The European Space Agency (ESA) Rosetta spacecraft has spent two years deploying comet 67P / Churyumov-Gerasimenko OSIRIS cameras circling more than 70,000 images of the strange duck-shaped body. In addition to sudden gas and dust eruptions, the researchers observed jets that developed each morning as the surface of the comet formed sun-warmed frost zones.
"When the sun rises over part of the comet, the surface becomes almost instantaneously active along the terminator," says Xian Shi of the Max Planck Institute for Solar System Research and lead author of a work in Nature Astronomy , "The rays of gas and dust that we observe inside the coma are very reliable: they are found in the same places and in a similar form every morning."
The early morning activity is the result of frost, which forms overnight, evaporates rapidly in the sunlight. OSIRIS lead researcher Holger Sierks said such eruptions "can often be traced to a small area on the surface where suddenly frozen water is exposed, for example, by a landslide."
"In the case of cometary activity at sunrise, this is different," he added. "The frost is fairly evenly distributed over the entire surface."
But it was not immediately clear why jets formed instead of a homogeneous cloud.
A new study shows that they are the result of 67P's unusual shape and jagged topography. The researchers analyzed images of the Hapi region at the "neck" of the comet, which were recorded at different angles. They found that the frost had evaporated very efficiently in heavily lit areas and that pits and concave pits heavily concentrated gas and dust emissions
The team was able to create computer simulations very close to Rosetta's early morning jets came.
"The complex shape of Rosetta's comet makes many investigations difficult," said Shi. "But for this study, it was a blessing." She said that gas and dust released by a globular or potato-shaped comet would be more evenly distributed and might not be as prominent in a coma's coma.