Early this year, NASA announced a bold robotic mission to capture an asteroid in a bag and return the rock to Earth orbit so it could be studied. The mission could serve as training and testing for astronauts en route to an eventual trip to the moon and Mars using the Orion spacecraft.
But a team of Northern Arizona University astronomers have shown that the asteroid NASA has been using as a reference target isn’t a suitable candidate. Using the Spitzer Space Telescope, the astronomers showed that the space rock is just 10 to 13 feet in diameter. It would fit into the average garage. They presented the research last week at a meeting of the American Geophysical Union in San Francisco and submitted it for publication in the Astrophysical Journal.
The asteroid’s diminutive size is likely too tiny to work as a target for the $2.6 billion Asteroid Redirect Mission. The space agency has said it wants an asteroid closer to about 20 feet across.
NASA had been using asteroid 2009 BD as a placeholder for its planned 2021 mission, which shocked some in the science community when it was announced. The mission was not done with the typical consultation. And presumably, astronomers say NASA picked 2009 BD because it would have been easy to reach based on its close Earth approach.
But no extensive studies had been done on the asteroid.
That’s why NAU post-doctoral researcher Michael Mommert and NAU astronomer David Trilling were asked to look at 2009 BD earlier this fall.
But the asteroid was so small that the infrared satellite couldn’t see it after staring for 25 hours. The astronomers detected nothing.
“We didn’t see it. It was too faint to be detected in our data,” Trilling said. “We know it has to be smaller than some size or we would have been able to see it.”
The researchers were able to combine their own observations with what was seen of asteroid 2009 BD when it squeaked between the Earth and the moon in 2011. They constrained the asteroid into two likely models, one where it was a dusty and bright chunk of bare rock about 10 feet across and the other where the asteroid is a dull rubble pile.
“Although we didn’t see it, we can constrain its properties quite well,” said Mommert. “You have to bear in mind that the majority of all asteroids have that size so we were pretty lucky that this guy was discovered and we were able to observe it. This tells us something about the population we knew nothing before about.”
The results are very unusual for what astronomers might expect to find in such a small asteroid. But their observations constitute the first time someone’s studied a space rock of that size in detail. Asteroid composition has also surprised scientists in the past.
Mommert added that it’s unfortunate that 2009 BD isn’t likely to be a candidate for the mission because it seems very interesting scientifically.
“It’s really weird what we found here,” Mommert said. “Either solution would be very special and hadn’t been seen before.”
And it’s a good thing that they looked. The asteroid already passed out of view of ground-based telescopes and won’t be seen for another decade. NASA could have ramped up for the mission and ended up calling an audible.
There are other candidate asteroids, so Trilling says it’s not a big deal for NASA to settle on one of the other 13 candidates on its published list. But those too have not been studied in detail.
Normally, a space mission would go through a rigorous process of target and goal submission and review before a final mission was announced, but that didn’t happen with the Asteroid Redirect Mission. President Barack Obama directed NASA to visit an asteroid and the agency determined that capturing one and bringing it back to Earth would be the easiest, most cost-effective way to do that.
“NASA said we’re gonna launch this thing, now lets go find an asteroid,” Trilling said. “They were casual about finding one because there are lots of asteroids. It turns out it’s not easy.”
Mommert and Trilling will look at the next asteroid on the list in February, named 2011 MD, to see if it might be a suitable candidate.
But the robotic mission has already drawn fire from Congress for its high cost, as reported in the New York Times and Washington Post. The 2014 NASA budget sets aside $100 million just to get the project kick-started.
Trilling, unlike some of his peers, he fully supports the project. The astronomer organized the Planetary Defense Conference in Flagstaff earlier this year and understands well the threats small asteroids can pose to Earth.
“If an asteroid were coming our way and we wanted to change its orbit, its good to practice,” he said. “It’s also good for science.”
Eric Betz can be reached at 556-2250 or firstname.lastname@example.org.