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UA space probe achieves orbit around asteroid

Osiris Rex to bring a sample back to Earth
Posted at 6:49 PM, Dec 31, 2018
and last updated 2018-12-31 20:49:50-05

TUCSON, Ariz. - A space probe managed by the University of Arizona is having a smoother trip -- to a distant asteroid -- than a lot of us had with our holiday travel.

The Osiris Rex probe arrived at the asteroid called Bennu earlier this month --

but Monday -- it moved into orbit around the space rock -- and it'll be the smallest object anyone has ever orbited.

Orbiting a small asteroid like Bennu is so tricky, Osiris Rex could not go into orbit right away.

Since arriving at Bennu in early December it's been zooming back and forth around it to measure its mass.

University of Arizona space scientist Dante Lauretta leads the Osiris Rex mission as principal investigator. He says, “The mass of the asteroid determines the speed, the spacecraft needs to go as it enters into orbit. So without knowing how massive it was, we couldn't figure out how to get the spacecraft where we needed to.”

Lauretta says get the mass wrong, get the speed wrong and Osiris Rex would probably zip past Bennu and not go into orbit.

Now that the spacecraft is in orbit it's aiming for the tightest orbit ever-- just one mile high.

Bennu's gravity is so weak Osiris Rex orbit has to be very slow, especially for an orbit around a very small object.

Lauretta says, “Because the gravity and the mass of the object is so low, it's going to take us two and a half days to complete one orbit around this asteroid. For comparison, the space station goes around the Earth every hundred minutes.”

Understanding Bennu's mass can help scientists figure out how to make it or another asteroid change course if they're threatening to hit the Earth.

But the main reason to explore Bennu is the idea that the asteroid is an example, frozen in time, that could help explain how planets, and even life formed.

Dante Lauretta says, “One of the great discoveries from the Osiris Rex mission already is that scientists at the University of Arizona and around the world have detected hydrated minerals. --- water on the surface of this asteroid means it's exactly the kind of material that we're hoping to get from the dawn of the solar system, the kind of object that may have delivered the water for our oceans and the organic material for life on our planet."

Now a lot of the work will be to pick a site for the probe to ease in, grab a sample of Bennu and return it to scientists waiting on Earth.