On January 3, 2013 comet C/2013 A1 was discovered photographically by Robert McNaught at Siding Spring Observatory in Australia. At the time it was over 7 times farther than Earth from the sun and extremely faint. Though far from Earth’s perspective, this dusty dollop of ice had probably been on its way from the Oort Cloud, a massive and distant comet repository at the fringe of the solar system, for millions of years.
Although not expected to pass particularly close to Earth next year, the comet will have a very close brush with Mars. Leonid Elenin, Russian comet hunter and discoverer of the famed Comet C/2010 X1 Elenin, has examined C/2013 A1’s orbit and found there’s a small chance it could collide with the planet Mars on October 19 next year.
Based on 74 days of observations plus the latest data from Elenin, which admittedly only cover a short piece of the comet’s arc, A1 could zoom as close as 22,990 miles (37,000 km) from the surface of Mars and shine 40 times brighter than Venus at magnitude -8.5 … as seen from Mars that is. Earth observers will see it around 8th magnitude, so you’ll need a pair of binoculars at minimum.
Since a comet’s tenuous outer atmosphere – called a coma – is typically around 62,000 miles (100,000 km) across, C’/2013 A1 is practically guaranteed to give the planet a gentle powdering.
Given the close brush, there’s even a possibility – for now – that it might crash right into the Red Planet.
This is where things get interesting. Astronomers estimate a comet’s size by measuring how its brightness changes during its approach to the sun. C/2013 A1 turns out to be a potentially BIG comet with a diameter estimated at up to 31 miles (50 km) across.
Its orbit is also tipped over so far (greater than 90 degrees to the plane of the solar system) A1 travels in retrograde motion opposite the direction in which the planets move around the sun. Should it aim for Mars, the two bodies will hit head-on with the comet speeding at 35 miles per second. Dare I say, the energy released from the impact would be prodigious.
Here’s Elenin’s take: “This kind of event can leave a crater 500 km (310 miles) across and 2 km (1.2 miles) deep. Such an event would overshadow even the famous bombardment of Jupiter by the disintegrated comet Shoemaker–Levy 9 in July 1994, which by some estimates was originally15 km (9 miles) in diameter.”
A blast that powerful would easily be visible from Earth as a brilliant flash of light followed by a massive cloud of debris expanding over the Martian landscape and high into the planet’s atmosphere. From Mars, the event could be photographed by one of several Mars-orbiting satellites or even the Curiosity rover. Even if the comet misses the planet, we’d hope NASA or ESA (European Space Agency) could point a camera to take the first-ever photos of a comet from another planet.
Could this all be crazy talk? Maybe. In order to make a firm prediction of exactly what path the comet is on, astronomers will accurately measure its position and refine its orbit in the coming months. Chances are, it won’t hit, but the possibility remains … for the moment.
As for Earth, we’re in the the clear. C/2013 A1 will miss us by 84 million miles even when closest in early September next year. If we assume for a moment that the impact will happen, sky watchers in the eastern hemisphere will have the best seats. I checked the the positions of comet and planet in SkyMap, a highly accurate planetarium program, and determined the time of closest approach to be around 5:30 a.m. Central Time Oct. 19, Mars won’t be up in the sky for the U.S. but will be for much of Russia, China and other eastern hemisphere countries. For observers there, a possible impact would occur during early evening hours on Oct. 20.
Mars will be in the constellation Ophiuchus at that time and low in the southwestern sky at the end of evening twilight. For observers in the U.S., Canada and South America, the planet and comet, should it survive, will be only about half a degree apart at dusk the evening of the 19th. Big blast or not, they’ll certainly make for a memorable sight in a telescope.