How NASA's mission to Bennu will keep itself safe from asteroids



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NASA's OSIRIS-REx mission will not only take beautiful pictures of the asteroid Bennu – it will also help scientists to find out if the rock will one day threaten Earth.

There are many reasons to study asteroids. They could be potential mines for precious resources like water and heavy elements, and they contain clues that we can study to learn about the Solar System in its early days.

But also, great things hitting the Earth can have some catastrophic consequences. So the scientists are also interested in this.

Bennu is a 487.68m asteroid that orbits the Sun relatively close to Earth. OSIRIS-REx, the NASA mission in charge of studying it, was launched in September 2016 and reached its goal last Monday. The spacecraft carries five instruments: a set of cameras, a LIDAR system (such as radar, but with a laser instead of radio waves) and three spectrometers, which measure different wavelengths of light to determine the composition of the asteroid.

Bennu is a particularly important target when it comes to our own survival. About six in every six years, it is relatively close to Earth ("near" in cosmic terms, but very far by any other measure). Models suggest that during their close approximations between the years 2175 and 2196, there is a probability of 2700 in colliding with us. This is still incredibly small (a chance to lose 99.963%), but Bennu is a big rock – even the minimum odds are too great to ignore when civilization is at stake.

Why do not astronomers know for sure if we are safe? There are many forces at play and small differences can change the odds. During some approaching approximations of the asteroid, Earth's gravity will give it a little shove that could put it on a collision course.

In addition, there is the Yarkovsky effect, according to a press release from the Jet Propulsion Lab: Irregular warming of the sun in such a light body can cause changes in its trajectory. It is not clear where Bennu will go after 2135.

OSIRIS-REx and the telescopes on Earth will continue to characterize the asteroid, tracing its path and determining how gravity and the Yarkovsky effect will influence its trajectory. The mission is expected to produce trajectories 60 times more accurate than current estimates, according to the press release.

So, what happens if Bennu becomes a threat? Well, you personally should not worry, because chances are very good that you're dead. Your children are also likely to be dead.

But researchers are working on some solutions. A mission called Double Asteroid Redirection Test will try to hit a spacecraft on an asteroid to cause a trajectory change. Maybe we could bomb asteroids.

Or, if we have enough time, maybe we can just paint one side to change the way it absorbs solar radiation, using the Yarkovsky effect in our favor.

There is a lot of data to be taken before we know what Bennu will do, and many other interesting science to drive. But know that Bennu is not the asteroid you should care about. The asteroids you we must worry about those that have not yet been detected.

[NASA JPL]

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