Study uncovers forces that hold gravity-defying near-earth asteroid together (Update)

August 13, 2014
An asteroid 1950 DA. Credit: NASA

Researchers at UT have made a novel discovery that may potentially protect the world from future collisions with asteroids.

The team studied near-Earth asteroid 1950 DA and discovered that the body, which rotates so quickly it defies gravity, is held together by cohesive forces, called van der Waals, never before detected on an asteroid.

The findings, published in this week's edition of the science journal Nature, have potential implications for defending our planet from a massive asteroid impact.

Previous research has shown that asteroids are loose piles of rubble held together by gravity and friction. However, the UT team found that 1950 DA is spinning so quickly that it defies these forces. Ben Rozitis, a postdoctoral researcher; Eric MacLennan, a doctoral candidate; and Joshua Emery, an assistant professor in the Department of Earth and Planetary Sciences, wanted to know what keeps the body from breaking apart.

Looking at thermal images and orbital drift to calculate thermal inertia and bulk density, the team detected the action of cohesive forces in an environment with little gravity.

"We found that 1950 DA is rotating faster than the breakup limit for its density," said Rozitis. "So if just gravity were holding this rubble pile together, as is generally assumed, it would fly apart. Therefore, interparticle cohesive forces must be holding it together."

In fact, the rotation is so fast that at its equator, 1950 DA effectively experiences negative gravity. If an astronaut were to attempt to stand on this surface, he or she would fly off into space unless he or she were somehow anchored.

The presence of cohesive forces has been predicted in small asteroids, but definitive evidence has never been seen before.

The finding provides important information for efforts aimed at stopping an asteroid from crashing into Earth.

"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," said Rozitis. "Understanding what holds these asteroids together can inform strategies to guard against future impacts."

This research reveals some potential techniques, such as a kinetic impactor which would deploy a massive object on a collision course with the asteroid, could exacerbate the impact's effects. For example, this technique could destabilize the cohesive forces keeping the asteroid together, causing it to break apart into several threatening asteroids headed for Earth.

This may be what occurred with the asteroid P/2013 R3, which was caught by the Hubble Space Telescope in 2013 and 2014 coming undone, possibly due to a collision with a meteor.

"With such tenuous cohesive forces holding one of these asteroids together, a very small impulse may result in a complete disruption," said Rozitis.

The researchers' findings also have implications for space exploration. For example, the European Space Agency's Rosetta spacecraft will land on Comet 67P/Churyumov-Gerasimenko's surface and may find a dusty surface dominated by such cohesive forces.

Explore further: Experiments show disproportionately large number of big boulders on asteroids likely due to Brazil-nut effect

More information: Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA, Nature,

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5 / 5 (5) Aug 13, 2014
As far as I know, the European Space Agency's Rosetta spacecraft did not land on the comet, but is circling it with a view to landing on it when a suitable spot has been found. First sending a probe, then landing itself at a later date.
5 / 5 (6) Aug 13, 2014
"...Rosetta spacecraft landed on Comet..."

NO, it did NOT. It is currently mooching around in a 100km triangle, trying to map the comet surface and mascons. Then, it will creep closer, hopefully establishing a safe orbit about 10km out. The small lander does not go in until September.
5 / 5 (7) Aug 13, 2014
I thought Philae was the lander and Rosetta was the orbiter, and Philae is not supposed to land for some months. Someone needs to fact-check articles here!
5 / 5 (3) Aug 13, 2014
This article makes some very bad assumptions.

Previous research has shown that asteroids are loose piles of rubble held together by gravity and friction.

Some asteroids, maybe, but from there this "study" goes to hell, logically and scientifically.
not rated yet Aug 13, 2014
How come the research is generalized? As mentioned , the effect has been observed in 1950 DA, so how can we say that trying to break the cohesive forces can save us from all asteroids.
Lex Talonis
1 / 5 (5) Aug 13, 2014
Naaaaa the BIG earth smashers - fire a nuke with a leading penetrator head into them, and the smaller ones, just use fly paper.
5 / 5 (3) Aug 13, 2014
Of the asteroids and comets that have been closely imaged:
2867 Šteins definitely isn't a rubble pile.
9P/Tempel doesn't look at all like a rubble pile.
81P/Wild doesn't look like a rubble pile.
67P/Churyumov–Gerasimenko might look like a duck but not like a rubble pile.
not rated yet Aug 13, 2014
Detonation of a nuke releases an instantaneous release of x-rays and gamma rays. This pulse if many times faster than any kinetic particles (neutrons, pieces of bomb plasma) since x-rays and gamma rays move at the speed of light. Depending on the proximity of the detonation, the energy pulse of X-rays and gamma rays will result in instantaneous heating and ablation of the surfaces facing the nuclear device. This in turn will result in a trajectory alteration of the asteroid. Any trajectory alteration will result in a near miss for the earth. Might result in trajectory alteration for a solid body as well. A kinetic impact not required. A Thermonuclear bomb is triggered by the energy pulse from a fission device.
1 / 5 (4) Aug 14, 2014
Cohesive forces lols, no-one lacks an amount of intelligent to realize that as small clumps came together to form the asteroid "they welded each other." So they have just found evidence of that, big deal so what. It was obvious on its face. Waste of print.
5 / 5 (1) Aug 14, 2014
This got me thinking, what if instead of moving an asteroid out of the way of Earth, a small thruster (Maybe Ion) could be attached and simply make the asteroid spin faster and faster until it broke apart.
Just thinking outside the box a little, maybe it's a dumb idea :-)
1 / 5 (4) Aug 14, 2014
Gravity IS cohesive a force which is electromagnetic, as are Van der Waal forces. The two are the same, so there conclusions may be a step in the right direction, even though they are not exactly correct.
1 / 5 (2) Aug 16, 2014
Gravity IS cohesive a force which is electromagnetic
That is an assumption, since gravity waves have yet to be detected.
Here is a discussion on the subject: http://www.tapir....dex.html particularly the second page.

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