Thursday, October 6, 2022

DART Mission Follow Up - The Asteroid Has a Tail

While lots of folks have covered the impact of NASA's Dual Asteroid Redirection Test probe with Dimorphos - the "moon" of asteroid Didymos - something showed up in the last couple of days that I haven't seen a tenth of that press about.  

The impact generated a comet-like tail of debris from Dimorphos that is huge.  The 525 foot wide Didymos has generated a tail that has been estimated to be 6,200 miles (10,000 kilometers) long by using the angular spread of the tail (from an instrument on the telescope) and the distance of the orbiting pair of asteroids from Earth.  This photo of the tail was taken two days after the impact and published at that link on October 3. 

The tail is sweeping to the upper right of this photo.  Photo credit to the 4.1 meter aperture Southern Astrophysical Research (SOAR) Telescope, at the National Science Foundation's (NSF’s) NOIRLab's Cerro Tololo Inter-American Observatory in Chile. Photo by astronomers Teddy Kareta (Lowell Observatory) and Matthew Knight (US Naval Academy).

The photograph is the start of lots of followup measurements to come - both with the SOAR and other instruments elsewhere. 

These observations will allow scientists to gain knowledge about the nature of the surface of Dimorphos, how much material was ejected by the collision, how fast it was ejected, and the distribution of particle sizes in the expanding dust cloud — for example, whether the impact caused the moonlet to throw off big chunks of material or mostly fine dust. Analyzing this information will help scientists protect Earth and its inhabitants by better understanding the amount and nature of the ejecta resulting from an impact, and how that might modify an asteroid’s orbit.

SOAR will continue to observe the aftermath of the DART impact, collecting data that will help researchers assess how successful this attempt to modify the orbit of an asteroid has been. SOAR is a key member of the Astronomical Event Observatory Network (AEON) of telescopes, which is dedicated to nimbly following up on reports of new astronomical phenomena.  Other instruments around the world will be observing as well. 



  1. Well, every astronomer expected a debris cloud, but after we saw the just-before-impact series of photographs, it looked like a conglomeration of rocks. Just like that asteroid that we sent a probe to so we could collect samples - can't remember the mission name, too lazy to look it up.

    Oh, yeah - OSIRIS-REx

  2. Space being space and all, the central question will be "Did we move its orbit, or did we just change its mass so much that orbital physics took over and did the heavy lifting? And if it's the latter, what's the point if none of that translates to more imminent threats?"

    1. This being space and "free body physics", remember if a body is on some trajectory and explodes, the center of gravity keeps going on the same trajectory. That seems to say the only effect the tail could have would be to change the location of the the target's (Dimorphos') center of gravity, probably not much, if some of the mass got re-centered on the parent body (Didymos). I don't know if it's possible some mass could have done that but my gut feeling is yeah it could, because reaching escape velocity isn't a big obstacle with a body the size of the target (525 feet wide).

      I think that might change the results from those expected, but that's where I run out of ideas. The mass of the system ought to remain the same but the distribution being different isn't something I feel I can solve in my head.