Simulation of the close approach of C/2013 A1 to Mars in Celestia using info from the Minor Planet Center.  Credit: Ian Musgrave/Astroblog.
Simulation of the close approach of C/2013 A1 to Mars in Celestia using info from the Minor Planet Center. Credit: Ian Musgrave/Astroblog.

Comets, Mars

Is a Comet on a Collision Course with Mars?

26 Feb , 2013 by

There is an outside chance that a newly discovered comet might be on a collision course with Mars. Astronomers are still determining the trajectory of the comet, named C/2013 A1 (Siding Spring), but at the very least, it is going to come fairly close to the Red Planet in October of 2014. “Even if it doesn’t impact it will look pretty good from Earth, and spectacular from Mars,” wrote Australian amateur astronomer Ian Musgrave, “probably a magnitude -4 comet as seen from Mars’s surface.”

The comet was discovered in the beginning of 2013 by comet-hunter Robert McNaught at the Siding Spring Observatory in New South Wales, Australia. According to a discussion on the IceInSpace amateur astronomy forum when the discovery was initially made, astronomers at the Catalina Sky Survey in Arizona looked back over their observations to find “prerecovery” images of the comet dating back to Dec. 8, 2012. These observations placed the orbital trajectory of comet C/2013 A1 right through Mars orbit on Oct. 19, 2014.

However, now after 74 days of observations, comet specialist Leonid Elenin notes that current calculations put the closest approach of the comet at a distance of 109,200 km, or 0.00073 AU from Mars in October 2014. That close pass has many wondering if any of the Mars orbiters might be able to acquire high-resolution images of the comet as it passes by.

But as Ian O’Neill from Discovery Space points out, since the comet has only been observed for 74 days (so far), so it’s difficult for astronomers to forecast the comet’s precise location in 20 months time. “Comet C/2013 A1 may fly past at a very safe distance of 0.008 AU (650,000 miles),” Ian wrote, “but to the other extreme, its orbital pass could put Mars directly in its path. At time of Mars close approach (or impact), the comet will be barreling along at a breakneck speed of 35 miles per second (126,000 miles per hour).”

Elenin said that since C/2013 A1 is a hyperbolic comet and moves in a retrograde orbit, its velocity with respect to the planet will be very high, approximately 56 km/s. “With the current estimate of the absolute magnitude of the nucleus M2 = 10.3, which might indicate the diameter up to 50 km, the energy of impact might reach the equivalent of staggering 2×10¹º megatons!”

An impact of this magnitude would leave a crater 500 km across and 2 km deep, Elenin said.

Fragments of Shoemaker-Levy 9 on approach to Jupiter (NASA/HST)

Fragments of Shoemaker-Levy 9 on approach to Jupiter (NASA/HST)

While the massive Comet Shoemaker–Levy 9 (15 km in diameter) that crashed into Jupiter in 1994 was spectacular as seen from Earth orbit by the Hubble Space Telescope, an event like C/2013 A1 slamming into Mars would be off the charts.

Astronomers are certainly keeping an eye on this comet, and they will refine their measurements as more data comes in. You can see the orbital parameters available so far at JPL’s Solar System Dynamics website.

We’ll keep you posted.

Sources: Astroblog, IceInSpace, SpaceObs, Discovery Space

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By  -        
Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

48 Responses

  1. danangel says:

    How would a direct collision affect the climate on Mars? Warmer and wetter? Might not be a bad thing.

    • <– I like that thinking. Let's just hope that if it happens there is:

      1. No life on Mars,
      2. It's far enough to not effect Curiosity
      3. Close enough to give Curiosity something to be curious about!

      • GregtheThird says:

        If there is an impact the likely result would be the death of the rovers since they rely on solar power. I am hoping for some spectacular pics from a close flyby.

        • Aaron Glafenhein says:

          Actually Curiosity doesn’t use solar power it is nuclear powered, it has too large of an energy requirement for solar power to be feasible none the less it would be awesome! i have not done the calculations yet for how much energy would be released but based on the speed and size it would certainly have a global effect.. i would like to see that simulation too

    • Ruslanchik says:

      I wonder if such an impact might cause bolster Mars’s atmosphere. The heat generated from the impact and the gases the comet is carrying might make Mars a much more comfortable location for human habitation.

    • GregtheThird says:

      This is a link to an article that has been referenced. It applies to Earth, but the effects would be similar on Mars:

      Dissipating 100 million megatons of kinetic energy onto Mars is going to generate an enormous amount of heat. Mars has a great deal of water and Co2 near the surface locked up in what is essentially permafrost. An impact event of this magnitude would release a great deal of both. Increased Co2 levels would bolster the atmosphere and warm the planet for centuries. How much is a good question, but beyond a few years after the event, probably not a lot. Flooding and mudflows would be likely on the surface, especially in and around the impact zone. Ultimately much of what is kicked up will be lost to space, but how much is too complicated a question for me to answer. Ultimately the effects of such an impact would be mindblowing and last for centuries.

  2. gmo says:

    How much debris would a direct hit of that magnitude eject outward at escape velocity? How long after a direct hit would such debris might arrive here?

  3. GregtheThird says:

    It is a nice coincidence that we happen to have a few rovers there not to mention a few eyes in the sky.

    • delphinus100 says:

      Indeed. I thought for some time, that were it not for Challenger, Galileo might have already been orbiting Jupiter (possibly with a functioning high-gain antenna, because the lubricants would not have degraded in extended storage) when Comet Shoemaker-Levy 9 arrived…assuming the instruments would not have been overloaded and dazzled.

  4. It seems like a 50km object would leave a deeper crater than a measly 2km.

    • Gusssss says:

      All I can think is that while the planet’s crust is solid rock, a comet is more composed of loose rubble mixed with a lot of water. A bit like firing a big stony snowball at a wall.

  5. gr8tfly says:

    The energy released could be 200 times that of the impactor which killed the dinosaurs (and almost everything else). (Chicxulub est. at 100*10^12 tons of TNT vs. 2*10^16 per this article).

    It seems like the odds of discovering an Earth impactor of this size just 20 months in advance would be the same as for Mars. I sure hope this, and the recent events, provide a wakeup call for those controlling the pursestrings on detection and deflection programs.

    • Not made o'money says:

      It would be a colossal impact to witness. Consider how much lower the odds are of a comet striking the much smaller planet Mars, as opposed to the odds of a comet striking Earth.

      • soul68 says:

        The size of Mars vs the size of Earth is a small factor in the probability of a collision. The expanse of the solar system is such that even getting comet within 50,000 km is a pretty big deal from a probability standpoint.

        It would be like shooting a bullet from california to new york and saying that its more likely to hit a pumpkin than a softball.

        • Not made o'money says:

          Excellent point – though, the softball is still less likely to be hit than the pumpkin. :)

  6. Tim Amato says:

    I would like the possibility of collision. As life may have began on Earth from a comet, this may be a prestine time in history to witness the creation of life on another world. Get your microscope ready.

  7. Dima R says:

    Could such a collision make a change to Mars’ orbit? Or maybe restart Mars’ magnetic field? Would this impact delay humans visiting Mars?

    • Budgets put a bigger sway on that. And it would take a really, really, REALLY big comet to knock Mars off its orbit, and something that big we’d see from a billion miles away.

    • GregtheThird says:

      Not a chance. To get some perspective on the matter read this:

      While reading, keep these numbers in mind:
      1 megaton= 4×10^15 joules
      proposed kinetic energy at impact= 1×10^8 megatons

    • newSteveZodiac says:

      Never mind that, what if it grazes Mars and gets deflected, what are the chances of it coming towards us??!

      • delphinus100 says:

        Earth is a point in the sky, from Mars. Ask yourself which of all possible directions it could go after that (I won;t try to discuss if such a ‘grazing impact and continuing on’ is even possible), would terminate here?

  8. Gozlemci says:

    Very exciting news ! I wish it had impacted to the Mars; but not to the rovers sites…
    It would be more easy to understand the Mars soil (after the debris settle down) !

  9. GregtheThird says:

    Numerous people have propsoed terraforming Mars by directing comets to impact the planet. Preferably ammonia rich comets impacting at the poles and with a lower kinetic energy upon impact to lessen ejecta into space. Much of what I found varies from conjecture to wild speculation, but I included a more scholarly reference for the curious to peruse:

    Another generally accepted conclusion is that it will take many more than one comet to have a significant long term effect on the Martian climate.

  10. Aqua4U says:

    oTay… remote as the possibility might be… am wondering if Mars will change this comet’s orbital parameters enough to cause concern for us on it’s incoming or outgoing passage?

    • Aqua4U says:

      The orbital diagram from Nancy’s JPL link above:;cad=1;orb=1;cov=0;log=0#orb

      This comet does not come any closer to Earth than Mar’s orbit so even a close encounter with Mars would not swing it toward Earth… right? Also, it _may_ have been irradiated by a passing CME and brightened substantially? Maybe not be as big as the estimate above? Then again… it could be even larger?

    • Aqua4U says:

      There has, in the recent past, been indicators that a HUGE ancient comet was on the way in. This one seems to fit?

      • GregtheThird says:

        The largest comet in recorded history was the comet Sarabat detected in 1729 with a nucleus estimated to be 100km in diameter. At 10km this comet is larger than average. A civilization ending comet only needs a nucleus of only 5km in diameter, which is about average size. Trying to look at meteor showers to determine ancient comet size and tracks to me is no better than divining with tea leaves. The most dangerous comets are the ones we can’t see coming. This particular comet gets uncomfortably close to several planets in the inner solar system, but with a 36 million km range of uncertainty it will very likely miss Mars. Nevertheless, we need an early warning detection system in place and some powerful laser or nuclear weapons in space to divert the one which has our name on it. This should be a wake up call to the citizens and governments of Earth.

        • Aqua4U says:

          “..divining tea leaves…” I was referring to looking at increased rates of ‘sporadic’ meteors, which SEEM to indicate an unknown source. In this case, a potentially large yet unknown prehistoric comet may be the culprit? The size and the date of passage of course, cannot be known.

  11. torque xtr says:

    I guess there wouldn’t be any pictures in case of impact. Even Chicxulub had immediate global effects. For 10^26 J, all the rovers will be blasted to martian hell by shockwaves and/or reentering debris, and the orbiters – by heat radiation. Even the single orbit with a newformed incandescent 3000 degrees K 500 km- lava lake in sight would incinerate them. And no direct radiotelescope receivement of Curiosity feed showing advancing walls of fire and falling skies, there’ll be plenty EM noise as well. So the only hope to get some pics with ad-hoc equipment comes if the MRO is in the direct visibility of the rover, but the impact isn’t, and there’ll be no more than few minutes.

    Urgent orbital refinement and, if the impact confirmed, special (ion-drive equipped) fleet development? Or at least, to reequip Hubble/ one of those two new NASA telescopes with suitable cameras? The dynamical range of 5-7 orders of magnitude and ability to adapt sensitivity by 6-8 OOM over hundreds of ms is needed, but with the process of crater formation and debris ejection properly filmed a great deal of data about matter behavior at ~10^5 K and gigabars of pressure, and internal dynamis of impacts could be obtained.

    And as I remember, there aren’t any (at least discovered) impact craters that size on Mars younger than LHB and only a handful on the other Solar System solid bodies- this could be a one-in-a-hundred-million-year chance!

  12. sardean says:

    I have a problem with the image at the top.The problem is the “tail” of the comet is shown north/south over Mars, provided I have identifyed it to be a pole (north?) on the left of the image. For this to work a pole needs to be with in 30 deg of Mars image center, or the “tail” to be rotated 90 degrees so that it points away from the SUN!

    • DarkGnat says:

      The image is rotated. In Celestia, comet tails are 3-D, and viewing it from different angles might give you a more accurate image.

  13. Daniel Nagle says:

    Could we send a spacecraft to alter its trajectory in less than a year and half? A direct polar cap impact would be a sight to behold! I wonder what kind of atmospheric changes there would be. How much atmospheric pressure would be gained? How fast would it be lost to the erosion of the solar wind? How much of a temperature gain would there be? Could any of it be enough to melt or sublimate the dust covered glaciers across the Martian surface? Could we see a global picture of Mars with clouds in the sky, if even for a short time? Would the resulting shockwave negate any greenhouse benefits of pressure change or water vapor in the air, significantly due to dust reflectivity? I want it to hit. I’d hate to see the rovers affected, but MRO would definitely have a lot work ahead of it. I am so happy to live in such exciting times. When I was a kid the planets gave me such a curious wonder, and now we have so much more information and so many more questions… I wonder how many of these events we never new happened while I was looking up at the sky as a small boy. Schumacher levy 9, for instance was such a great set of pictures. Lets hope they can get all this squared out to take pictures of this event in the spirit of the parachute pictures of Phoenix and curiosity.

    • Skipdallas says:

      Excellent questions and ruminations! I too have always been fascinated by the stars and planets. A cometary impact on Mars would indeed give scientists years worth of data to study. We will see!

    • Not made o'money says:

      Are you suggesting that we intentionally divert this comet so that it DOES hit Mars? It would be good practice, I suppose.

    • chicagorich says:

      How much and what particle size distribution would be ejected from mars in the process? Might a sizable piece of that be a hazard for us?

  14. Skipdallas says:

    Would this approach be on the inward leg of the comets journey, or on its way back out?

  15. Ronnie Yates says:

    Using the impact calculator found here (which, of course, is meant for Earth, but I think we could expect similar if not worse results for Mars):

    I came up with the following:
    Distance from Impact: 1000.00 km ( = 621.00 miles ) Projectile diameter: 50.00 km ( = 31.10 miles ) Projectile Density: 1000 kg/m3 Impact Velocity: 56.40 km per second ( = 35.00 miles per second ) Impact Angle: 20 degrees Target Density: 2750 kg/m3 Target Type: Crystalline Rock

    Energy before atmospheric entry: 1.04 x 1026 Joules = 2.48 x 10^10 MegaTons TNT

    Transient Crater Diameter: 200 km ( = 124 miles )Transient Crater Depth: 70.6 km ( = 43.9 miles )
    Final Crater Diameter: 400 km ( = 248 miles )Final Crater Depth: 1.8 km ( = 1.12 miles ) The crater formed is a complex crater. The volume of the target melted or vaporized is 316000 km3 = 75800 miles3 Roughly half the melt remains in the crater, where its average thickness is 10.1 km ( = 6.26 miles ).

    Time for maximum radiation: 16.7 seconds after impact
    Visible fireball radius: 861 km ( = 535 miles ) The fireball appears 196 times larger than the sunThermal Exposure: 4.43 x 1010 Joules/m2Duration of Irradiation: 3.39 hoursRadiant flux (relative to the sun): 3630

    The major seismic shaking will arrive approximately 3.33 minutes after impact.Richter Scale Magnitude: 11.6 (This is greater than any earthquake in recorded history)

    The ejecta will arrive approximately 8.24 minutes after the impact.At your position there is a fine dusting of ejecta with occasional larger fragmentsAverage Ejecta Thickness: 14.2 meters ( = 46.7 feet ) Mean Fragment Diameter: 6.32 mm ( = 2.49 tenths of an inch )

    The air blast will arrive approximately 50.5 minutes after impact.Peak Overpressure: 7.79e+06 Pa = 77.9 bars = 1110 psiMax wind velocity: 2230 m/s = 4990 mphSound Intensity: 138 dB (Dangerously Loud)

    Needless to say, such an impact would be devastating.

  16. lcrowell says:

    This would certainly be interesting for Curiosity or Opportunity, if it is still rolling, to watch. The effects of such an impact would be nowhere as severe as it would be on Earth. The main explosive thermal-mechanical effects of such impacts are with the atmosphere. Mars has rather little atmosphere to carry a strong shock wave. The unknown in this is what would happen if the impact occurs on a subsurface ice pack or glacier. The release of water or carbon dioxide as a gas could be at least regionally fairly explosive. The ejecta is probably the biggest killer. The rovers may stand a chance of being hit by rocks that arc over Mars in suborbital trajectories and re-enter the atmosphere and reach the surface. These will come back as extremely high velocity bullets.

    By October 2014 Curiosity will be presumably near the end of its life cycle. So by this time it may have completed most of its studies of Gale crater.


  17. Doug Jones says:

    Radius of Mars, 3389 km

    Closest approach 109000 km

    Rpass/Rmars =32

    Apass/Amars ~= 1000

    A 1:1000 chance of a catastrophic impact. Wow.

  18. bugzzz says:

    This would be totally wild if it happened and we got to witness the transformation of a planet. Can you imagine if it eventually rendered Mars habitable? Then we can get started on populating it so that there’s an eventual war between Earth & Mars. WHOO HOO!

  19. Gozlemci says:

    Anyway, discussions were good !
    It is obvious that hoping “not to impact to anywhere” may not be enough to save life on Earth… We live and see that a harmful impact may be more probable than expected ! It seems the climate of the universe may be changing like on the Earth !

  20. gemmell says:

    See what Carol Rosin says that Werner von Braun had to say about this in the 70s

  21. Bill Simpson says:

    If it were heading our way, with this little notice, we would join the dinosaurs. Deflecting something that massive, moving that fast, would probably take a 5 year global effort, minimum. They are so rare, and Earth is such a small target, that none will probably hit before the Sun expands and toasts this planet. Probably, but not certainly.

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