NASA's Orion capsule and its test dummies swooped one last time around the moon Monday, flying over a couple Apollo landing sites before heading home.

Studying an atomic clock on-board a spacecraft inside the orbit of Mercury and very near to the sun might be the trick to uncovering the nature of dark matter, suggests a new study published in Nature Astronomy.

Dark matter makes up more than 80% of mass in the universe, but it has so far evaded detection on Earth, despite decades of experimental efforts. A key component of these searches is an assumption about the local density of dark matter, which determines the number of dark matter particles passing through the detector at any given time, and therefore the experimental sensitivity.

In some models, this density can be much higher than is usually assumed, and dark matter can become more concentrated in some regions compared to others.

One important class of experimental searches are those using atoms or nuclei, because these have achieved incredible sensitivity to signals of dark matter.