# Can earth grazers skip on the atmosphere more than once?

Earth grazing fireballs are asteroids that enter the atmosphere at a low angle, and skip off it, leaving to space again. Would it be possible that they skip more than once and still leave the atmosphere?

• “enter the atmosphere at a low angle, and skip off it” – I don't think that's how it works, generally speaking. (Skipping off, whether on water or on air, requires a shape that provides stable lift in up-direction; meteoroids don't have such a shape.) Rather, the fireball simply is on an orbit that would have left the atmosphere again anyway (because of the Earth curvature). Sep 18, 2021 at 17:15

I believe the answer is yes, when the asteroid after the initial pass through the earth's atmosphere no longer has escape velocity relative to the earth, but enters an elliptical orbit around the earth. The perigee of the orbit will be within the atmosphere, so on the next pass the newly-captured earth satellite will lose more energy, lowering the perigee until it eventually burns up in the atmosphere (or hits the ground).

• I did voted for both current answer although one says yes and the other not :) I do have a little question. Since the phenomenon occurs at least for object disintegrating or landing, can it explains certain waving falling stars that I have seen in photos with an otherwise unblurred firm background? Sep 18, 2021 at 9:54
• This answer is contrary to the OP's "and still leave the atmosphere". Sep 18, 2021 at 12:35
• @Ruslan No, it can capture into Earth orbit but still have apogee well above the atmosphere, so it leaves the atmosphere before re-entering it. Sep 18, 2021 at 12:40
• @MikeScott I think the intent is in the first sentence of OP "leaving to space again", so it shouldn't eventually reach the earth, because "skipping more than once" already means touching/entering the atmosphere and the coming out, before coming back again. And so adding "and still leave the atmosphere" would very reasonably intend to mean that the asteroid eventually move away from earth. Sep 19, 2021 at 13:22
• @justhalf Indded, if we consider "skipping" to be "bouncing off the atmosphere", the literal question becomes "Would it be possible that they bounce off the atmosphere more than once and still leave the atmosphere?" which doesn't seem very sensible question to me, unless "leaving" means not remaining in orbit.
– hyde
Sep 19, 2021 at 17:29

If by "more than once" you mean "more than once in a single visit", then that would seem impossible.

After the first skip, the object is moving away from the earth. Either it has sufficient energy to depart or it doesn't. If it returns, then it doesn't have enough. Further interactions with the atmosphere won't give it any additional energy (in the earth's rest frame).

• an object can have an orbit that goes through the atmosphere, just not long enough to fall completely. It's easy to observe in KSP Sep 19, 2021 at 10:39
• Sure, but that seems uninteresting to me. That was why I limited my answer to those entering twice in a single visit. I would regard taking a full orbit a different visit. Sep 19, 2021 at 15:30
• could a moon boost lead to escape after a couple of skips Sep 19, 2021 at 20:27
• Another body could interact and boost the object, but only over the course of an orbit. During atmospheric interactions, it will be too small of a force. Sep 19, 2021 at 22:23

I will not commit to a "yes" or "no" answer, but instead refer to examples of artificial objects that do go at least down-up-down.

From Space Exploration SE:

Several answers 1, 2, 3, most often by @MarkAdler of JPL fame mention that aerobraking at Mars and Venus has been used lower the energy of spacecraft. However I am not sure how many times something coming in at a positive $$C_3$$ relative to the planet can skip without also using some energy-lowering propulsion as well. Also the shapes of these spacecraft are not necessarily asteroid-like; they may have been engineered to provide some amount of lift.

@MarkAdler also points out that both Apollo and the Space Shuttle were qualitifed to implement skip-reentries but only Apollo actually used it.

@OrganicMarble's answer includes the following data for an Apollo capsule