Re: Fw: [meteorite-list] meteor velocity

[GeoZay]

Hello Jose, Iâm not sure of the source...perhaps from IMOâs Meteor Observing Guidebook? I donât have a copy handy anymore, So Iâm gonna try to wing it with the interpretation that I got from it all. Basically, meteoroids coming from parent objects in the asteroid belt, have a relatively slow orbital speed when compared to particles that come from in-coming comets that are in long range orbits around the sun. I believe this is shown in one of Keplers Laws? Most of the asteroids in the asteroid belt and near earth, orbit the sun in the same direction as the planets. For any of these asteroidal objects to enter the earthâs orbit, they would have to play âCatch upâ with the earth. Thus they would tend to enter the earths atmosphere during a period from afternoon to  before midnight. Subtracting their orbital speed, which is in the vicinity of earths orbital speed, would mean they would be entering at velocities that would appear very slow. If they are entering directly behind the earth, then the speed would be no faster than about 11 km/s. The exact velocities can vary a little since the exact entry angle from behind could be a little off.  For the most part, for an asteroidal meteoroid to survive the rigors of passing thru our atmosphere, they should have velocities less than 29 km/s. Any faster they would have the tendency to burn up or explode. A meteoroid entering the earths atmosphere at velocities near 11 km/s would appear to move quite slowly to the eye. Those that have entry velocities of around 29 km/s would appear to be moving at best from medium slow to medium.  Thatâs what you can expect from an asteroid that produces meteorites. To the best of my knowledge, these are the only kind of meteorites, with a few exceptions such as those from the moon and mars.  As for the meteors that come from comets. The parent comets and their particles that are in the similar highly elliptical orbits come from way out...most beyond Neptune with a few exceptions. By the time comets and their particles get in the vicinity of the earth, they have a much higher velocity than an object with asteroidal origins. Again one of the Kepler laws.  Comet particles tend to meet up with the earth coming from all directions....behind, straight on and obliquely. These different directions basically dictate the entry velocites in the long run. They can enter from behind and have the same velocity as an asteroidal object. They can enter from the front with a velocity up to 72 km/s....way faster than what an asteroidal object can. In order for an asteroidal object to have this kind of velocity from behind, it would mean it is no longer in orbit around our sun. Itâs basic orbital velocity in the vicinity of earth and the asteroid belt is locked in at a slower velocity than something coming in from beyond Neptunes orbit.  Now with this all said, If Mike said he saw a meteor appear to be traveling Very Fast....then its not likely to be of asteroidal origin, nor drop any meteorites. Most likely of cometary origin. It is possible to have a cometary particle entering the earth with Slow to Very Fast Velocities, but highly unlikely for an asteroidal particle to have anything other than Slow to maybe Slow to Medium velocities. I donât know how fast Mikeâs fireball was traveling, but do know if one has seen a few meteor showers, you can quickly gain a âsenseâ of whether itâs traveling Very Slow(typical meteorite dropping velocity) to one that is Very Fast(cometary velocity with no meteorite survival expected). I hope my wording makes some sense?I don't have the math expertise, but I believe I understand the concepts quite well? :o) George Zay