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Sean Clayden
2008-Mar-03, 02:24 PM
What is terminal velocity for an asteroid ? And, what is the speed of the current fastest travelling asteroid ?

MeteorWayne
2008-Mar-03, 02:41 PM
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

Sean Clayden
2008-Mar-03, 02:44 PM
Thanks. My point or goal was, could an asteriod travelling at an unknown speed hit us before we can detect it ?

MeteorWayne
2008-Mar-03, 02:47 PM
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

MeteorWayne
2008-Mar-03, 02:50 PM
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.

Sean Clayden
2008-Mar-03, 02:51 PM
Is it solid or a porous ?

MeteorWayne
2008-Mar-03, 02:55 PM
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.

Sean Clayden
2008-Mar-03, 02:57 PM
If its like candy floss, no problem, if its iron, thats another story........

Noclevername
2008-Mar-03, 06:57 PM
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.

Anthrage
2008-Mar-04, 05:31 AM
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.

MeteorWayne
2008-Mar-04, 04:52 PM
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

Sean Clayden
2008-Mar-05, 11:04 AM
Thanks guys. Will sleep with one eye open........

Gandalf223
2009-Feb-12, 07:04 PM
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...]:boohoo:

Jens
2009-Feb-13, 06:08 AM
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. :)

loglo
2009-Feb-14, 04:27 AM