How NASA May Soon Find Hundreds of Thousands of Asteroids and Comets Heading for Earth

asteroid earth artist impression
Artist impression of an asteroid heading for Earth. iStock

Twenty one years ago, NASA set out the goal of finding 90 percent of the asteroids and comets near Earth that were bigger than 3,200 feet in diameter. This was extended seven years later to include objects over 460 feet.

As of April 2019, the space agency has found close to 20,000 of these 'Near Earth Objects' (NEOs)—of which almost 900 are above 3,200 feet. However, there are still more to find and NASA has many different surveys dedicated to detecting NEOs.

None of the NEOs currently detected pose a risk to Earth—it is the ones we are yet to find that are the problem. And the consequences of a large asteroid smashing into Earth could be catastrophic. Indeed, 66 million years ago a six mile-wide asteroid helped wiped out an estimated 75 percent of all the species on Earth—including all non-avian dinosaurs.

We were reminded of the potential danger space rocks pose in 2013, when a 66 foot meteor crashed into Chelyabinsk, Russia. It landed in a lake in a remote region, so damage was fairly minimal—but had it impacted on a town or city, the consequences could have been devastating.

At some point in the future—possibly millions of years from now—a large asteroid will end up on a collision course with Earth. Amy Mainzer is principal investigator for NASA's NEOWISE program—essentially its asteroid hunting mission. Mainzer and colleagues have found a new way to track down NEOs by using heat.

Finding NEOs is difficult because they are dark—and very far away. However, as they get closer to the Sun, they glow in certain wavelengths, specifically infrared. Mainzer and her team are proposing a new telescope called NEOCam, which uses cameras to better map asteroids and measure them.

In an interview with Newsweek, Mainzer discusses her work with NASA and how NEOCam could lead to the detection of hundreds of thousands of NEOs in the future.

What made you want to study NEOs?

I personally got interested in NEOs through my work on NASA's Wide-field Infrared Survey Explorer (WISE) mission. WISE is an all-sky survey telescope, and while its original scientific objectives were not focused on asteroids, it was clear that much could be done to learn about these objects using the data. I was excited to learn about the topic and see what could be done using WISE. With WISE, we've learned about the ratio of bright to dark NEOs, and we now know that the proportion of bright to dark objects is roughly the same over a fairly wide range of sizes. We have also learned that Earth has a so-called Trojan asteroid, 2010 TK7; this object tags along with Earth in its path around the Sun.

What are the biggest challenges in hunting asteroids?

NEOs are challenging to find because even though they can be as large as mountains, space is far vaster. In addition, we know that some of the objects are as dark as printer toner or coal. Consequently, NEOs can be intrinsically dim and hard to spot, and they are spread over a huge area of the sky, including the regions close to the Sun where it is difficult for telescopes (especially those on the ground) to search.

How did the team come up with NEOWISE and how many asteroids has it been used to find so far?

NEOWISE comprises both a set of image processing and database tools developed to search the WISE data for moving objects, and it's also the name of the restarted WISE mission. When WISE completed its prime mission in early 2011, it was placed into hibernation. However, based on its success at finding and measuring the sizes and albedos of NEOs during the prime mission, the NASA Near-Earth Objects Observations Program asked our team to restart it in 2013.

So far, NEOWISE has discovered more than 30,000 objects, including 281 NEOs. The NEOs we find tend to be fairly large and dark, representing a complementary dataset to ground-based telescopes searching in visible light. In addition, we have detected about 193,000 objects in total, allowing measurements of their sizes and other physical properties.

How would you go about devising a defense strategy if an asteroid was found to be on a collision course with Earth?

In my opinion, the two most important items to understand for purposes of planning a defense strategy are when an impact would occur, and how much impact energy it would have. The choice of strategy depends heavily on time until impact, and how much mass the object has. Thus, the first order of business in my mind is to build a survey capable of both discovering the objects well before any potential impacts could occur (ideally decades ahead) and measuring mass, which depends strongly on the objects' sizes. Knowing these parameters opens up the widest array of possible strategies, ranging from the simplest (such as nudging an object out of the way with a spacecraft) to the more complex (including tugging on it with gravitational force from a spacecraft or pushing using explosives.)

How could NEOCam help?

NEOCam is optimized for finding larger NEOs when they are still quite far away from Earth, so that impacts can be predicted well in advance. By using thermal infrared wavelengths, it is roughly equally sensitive to both bright and dark NEOs, and it can also set strong constraints on their sizes. The objective is to find, track, and characterize the NEO population in an efficient manner.

We expect the mission, if NASA goes forward with it, would find hundreds of thousands of NEOs and millions of more distant objects in the main asteroid belt. We would measure sizes for all of these objects, and in cases where we have complementary visible light data from a ground-based telescope, we could compute the surface reflectivity or albedo, which gives us information about possible composition.

How does NASA work with other space agencies to protect Earth from asteroids?

NASA works cooperatively with other space agencies through agreements that were negotiated by the United Nations Committee on the Peaceful Uses of Outer Space and supported through the U.N. Office of Outer Space Affairs. The agency participates in the International Asteroid Warning Network, which is an international group of asteroid observers and modelers who work together to search for NEOs and predict potential impacts.