Asteroid spotting with NEOWISE

Joe Masiero, a scientist with the
NEOWISE project, spoke at the meeting
 of the Seattle Astronomical Society
Nov. 16, 2016. Photo: Greg Scheiderer.

The solar system seems like a big place with lots of empty space in it, at least until an astronomer plays a simulation of the orbits of its asteroids. Such a simulation looks like an angry swarm of bees, and Earth appears likely to be stung by them several times per day.

Some scientists at NASA’s Jet Propulsion Laboratory convinced the agency a few years ago to give them the keys to a hibernating but still semi-functional space telescope, and now the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) is on the hunt for asteroids and other near-Earth objects. Mission scientist Joe Masiero talked about NEOWISE at this week’s meeting of the Seattle Astronomical Society.
Masiero explained that NEOWISE is a part of NASA’s near earth object observation program.

“This is one of the funding lines that NASA has specifically dedicated to discovering and characterizing objects that come close to the Earth,” he explained. “It’s one of a number of missions and a number of telescopes that do these surveys for near-Earth objects trying to look out to see if anything is posing a hazard to our planet.”

Used scope for sale

That important work is being done by a hand-me-down space telescope. WISE launched in December of 2009 on a mission to essentially build an infrared atlas of stuff to help scientists decide where to point the James Webb Space Telescope when it becomes operational. WISE looked for the most luminous galaxies in the universe, close and cold brown dwarfs, and other sorts of objects for Webb to explore. That mission complete by the following September—and two of four infrared wavelength detectors shot because their coolant ran out—WISE was put into hibernation for almost three years. But the JPL team thought the 40-centimeter scope could still be used for science with the two infrared detectors that didn’t need cooling, and convinced NASA to resurrect WISE as NEOWISE. They fired the scope up again in December of 2013.

“The goals of the NEOWISE mission are to survey near-Earth objects,” Masiero explained, “both to discover new ones, but even more importantly, to characterize ones that we currently know about, to figure out how big they are and how reflective they are, because it’s the reflectivity, the albedo of an object, gives you an initial hint as to what it’s made of.”

There are a number of programs looking for near-Earth objects, such as PanSTARRS and the Catalina Sky Survey, but Masiero said NEOWISE brings something different to the table.

“One of the benefits of NEOWISE as an infrared survey is that we’re discovering a lot of these objects that are very dark—that look like a lump of coal—and sometimes that are very big,” he explained, adding that this is the mission’s special niche.

“There are other surveys finding more near-Earth objects than we are,” he said, “but what we excel at is finding these very dark objects that other telescopes miss.”

The mission has been prolific. Between WISE and NEOWISE, Masiero said they’ve discovered about a thousand near-Earth objects larger than a kilometer.

“Those are the dinosaur-killer level,” he said. In addition, they’ve found about 20,000 objects in the 100-meter class; the type that could cause a “bad day” were they to hit Earth.

Science, too

Possible mass extinction is reason enough to keep an eye out for near-Earth objects, but Masiero notes that there’s science to be done as well. Since these objects are close in they’re easier to study and visit, and there are a number of future missions planned to do just that. Asteroids could also give clues to the formation of the solar system.

Masiero’s particular interest is in looking at main-belt asteroids, which don’t get as much study because they’re so hard to see. One interesting thing they’ve been able to do with NEOWISE is to determine the albedo of asteroids. They’ve found that many objects with a matching albedo also share the same orbital inclination. These asteroid “families” traveling in clusters also often match in optical color.

“This is a single large object that something crashed into and shattered into hundreds or thousands of smaller pieces,” Masiero said. “Because it came from a single object, they all have a similar composition.”

These families are pretty new, geologically speaking. Masiero said that families that formed in the last billion years or so make up over a third of all the objects we know about in the main asteroid belt. NEOWISE data may help scientists track the families, learn what they’re made of, and how they evolved.

The next generation

NEOWISE is funded through next summer, and while they’re hoping to get an extension, eventually the satellite’s orbit will decay and it will burn up in the atmosphere. Masiero said they’re now proposing a new mission, called NEOcam. This would be similar to NEOWISE, except the telescope would be a bit bigger, with a 50-centimeter mirror, and they would fly it out to the first Lagrangian point—L₁—where it would stay cold and work indefinitely.

NEOcam: NASA/JPL-Caltech

“If we’re selected we would fly this space telescope specifically designed to search for near-Earth asteroids in the infrared,” Masiero said. “The goal of this survey is to characterize these objects, quantify them, and help us predict what kind of hazard they could pose to the Earth.”

NEOcam could take longer exposures and thus look deeper into space and find more objects. He expects a five-year survey would find some 300,000 near-Earth objects and eight million main-belt asteroids—an increase of an order of magnitude for both.

“This would improve upon the census taken by NEOWISE, helping us characterize the hazard, but also—very interesting from a scientific point of view—figure out where these populations turn over, how many you have in each size band, and hopefully trace them back to where they come from,” Masiero said.

Citizen science

If you want to sift through the data on your own, it’s all available online. Masiero said it is all on the Infrared Science Archive (IRSA), where there are millions of images and only a few people to look at them. He said the Planetary Data System and NASA’s Horizons tool have also incorporated NEOWISE data.

Perhaps you will spot a killer asteroid or figure out how the solar system formed.