraft Philae will land on the comet’s nucleus 67P / Churyumov-Gerasimenko, and meanwhile Rosetta is approaching the comet and has already transmitted intriguing scientific information.
The comet Churyumov-Gerasimenko was discovered in 1969 by Soviet scientists Klim Churyumov and Svetlana Gerasimenko. It is classified as a short-period comet, meaning that it does not fly away into the depths of the Oort Cloud to the outskirts of the solar system, but travels only a little farther than the orbit of Jupiter. Every 6.6 years it is moving closer to the Sun, but not enough to evaporate, like ISON. 67P does not get even as close as the Earth’s orbit.
Comet Churyumov-Gerasimenko was selected by the European Space Agency (ESA) for a thorough exploration by probe Rosetta with lander Philae. This choice happened partly by accident. Originally, the scientists planned to study the comet Wirtanen, but had to postpone the launch of Rosetta due to a faulty rocket Arian-5. When the problem with the rocket was solved, they decided comet that Churyumov-Gerasimenko was the most opportune.
The peculiarity of Rosetta mission is that previously all research stations studied comets on a collision trajectories and close rendezvous ended in a matter of hours or minutes.
Currently Rosetta is catching up to the comet and in August will be on its orbit (or rather will just rotate close by).
As it turned out, the unexpected hitch with the launch vehicle gave the scientists a chance to conduct an even more complex and fruitful research than they expected. The comet has tossed a few surprises that no one expected.
Now the comet comes closer to the Sun, so when in April its gas-dust coma began to grow no one was surprised. But in May, the growth of the coma stopped, and in June it was back to the shape of an almost bare piece of rock and ice.
In June, NASA scientists used one of their three instruments, placed on Rosetta in agreement with their European counterparts, to estimate amounts of water vapor emitted by the comet. The emission was about 300 milliliters of water per second. For they three-mile “snowball” this result seems rather modest, although almost 26 tons per day – sounds more impressively.
In June we began to receive the first pictures in which the nucleus of the comet began to occupy more than one pixel. Previously, the form of the comet was modeled on the basis of the images from the Hubble telescope, and for a long time this data was the most accurate. ESA has prepared a lot of illustrations the images obtained by Hubble.
On June 28, when the distance to 67P was 86 thousand kilometers, the scientists were able to obtain a series of images allowing to see the rotation of the nucleus.
But it took another half of this distance to begin to discern its shape. On July 4 the distance to the comet was 37 thousand kilometers and the new images showed that the comet is different from what we expected.
On July 14 from a distance of 12 thousand kilometers we opened a new sensational detail: Comet 67P / Churyumov-Gerasimenko seems to have two cores!
Nothing like this has ever been observed. Earth probes have already encountered asteroids stuck together, such as Itokawa, but not a comet. This could be the result of the collapse of a larger nucleus when the comet disintegrated from the heat and then the fragments were joined together again by the forces of gravity. But it may be that 67P / Churyumov-Gerasimenko – is the result of the meeting of two different cometary nuclei. We will be able to tell by analyzing their structure and the nature of gas and dust emissions. If it turns out to be the second option, it will open up a unique opportunity for scientists to study two comets at once. They could not dream of such a gift from the solar system.
Wags have already compared the shape of the comet’s nucleus to a toy duck, and suggested that one part should be called “Churyumov” and the second “Gerasimenko.”
Now Rosetta is approaching the comet at a speed of about 2 thousand kilometers per day, so every day we receive more accurate and detailed pictures. Today, the distance from the probe to 67P should be about 4-5 thousand km, and the surface details must already be visible.
The trouble is that the ESA scientists don’t generally publish all pictures as they become available, as does NASA, for example, with frames from Curiosity. First, the Europeans want to write articles, monographs and dissertations, and only then are ready to share the results of Rosetta with the world. As a result of this policy, a detailed survey of the comet will have to wait 6 months to a year, and for now we will have to do with the content that publishes ESA after coordination between all research groups.
We’re now watching the developments.