It’s not just the history of our own planet that we continue to try and understand; it’s the history of the solar system. And one of the ways we try to understand our solar system is by studying asteroids and comets – those smaller bodies that formed in the very young solar system, about 4.6 billion years ago. In a new study published in Nature, scientists have taken a look at the atmospheres of about twenty comets to try and understand these icy bodies.

Yes. Comets have atmospheres. In fact, a separate team studying interstellar comet 2I/Borisov found nickel vapor in its atmosphere. And this team found both iron and nickel vapor in the atmospheres of their twenty comets. These results were surprising all around because, while the metals are expected in the interiors of the comets, they weren’t expected in the atmospheres. Heavy metals don’t become gaseous at low temperatures.

Even more strange, the two metals were found in equal amounts in these atmospheres when normally, there is ten times more iron than nickel. So why were there iron and nickel vapor in the atmospheres of comets some 480 million kilometers away from the Sun? That’s the new question being asked. Co-author Emmanuel Jehin noted: Comets formed around 4.6 billion years ago, in the very young Solar System, and haven’t changed since that time. In that sense, they’re like fossils for astronomers.

These results mean we still don’t completely understand our early solar system, but co-author Damien Hutsemékers explains: We came to the conclusion [iron and nickel] might come from a special kind of material on the surface of the comet nucleus, sublimating at a rather low temperature and releasing iron and nickel in about the same proportions.

More work still needs to be done, and we’ll update you as we learn more.

More Information

ESO press release

“Iron and nickel atoms in cometary atmospheres even far from the Sun,” J. Manfroid, D. Hutsemékers, and E. Jehin, 2021 May 19, Nature

“Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov,” Piotr Guzik and Michał Drahus, 2021 May 19, Nature