A once-in-a million year event will take place this weekend as a comet about the size of a small mountain is set to flyby very close to planet Mars.
The comet known as Siding Spring will pass within 87,000 miles of the Red Planet, or about one third of the distance from the Earth to the moon, at a speed of 126,000 mph on Sunday, Oct. 19. In astronomical terms, the proximity is a hair's breadth and no comet is known to have gotten this close to Earth before.
Siding Spring, whose nucleus is estimated to be no smaller than a half mile in diameter, will get very close to Mars that astronomers expect the Red Planet to be enveloped by the comet's dust and gas.
As a precaution, NASA already decided to move its orbiters away from where they could be endangered by the comet's approach. The European Space Agency (ESA) did the same with its Mars Express as well as the Indian Space Research Organization (ISRO) with its Mangalyaan spacecraft, the first interplanetary spacecraft launched by the country, which arrived in the Martian orbit last month.
Scientists have expressed their excitement over the event described as a once-in-a-lifetime opportunity given the possibility of observing it with the availability of sophisticated spacecraft and instruments studying and even stationed in the Red Planet.
The comet, which hailed from Oort Cloud, one of the coldest and most remote regions of the solar system, was formed during the first two millions years of the birth of the solar system and only comes around once in every one or more million years.
"The close fly-by of Mars by Comet Siding Spring is unique, unexpected, and lucky for us," said space scientist David Humm, from the Johns Hopkins University Applied Physics Laboratory (APL). "The likelihood of being this close to a new comet is really very small, and we're operating well beyond our design lifetime, so this exciting an opportunity is completely unexpected."
Johns Hopkins University astrophysicist Carey Lisse said that by studying the composition and structure of comet Siding Spring, scientists hope to get valuable information that could shed light on how planets form. Scientists also want to see the effects of the comet's close approach to Mars.
"Think about a comet that started its travel probably at the dawn of man and it's just coming in close now," Lisse said. "And the reason we can actually observe it is because we have built satellites and rovers. We've now got outposts around Mars."