Since Mars is much closer to the asteroid belt, is it also more likely an asteroid large enough for planetary devastation (~1 kilometer) will strike it? I'm especially wondering how such a possibility would factor into colonizing Mars. If the chances are high enough, it would seem an argument against establishing a Martian colony as a backup plan to avoid the extinction of the human race on Earth.

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    $\begingroup$ This appears to be a straightforward astronomy question rather than a worldbuilding one. $\endgroup$
    – Gene
    Nov 8, 2022 at 17:28
  • $\begingroup$ @Gene it isn't an unreasonable worldbuilding question, though asking the astrologers might get better answers. I suspect the answer will be pretty vague, though... we haven't got a really good handle on the chances of a large asteroid hitting Earth. $\endgroup$ Nov 8, 2022 at 17:45
  • $\begingroup$ On 24 December 2021 Mars was hit by a not-quite-small meteorite, which made a crater 150 meters (490 feet) across and 21 meters (69 feet) deep; by sheer luck there was a still functional seismometer on Mars, the InSight lander, which, sadly, is rapidly approaching end of life. But on the other hand consider that Mars is a much smaller target than Earth... $\endgroup$
    – AlexP
    Nov 8, 2022 at 18:46
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    $\begingroup$ Hi Kickaha. Just to make a point, since the help center states that our goal is to help you build an imaginary world, then the chances of a large asteroid hitting Mars in your world (let's say "your universe") are 100% if you want it to and 0% if you don't. From a worldbuilding point of view, why do you need the Real Life statistic? (If you're asking this question from the perspective of colonizing Mars in the Real World, then the question is off-topic for Worldbuilding.) $\endgroup$
    – JBH
    Nov 8, 2022 at 19:17
  • $\begingroup$ "Planetary devastation" is a moot point if an asteroid strikes near you. On Earth an estimate of 6000 meteors a year reach the ground. Many more burn in the atmosphere. In the thin Martian atmosphere there are going to be many more reaching the ground and at a higher speed. Probably another driving factor to lava tunnels habitats. $\endgroup$ Nov 9, 2022 at 16:54

2 Answers 2


The chance would be close to the chance of the asteroid hitting the Earth.

Space is big [everyone say the quote]. Both Earth and Mars are very small compared to the amount of space they reside in.

The Earth is bigger but it has "LunaSweeper 2000" that, if you look at the far side of it, catches some of the stuff headed our way from its side of the planet.

Mars is closer to the asteroid belt so it is the first in line for asteroids that are disturbed inward by Jupiter.

Luckily there isn't a hard science tag on this question because I don't have the numbers but with the pluses and minuses, I can't see the chance being significantly different between Mars and Earth.

Now, Mars, having little atmosphere, would have more stuff reach its surface.

  • $\begingroup$ Small question here, why didn't you mention the new Galaxy Deimos 5, or PhoBOSCH last model of sweeper around Mars ? I'm no expert but aren't these two satellites catching a lot of hits too ? Anyway, nice and funny answer, take your +1. $\endgroup$
    – Kaël
    Nov 8, 2022 at 21:18
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    $\begingroup$ @Kaël You're forgetting that Luna is abnormally large in relation to its parent planet. Deimos and Phobos have average diameters of 12 km and 22km, respectively. They're not much larger than the asteroids that the question is hoping to divert, and one that size hitting them could possibly annihilate them. By comparison, Luna's average diameter is 3475 km, and has a mass over a million times larger than Phobo's. It can take a hit from a 1km impactor without anything more than a shiny new crater to mark the occasion. $\endgroup$
    – Salda007
    Nov 9, 2022 at 8:24
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    $\begingroup$ @Kaël, as Salda007 mentioned, Mars' two moons are very small. It would be like trying to protect yourself from a bullet by holding a bullet in front of you. The Earth's moon would be like holding a viking round shield in front of you. $\endgroup$
    – ShadoCat
    Nov 9, 2022 at 17:55

Considering that the orbital stabilization work has been done in the young age of the solar system, it's not very likely that bodies from the asteroid belt will start falling toward the inner solar system, unless some large perturbation happens.

Also, considering that Mars is less often in a given position of its orbit (once every 687 days), which is longer than Earth (once every 365 days), it might even be that the chances of an impact in a given location are lower with respect to Earth.

  • $\begingroup$ Are you sure about the math behing your second point? Mars has indeed a given position once every 687days but the orbit is slower which result with Mars having a longer "given positon" and so easier for an asteriod impacted by the Mars' gravity to target the planet. I know I spoke with extremely basic scientific concept but I think you get the idea. I don't think it's a good key point compared to your first one. $\endgroup$
    – ohpif
    Nov 9, 2022 at 16:19

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