1. ## Asteroid velocity

What is terminal velocity for an asteroid ? And, what is the speed of the current fastest travelling asteroid ?

2. ## Asteroid Speeds

Not sure what you mean by terminal velocity.

If you mean, correctly, the speed of a falling rock once it's lost it's interplanetary speed it's several hundred miles an hour depending on the shape and mass of the meteoroid. A perfectly spherical large rock will fall faster through the air than an oddly shaped, smaller and lighter one.

As far as asteroids orbiting the sun, the maximum speed at 1 AU, where the earth resides, is about 41 km/sec or ~ 100,000 mph.

They move faster closer to the sun, and slower further away.

For example, the earth (at 1 AU) travels about 30 km/sec in it's near circular orbit; that 41 km/sec is more likely for a comet on a highly elliptical orbit.
If it travels (or is accelerated) beyond that speed, it is no longer bound to the sun and will leave the solar system.

Most asteroids orbit the sun in the same direction as the earth, so approach the earth from behind or the side at speeds between 5 and 30 km/sec; then of course they are accelerated by the earth's gravity to a minimum speed of 11.2 km/sec, about 25,000 mph before hitting the atmosphere. That's for an asteroid (or meteoroid) that is traveling at zero speed relative to the earth before gravitational capture.

A few comets, which are in retrograde orbit (and the meteors that come from them) hit the earth head on at a combined speed of nearly 72 km/sec and produce the fastest meteors. They include comet Tempel-Tuttle (parent of the Leonids), Comet Swift-Tuttle (parent of the Perseids) and of course Halley's comet, parent of the eta-Aquarid andOrionid meteor showers, however there are no known asteroids in such orbits.

Hope this helps.

Meteor Wayne

3. Thanks. My point or goal was, could an asteriod travelling at an unknown speed hit us before we can detect it ?

4. ## Current fastest approaching asteroid

Just to follow up, the fastest asteroid that is on the current JPL risk page is
2005 EL 70, approaching at 35.5 km/sec. After adding in the effect of the earth's gravity, it will hit the atmosphere at 37.2 km/sec or 83,214 mph.

It has a 2 in a million chance of hitting the earth in March 2034

MW
Last edited by MeteorWayne; 2008-Mar-03 at 02:52 PM. Reason: Added date and odds

5. Originally Posted by Sean Clayden
Thanks. My point or goal was, could an asteriod travelling at an unknown speed hit us before we can detect it ?
BTW, an interstellar asteroid from outside the solar system could hit at any speed from any direction, but so far no comet or asteroid has ever been unequivocally shown to be from outside the solar system.

6. Is it solid or a porous ?

7. Originally Posted by Sean Clayden
Is it solid or a porous ?
No way to tell, asteroids come in all shapes, sizes, densities and pososities.

It's only 50 meters (~164 feet) across.

8. If its like candy floss, no problem, if its iron, thats another story........

9. Originally Posted by Sean Clayden
Thanks. My point or goal was, could an asteriod travelling at an unknown speed hit us before we can detect it ?
Depends on a lot of factors, like how fast, how bright and where we're looking.

10. Originally Posted by Sean Clayden
Thanks. My point or goal was, could an asteriod travelling at an unknown speed hit us before we can detect it ?

It certainly could. There have been several instances of very close passes discovered only after they had done so. Yes, it is possible. For objects of a larger size, it is less likely. More likely for objects with a higher velocity, and/or coming from certain directions.

11. ## Small Asteroid Discoveries

We are now detecting several small (<100m) asteroids with closest approaches of less than 10 lunar distances per week.

It has become much harder for anything to sneak up on us.

MW

12. Thanks guys. Will sleep with one eye open........

13. Established Member
Join Date
Jan 2009
Posts
277
MeteorWayne gave us the same numbers I've found elsewhere.

As for sleep, I'll do so soundly. No point in worrying about things we have NO control over. [Cue Doris Day...]

14. Originally Posted by Sean Clayden
Thanks guys. Will sleep with one eye open........
Don't know if that will help much. Don't expect to be able to run very far once you see it coming.

16. Longer than that. This one is only 11 months old, not 23.

Fred

17. Hmm, thats what you get for having multiple threads open at same time! lol

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