“Asteroid Surface Gravimetry, Weighing Boulders On Asteroids”
One well-known geophysical technique that has been used on Earth for many years is ground gravity surveying, in which a highly sensitive gravimeter is used to make measurements of the local gravity field strength at many locations on the ground in an area being surveyed. Variations in those measurements reflect variations in the density of the rock beneath the survey area, which in turn can provide indications of the local geology. That has both scientific and practical (resource prospecting) uses.
The same principles hold true for other planetary bodies. Here we discuss the potential for using surface gravity surveying to characterise the internal density distribution of asteroids. An instrument being developed for this application by Gedex, the Vector Gravimeter for Asteroids (VEGA), will be described. VEGA is the first space gravimeter of sensitivity high enough to be useful in the asteroid prospecting application. Examples will be shown of the sort of measurement results that might be expected from an asteroid surface gravity survey.
As a result of VEGA’s expected high accuracy, and the vector nature of its measurement, this instrument also enables some peculiar new capabilities. One of these is an ability to directly “weigh” a boulder on the surface of an asteroid, by determining the deflection of the vertical as the gravimeter is brought close to the boulder. This capability may be useful for NASA’s ARRM mission. From a boulder’s mass, its density can be estimated. Unexpectedly low or high density may be indicative of a boulder that is unsuitable for collection, e.g., due to a high void content (too weak, might crumble), or due to being too massive to be able to be brought back to Earth orbit. An asteroid lander/rover (GRASP = “GRavitational Asteroid Surface Probe”) carrying a VEGA instrument, capable of making these measurements, will be described.
The presentation can be seen here.