The asteroid Bennu continues to spin faster. And scientists do not know why



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The asteroid Bennu continues to spin faster. And scientists do not know why

Views of the OSIRIS-REx probe on the North Pole of the asteroid Bennu, during the first reconnaissance of the probe on December 4, 2018.

Credit: NASA / Goddard / University of Arizona

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

At present, the asteroid known as Bennu rotates once every 4.3 hours. But scientists working on NASA's OSIRIS-REx mission in space have used the data collected before the arrival of the probe to calculate Bennu – d & # 's rotational speed acceleration. 39, about 1 second per century.

"As speed increases, things have to change, so we're going to look for those things and to detect that speed gives us some clues about what kind of things we should look for," Mike Nolan, lead author on the new research and geophysicist at the Lunar and Planetary Laboratory of the University of Arizona, who also heads the scientific team of the OSIRIS-REx mission, said in a statement issued by the American Geophysical Union, which released the new study . "We should look for evidence that something was different in the fairly recent past and that it is conceivable that things change as and when."

Related: OSIRIS-REx: Mission Back NASA's Asteroid Samples in Images

The new research, despite the links that unite the OSIRIS-REx mission, is not based on the measurements of this probe; Instead, it looks at data collected by two ground-based telescopes between 1999 and 2005 and the Hubble Space Telescope in 2012. This latest data attracted the attention of scientists because they did not match the forecasts that astronomers had calculated with the Earth system. The data.

"You could not make sure that the three fit perfectly," said Nolan. "It was at that time that we had this idea that we needed to speed up."

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

One possible explanation is that material moving on Bennu's surface or leaving the asteroid completely could allow the speed of rotation to accelerate. The other explanation is more complicated, the effect Yarkovsky – O 'Keefe – Radzievskii – Paddack (YORP). This effect is caused by the sun's rays that bounce off the asteroid and slightly alter the speed of rotation more or less quickly depending on the shape of the object. For particularly weak asteroids, the YORP effect can actually tear up space rocks.

Scientists at the origin of the new research suspect Benny to suffer the YORP effect. And over the next two years, OSIRIS-REx will provide more data, including detailed block analysis and gravitational measurements. Scientists can use these observations to confirm what is happening in Bennu and determine local levels of YORP.

These figures can also help scientists understand the behavior of other asteroids, who will never see a dedicated spacecraft.

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

Email Meghan Bartels at [email protected] or follow her @meghanbartels. Follow us on twitter @Spacedotcomand on Facebook.

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