Once-in-a-million-years comet encounter on Sunday could spark rare Martian auroras

Friday, October 17, 2014, 4:58 PM - An event a million years in the making, and anticipated by scientists and amateur astronomers alike for over 21 months now, is taking place early Sunday morning, as Comet C/2013 A1 (Siding Spring) makes an incredible close pass by the planet Mars.

Not only will this give us our first close-up look at a comet's first trek through the inner solar system from the Oort Cloud, but also our closest view yet of the interaction between a comet and a planet's atmosphere, which may cause regions of Mars' atmosphere to light up with alien auroras.

The Oort Cloud, the hypothetical cloud of icy objects that has surrounded our solar system since its birth, is a treasure trove of scientific discoveries, just waiting out there for us to reach it. However, seeing as it's taken the Voyager 1 probe over 37 years just to reach the edge of interstellar space, and there's still a long way for it to go before it reaches the inner edge of the Oort Cloud, it's very unlikely that we'll be getting out there to study these objects anytime soon.

Fortunately for us (and for science) a chance encounter this weekend will be delivering a taste of that bounty within our reach. Comet C/2013 A1, aka Comet Siding Spring, is flying past the planet Mars early on Sunday morning. Very likely a 'fresh' comet, making its very first pass through the inner solar system, it will be coming within 140,000 kilometres of Mars' surface. Comparatively, that's just about one-third the distance between Earth and the Moon, and roughly ten times closer than any comet we've identified has ever come to Earth (presumably many unidentified ones, or perhaps just several large ones got much closer earlier in Earth's history, as that may have been the origin of the planet's oceans).

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While Mars is quite far away from the Earth right now (244 million kilometres!), the fortunate part is that we've turned that planet into one entirely populated by friendly robots!

Five different spacecraft are currently orbiting the planet - Mars Odyssey, the Mars Reconnaissance Orbiter and MAVEN from NASA, the ESA's Mars Express and India's Mars Orbiter Mission - all standing by to take the closest images yet of a 'brand new' comet. Also, NASA's Opportunity and Curiosity rovers will be able to give us a spectacular view from the surface.

Preparations for this encounter began months ago, with the different mission teams looking into exactly what their particular robot explorer would be capable of seeing or recording as Siding Spring passes by. They even took special precautions to protect the spacecraft from being scoured by comet dust and debris, adjusting the spacecraft orbits ever-so-slightly, so that they would all be on the opposite side of the planet as the comet passes.

Joining the effort are satellite telescopes and observatories around Earth - Hubble, NEOWISE, SOHO, Swift and Spitzer - plus the STEREO satellites travelling around the Sun and various ground observatories. Amateur astronomers are gearing up for the encounter as well.

Credit: NASA

In a special, exclusive NASA Social event on Monday, October 13, scientists from the various Mars mission teams gave a live presentation at NASA's Jet Propulsion Laboratory, in Pasadena, Calif, and The Weather Network was there to take part. In the two-part presentation, to discuss not only the Siding Spring encounter but also the Rosetta mission's comet landing on Nov. 12, each team member discussed what they hoped to discover during the Siding Spring event, but the unanimous decision of all was that the data returned by the Mars Reconnaissance Orbiter's HiRISE camera was the most anticipated. 

This incredibly high-resolution camera, which normally points down at the planet's surface and produces images where each pixel represents an area of only about 30 centimetres across, will be aimed at the comet's nucleus as Siding Spring flies past.

"If HiRISE's images occur the way we're all planning, and if the comet cooperates, we're hoping to be able to see the nucleus with the back-lighting from the inner coma," Sarah Milkovich, the MRO HiRISE Investigation Scientist, said during the presentation. "We're also hoping to see the rotation rate of the nucleus, which is really awesome!"

"These are images that are not going to be what you think of as really pretty comet images," she added, "but scientifically they're going to be really awesome!"

WATCH THIS SPECIAL PRESENTATION BELOW: NASA JPL scientists and engineers discuss the amazing encounter with Comet Siding Spring, and answer questions from TWN Meteorologist Scott Sutherland about the potential for Martian auroras.