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The asteroid Bennu turns faster. And scientists are not sure why



  The asteroid Bennu turns faster. And scientists are not sure why

The views of the OSIRIS REx spacecraft over the north pole of the Bennu asteroid during the probe's early reconnaissance on December 4, 2018.

Credit: NASA / Goddard / University of Arizona [1

9659004] On In a distant space rock being explored by a NASA probe, the days are slowly getting shorter – and scientists are still trying to figure out why.

Currently, the asteroid, known as Bennu, spins once every 4.3 hours. However, scientists working on NASA's OSIRIS REx mission in space rock have used data collected prior to the arrival of the probe to calculate that Bennu's rotational speed will increase by about one second over time.

"The acceleration of things should change, and so we will look for these things, and the determination of that speed gives us clues to the kinds of things we should look for." Mike Nolan, lead author of the new research and Geophysicists At the University of Arizona's Lunar and Planetary Laboratory, which also heads the science team of the OSIRIS REx mission, the US Geophysical Union said in a statement that the new research has been published. "We should look for evidence that something has been different in the recent past, and it's possible that things will change over time."

Related Topics: OSIRIS-REx: NASA's Asteroid Return Mission in Pictures

Despite the links to the OSIRIS REx mission, the new research is not based on measurements of this probe. Instead, data collected from two ground telescopes between 1999 and 2005 and the Hubble Space Telescope in 2012 are considered. These latest data caught the attention of scientists because they did not agree with the predictions astronomers had calculated with ground controls data.

"They could not make all three match properly," Nolan said. "That was when we came up with the idea that it had to be accelerated."

This is not an unknown phenomenon, but it is rare, and scientists only confirmed their first example of how the rotation of an asteroid in 2007 accelerated. Even with Bennu, the observations leave the mystery of what causes them.

One possible explanation is that material that moves on the surface of Bennu or completely leaves the asteroid could accelerate the rotation speed. The other explanation is more complicated, the Yarkovsky-O & # 39; keefe-Radzievskii-paddack (YORP) effect. This effect is caused by the sunlight bouncing off of the asteroid and the spin speed becoming faster or slower depending on the object shape. For very weak asteroids, the YORP effect can actually disrupt space rock.

The scientists behind the new research suggest that it is the YORP effect that Bennu experiences. Over the next two years, OSIRIS-REx will provide more data, including detailed boulder analysis and gravity measurements. Scientists can use these observations to confirm what Bennu is doing and to set the local YORP levels.

These numbers can also help scientists understand the behavior of other asteroids that will never see a special spaceship.

The research is described in an article published on January 31 in the journal Geophysical Research Letters.

Mail Meghan Bartels to mbartels@space.com or follow her @meghanbartels . Follow us on Twitter @Spacedotcom and on Facebook


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