Mars has Front-Row Seat for 2014 Comet

Comet Siding Spring (C/2013 A1), discovered in January and now inbound from the Oort Cloud, promises to put on a spectacular show in October 2014 — for the spacecraft on and around Mars.

Update: NASA used additional observations to revise the comet's orbit calculations about a month later, announced in an April news release. The revised estimate of closest approach is 68,000 miles (110,000 kilometers). The new data also shows a reduced probability of Comet Siding Springs hitting Mars: 1 chance in 120,000.

We're just a couple weeks away from getting decent naked-eye views of Comet PanSTARRS, and later this year we might be treated to even better views of Comet ISON.

But to see a really amazing spectacle, comet-lovers are imagining how they might magically transport themselves to the ruddy plains of Mars late next year.

Mars and Comet Siding Spring
How close will Comet Siding Spring (C/2013 A1) comet to Mars in October 2014? Early predictions suggest a collision is possible.
JPL Horizons
That's because Comet Siding Spring (C/2013 A1) is going to pass very close to the Red Planet on October 19, 2014. In an update issued April 12th, celestial dynamicists at the Jet Propulsion Laboratory estimate that the comet should miss the planet by about 32,000 miles (50,000 km), but there's still about a 1-in-600 chance of an outright collision.

You can follow the comet's interplanetary motion using the excellent orbit simulator provided by JPL's Horizons website. (Here's a comical adaptation of that site's output by Rob Kaufman of Australia's Bright Astronomy Club.)

Ace comet sleuth Rob McNaught discovered this object on January 3rd using the Uppsala Schmidt Telescope at Siding Spring Observatory in Australia. (Notably, this came just 10 days before a wildfire overran part of the observatory, destroying his home and others'.) Almost immediately, astronomers in Arizona found the object in Catalina Sky Survey images taken a month earlier.

Those observations, combined with others chipped in by observatories elsewhere, show that the comet has a highly inclined, retrograde orbit that will come no closer than 1.4 astronomical units (140 million miles) to the Sun. That's nowhere near Earth, but 1.4 a.u. is just about at the orbit of Mars.

A few days ago Russian amateur (and comet discoverer) Leonid Elenin identified the comet's close approach to the Red Planet next year. Turns out he wasn't the first to notice. "The JPL small-body system automatically checks for close approaches to all planets and the Moon," comments dynamicist Paul Chodas, "and we've been monitoring this impact probability for several weeks now."

As they draw closer together, the two bodies will be racing toward one another at 35 miles (56 km) per second, and early estimates suggest that the nucleus of C/2013 A1 could be 30 or 40 miles across. So a collision would mean a very bad day (er, sol) on Mars. Purdue impact specialist H. Jay Melosh ran the numbers using a powerful crater calculator he developed. Since no one yet knows how big the nucleus actually is, he ran simulations using diameters of 5 and 30 miles (8 and 50 km).

Both simulations yielded craters at least 6 miles (10 km) deep. The smaller assumption creates a basin 100 miles (160 km) across. But the larger one's outcome is off the charts: an enormous pit more than 500 miles (800 km) across. Size-wise, this would be one of the top 10 impacts ever on the Red Planet!

"These would be really big holes in the ground," Melosh says. "But since the average recurrence interval for such large craters is very long, we would have to be very, very lucky to have such a thing happen in our lifetimes."

Comet Siding Spring as seen from Mars
This plot shows how Comet Siding Spring (C/2013 A1) will appear as seen from Mars. The "best observing" occurs when the comet's total brightness is at least magnitude 12 and its elongation from the Sun is 30° or larger. Click on the image for a larger view.
Jon Giorgini / NASA / JPL
Hit or miss, Comet Siding Spring is going to put on one helluva show as seen from Mars. As calculated by small-body aficionado Bill Gray, the comet will approach Mars from the south and sweep into its northern-hemisphere skies over just a few hours. "It probably won't reach the magnitude -8.8 shown in the ephemeris," he cautions. "Still, maybe it'll be bright enough (and suitably placed) for something on Mars to get a nice picture or two."

That possibility hasn't escaped the notice of NASA mission managers. Right now three craft are circling the Red Planet right now (Mars Reconnaissance Orbiter, Mars Odyssey, and ESA's Mars Express), and both Curiosity and Opportunity are roving its surface. Potentially any of them might be commanded to take some comet pictures.

For example, one of Curiosity's Mast Cameras has a 100-mm focal length and color capability. If the comet performs as expected, says Michael Ravine of Malin Space Science Systems, which built the cameras, some imaging will definitely be planned. "I'm imagining the bright comet spectacularly positioned over a landscape that includes Mount Sharp," he muses.

Or what about MRO? It's got a bunch of "imaging assets." So I put the question to MRO project scientist Richard Zurek.

"Just off the top of my head," Zurek replies, "there are several instruments that could come into play: MARCI with its multi-color imaging (including in the ultraviolet), CTX with its moderately high resolution in a wide field of view, and CRISM and MCS can add information in the near and mid infrared. Most of this would be focused on the coma for CTX and and the rest on the tail, depending on comet's evolution. And of course we would try something with HiRISE with its very high spatial resolution (possibly many pixels on the nucleus), assuming the slew rates of the spacecraft are reasonable.

But C/2013 A1 poses danger for these craft as well. The comet should pass by close enough to completely immerse Mars in its gas-and-dust coma. Who knows what might rain down onto the Martian surface?

One way or another, it should be quite a spectacle!

15 thoughts on “Mars has Front-Row Seat for 2014 Comet

  1. Anthony BarreiroAnthony Barreiro

    There are a number of mistakes that make this article hard to understand. Is the comet’s orbit highly inclined? Would an impact really create a crater 2300 miles across? And there are several sentences that just don’t make sense as written. Journalism is the first draft of history, but this chapter needs a rewrite.

  2. G. H. Martin

    Surely the comet passing this close to Mars will affect its orbit. Of course, there’s no way to calculate how much and in what direction until we have a better idea of its mass and orbital path.

  3. Michael Zeiler

    Fascinating! The MAVEN spacecraft will be arriving at Mars just before Comet Siding Spring (C/2013 A1), now scheduled for September 22, 2014. Will this be a spectacular science opportunity to study the coma’s interaction with the thin Martian atmosphere or will the comet debris be a spacecraft hazard that will motivate MAVEN mission planners to delay arrival at Mars?

  4. Anthony BarreiroAnthony Barreiro

    William — My previous comment was in response to an earlier unedited version of this story. I was too quick to criticize. I’ll blame Mercury’s current retrograde motion for my impatience.

  5. A.Szautner

    With comet C/2012 S1 (ISON) also passing quite close to Mars (only about 6,700,000 miles) on its inbound leg this October 1st, one trusts that the teams controlling the fleet of operational orbiters and rovers there are cautiously bold enough to obtain images of each, as geometry and circumstance may allow…

  6. Bruce

    While the odds for a direct hit may be 1 in 10,000, what would the odds be for this comet to pass close enough (within its Roche limit) to Mars to cause it to break up like Shoemaker-Levy 9 did when it had a close encounter with Jupiter about 20 years prior to that comet’s ultimate collision? Admittedly, the gravity well of Mars is wimpy compared to that of Jupiter, but wouldn’t the likelihood of a disruption event for C/2013A1 be greater than the odds for a direct collision?

  7. Justin SJustin

    I cannot help but wonder if an impact would blast enough rubble into the space around Mars to make space nearby dangerous for exploration.

    I hope we receive updates as the orbit of the comet is refined.

  8. Bruce

    Hit or miss, this show looks to be spectacular. But if it hits, WOW. Justin, an impact like this would most definitely render the space around Mars hazardous for anything orbiting Mars, since the excavation of a crater 8 miles deep and 500 miles across would send hundreds of cubic miles of Martian rock at least temporarily into space, and ejecta from the blast would even effect areas all around the surface of Mars from secondary impacts. The Martian moons Phobos and Deimos could very well receive strafing from the spray of supersonic shrapnel, and a little of this material would likely even eventually fall to earth as meteorites. Justin, I share your desire for updates about this close encounter of the planetary kind, for, while I have the utmost confidence that the JPL people and their computers can calculate exactly were MARS will be on Oct. 19, 2014, how can they be so sure about Comet Siding Spring? Consider the list of unknowns: The comet’s mass, size, spin rate and orientation, the unpredictable nature of cometary out-gassing and even possible gravitational tugs from other close encounters with objects we haven’t even discovered yet. Even now Mars and Comet Siding Spring are pulling at each other with a gravitational attraction that will continually grow until the moment of closest approach. Then, if the comet misses as JPL now predicts, the comet’s orbit will have to be altered as G.M.Martin pointed out, and the comet may even be torn asunder like Comet Shoemaker-Levi 9 was as the gravitational attraction to Mars switches instantly from an accelerating to a decelerating force at the moment of closest approach. This is going to be fascinating, no matter what happens at Mars on Oct 19, 2014. Save the date y’all.

  9. cmarrou

    No matter where I am on Earth, I feel certain that on October 19, 2014, the skies above me will be cloudy. Just a feeling.

  10. gizmowiz

    The Russian lab calculated a trajectory with a minimum of 24,860 miles. But another lab combined the data from the both the Russians and JPL labs to calculate a trajectory of ZERO miles.

    In fact that raised the odds of a collision from .08% (JPL) and .12 (Russia) to 5%. So 1 in 20 chance of a collision.

    That’s scary since Earth will be rounding the Sun just about the time a possible martian meteor swarm would be passing along in the vicinity of Earth’s orbit. So Earth could see a sizable swarm itself that it hasn’t seen for Millenia.

    There is simply no way of knowing if Earth would be impacted since an impact a varying angles could throw the bulk of the swarm in so many different directions–but it will throw it into 360 degrees so Earth would probably encounter at least a few.

    Those Russians better get busy and duct tape their windows ha.

  11. wowlfie

    Russian labs have calculated a trajectory that brings it withing 24,860 miles, JPL new data released has it at 33,000 miles.

    But get this–a lab which combined the results from both labs calculated a trajectory with ZERO miles! That’s not a misprint.

    So the odds of an impact are very real and this lab sets it at 5% or 1 in 20.

    If so Earth will surly be impacted if it hits because fallout from the collision will throw martian rocks into space in a 360 direction and so some would obviously be in the direction of Earth’s orbit as the Earth comes around the Sun in about 5 months after the impact.

    So Russia would do well to duct tape all their windows!

  12. Vincent

    Russian labs have calculated a trajectory that brings it withing 24,860 miles, JPL new data released has it at 33,000 miles.

    But get this–a lab which combined the results from both labs calculated a trajectory with ZERO miles! That’s not a misprint.

    So the odds of an impact are very real and this lab sets it at 5% or 1 in 20.

    If so Earth will surly be impacted if it hits because fallout from the collision will throw martian rocks into space in a 360 direction and so some would obviously be in the direction of Earth’s orbit as the Earth comes around the Sun in about 5 months after the impact.

    So Russia would do well to duct tape all their windows!

  13. Marc

    All wild speculation about possible impact on Mars aside, what are the prospects for observing this comet from good ol’ Earth? With an estimated diameter of upto 40 miles, this thing is really big as far as comets go, and even at 1.4 AU from the sun this may well be fairly easy to observe from Earth.

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