Asteroids can rotate faster than they should to be able to remain whole, suggesting an unusual force may be holding the space rocks together.
One celestial body, 1950 DA, rotates once every 2 hours, six minutes. Forces acting on the body at this great of a rate should tear the asteroid apart. This time is about six minutes faster than shortest rotational rate normally seen in such bodies. Centrifugal forces normally tear apart asteroid that start to rotate faster than that rate.
Astronomers have found several dozen of these objects spinning faster than the critical rate, although the reason they seem to stay together remains a mystery. Some researchers favor the hypothesis that these asteroids contain large amounts of metal, allowing them to stay in one piece. Others hold to the hypothesis that these "single" bodies are actually vast collections of smaller rocks, held together by gravity in a swarm that appears, from Earth, to be a single structure. These are known as "rubble pile" asteroids.
Ben Rozitis, a planetary scientist at the University of Tennessee, and his team believe van der Waals forces may be holding these bodies together at rotational rates that should tear them apart. Some materials, known as polar molecules, can generate weak attractions between molecules. Water is a classic polar material, and this force generates the rounded top, called a meniscus, that can rise slightly above the top of a glass. Moon dust clung to spacesuits worn by Apollo astronauts through the same process.
The mass of 1950 DA was investigated by studying the tiny push provided by heating, caused by sunlight striking the asteroid. The size and shape of the body were fairly well understood, allowing researchers an opportunity to calculate the mass of the asteroid by knowing the degree of movement provided by solar heating.
Investigation of the forces holding these bodies together in space can assist astrophysicists in study of asteroids that could potentially threaten Earth. Most laboratory tests have used perfectly spherical bodies in tests. Future research will investigate how the process would be affected by more complex shapes and textures.
The asteroid 1950 DA has a small chance, one in 19,800, of striking our home planet in the year 2880. When the close encounter was first predicted in 2002, astronomers placed the chance of the asteroid striking the Earth at one in 300.
"Following the February 2013 asteroid impact in Chelyabinsk, Russia, there is renewed interest in figuring out how to deal with the potential hazard of an asteroid impact. Understanding what holds these asteroids together can inform strategies to guard against future impacts," Rozitis said.
Study of 1950 DA and similar asteroids that may be exceeding rotational rates higher than normally possible was detailed in the journal Nature.