Feb 262013

C/2013 A1 was discovered January 3, so it has not been observed for terribly long. However, current orbital projections for October 19, 2014, has it passing within 0.0007 AU (63,000 miles). But due to uncertainties, it could pass as far away as 0.008 AU… or it could impact. If it does, it’ll hit at an impressive 35 miles per second.

And in this case, I really, *really* hope that it hits. Because it’ll hit *Mars,* not Earth.

If it hits, the impact will be a hell of a thing to watch (and very likely the *last* thing the Mars rovers and flotilla of Mars orbiters will ever observe. If it misses, the spacecraft might still get an impressive show, depending on whether the comet has started to substantially outgas (not at all certain). The size and mass of the comet are still unknown. But if it hits *and* if it’s a large enough comet, we just might maybe possibly see major changes to the climate of Mars. A substantial influx of water vapor, coupled with a vast amount of liberated subsoil water vapor and carbon dioxide, just might serve as enough of a “greenhouse” to raise planetary temperatures. This won’t be enough to terraform Mars… Mars has been whacked often enough that if a single comet strike were going to do so, it would have done so. But it might give Mars a temporary flicker of warmth. Would it last months? Years? Decades? Centuries? Dunno. My guess would be months to maybe years. But if it lasts decades, that’s long enough for humanity to get off its ass and do something with it. A warmer, thicker atmosphere would make landing on Mars easier; the asteroid mining companies could do their thing to lob *more* rocks and iceballs at Mars to keep the warming and wettening process going.

The comet will almost certainly miss. But a man can dream.


UPDATE: Possible size of the comet from HERE:

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 megatonnes! This kind of event can leave a crater 500 km across and 2 km deep.


An impact like this would not be a once-in-a-lifetime event. it would not be a once-in-a-millenium event. It’d be a once in… what? Ten million year event, for something this big to whack one of the terrestrial planets?

 Posted by at 12:15 pm
  • brt

    If it hits, it will be spectacular. And also dangerous for us. The ejecta are likely to make Mars unapproachable for millenia. Some significant portion of the ejecta might make it to our neighbourhood and make the space junk problem substantially worse, including the possibility of rather large chunks hitting us. Much as it would be fun to watch the event, I’d just as soon miss it, for now.

    • Anonymous

      > The ejecta are likely to make Mars unapproachable for millenia.

      Doubtful. The ejecta will go up, then come back down. Very little will go into orbit… stuff sent up would need to be acted upon *again* once in space. all there is to do that are Phobos, Deimos and the Sun, all of which would be very weak at tugging stuff into a longer-term orbit. And stuff that does go into orbit will be in elliptical orbits with low perigees (“perimars?”), and given how the Martian atmosphere will likely be puffed up some via global warming, most of the junk will be dragged down pretty quick.

      > the possibility of rather large chunks hitting us

      *Vanishingly* unlikely.

      • Ken R

        This is exactly the sort of thing that brought meteorite ALH 84001 to Earth. It was ejected from Mars into solar orbit by a major impact about fifteen million years ago and is thought to have landed on Earth thirteen thousand years ago.

        So all the material kicked loose from Mars in that long ago impact scattered and only a tiny bit impacted the Earth, spread out over a long time.

        I’m not worried. Be one neat light show if the comet hits!!

      • Herp McDerp

        The ejecta will go up, then come back down. Very little will go into orbit…

        Some of the ejecta would go into solar orbit, though. Rocks launched on ballistic trajectories at greater than martian escape velocity would go into “epicyclic” orbits and re-encounter the vicinity of Mars every so often. (Something similar happens to Earth with spent Apollo upper stages.) A few trillion ball-bearing-sized tektites running around loose out there could make the approach and departure trajectories for spacecraft a bit more “interesting.”

      • Jason Miller

        “Periareion” is the accepted term. Since “peri” and “apo” come from Greek, it is considered more correct to use the Greek deities.

        Yay pedantry!

  • Michael the Somewhat Civilized

    The little boy in me wants to watch. I will worry about the bits and pieces of both Mars and the comet. Is C/2013 A1 related to the thing that hit Russia?

    • Anonymous

      > related to the thing that hit Russia?

      Nope. The meteor was a chunk of rock and metal on a sedate elliptical orbit about the Sun; the comet is a chunk of ice screaming in on a hyperbolic orbit from interstellar space (or at least the Oort cloud). Entirely different things on entirely different orbits.

    • Anonymous

      The Mars Reconnaissance Orbiter would have a front row seat. Too bad it doesn’t have HD video cameras. 🙁

      • Anonymous

        If it is confirmed to hit Mars, there will almost certainly be an armada of spacecraft heading out that way. While 18-20 months is a *really* short time to get a spacecraft sent to Mars, it can clearly be done (fire the bureaucrats and obstructionists). And this would be the best celestial show in… what? A hundred million years?

        From the JPL orbit diagram for Oct 20, 2014, it looks 50-50 whether it hits on the Earth-facing side. So we might need to have spacecraft *beyond* Mars in order to see the actual impact. But even if NASA were to fall victim to its own inertia… I’d bet good money that there are some billionaires out there more than happy to fund a digital IMAX camera to get shot out there on a SpaceX Falcon 9 or some such. These would be the last-ever photos of Mars as mankind has known it since Galileo.

  • Anonymous

    Paging Kim Stanley Robinson, though he never imagined a Mars impact of 200 petatonnes.

    Did I get my math right? If so, anything on the surface is toast. Even Mars’ thin atmosphere should be able to sustain a sufficient shockwave to clear out the lander population.

  • LordJim

    You WANT this to hit Mars? Don’t you give a damn about the impact this will have to any potential life on Mars? Seems to me this is a good excuse to attempt a cometary realignment. Consider it a test of our planetary defenses.

    • Anonymous

      Are you in fact kidding?

      • LordJim

        No, I think humanity has the responsibility to protect all life that it encounters. And, as I said, it is a good test of our defenses. I am not willing to roll over in the face of 50km comet. If it were headed for Earth, we would try something.

        Additionally, there is the possibility that this a test of humanity. An advanced civilization from beyond our solar system might want to see if we will expend the vast effort required to save life not of our own world. If we fail this test…who knows the consequences…

        • Anonymous

          > humanity has the responsibility to protect all life that it encounters

          Newage horesehockey.

          > If it were headed for Earth, we would try something.

          Fine. That’s always an interesting excercise. And let’s see you do it. So, start with this:

          – 18 months till impact

          – coming in at 55 km/sec

          – 50 km diameter ball, density of water ice

          And produce this:

          – What propulsive impulse required at what time-to-impact to *assure* a miss

          – what propulsion system is required to get how far out, how fast

          – how long will it take to get it all ready and launched

          Show your work.

          >An advanced civilization from beyond our solar system might want to see
          if we will expend the vast effort required to save life not of our own

          Great. What does that have to do with Mars? If these interstellar assholes are going to pound a lifeform *not* of Earth in order just to see how Earth would act to save said life, wouldn’t it make sense for them to demonstrate to us that there actually *is* life on Mars?

    • Anonymous

      > You WANT this to hit Mars?

      Damned straight I do!

      > Don’t you give a damn about the impact this will have to any potential life on Mars?

      Damned straight I do. That’s why I want it to hit Mars. It might be a good kick-start towards terraforming the place. Best case – which of course never seems to happen – we could move in and start tinkering in the aftermath. In a few centuries, Mars might be *green* and *alive.* Right now it’s dead, dead, dead. Any life that might exist there now is in a slow, inevitable decay. I’d rather replace some dying Martian bacteria with terrestrial algae, lichen, ferns and bunny rabbits. Wouldn’t you?

      > Consider it a test of our planetary defenses.

      Errr, no. It’s going to hit *Mars* (maybe) in a year and a half or so. We’d have difficulty with something targeting the *Earth* in that timeframe. Additionally, if the guesstimate of 50 km is accurate… there’s not a damned thing we could do to it. The dinosaur killer was about 17 km in diameter, as memory serves. This sort of thing looks like an event out of the early bombardment period, *billions* of years ago.

      • Herp McDerp

        This could be what’s required to get us off our butts and into space. With this comet following on the heels of the Russian bolide, space advocates would be able to say “Look, if you want to prevent this sort of thing from happening to you, you’d better put lots of resources into locating and diverting comets and asteroids … and that requires a vigorous space program!”

        Too bad the potential target isn’t Venus, though. We pretty much know what would happen with Mars, but a truly massive and high-velocity impact on a terrestrial planet with a dense atmosphere might have all sorts of interesting and even useful effects.

  • So Elton Musks Married Mars Mission will arrive about five years after the event, going to be a very important observation post if it happens.
    I seem to remember Larry Niven having a Protector drop a comet on Mars to eliminate the creatures that lived in dust bowls, there is always a prediction in literature if you look for it.

  • Graham

    Ran an Earth Impact Calculation based on the stats presented at http://impact.ese.ic.ac.uk/ImpactEffects/

    Please note: the results below are estimates based on current
    (limited) understanding of the impact process and come with large
    uncertainties; they should be used with caution, particularly in the
    case of peculiar input parameters. All values are given to three
    significant figures but this does not reflect the precision of the
    estimate. For more information about the uncertainty associated with
    our calculations and a full discussion of this program, please refer to
    this article

    Your Inputs:
    Distance from Impact: 3000.00 km ( = 1860.00 miles )
    Projectile diameter: 50.00 km ( = 31.10 miles )
    Projectile Density: 1000 kg/m3
    Impact Velocity: 55.00 km per second ( = 34.20 miles per second )
    Impact Angle: 45 degrees
    Target Density: 2500 kg/m3
    Target Type: Sedimentary Rock

    Energy before atmospheric entry: 9.90 x 1025 Joules = 2.36 x 1010 MegaTons TNTThe average interval between impacts of this size is longer than the Earth’s age.Such impacts could only occur during the accumulation of the Earth, between 4.5 and 4 billion years ago.

    Major Global Changes:
    The Earth is not strongly disturbed by the impact and loses negligible mass.The impact does not make a noticeable change in the tilt of Earth’s axis (< 5 hundreths of a degree).Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 199 milliseconds.The impact does not shift the Earth's orbit noticeably.

    Crater Dimensions:
    What does this mean?

    Transient Crater Diameter:
    260 km ( = 161 miles )Transient Crater Depth: 91.9 km ( = 57.1 miles )
    Final Crater Diameter:
    539 km ( = 335 miles )Final Crater Depth: 1.96 km ( = 1.22 miles ) The crater formed is a complex crater.
    The volume of the target melted or vaporized is 623000 km3 = 149000 miles3
    Roughly half the melt remains in the crater, where its average thickness is 11.7 km ( = 7.28 miles ).

    Thermal Radiation:
    What does this mean?

    Time for maximum radiation: 16.8 seconds after impact
    Visible fireball radius: 232 km ( = 144 miles ) The fireball appears 17.5 times larger than the sunThermal Exposure: 7.59 x 108 Joules/m2Duration of Irradiation: 3.34 hoursRadiant flux (relative to the sun): 63.1
    Effects of Thermal Radiation:

    Clothing ignites

    Much of the body suffers third degree burns

    Newspaper ignites

    Plywood flames

    Deciduous trees ignite

    Grass ignites

    Seismic Effects:
    What does this mean?

    The major seismic shaking will arrive approximately 10 minutes after impact.Richter Scale Magnitude: 11.5 (This is greater than any earthquake in recorded history)Mercalli Scale Intensity at a distance of 3000 km:

    VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

    VII. Damage negligible in buildings of good design and
    construction; slight to moderate in well-built ordinary structures;
    considerable damage in poorly built or badly designed structures; some
    chimneys broken.

    Ejecta: What does this mean?

    The ejecta will arrive approximately 17 minutes after the impact.At your position there is a fine dusting of ejecta with occasional larger fragmentsAverage Ejecta Thickness: 1.51 meters ( = 4.96 feet )
    Mean Fragment Diameter: 467 microns ( = 18.4 thousandths of an inch )

    Air Blast: What does this mean?

    The air blast will arrive approximately 2.53 hours after impact.Peak Overpressure: 640000 Pa = 6.4 bars = 90.9 psiMax wind velocity: 592 m/s = 1320 mphSound Intensity: 116 dB (May cause ear pain)Damage Description:

    Multistory wall-bearing buildings will collapse.

    Wood frame buildings will almost completely collapse.

    Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

    Highway truss bridges will collapse.

    Highway girder bridges will collapse.

    Glass windows will shatter.

    Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

    Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

  • publiusr

    Wouldn’t Mars lose atmosphere from an impact this large? I don’t think it was just the lack of a magnetic field that caused all the loss. Whatever carved out Hellas was probably larger.

    I’d rather the thing hit Venus too–a great look at what early Earth might have looked like during Heavy Bombardment, perhaps?

    It would be more of a wake up call than Shoemaker Levy. Hard to feel sorry for that big bully Jupiter, and Mars is dead or dying, but Venus–being Earths near twin in mass–allows for a great demonstration on why a space program is a must.

    • Anonymous

      > Wouldn’t Mars lose atmosphere from an impact this large?

      Probably some. However, would it lose more than it would gain?

      • publiusr

        Depends on the angle. The worse-case scenario would be neither a clean miss or a solid hit, where the comet would deposit its volatiles. A grazing strike would scatter chuncks and strip off atmo’ I would think.

        I’d feel better if we had a steady stream of sub-50km comets with slower speeds to warm the planet. But I’m not Q from TNG.

  • Anonymous

    Can we send a spacecraft to give it a nudge so it will CRASH on Mars? Would be a cool experiment and useful to see if we could deflect such a thing when it heads towards us!

    • Anonymous

      > Can we send a spacecraft to give it a nudge so it will CRASH on Mars?

      Realistically? No.

  • publiusr

    Looks like a near-er miss by a smaller body:


    Max distance went from 0.0079 to 0.0021–but the chance of impact will decrease as the uncertainty has decreased.

    It just dropped in size though “Estimation by Jakub Černý is 2.7-5.4 km.”