Deep space ‘dirty snowball’ to skim past Mars at 193,000kph

A comet that was born before the Earth formed is flying in from the edge of the solar system, bound for a dramatic date with Mars on Sunday. Comet Siding Spring — unknown and undiscovered until 2013 — will zoom past the Red Planet in an encounter that could help scientists better understand how the solar system came to be. Siding Spring will fly 139,500 kilometres from Mars at 18:27 (GMT) Sunday, about one-third of the distance from the Earth to the moon. Researchers will observe the close encounter with a fleet of orbiters and rovers at the Red Planet. Its close encounter with Mars is not likely to be visible to sky watchers on Earth.

Anything that comes off the comet that hits either Mars or the spacecraft is going to pack a real large amount of kinetic energy — a real wallop — so that’s one of the things that we’ve been worried about.

Carey Lisse, senior astrophysicist at the Johns Hopkins University Applied Physics Laboratory

Siding Spring is the first comet from the Oort Cloud, a collection of icy bodies at the edge of the solar system that will be observed up close by spacecraft. All comets examined in the past came from closer in, around Jupiter’s orbit or the edge of the Kuiper Belt, a huge set of icy objects beyond Neptune. Half of the comet is rocky, and the other half is made up of volatile ices, such as water and carbon dioxide. Its flight past Mars is the first time it will make it into the solar system, past Jupiter’s orbit. The comet just recently crossed the “water-ice line,” the point where water can exist as a liquid in the solar system.

Science Siding Spring