UPDATE: Thanks for joining our Reddit AMA about DART! We're signing off, but invite you to visit http://dart.jhuapl.edu/ for more information. Stay curious!

Join experts from NASA and the Johns Hopkins University Applied Physics Lab (APL) for a Reddit ‘Ask Me Anything’ on Monday, April 22, at 11:30 a.m. EDT about NASA's Double Asteroid Redirection Test. Known as DART for short, this is the first mission to demonstrate the kinetic impactor technique, which involves slamming a spacecraft into the moon of an asteroid at high speed to change its orbit. In October 2022, DART is planned to intercept the secondary member of the Didymos system, a binary Near-Earth Asteroid system with characteristics of great interest to NASA's overall planetary defense efforts. At the time of the impact, Didymos will be 11 million kilometers away from Earth. Ask us anything about the DART mission, what we hope to achieve and how!

Participants include:

  • Elena Adams, APL DART mission systems engineer
  • Andy Rivkin, APL DART investigation co-lead
  • Tom Statler, NASA program scientist

Proof: https://twitter.com/NASASocial/status/1118880618757144576

Comments: 1410 • Responses: 48  • Date: 

ThProphet858 karma

At this point, what would you say is the largest asteroid you could deflect, and what would be the consequences if it wasn't deflected?

nasa1371 karma

The DART spacecraft will change the speed of Didymos B by a bit less than a millimeter per second. So, my question in return is how much warning time we have. If we had decades to a century of warning time, and could build as big an impactor as we want, we could move something a kilometer or two in diameter. if one of those made it through, we think it would cause civilizational collapse. With less warning time, we might need to use a nuclear device to deflect large asteroids. This is part of the impetus to find potential impactors early!


xPray4Deathx376 karma

Andy, is there not a treaty forbidding that? Or does this exclude it?

nasa1112 karma

Well, funny thing. International law does forbid doing nuclear tests in space, and a lot of us are working on DART-like mission to provide non-nuclear options. Having said that, I think we all assume that if the future of humanity were at stake that the UN Security Council would support using nukes as a deflection method (since it's not a "test" and not being used as a "weapon". But formally the jury is out (no pun intended).


killmonger-7647 karma

If an asteroid is approaching earth, can NASA directly use its defense technique and destroy it or does it have to wait for a US government order,or wait for the whole world to take a decision with agencies like the UN?

nasa963 karma

Part of NASA's job is to research and develop techniques for asteroid deflection. But not to go and DO it without direction. If we discover an asteroid with a significant chance of impacting Earth, NASA's responsibility is to inform U.S. Government leaders, who would then inform the international community if needed. -Tom

computertech379 karma

Hi - My dad is letting me use his account to submit this question. My name is Sol and I'm 13. Thank you for doing this and I have two questions:

Would this project help with asteroid mining? and with current technology, could we change the course of an asteroid the size that killed the dinosaurs?

nasa301 karma

Hi Sol!

I certainly think that some of the things we learn about Didymos can help with asteroid mining, particularly the nature of asteroid surfaces and how to guide ourselves to them. As far as the KT-impactor, if we had enough warning time we could probably deflect something that size. Happily, we are very confident we already know that nothing that size is on a collision course!


Dar2De2336 karma

Hi team! Thanks for doing this AMA. To your knowledge, what is the closest to major catastrophe have large populations been and not really known? And, what is the most boring or mundane part of your job?

nasa502 karma

To my knowledge, that'd be the Tunguska impact in 1908. If its incoming path was only slightly different, it would have hit St. Petersburg, the Russian capital. Because it hit in Siberia just before a period of European unrest, it took a while to figure out what happened.

As for number two, that'd be the telecons and nearly-endless parade of spreadsheets that come from making sure a project will be done correctly... --Andy

SaltyMarmot5819270 karma

Hey team! My question is are we looking at a big possibility in the near future (say 1000 years) to face a problem of this kind and are we ready to prevent it? Other than that thanks for your work towards saving this blue dot!

nasa442 karma

We are pretty sure we have found 90% to 95% of the NEOs of dinosaur-killing scale, and none of them is a danger in the next century. Beyond that, we have to make statistical predictions. Statistically, over 1000 years, we'd expect a handful or two of impacts of a scale that could be locally or regionally very serious. Unless we find the objects and prevent the impacts, of course. -Tom

nasa118 karma

We're doing our best. NASA is actively tracking asteroids, studying them and we're doing our first asteroid mitigation mission! -Lena

TylerSpicknell173 karma

What would you do for incredibly large meteors the size of a small country?

nasa272 karma

Small country like Monaco, or small country like Ecuador? :) --Andy

TylerSpicknell116 karma

I guess Monaco

nasa218 karma

OK, For a Monaco-sized impactor (maybe a mile or so across), we can handle it given enough warning time by ramming it with spacecraft like DART or perhaps using nuclear devices to vaporize and propel the asteroid. Not necessarily a situation we want to be in, but I think it is doable given current technology.


TylerSpicknell107 karma

Alright, but what about an Ecuador-sized one?

nasa260 karma

Luckily, there is only one asteroid that big, and it's not going anywhere. :) Otherwise, I suppose I might point you toward the movie Melancholia, which I understand might be relevant...


Sir_Pold124 karma

We read stories about huge asteroids that we don't even see until they're already super close or have already past us. Is there really any way to combat these?

nasa189 karma

Part of the reason we don't see these asteroids is that we've had limited ability to look in some directions using our ground-based telescopes. One of the ways to combat that is to put search telescopes in space, for instance a successor to the NEOWISE orbiting telescope


nasa123 karma

Yes, basically you'd want to build the right kind of telescopes that can find them. Remember that the asteroids are orbiting around the Sun, like the Earth is. So the fact that we find them as they go by (no matter how close) is a good thing, because they are going to come around again... and we want to make sure that none of those future close passes are too close. -Tom

ChaosBlaze9113 karma

Hey NASA and the JHUALP Team,

I'd like to thank you for hosting this reddit_AMA discussion.

My Questions are:

  1. How often do you suspect these planetary defense missions to be used ones they're rolled out in the future?

  2. How is the reduced budget of NASA going to play into the develeopment of the planetary defense missions?

  3. Once finished, will this be part of NASA or the recently created Space Force?

  4. What is your favorite planet? ;)

Thanks again for hosting this AMA and looking forward to hearing back from you.

nasa182 karma

Hi! I'll tackle half of your question: Number 1. In terms of how often we'd want to launch demonstration missions like DART, there are plenty of planetary defense objectives that would benefit from a mission, including a telescope to survey to see just what's out there. So, at least for a while we'd hope missions would fly as often as resources and interest allows.

Number 4. My favorite planet is Earth. No question. I'm not just saying that because it's Earth Day. :)


nasa189 karma

My favorite planet hasn't been discovered yet. -Tom

Wthermans87 karma

Alright Tom, stop being cheeky, and tell us which of the currently discovered planets you consider your favorite.

nasa204 karma

OK, OK... I never EVER get tired of giving somebody their first-ever view of Saturn through a telescope. It's a life-changing experience for so many people that I have to say Saturn is my favorite. That's not a scientific answer but it's mine. So there. -Tom

nasa160 karma

Question 2. Planetary defense is now explicitly a part of the NASA budget, where not very many years ago it wasn't. So that's an improvement! The Planetary Defense Coordination Office will carry out its mission with the resources that Congress appropriates.

Question 3. Planetary defense is definitely in the purview of NASA.


polarinc85 karma

Is there a specific type of asteroids you are really afraid of?

nasa222 karma

One whose orbit intersects Earth. :) -Lena

nasa184 karma

One whose orbit intersects Earth AND we haven't discovered yet! (But really, being afraid isn't the right response to this natural hazard. Being aware and smart is.) -Tom

drewgovans63 karma

Where was this spacecraft built and designed?

nasa84 karma

It's being built and designed at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. -Lena

Iwouldloveto697462 karma

Are other countries that have a strong foundation in space-tech (such as china, russia,etc) preparing as well to deflect asteroids from demolishing our lovely earth to smithereens?

nasa80 karma

The US works with other countries on the problem, both through the UN and otherwise. The DART team has members from around the world, and a European spacecraft called Hera may be selected (we hope so!) to visit Didymos a few years after the DART impact to do a thorough assessment of what DART did.


xp19453 karma

If you launch a mission in our lifetime, will you be singing Aerosmith songs as the rocket launches? Enquiring minds need to know.

nasa51 karma

I've been hoping for Shakira, but would settle for this one from Thomas Dolby:



djnvinn46 karma

Should we be more worried about a decent sized asteroid hitting earth or a small asteroid hitting a satellite?

nasa82 karma

It would probably depend on the exact sizes and the warning time, actually. We would try to move an asteroid threatening Earth, but we would try to move a satellite if we thought an asteroid might hit it. All in all, assuming you choose to worry about either, it'd be the asteroid hitting the Earth. For your day-to-day purposes, though, worry more about other things than either one. :)


Ilyich2343 karma

I have a few questions:

1) Does the target asteroid actually present any risk to the Earth?

2) Is the target asteroid representative in size/speed/material of what we would expect in a real scenario?

3) Is there a significant risk of asteroid impacts on Earth? How likely are they?

Thanks in advance!

nasa85 karma

  1. No it does not
  2. Yes, that's one of the reasons that we chose Didymos
  3. No known asteroid poses a significant risk of impact with Earth over the next 100 years.The highest risk of impact for a known asteroid is a 1 in 714 chance of impact by an asteroid designated 2009 FD in 2185, meaning that the possibility that it could impact then is less than 0.2 percent. The Sentry Impact Risk Table, which is maintained by the Jet Propulsion Laboratory’s Center for NEO Studies, is updated continuously as new asteroids are discovered and known asteroids are further observed. To see it, go here:https://cneos.jpl.nasa.gov/sentry/


nocfenix37 karma

In regards to movies, which was more realistic about a possible asteroid strike, Impact or Armageddon?

In regards to real life, what is the realism of dealing with an asteroid that is of the kind mentioned in aforementioned movies? Would they really destroy the planet? Could we actually do something about it?

What are the chances of a DART test impact actually redirecting the course of an asteroid into an earth impact scenario instead of preventing it?

nasa68 karma

Impact, hands down. Of course, I cannot remember the sizes of those asteroids, so hard to say. Just as an example, the dinosaur killer was 10 km. And we found >99% of the Near Earth asteroids of that size.

The chances are pretty much none. The DART mission will target a binary asteroid system called Didymos, which is comprised of a football-stadium-sized object orbiting around an object about a half mile wide. The DART spacecraft—which is the kinetic impactor—will impact the smaller moon so we can see how the moon’s orbit changes around the larger body. This will not change the path of the Didymos system with respect to Earth but rather just change the path of the smaller asteroid about the larger asteroid in the Didymos binary asteroid system. -Lena

heartypasta27 karma

Have you guys located the infinity stones yet?

nasa55 karma

Unfortunately, the project I'm working on with Dr. Jane Foster has totally ground to a halt.


aseasyas22 karma

So is the craft meant to be, for lack of a better term, a punch to the asteroid? I've always had an idea that you could spike rockets into an asteroid to thrust it off its path. Is this similar?

nasa40 karma

Yes, exactly, but a bit of a friendly punch, a fist-bump. The small moon orbits the bigger moon in 12 hours, and we're going to change it's orbit by ~8 min. Not much of a punch, but readily observable from Earth.

ShotSociety20 karma

Any chance you can allow me to try and punch an asteroid?

nasa47 karma

I'm game, but you'll need to arrange your own ride.


nasa13 karma

Right, and take pictures! -Lena

Shit___Taco19 karma

How much will the kinetic impactor actually move the asteroid at it's current location when the impact occurs? I understand you are trying to alter the trajectory of the asteroid, but what type of movement at the time of impact is required to change the trajectory? Is it millimeters, centimeters, inches, feet, ect.?

nasa49 karma

Orbits and the math involved with orbits are not intuitive compared to our everyday experience. We expect DART to change the orbit speed of Didymos B around Didymos A by a fraction of a millimeter per second. That should change the orbit period by something like 6-10 minutes, and the distance between them by something like 20-40 feet. We don't want to change the orbit speed by toooooo much at once, because we don't want to disrupt the asteroid rather than move it (like throwing a snowball that's loosely compacted).


squid50s17 karma

Can you ELI5 (explain it like I’m five), how you’re going to ram something into a moving asteroid in order to change the asteroids orbit?

nasa108 karma

Like you're 5? OK, try running as fast as you can into your big brother as he's walking down the street and see if his motion changes. Bet it works. -Tom

nasa20 karma

We’re going to aim at the asteroid and continuously take pictures of it as we are moving toward it. The pictures are fed into the spacecraft, and the onboard computer will make small rockets on the spacecraft change our direction. Slamming into something at high speeds makes it change its orbit. -Lena

asoue016 karma

Does NASA communicate with other countries if an asteroid is on course to hit Earth?

nasa36 karma

Yep, there's definitely communication. The asteroid 2008 TC3, which was about 4 meters in size, was discovered about 48 hours prior prior to its impact, and the Sudanese/Egyptian governments were informed. It mostly burned up in the atmosphere, and an expedition went to pick up the pieces afterward.



yes_its_him15 karma

Can we assume that you are successful, since there haven't been any (big) asteroids striking earth lately?

I assume the whole dinosaur extinction event was before you got involved.

nasa15 karma

Nah, we let that happen. Just kidding.

We have been very lucky so far in that the asteroids that have hit Earth that have been large enough to do extensive damage have either hit in remote areas or not when humans were around. However, we take this threat very seriously... -Lena

Jack_Attacc13 karma

Hi team!

What do you do all day?

nasa63 karma

Sit in meetings, reply to emails, build spacecraft, review thousands of documents, and ... oh wait, save Earth. :) -Lena

smallchunkofstardust12 karma

When do you expect to deflect your first asteroid?

nasa21 karma

Late September, early October 2022!!! Woo-hoo! -Lena

fugensnot12 karma

What are the consequences of deflecting a large astroid? Would chunks of it bounce off and create some cosmic chain reaction that would destroy Jupiter's rings or Mercury's version of the dinosaurs? Or would they just burn up in the atmosphere and Australia would have a lovely light show?

Thoughts on the movie Armageddon?

nasa17 karma

Well, can't answer for all of the asteroids, but for DART Didymoon, we don't expect the dust created by the impact to come back to Earth. As for Armageddon, a fun movie, but they did have grass growing on the asteroid... -Lena

Yoda877811 karma

How do you test the technology and techniques you develop?

nasa13 karma

For DART, we do a lot of simulations on the ground using hardware that we will be flying on the spacecraft. To test the targeting of the asteroid, we will run those algorithms in flight, practicing on the moons of Jupiter and possibly another binary asteroid system.

Do you all have suggestions?


mattybigs11 karma

How often does NASA actually have to intervene and deflect asteroids from impact?

nasa20 karma

Never been done yet. -Tom

McJumbos7 karma

I just had to ask - do you guys enjoy playing the game asteroids? And who is the best?

nasa17 karma

I've been an Asteroids player from back in the day. I was much better at Centipede, Joust, and Tempest (particularly Joust), but I'm confident I could beat Lena and Tom if we had an Asteroids tournament. ⊗


Beatle48707 karma

How long will it take for the spacecraft to get to the asteroid on the first test launch?

nasa13 karma

If we launch on the first day of our primary trajectory, 14 months. -Lena

safariG7 karma

Is there a threshold of risk (in terms of damage, cost to living beings, etc) for when you all would consider an intervention necessary?

nasa9 karma

This may be seen as a cop-out, but that's in the purview of the policy folks. It also changes depending on the information we have. A decade ago, we didn't know the orbits of all of the 1-km objects, which would cause global devastation. Now we are confident we know where those are, and most of the remaining risk is in objects between 140-1000 m in size. That's where the discovery push is today.


CryptoMonkey33437 karma

What if a 200km asteroid was hurtling towards Australia, Sydney and you recieved an unlimited budget to stop it, with 1 months notice... how/could you stop?

nasa46 karma

200 km and 1 month? Under those conditions I'd throw the biggest party I could conceive of with my unlimited budget.

Doesn't matter where that would hit, it'd be bad for everyone. :(


Theone231316 karma

How often do high speed asteroids approach the Earth?

nasa8 karma

You can get this information at the Center for NEO Studies website: https://cneos.jpl.nasa.gov/ca/intro.html -Tom

DrunkWino5 karma

How often do you folk crank up some Aerosmith in the lab?

nasa8 karma

As I said elsewhere, I'm more a Shakira guy TBH. --Andy

send_me_dog_pictures4 karma

Hi DART team (psst hi Andy)

How do the current Hayabusa and OSIRIS-REx missions inform the DART mission?

How much ejecta do you expect to form from the DART impactor, or of what size/frequency distribution?

nasa7 karma


Great question. We only get one shot on DART, so it's important to understand what the range of possible asteroid properties is. We think Didymos A is the same kind of shape as Bennu and Ryugu, and the rockiness of their surfaces is making us consider how that might affect the momentum transfer between spacecraft and target.

I don't know the ejecta amount, exactly, but I believe we expect the DART impact to make a crater about 10 meters in diameter...


bhind452 karma

Is there any likelihood or fear that you might somehow unintentionally "deflect" an asteroid at Earth?

nasa3 karma

No, we have studied that extensively. We are just changing the path of the moon, it's going to continue orbiting the larger asteroid. -Lena

JaysonBlaze0 karma

Have you thought about getting bruce Willis and a specialised team to help?

For real though how worried should people be about things hurting the earth?

nasa5 karma

Bruce is an actor so he's not really going to be much help. But really, "worried" isn't the word. "Aware" is better. For instance, the probability that sometime during your life there is an asteroid impact large enough to indirectly affect most people's lives is likely to be higher than the probability that sometime in your life you'll be in a plane crash. Speaking for myself, I don't want either one to happen. So doing what we can to prevent these bad events is a good idea. -Tom

AstroManishKr0 karma

Thanks for doing this AMA!

When will the next asteroid hit Earth?

nasa3 karma

We get hit by something chair-size a few times a year. Every time you see a "shooting star", it's a grain of sand coming through the atmosphere. So, depending on the size you're concerned with, it could be very soon. :)