When Jupiter's tides ripped Comet Shoemaker–Levy 9 to shreds, only for the icy chunks to succumb to the intense Jovian gravity, ultimately slamming into the gas giant's atmosphere, mankind was treated to a rare cosmic spectacle (in human timescales at least). That was the first time in modern history that we saw a comet do battle with a planet... and lose.
But next year, astronomers think there's a chance - albeit a small one - of a neighboring planet getting punched by an icy interplanetary interloper. However, this planet doesn't have a generously thick atmosphere to soften the blow. Rather than causing bruises in a dense, molecular hydrogen atmosphere, this comet will pass through the atmosphere like it wasn't even there and hit the planetary surface like a cosmic pile-driver, ripping into the crust.
What's more, we'd have robotic eyes on the ground and in orbit should the worst happen.
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I am, of course, talking about Mars. And the comet? C/2013 A1 - a fresh lump of dusty ice that was spotted by the Australian Siding Spring Observatory on Jan. 3 making its dive from the outermost regions of the solar system.
Non-Negligible ... So There's a Chance?
Presently, astronomers only have a short period of observations to forecast the comet's path through the inner solar system and they know the probability of Mars "taking one for the celestial team" on Oct. 19, 2014, is small - in all likelihood the comet will fly by, creating a wonderful astronomical event for Earth and Mars-based observers alike. But...
"There is a small but non-negligible chance that Comet 2013 A1 will strike Mars next year in October of 2014," said Don Yeomans of NASA's Near-Earth Object Program at NASA Jet Propulsion Laboratory in Pasadena, Calif. "Current solutions put the odds of impact at 1 in 2000."
The odds may be low, but they're certainly not "winning the lottery" small, or "getting hit by lightning" small; in scientific terms the odds are "non-negligible," meaning there's a fascinating possibility - a non-zero chance of a planetary collision.
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According to NASA, the comet is likely 1-3 kilometers (0.6-1.9 miles) wide and traveling at 56 kilometers per second (125,000 mph). "It if does hit Mars, it would deliver as much energy as 35 million megatons of TNT," added Yeomans. That would be a violent impact with global effects "I think of it as a giant climate experiment," said Michael Meyer, lead scientist for the Mars Exploration Program at NASA headquarters. "An impact would loft a lot of stuff into the Martian atmosphere - dust, sand, water and other debris. The result could be a warmer, wetter Mars than we're accustomed to today."
Heads Up, Rovers!
We currently have three satellites orbiting Mars - NASA's Mars Reconnaissance Orbiter and Odyssey, plus Europe's Mars Express - and two operational rovers - NASA's Opportunity and Curiosity. Should Mars be the scene of a cometary smash-up, wouldn't that be bad news for the rovers?
Barring a direct hit over Gale Crater or Endeavour Crater (Curiosity and Opportunity's homes, respectively), both rovers should survive the impact, with varying results.
An amazing climate experiment it may be, but Opportunity, a solar powered robot, would suffer if the atmosphere became thick with light-obscuring dust after impact. Mars' newest arrival, Curiosity, however, should carry on just fine as the larger robot is nuclear powered, drawing its power from a radioisotope thermoelectric generator (RTG).
So we'd not only have eyes in orbit, we'd also have two tenacious observers on the ground capable of carrying out "event science" right at time of impact.
ANALYSIS: Mars Gets Hit By Cosmic Buckshot
But this wouldn't only satisfy our macabre fascination with seeing a real doomsday scenario play out on our cosmic doorstep, it might also motivate manned exploration of Mars.
For decades, NASA has been aiming to get the first human on Mars, but the lack of political will and the inevitable funding restraints has stymied our Martian dreams, resigning us to watching robots do the exploring and hope the private sector may one day build a viable business model around joyrides to Mars.
A massive impact event, however, could be the motivation for us to finally take the interplanetary plunge and send a manned expedition.
The motivation to send a mission to the site of a recent cometary impact would be several-fold.
As Meyer points out, this would present a fascinating opportunity to witness climatic changes to a rocky world after impact. Furthermore, if we could send a manned expedition to a geologically-recent deep impact excavation site, the upper layers of fresh Martian crust will be laid bare for geologists to explore. This wouldn't be a million, or billion year-old crater eroded and sanitized by the sun's radiation, fresh deposits would be accessible just below the surface inside the comet's impact basin.
Was there ever life on Mars? The pristine basin may hold the best clues yet. Is there life on Mars? All Mars astronauts would need to do is chisel into the crater sides to definitively answer that question.
ANALYSIS: Could a Comet Hit Mars in 2014?
Although much of the comet's water and other volatiles would have been blown far and wide, evaporating and sublimating in the immense energies of impact, some will inevitably remain, perhaps coating the upper layers of the crater with a supply of accessible water. A drop of water in an arid desert it may be, but some comet ice may remain locked underground or remain as chunks surrounding the impact basin. Water will be to Mars explorers what gold was to Californian prospectors in the mid-19th Century.
From a practical standpoint, Mars is a rough place for human biology. The carbon dioxide-dominated atmosphere is ridiculously cold and tenuous - 100 times thinner than Earth's atmosphere. Combine this with the fact that the small planet doesn't possess a global magnetic field, humans on Mars would experience prolonged exposure to solar radiation and high-energy cosmic rays. If the comet did have an impact on climate - perhaps warming the atmosphere, or suspending radiation blocking dust for years in the upper atmosphere - the more the better; we'd need all the help we can get.
And then there's the rich astrobiology that could be done. Complex chemicals, known precursors to the amino acids that form the building blocks of known biology, can be found in comets. Where better to mine for the forensic evidence of a recently crashed ancient "dirty snowball" strewn across a planetary landscape?
In short, the aftermath of a cometary collision would be a scientific smorgasbord. If we ever needed to be "pushed" to send a manned mission to the surface of Mars, I can think of no better time than in the years after a massive comet strike.
A 1 in 2000 chance it may be, but it's hard not to think how awesome a Mars comet impact would be.
Image credit: NASA (edit by Ian O'Neill)