9 October 2008
Dark matter is one of those mysterious physics problems that, while really awesome in theory, almost never seems to have applications back here in the solar system. However, a new theory claims that dark matter might be lurking just overhead.
A new study (Adler, J. Phys. A) has come out that sets an upper limit on the amount of dark matter between Earth and the orbit of the moon: 1500 trillion kilograms! To put this number in perspective, that’s four billionths of the mass of the Earth, or .02 millionths of the mass of the moon.
If the dark matter was spread out evenly over the sphere around the Earth, the density would be 0.002 kg per cubic kilometer, which doesn’t seem like enough to affect anything. However, one of the mysterious properties of dark matter is that it tends to clump together. So if the 1500 trillion kg was present as clumps, we might be able to detect changes in the local gravity field due to it.
Adler claims that we have detected these clumps, in the form of anomalous accelerations of spacecraft during fly-bys and orbits of Earth.
I get the impression that this theory is considered pretty out there, but it’s interesting nonetheless. If Adler’s right, I’m calling first rights to the phrase “backyard cosmology”.