DART Impact Successfully Changed the Asteroid's Orbit

The results of the DART mission impact were released in a press conference this morning and the mission met it's objectives easily.  Hat Tip to Space.com for the coverage.  

The Double Asteroid Redirection Test (DART) spacecraft slammed into a small asteroid called Dimorphos on Sept. 26. The mission was meant to test a potential planetary defense technique in case a large space rock ever threatens to collide with Earth, although NASA knows of no such threats in the foreseeable future. DART's goal was to shorten Dimorphos' orbit around a larger asteroid by at least 73 seconds, although scientists hoped the effect would be more like 10 minutes.

But the first calculations are in, and DART blew those milestones away, shortening Dimorphos' nearly 12-hour orbit by a whopping 32 minutes, NASA officials announced during a news conference on Monday (Oct. 11).

As Lori Glaze, head of NASA's planetary science division, said during the news conference; "let's all just kind of take a moment to soak this in.  For the first time ever, humanity has changed the orbit of a planetary body, of a planetary object. First time ever."  Dimorphos' orbital period dropped from 11 hours 55 minutes down to 11 hours 23 minutes.

While intercepting the orbit of the orbiting pair of asteroids isn't particularly new science or technology, there's a lot of assumptions that go into deciding what's going to happen when nobody had actually seen the two bodies until the probes arrived.  The things that can be measured from Earth are things like the brightness and the orbital period.  The makeup of the two, whether they're smaller, denser rocks or larger and less dense is inferred based on some assumptions, and those characteristics are going to greatly affect the asteroid's behavior when it gets hit.  The impact came from a probe weighing close to 800 pounds slamming into Dimorphos at 14,760 mph.  

As DART beamed photos back to Earth in the final few minutes, scientists got their first good look at Dimorphos, since from Earth, the moonlet and the larger Didymos appear as a single dot in a field of stars. Those images showed first an egg-like agglomeration of rocks, then finally a field of boulders, gravel and dust.

That alone was enough for Tom Statler, program scientist for DART, to be confident the mission had moved Dimorphos more than its goal.

"When I saw Dimorphos come into view and when I saw there was not a single crater on it and there were a lot of what appeared to be loose rocks — and this was a totally non-scientific, by-eye measurement — I looked at it and I said, 'This is not going to be 73 seconds.' And it wasn't,'' he said during the news conference.

Which leads us to the asteroid's tail mentioned last Thursday.  The tail is probably from Didymos being not a single large rock but an agglomeration of smaller rocks.  Those smaller rocks were apparently hit hard enough to escape the gravitational attraction of the system.  Nancy Chabot, coordination lead for DART at the Johns Hopkins Applied Physics Laboratory, said during the news conference that the orbital change, which represents a 4% difference from Dimorphos' previous orbit, may have been enhanced by the amount of debris in that tail. 

Last frame from DART before impacting Dimorphos.  (Image credit: NASA/JHUAPL) 

Well done to all involved.