Co-orbital Asteroid

[DaCaptain]

Is it possible that the earth and a co-orbital asteroid could eventually "touch" together? Not that the two would run into each other with significant force. Any ideas of what might happen? Guess it would depend on the size of the asteroid.

[grant hutchison]

The asteroid is going to be orbiting faster than the Earth rotates. So--sonic boom in the atmosphere, friction with the surface of the Earth, widespread destruction and energy release proportional to the mass of the asteroid, asteroid quickly deorbits and comes to relative rest with the Earth's surface, with more destruction and energy release.

Grant Hutchison

[antoniseb]

It would hit the Earth with a minimum of Earth's escape velocity, which is about 7 miles per second.

[DaCaptain]

The asteroid is going to be orbiting faster than the Earth rotates. So--sonic boom in the atmosphere, friction with the surface of the Earth, widespread destruction and energy release proportional to the mass of the asteroid, asteroid quickly deorbits and comes to relative rest with the Earth's surface, with more destruction and energy release.

Grant Hutchison

Interesting. I was thinking that the path of the asteroid around the sun would be very similar to the earths, we'd slowly meet. Then the collision would not be as destructive as an asteroid on a different ecliptic. Which it is, but it's still not good news for earth.

[grant hutchison]

Interesting. I was thinking that the path of the asteroid around the sun would be very similar to the earths, we'd slowly meet. Then the collision would not be as destructive as an asteroid on a different ecliptic. Which it is, but it's still not good news for earth.

If your co-orbital satellite gets close to the Earth, it's going to be effectively in an orbit around the Earth, under the influence of Earth's gravity. Your scenario of a slow meeting would only work if the Earth were massless.
Worse-case scenario is antoniseb's, with the asteroid arriving as if it had fallen in from a large distance. When you invoked the idea of the asteroid and Earth "touching", I presumed you were imagining some unlikely series of events in which the coorbital state evolved into a contact binary. In that setting, the asteroid would be whipping around the Earth once every hour-and-a-half or so, so Bad Things would happen as I described.

Grant Hutchison

[cjameshuff]

Worse-case scenario is antoniseb's, with the asteroid arriving as if it had fallen in from a large distance.

That's the best case. You can't get a lower impact velocity than you get by starting out at a relative halt, and anything falling in from solar orbit will be doing so from "a large distance" as far as Earth's gravity well is concerned. You can't even get around it with a gravitational assist from the moon, since the moon itself is far enough for that to be a good approximation. Realistically, impactors from solar orbit are going to hit at something greater than 11.2 km/s.

[grant hutchison]

That's the best case. You can't get a lower impact velocity than you get by starting out at a relative halt, and anything falling in from solar orbit will be doing so from "a large distance" as far as Earth's gravity well is concerned. You can't even get around it with a gravitational assist from the moon, since the moon itself is far enough for that to be a good approximation. Realistically, impactors from solar orbit are going to hit at something greater than 11.2 km/s.

Well, I described the "best case" I imagined from DaCaptain's description of the asteroid eventually "touching" the Earth--some undisclosed energy transfer that brought a (presumably monolithic) asteroid and Earth together as a contact binary. That's a lower-velocity encounter, but still catastrophic unless we also manage to spin down the Earth tidally during the process.
There seems to be no conventional way in which Earth vs. asteroid in the manner you and antoniseb invoke could be interpreted as "touching", but I'm sure DaCaptain can clarify.

Grant Hutchison

[Warren Platts]

Is it possible that the earth and a co-orbital asteroid could eventually "touch" together? Not that the two would run into each other with significant force. Any ideas of what might happen? Guess it would depend on the size of the asteroid.

Actually, what you describe is thought to have maybe happened to the Moon. The idea is that as a planet grows out of a bunch of planetesimals that are more or less running in the same orbital channel, as it were, at some point you will have the biggest protoplanet, and there will be another one that will be the 2nd biggest. At some point they must meet up; and yes, it will happen at a relatively slow velocity compared to the Velikovskian impact thought to have formed the Moon.

With regard to the lunar impact, the thinking is the sister moon pancaked on to the Moon forming a carapace that became the Far Side highlands. Meanwhile, the impact would have deformed mantle downwards, and hence upwards on the Near Side thus possibly causing the lava flows that formed the lunar maria.

The model leads to some predictions: e.g., as the Moon formed, siderophilic elements like gold would tend to separate and get concentrated in the core. But the sister moon would have the same primordial bulk gold composition as the main Moon. Thus if the sister moon was converted into a carapace after the main crust had formed, the Far Side should be concentrated in gold compared to the rest of the Moon.

https://sservi.nasa.gov/articles/for...ompanion-moon/

[DaCaptain]

If your co-orbital satellite gets close to the Earth, it's going to be effectively in an orbit around the Earth, under the influence of Earth's gravity.
Grant Hutchison

Hmmm, do we have more than one moon? Maybe I should call them rocks in orbit. They all have probably been absorbed by the earth or the moon, or flung out into space.

When you invoked the idea of the asteroid and Earth "touching", I presumed you were imagining some unlikely series of events in which the coorbital state evolved into a contact binary.
Grant Hutchison

This was my original thought, a contact binary.

In that setting, the asteroid would be whipping around the Earth once every hour-and-a-half or so, so Bad Things would happen as I described.
Grant Hutchison

If they do touch, I think the earth gain or lose spin as well. Yes bad things for sure.

[cjameshuff]

For the two bodies to gently contact each other, they would need to be small and solid enough that their tidal forces can't pull each other apart, and similar enough in size that they can mutually tidal-lock each other, or the larger one must just happen to already be rotating at such a high speed that its surface is moving at close to orbital velocity. I think the two bodies will have to be near-identical in size until you get down to the level of asteroids or not-too-big moons merging together, where a solid rock is strong enough to withstand the tides of a larger body.

[grant hutchison]

Yes, if Earth had no atmosphere and was equipped with some sort of frictionless racetrack around the equator, you could theoretically set down a monolithic asteroid (that is, one held together by chemical bonds, rather than gravity) as a contact binary, which would whizz around the Earth once every eighty minutes or so. And you could do the same thing with a gravitationally-bound object significantly denser than the Earth, which would have enough surface gravity of its own to hold together against the tidal effect of Earth's gravity.
But you can't spin up the Earth to rotational lock with this asteroid, because then the surface of the Earth would be moving at orbital velocity, and the Earth would fall apart. And on the real Earth, with an atmosphere and no frictionless racetrack, all you get is an asteroid dipping into the atmosphere at Earth-orbital velocity. Which is only half as damaging (in terms of energy released) as the same object arriving at Earth escape velocity. But still.

Grant Hutchison