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NASA: Mars satellites menaced by speeding SPACE ALIEN

Strange object Siding Spring is older than mankind, moving 33 miles a second

Pics On October 19, comet Siding Spring will make a very close flyby of Mars. And that's why NASA will hide its satellites in the area behind the Red Planet – to protect the agency's valuable hardware from passing comet debris.

Siding Spring duck and cover

Everybody hide!

The comet, first spotted on January 3 last year by Robert McNaught at Australia's Siding Spring Observatory, will swoop 87,000 miles (139,500 kilometers) over the Martian surface as it heads sunwards.

The comet is traveling at 33 miles per second (or 1.7715 per cent of the maximum velocity of a sheep in a vacuum in El Reg units). NASA was worried that the impact of any dust particles from the comet's 300,000-mile-long tail could punch through the agency's birds.

Shortly after NASA determined quite how close the comet will pass Mars, it began changing the orbit of its satellites around the planet to get them out of the way. After the speeding cosmic rock has passed, the probes will get the first-ever chance to observe an Oort Cloud-comet from close up.

Siding Spring Mars flyby

What the comet could look like if an artist was in orbit

Siding Spring (boringly also known as C/2013 A1) formed in the Oort Cloud about 4.5 billion years ago from material that didn't accumulate enough to make it to a planet-sized body. The comet was knocked towards the Sun by a passing mass and will now be viewed close up for the first time thanks to mankind's exploration of the Solar System.

"This comet started on its trip before the evolution of mankind," said Carey Lisse, a senior astrophysicist at the Johns Hopkins University Applied Physics Laboratory, at a press conference on Thursday.

"The only reason we're able to observe it this closely is because we've built the satellites and rovers capable of going to another planet. That's really exciting."

In all, NASA will have 16 satellites observing Siding Spring as it whizzes past, including four in orbit around Mars and other observatories such as Hubble, Spitzer, and Kepler. Negotiations are also underway to use the Indian MOM Mars satellite to view Siding Spring, and amateur astronomers will also be adding data.

The Curiosity and Opportunity rovers on the Martian surface will also be pointing their cameras skywards to get a look at the comet, but their input is expected to be minimal. It's autumn on Mars where they are, which is dust storm season, and the chance of a close view is considered unlikely.

We already have pictures of the comet and it has been closely studied ever since it was spotted. It is estimated to be between half a mile and five miles across, but its actual composition is what's getting astronomers' hearts beating faster.

Hubble image of Siding Spring

Twinkle, twinkle, little comet, how we wonder just what's in it (click to enlarge)

The reason Siding Spring was spotted so early was because it was much brighter than expected. It's thought that this may be because the comet may contain exotic chemicals that caused the unexpected brightening as they heated up.

Since that initial burst of light, the comet has dimmed to about half the brightness theoretical models would suggest. Astronomers speculate that these volatile chemicals may now have burned off, leaving much less material behind.

The other possibility behind the dimming is that the comet has started to break up as it warms. Lisse said the composition of most comets is incredibly fragile – likening it to a meringue dusted with talcum powder – but said that Siding Spring is expected to stay intact during the Mars flyby. ®

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