First mission for close-up study of binary asteroids gets NASA go-ahead

NASA has given the University of Colorado Boulder and Lockheed Martin the green light for the Janus mission, which will see a pair of small satellites launched in 2022 to study two pairs of binary asteroids. About the size of carry-on luggage and weighing about 80 lb (36 kg) each, the twin spacecraft are tasked with returning the first high-resolution images of such unusual objects.

We're used to the idea of a planet being orbited by one or more moons, but it wasn't until 1993 when the Galileo deep space probe flew by the asteroid 243 Ida that it was shown that even asteroids can rotate around one another in pairs called binary asteroids.

Today, there are a number of known binary or even trinary asteroids, with one binary pair being the focus of an asteroid redirect mission designed to find ways to protect the Earth from catastrophic impacts, but very little is understood about the nature of binary asteroids or how they formed. Part of the problem is the lack of proper imaging and data collection.

"Binary asteroids are one class of objects for which we don't have high-resolution scientific data," says Daniel Scheeres, the principal investigator for Janus and a professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at CU Boulder. "Everything we have on them is based on ground observations, which don't give you as much detail as being up close."

Named after the two-faced Roman god of beginnings, gates, transitions, doorways, passages, and endings, the Janus mission was given the go-ahead by NASA on September 3, 2020, after a project review as part of the agency's SIMPLEx program. The mission consists of two identical spacecraft that are smaller than most interplanetary probes, reflecting the latest technological advances that allow for smaller and more nimble craft.

After launch the Janus probes will be set on different trajectories to rendezvous with the two binary asteroid systems 1996 FG3 and 1991 VH, which have different orbital patterns from one another that are hard to predict. The probes will make an orbit around the Sun and then do a flyby of the Earth to place them into sling-shot orbits to rendezvous and match trajectories with their targets out beyond the orbit of Mars.

"Once we see them up close up, there will be a lot of questions we can answer, but these will raise new questions as well," says Scheeres. "We think Janus will motivate additional missions to binary asteroids."

Source: Lockheed Martin