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Tuesday, October 11, 2022

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. 

 


14 comments:

  1. Okay, now I get it. Increase the spin rate and center of mass. Like a curve ball in vacuum. Still think it should have been 'Twin Asteroid Redirection Test' so that the ABC and BBC could run with the line 'NASA hits up TART', but that's just my juvenile sense of humo(u)r.

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    1. ... that's just my juvenile sense of humo(u)r Maybe so, but it gave me a real, "why didn't I think of that?" moment. From now on, I'm going to call it TART.

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    2. Go all-out: Fluffy Asteroid Redirection Test.

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  2. Gee, sounds like everything I said about intercepting an asteroid. Distances, unknown composition yada yada.

    And we (the USA and NASA) did it. WHOOOO!!!!!

    Excellent synopsis of what happened. That would have been fun to be in the control room.

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    1. It's hard to imagine how weak the gravity is on Dimorphos. It's like a 500 foot wide dust bunny, except not household dust. It's dust, gravel and some bigger chunks. It's amazing it holds together well enough, but nothing messes with it. Pluto is 1500 miles diameter and has 1/12 the gravity of Earth, such that a 100 pound weight is 8 pounds on Pluto (just looked it up) What would that weigh on Dimorphos?

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    2. And to hit and actually move and/or break up the dust bunny. How do you target fluff? Crazy.

      As to how Dimorphos holds together, well, hmmmm... gravity is weak, wonder if it's due to static charging from solar radiation. Like, well, dust bunnies and dryer lint (until said bunny or lint becomes loose felt, that is.)

      The universe is a seriously weird and wacky place. Gravity waves surrounding our solar system, rafts of galactic junk floating in 'empty space,' said above electric charging due to solar or non-solar radiation, water everywhere... Can't wait to see what's next, and what's after that.

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    3. Well said. You may know of Ben Davidson, YouTube channel Suspicious 0bservers (note the zero). Ben is kind of the "poster child" promoter of catastrophism and the role of electric fields in the universe. Catastrophes come in 30,000 or 12,000 year cycles and the next one is coming soon!!

      The strongest argument for electric fields doing things on an astronomical scale is that the gravitational constant is 20 orders of magnitude weaker than the electric field.

      I "grew up" with the standard model that over "millions and millions" of years, those little dust bunnies were attracted to each other and grew, eventually becoming something like Dimorphos or Bennu that is loosely aggregated but not enough to fuse the rock pieces. Add in some electric charge from the solar wind or CMEs, though, and it could happen much faster.

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  3. Reminds me of the Ranger 7 mission where it was transmitting back it's last frame before impact. Nobody had ever seen the Moon up that close, and the scientists were marveling at their luck. https://en.wikipedia.org/wiki/Ranger_7

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    1. When I first read this, I nodded, thinking I remember watching the impact on TV. Then I started wondering if that's a real memory or if I'm thinking of another mission. Regardless, I saw the pictures and they were a highlight of my life.

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  4. Saw the photographs in National Geographic when I was a kid, always fascinated me.

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  5. Wonders never cease.

    Lemmee get this straight. A loose aggregation flying in formation (you know, like a helicopter) all orbiting around a larger body. The gravity of the heli, er, the wee bit is strong enough for the bits to remain together all the while the gravity of the larger bit is strong enough to hold it in orbit but not strong enough to decay its orbit.

    Wait, there's more. The humans shot a rocket with enough lead that months later it hit dead center a thing they couldn't even see.

    You know what this means, doncha? The flat earthers and fake landers are gonna go right out of their heads. In that case, I say well done NASA. And a hearty handshake.

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    1. Igor, I am not sure how my comment ended up as a reply to you; it was intended to be in 'the open'.

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  6. IOW, they sent a known-value warhead into something of unknown mass and cohesiveness, and it turns out it was 32x less massive, and nowhere near as cohesive as they assumed, as evidenced by leaving untold quantities of itself floating through the cosmos in trail.

    Knowledge was indeed advanced, but not exactly the way they were expecting.

    This should come in handy if we're ever threatened by the intergalactic Stay-Puft Marshmallow man, right?

    "Dust bunnies" indeed.

    Neither DART nor TART is apropos.
    I nominate instead the nemesis of all dust bunnies, "BROOM":
    Big Rocket Overwhelms Orbital Marshmallow.

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