Would it be possible for an asteroid in solar orbit to go near enough to the Earth that the Earth's atmosphere slows it down into an orbit that is, aside from its low perigee, stable without using a third object (such as the moon) to slow down? Or would the necessary forces destroy the asteroid?

If this is possible, could it then gravity assist off of the moon to get in a truly stable orbit? Also, if it is possible, what would happen on Earth?

  • $\begingroup$ My gut feeling is that by the time you are talking about aerobraking, the periapsis of the orbit will be sufficiently low that the object (asteroid, in this case) will quickly deorbit simply due to effects of drag over time. For efficient aerobraking, you'd probably need to go far below the ISS' orbit, and ISS already requires frequent orbit reboosts due to drag. At that point, well... it'll be a bad day somewhere. $\endgroup$ – user Jul 8 '16 at 15:21
  • $\begingroup$ Since your question is about aerobraking, I'll not post this as an answer, but consider looking into 2014 OL339 it's an asteroid that have a peculiar orbit around the sun, that make it to appear that is orbiting earth. $\endgroup$ – Lucas Leite Jul 8 '16 at 15:47

While an aerocapture could slow an asteroid down enough to keep it from escaping back out into deep space, the problem you would face without a third body or additional applied force is that the periapsis (lowest point of orbit) now lies within the atmosphere. Subsequent orbital rotations would continue to slow it down until it falls into the atmosphere for good.


Here's an image for reference (source). For every pass, the point at which it contacts the atmosphere remains nearly the same, but the apoapsis (highest point of orbit) will continue to reduce until the path becomes suborbital, and into the planet it goes.

If you do have a third body such as the Moon however, it could potentially (if improbably) temporarily stabilize the orbit. I say temporarily because in order for the Moon to have enough influence on the asteroid to stabilize the orbit, the asteroid must continue to pass close enough to the Moon's orbital path that another such encounter would inevitably occur, throwing the asteroid into a different orbital path each time. This could eventually result in an Earth or Lunar collision, but not an escape, since too much energy would have been lost during the aerocapture.

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    $\begingroup$ Agreed. All captures require either a propulsive maneuver or a third body interaction. Aeromaneuver can reduce the amount required but there is still a requirement. $\endgroup$ – Jim2B Jul 8 '16 at 15:50
  • $\begingroup$ Your answer is excellent. However, aerocapture would be possible with the help of a third body, and for that we have the moon. Granted, this would have to be such a precise maneuver that it would be incredibly improbable. But check Josh King's answer. $\endgroup$ – The Square-Cube Law Jul 8 '16 at 17:12
  • $\begingroup$ @Renan I guess I misunderstood "...without using a third object..." to mean we wouldn't consider the third body, and answered based on that premise. Given the second paragraph though, it seems that the third body is acceptable for use for stabilizing the orbit after aerobraking. I'll edit my answer to make that more clear, thanks =) $\endgroup$ – Mwr247 Jul 8 '16 at 17:27
  • $\begingroup$ Now that you mentioned it, I am kinda in doubt about what the OP meant there. Anyway, you have my upvote. $\endgroup$ – The Square-Cube Law Jul 8 '16 at 18:21
  • $\begingroup$ @Renan From how I understand it now, the Moon shouldn't be used to slow down the asteroid pre-aerobrake, but can be considered post-aerobrake for orbital circularization. And thanks! :D $\endgroup$ – Mwr247 Jul 8 '16 at 18:24

Yes, I would say not impossible, but highly unlikely to happen naturally. Everything would have to happen perfectly for this to ever happen.

How it could happen:

The asteroid would need to be mostly a metallic variety and shaped and oriented correctly (Blunt body aerodynamic shape faced into the atmosphere, like space capsules during re-entry) to withstand the atmospheric entry and deceleration forces intact. As well as correctly aimed into the atmosphere so as to slow the correct amount, to little and it skips off the atmosphere back into a solar orbit, too much and it impacts earth.

After the initial aerocapture entry into the atmosphere the upper end of the orbit (apoapsis) would need to be oriented such that the moon's gravity would alter the orbit into a more stable configuration (it would need to accelerate the asteroid to raise the periapsis above Earth's atmosphere)

And even after that your interactions with the moon could make your orbit unstable, it would be a very complicated orbital maneuver. We have only performed aero braking on a few space missions, and have never tried an aerocapture maneuver and that is with craft able to supply some maneuverability.

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    $\begingroup$ I have aerocaptured spacecraft in Kerbal Space Program a number of times (both in Kerbin and in the Joolian system, gonna try Eve next). Excelent answer. $\endgroup$ – The Square-Cube Law Jul 8 '16 at 17:12

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