As you might know, NASA will be sending the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (Osiris-REx) spacecraft into space on Sept. 8 in order to collect material from Asteroid Bennu (yes, the same one that has a minuscule chance of hitting the Earth in the 22nd century). Of course, there are plenty of asteroids that NASA could have picked for the mission, so why did it pick that one?
Because it's the best one, according to NASA.
In a news conference in Washington, D.C. on Tuesday, Christina Richey revealed that there were three primary factors in choosing from the thousands of candidates for the mission: size, composition and familiarity. Of the potential candidates, only five made it to the second round, and of those five, Bennu was the last one standing.
"Bennu's size, primitive and carbon-rich composition and orbit make it one of the most fascinating and accessible asteroids, and that is why it was ultimately chosen as the target asteroid for the Osiris-REx mission," Richey said.
Size
Size was one of the most important factors in determining which asteroid to choose for the mission. Why? Because it plays a large part in the chances that any material will actually be obtainable from its surface.
In this case, Richey mentioned that asteroids less than 660 feet are especially difficult to obtain samples from due to their heightened rotation speed. Not only is it difficult for a spacecraft to match the rotation speed of a rapidly-rotating object, but even it does, the rotation speed might have caused the asteroid to lose material from its surface, thus leaving less for the spacecraft to recover.
Bennu, on the other hand, is rather large, measuring nearly 1,640 feet in diameter and rotates only once every 4.3 hours. Not only does this theoretically allow Osiris-REx to match Bennu's rotation speed, but there will also be plenty of materials available to collect.
Composition
The inside matters just as much as the outside, and Bennu fits the bill perfectly, according to NASA.
Bennu, believed to be carbon-rich due to its "very dark, black surface," has recorded "the earliest history of our solar system because its composition probably has remained unchanged since it formed some four billion years ago." What's more, Bennu could possibly contain natural resources such as water, organics and precious metals — precursors to the origin of life.
"We're really interested in bringing back a pristine sample of the early solar system," Osiris-REx principal investigator Dante Lauretta of the University of Arizona said last month. "Did these kinds of bodies [like Bennu] deliver organic material and water, in the form of hydrated minerals like clay, to the surface of our planet that created the habitability and the environments that may have led to the origin of life?"
Familiarity
Probably the most important factor in coming to Bennu as the asteroid of choice was the familiarity with the space rock.
For the average consumer and general media, Asteroid Bennu is known as the "armageddon" asteroid that could mean the end of civilization if it beats the 0.037 percent odds and actually collides with Earth. This, of course, isn't quite true. Yes, it will cause quite a bit of death and destruction upon impact, but it simply lacks the size to deal that much damage (in comparison, the asteroid that wiped out the dinosaurs is believed to be about six miles in length).
On the other hand, for NASA, Bennu is the asteroid that is the most known. Discovered in 1999 and named after an Egyptian mythological bird by a North Carolina third grader who won an asteroid-naming contest, it is the best-understood near-Earth asteroid that has never been visited by a spacecraft.
In fact, astronomers know so much about it that this knowledge is what sealed the deal for Bennu. Aside from size and rotation speed, NASA also knows that it completes one lap around the sun every 1.2 years, comes "near" Earth every six years, and that its orbit is inclined by just six degrees compared with that of Earth.
"We selected asteroid Bennu as the final target of Osiris-REx because it was so well characterized, with the radar data and telescopic data, that we felt that really reduced risk to the mission profile," Lauretta said during the news conference.
With that said, what is the point of all this? NASA wants to learn more about the role asteroids may have played in providing Earth with the necessary components of building life. After that, the fact that Bennu was chosen is simply icing on the cake. NASA can use Osiris-REx's observations to fine-tune their understanding of Bennu's orbit and properly assess the threat it poses to Earth. Sure, Bennu only has a smidgen of a chance to hit Earth, but NASA would like to reduce the possibility of that to zero.
