Comments on: Solving the Asteroid â€“ Meteorite Puzzle

By: Isadora

Isadora — Sat, 23 Aug 2008 18:30:17 +0000

My father found a rock in the desert, and this rock is already check by a spectrometer. they tell as , the component of this meteorite they "shouldn't exist".
This people want to send the meteorite to Washington DC to fallow up the studies, and We need to know what to do well.
Any info we really appreciate.

Isadora, CA

By: Gerald, Walnut Creek, CA

Gerald, Walnut Creek, CA — Thu, 14 Aug 2008 17:25:50 +0000

This article suggests that the Yarkovsky effect is too weak to move large asteroids out of the main belt into Earth crossing orbits. But several other researchers (see for example Morbidelli & Vokrouhlicky, Icarus 163, 2003) have shown that the Yarkovsky effect, and the related YORP effect, contribute signficantly to the migration of kilometer sized asteroids into Earth crossing orbits. Also, most NEOs are S-type asteroids, and at least half of the S-types are iron. In fact, looking at meteorite samples recovered from the relatively few large impact craters on Earth, half of them are irons.

By: Aodhhan

Aodhhan — Thu, 14 Aug 2008 12:41:36 +0000

I wouldn't mind seeing Binzel's full report on this. Something is scratching me the wrong way (more than the poor writing skills of Mr. Chandler at MIT's News office).
For instance, if 95% of the LLC's are less than 5 meters, then who cares? The likelyhood they will cause damage is near nil.

This reports shows us how and why we get plastered with a disproportionate amount of small LLC's; it indicates this method only affects small rocks; those which will cause little if any damage. So why are they in the equation?

I want to know about those which can cause damage (> 1km), not "ALL". Since the majority will burn up in the atmosphere to the point where they aren't a threat; adding them to the equation is going to mess up the results.

Where is the part of the study which talks about the largest near-Earth asteroids? How do/did they get here? How did you confirm their composition and ratio?

By: Adam

Adam — Thu, 14 Aug 2008 07:54:55 +0000

"… most NEAs â€” about two-thirds of them â€” match a specific type of meteorites called LL chondrites."

Any clues as to why this particular type is so overrepresented among NEAs?

/Adam

By: Astrofiend

Astrofiend — Thu, 14 Aug 2008 01:45:13 +0000

I have been fascinated by this discrepancy too. It certainly demands explanation…

By: tacitus

tacitus — Wed, 13 Aug 2008 23:56:05 +0000

Wait a minute, Gerald. The researcher just said:

"Odds are, an object we might have to deal with would be like an LL chondrite..,"

So are you saying they're wrong? What evidence do you have to say otherwise?

They are not claiming that *all* impactors are LL chondrites, just a large majority of them (66%). It makes perfect sense to focus first on the type of asteroid that is twice as likely as all the other types put together to hit us.

By: Gerald, Walnut Creek, CA

Gerald, Walnut Creek, CA — Wed, 13 Aug 2008 23:04:30 +0000

I would not assume that the NEA threat is mostly from LL chondrites. A significant number of NEAs and potential impactors are not LL chondrites. For example, the meteorite that caused Meteor Crater near Flagstaff, Arizona, was an iron meteorite, which has signficantly different properties than an LL chondrite. Several other existing large impact craters on Earth are also known to have been caused by iron or stoney iron meteorites.