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The Asteroid Bennu Keeps Spinning Faster. And Scientists Aren’t Sure Why



  The asteroid Bennu continues to spin faster. And the scientists are not sure Why

The images of the OSIRIS-REx probe on the north pole of the Bennu asteroid, during the first reconnaissance of the probe on December 4, 2018.

Credit: NASA / Goddard / University of Arizona

a distant space rock is being explored by a NASA probe, the days are slowly shrinking ̵

1; and scientists are still trying to figure out why.

At the moment, the asteroid known as Bennu runs once every 4.3 hours. But scientists working on NASA's OSIRIS-REx mission in rock space have used the data collected before the arrival of the probe to calculate that Bennu's rate of rotation is accelerating over time – about 1 second each century.

"As it accelerates, things should change, so we'll look for these things and picking up this speed will give us some clues about the kind of things we should be looking for," Mike Nolan, lead author of the new research and a geophysicist at the Lunar and Planetary Laboratory of the Arizona University, which is also head of the OSIRIS-REx scientific team, said in a statement released by the American Geophysical Union, which published the new research. "We should be looking for evidence that something was different in the past fairly recently and it is conceivable that things are changing."

Related: OSIRIS-REx: the return mission of NASA asterisks in images

The new research, despite the links with the OSIRIS-REx mission, is not based on the measurements of this probe; instead, look at the data collected by two ground-based telescopes between 1999 and 2005 and by the Hubble Space Telescope in 2012. These latest data have captured the attention of scientists because they did not align with the forecasts that astronomers had calculated with the land data.

"It is not possible that all three fit perfectly," said Nolan. "That was when we thought he had to speed up."

It is not an unknown phenomenon, but it is rare, and scientists have only confirmed their first example of accelerating an asteroid in 2007. Even in Bennu, the observations leave the mystery of what caused it.

A possible explanation is that the material that moves on the surface of Bennu or that leaves entirely the asteroid could allow the rate of rotation to accelerate. The other explanation is more complicated, the Yarkovsky-O & # 39; Keefe-Radzievskii-Paddack (YORP) effect. This effect is caused by sunlight bouncing off the asteroid and slightly changing the speed of rotation faster or slower depending on the shape of the object. For particularly weak asteroids, the YORP effect can actually destroy space rocks.

Scientists behind the new research suspect that it is the YORP effect that Bennu is experiencing. And over the next two years, OSIRIS-REx will provide more data, including detailed analysis of the boulders and gravitational measurements. Scientists can use these observations to confirm what is happening at Bennu and define local YORP levels.

These numbers can also help scientists understand the behavior of other asteroids, those that will never see a dedicated spacecraft.

described in an article published January 31 in the journal Geophysical Research Letters.

Email Meghan Bartels at mbartels@space.com or follow it @meghanbartels . Follow us on Twitter @Spacedotcom and on Facebook.


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