by Remo » Tue Aug 12, 2014 7:01 am
BillBixby wrote: How much gravity is required for this comet to acquire a satellite for a moon? ... What would b the orbit time and distance.
Bill
Doesn't take much. It has a pathetically small gravity well. The escape velocity off of Comet Churyumov-Gerasimenko has been estimated to be 1 ft/sec (.3 m/sec), but that is dependent on volume and density and density has yet to be determined (density will be determined experimentally from actual orbital data). However, acquiring is kind'a complicated because you need something to slow down the satellite.
Funny thing though, satellite orbit times scale linearly (i.e., based on diameter). So if you made a scale model of the earth with its same density, satellites will have the same orbital periods as they do now. For example, if we modeled the earth as a ball with a diameter of .5m, then the moon would be 30 m away, and the orbital period would be ~29 days, and a geostationary satellite would be ~1.7 m away from the center of the ball and have an orbit of 24 hours.
An ice ball like Comet Churyumov-Gerasimenko is not going to be too dense, so if we assume a density of 1/8th that of earth, instead of a ball of .5m diameter, we would use a ball of 1m. The position of the geostationary satellite (1.7m) and our moon (30m) would be the same relative to the center of the ball. I suspect that the ESA guys are going to want to position Rosetta as close as possible to the comet without endangering its mission which would probably mean an orbit of some place between 12 and 48 hours.
[quote="BillBixby"] How much gravity is required for this comet to acquire a satellite for a moon? ... What would b the orbit time and distance.
Bill[/quote]
Doesn't take much. It has a pathetically small gravity well. The escape velocity off of Comet Churyumov-Gerasimenko has been estimated to be 1 ft/sec (.3 m/sec), but that is dependent on volume and density and density has yet to be determined (density will be determined experimentally from actual orbital data). However, acquiring is kind'a complicated because you need something to slow down the satellite.
Funny thing though, satellite orbit times scale linearly (i.e., based on diameter). So if you made a scale model of the earth with its same density, satellites will have the same orbital periods as they do now. For example, if we modeled the earth as a ball with a diameter of .5m, then the moon would be 30 m away, and the orbital period would be ~29 days, and a geostationary satellite would be ~1.7 m away from the center of the ball and have an orbit of 24 hours.
An ice ball like Comet Churyumov-Gerasimenko is not going to be too dense, so if we assume a density of 1/8th that of earth, instead of a ball of .5m diameter, we would use a ball of 1m. The position of the geostationary satellite (1.7m) and our moon (30m) would be the same relative to the center of the ball. I suspect that the ESA guys are going to want to position Rosetta as close as possible to the comet without endangering its mission which would probably mean an orbit of some place between 12 and 48 hours.