The Rosetta spacecraft of the European Space Agency spent two years orbiting Comet 67P / Churyumov- Gerasimenko, using his OSIRIS camera to capture more than 70,000 images of the strange body in the shape of a duck. In addition to sudden bursts of gas and dust, the researchers observed jets that developed every morning when sunlight warmed a bit of frost on the surface of the comet.
"When the Sun rises over a part of the comet, the surface along the terminator is almost instantly activated," said Xian Shi of the Max Planck Institute for Solar System Research and lead author of an article in Nature Astronomy . "The jets of gas and dust, which we then observed inside the coma, are very reliable: they are found every morning in the same places and in a similar way."
The activity of the morning is the result of frost, which forms during the night, evaporating quickly in the sunlight. The OSIRIS principal investigator, Holger Sierks, said that these outbursts "often go back to a small area on the surface where suddenly frozen water is exposed, for example due to a landslide."
"In the case of cometary activity at dawn, it is different," he added. "The frost is distributed fairly evenly over the entire surface."
But it was not clear why the jets were formed instead of a homogeneous cloud.
A new study shows that they are the result of irregular shape and irregular topography of 67P. Analyzing images of the Hapi region in the "neck" of the comet taken at different angles, the researchers discovered that frosts evaporated very efficiently in strongly illuminated areas and that concave depressions and depressions concentrated gas and dust emissions in a way that similar to lens.
The team was able to build computer simulations that closely mirrored the early morning jets seen by Rosetta.
"The complex shape of the Rosetta comet makes many investigations difficult," Shi said. "But for this study it was a blessing." He said that the gas and dust released from a spherical or potato-shaped comet would be distributed more evenly and might not be as prominent in a comet's coma.