Once in a million yrs: Siding Spring comet flies by Mars

Once in a million yrs: Siding Spring comet flies by Mars
A pristine comet has swept past Mars, passing it closer than one-third of the distance from the Earth to the Moon. Astronomers had a unique chance to observe the celestial body up close, as such an astronomical event occurs just once in a million years.

At a speed of 202,000 kph (126,000 mph) the Siding Spring comet – a mountain-sized ice ball, accompanied by a gigantic trail of dust – missed the red planet by just about 140,000 km at 18:27 GMT on Sunday. Named after the Australian observatory where it was discovered in 2013, the comet has a nucleus, or icy core, with a diameter estimated at 0.8 to 8 km.

The closest observers of this historic event were three NASA robotic explorers, India's Mangalyaan spacecraft and Europe's Mars Express. Using a "duck and cover"strategy after the observations, the orbiters have been repurposed to hide for about 20 minutes behind the planet’s body. This protected them against the comet’s potentially harmful trail, which is as long as from here to the moon and is expected to engulf the entire planet.

Mars orbiters 'duck and cover' for comet Siding Spring encounter, spacecraft not to scale (Image from nasa.gov)

However, the Opportunity and Curiosity rovers were set to get the best view from the surface of Mars.

"We certainly have fingers crossed for the first images of a comet from the surface of another world," said Kelly Fast, NASA program scientist, adding "This is kind of a dusty season on Mars, too, and so the dust is going to make the comet even less bright."

Astronomers were anticipating the encounter, monitoring it via Earth-based and space telescopes, such as the Hubble Space Telescope. "We're getting ready for a spectacular set of observations," said Jim Green, head of NASA's planetary science division.

South Africa and Australia were topping the list of best places for viewing via binoculars or telescope. In the Northern Hemisphere, it was quite difficult to catch a glimpse of the comet.

But the Siding Spring observation campaign will be prolonged, should the comet survive after its encounter with Mars. Scientists are planning to follow its way back home, the Oort Cloud, located on the outskirts of the solar system, which marks the border of the Sun’s gravitational force.

The Cloud formed during the first one or two million years of our solar system's birth 4.6 billion years ago and is a home to various icy objects. Its comets venture to the inner solar system once in every million years or so.

NASA’s Neowise space telescope checks on comet C/2013 A1 Siding Spring (Image from nasa.gov)

C/2013 A1, another name for the cosmic wanderer, will be the first comet originating from the Oort Cloud to be so thoroughly studied.

"We can't get to an Oort Cloud comet with our current rockets ... so this comet is coming to us," said Carey Lisse, senior astrophysicist at Johns Hopkins University's applied physics laboratory.

"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."

According to the astrophysicist, scientists are eager to learn more about the way the planets formed by examining the comet’s composition and structure, as well as the after-effects of the comet’s close approach to the red planet.

Hubble Space Telescope image of comet Siding Spring taken in March, 2014 (Image from nasa.gov)

Six days after its Mars flyby, Siding Spring will head back to the outskirts of the solar system, passing close by the sun, and prepare for a glorious comeback in another million years.