by apodman » Mon Jun 08, 2009 1:31 am
fingersfray wrote:surely the impact it's self would have displaced Eros a small amount? and while in orbit the gravitational effects should have been noticeable no matter how small. ???
Eros has a mass of nearly 7,000,000,000,000,000 kg. While I can't find the mass for NEAR, it is probably less than 1,000 kg which would make the mass ratio more than 7,000,000,000,000 to 1. You would need quite a sensitive instrument to detect the gravitational perturbation caused by NEAR in orbit with a ratio like that (the wobble of Eros on its center caused by the orbiting NEAR would be small, and the perturbation of Eros' orbit around the sun would be many orders of magnitude smaller yet). The impact might produce a measurable effect (with its position measured one or many more orbits around the sun later) if you slammed NEAR into Eros at a very high speed, but in this case it was a fairly soft - 8 km/h is walking speed - crash landing (unlike the higher velocity Deep Impact probe and its target comet).
Don't get me wrong. I'm all in favor of ingenuity including gravity tractors for deflecting dangerous asteroids, and I'm all in favor of NEAR and its mission. I just think that NEAR's mission was a good step in the research process that wasn't intended to produce all the results you are asking to attribute to it. In a later mission I'm sure we will try more massive spacecraft with more provocative orbits or faster impacts.
[quote="fingersfray"]surely the impact it's self would have displaced Eros a small amount? and while in orbit the gravitational effects should have been noticeable no matter how small. ???[/quote]
Eros has a mass of nearly 7,000,000,000,000,000 kg. While I can't find the mass for NEAR, it is probably less than 1,000 kg which would make the mass ratio more than 7,000,000,000,000 to 1. You would need quite a sensitive instrument to detect the gravitational perturbation caused by NEAR in orbit with a ratio like that (the wobble of Eros on its center caused by the orbiting NEAR would be small, and the perturbation of Eros' orbit around the sun would be many orders of magnitude smaller yet). The impact might produce a measurable effect (with its position measured one or many more orbits around the sun later) if you slammed NEAR into Eros at a very high speed, but in this case it was a fairly soft - 8 km/h is walking speed - crash landing (unlike the higher velocity Deep Impact probe and its target comet).
Don't get me wrong. I'm all in favor of ingenuity including gravity tractors for deflecting dangerous asteroids, and I'm all in favor of NEAR and its mission. I just think that NEAR's mission was a good step in the research process that wasn't intended to produce all the results you are asking to attribute to it. In a later mission I'm sure we will try more massive spacecraft with more provocative orbits or faster impacts.