The spacecraft is tiny. To get an idea of what it could do it's like a human being running into an oil tanker You couldn't do much to change the direction of an oil tanker by running into it if you could somehow do it.
Fires projectile at Didymoon, so it orbits Didymos a little faster. Neither can hit Earht in the future for centuries. Gives ultraprecise data by measuring how long it takess for Didymoon to orbit Didymos.
Some dust from the DART impact just might hit Earth six months later as harmless shooting stars but nothing large enough to harm anyone - like the way a club can hit a golf ball much further than a cannon ball.
Some dust from the DART impact might hit Earth 6 months later as harmless shooting stars. Bigger bits can’t get here. Like how a club can hit a golf ball further than a cannon ball.
Golf club photo from here https://www.pexels.com/photo/golf-club-beside-a-golf-ball-9366508/
Cannon ball from here File:Post-medieval cast iron cannon ball (FindID 415344).jpg - Wikimedia Commons
I write titles of sections like mini abstracts - you can get a first idea of the article by reading just the titles and looking at the graphics - then drill into any section of special interest
They measure the orbit with telescopes on Earth. If the asteroid is more or less solid then the orbit is changed a smaller amount. If it managed to excavate a crater and throw off a lot or material that works a bit like a rocket exhaust and makes a bigger difference to its orbit.
Then there's an interplanetary cubesat that will send back images tooand Hubble and James Webb and Lucy which is a spacecraft headed for the Jupiter trojan asteroids will be photographing it from a distance and may see the plume too.
It will take some time to know how well it worked. A companion that launched with DART, LICIACube, will capture images of DART’s demise from a vantage point relatively close to the asteroid.
Other spacecraft, including the Hubble Space Telescope, the James Webb Space Telescope and another recently launched mission, Lucy, will be using their instruments to monitor the collision from farther away. Telescopes on Earth will also watch for changes in the dimming of Didymos as Dimorphos crosses in front of it.
. NASA Is About to Crash Into an Asteroid. Here’s How to Watch.
Then there's a mission called HERA which will be launched in 2024 which will examine the impact crater close up to give a lot more detail about what happened.
This is about HERA Hera
https://www.nytimes.com/2022/09/25/science/nasa-dart-asteroid.htmlIf Dimorphos is solid, and DART carves only a small crater, then the change will follow the basics of a Physics 101 problem — two objects colliding and sticking together. Because DART is moving in the direction opposite to Dimorphos, it will sap some of the asteroid’s angular momentum, causing it to move closer to Didymos and speed up.
But if Dimorphos is more like a pile of rubble held together by gravity, then the impact will create a deep crater and send a shower of debris flying into space. That cascade of rock will be like the thrust of a rocket engine pushing against the asteroid. In that case, the orbit of Dimorphos (whose name is Greek for “having two forms”) will descend even closer to Didymos (that name is Greek for “twin”).
The impact will send some small particles of dust and maybe small pebbles into space from the impact. If the impact happens on the 1st October it takes thousands of years for it to reach Earth unless it is ejected with unexpectedly high ejection speeds If it happens earlier on the 1st September some of the debris will get to Earth half a year later.
A detector or camera has a collecting area of around 1000 square kilometers of the atmosphere which it’s observing. This would likely spot only one shooting star from the impact in 10 days of observing during the time of the meteor “shower”.
They also consider an “edge case” where the moon has unusual properties to the extent that this small impact breaks it apart so much that 1% of the entire moon is turned into dust and ejected.
In this case of 1% of the moon turned to dust by the impact, a shooting star camera detector would spot around one shooting star a day on average for 10 days. That is still too low a flux to be noticed as anything unusual. It’s far far less thanthe background level of 180 very faint but detectable sporadic millimeter sized shooting stars per hour.
I am not sure how many of those you can see with naked eye with good vision on a very dark night. Nowhere near 180 - this is about what you can photograph with an ultra sensitive camera.
So - it’s not likely we can detect the shooting stars but a few specks of dust from the impact might get to Earth. Especially with the earlier impact on 1st September it’s not impossible that someone sees a shooting star that actually comes from the impact - but they would never know where it came from.
[These figures are from the paper]
. On the Delivery of DART-ejected Material from Asteroid (65803) Didymos to Earth
They do say though that we need to consider this more carefully if we do many more operations like this that can break up asteroids, whether it would add to the meteor showers and possbily be a risk e.g. for big sensitive telescopes in orbit that could be damaged by micrometeorites.
It won’t do anything to Earth. The scientists do take care with experiments not to harm Earth! It’s a very small spacecraft compared to the mass of the moon, it’s about equivalent to you running into an oil tanker docked at a port. It would hardly move. If the dust is hit away at an especially high speed - then some of the dust from the impact might reach Earth half a year later and show up as shooting stars but they’d be impossible to tell apart from the many other shooting stars we see. It was possible for dust to reach Earth if the impact was 1st September, almost impossible for 1st October, now that it’s happening on 26th September, there may be a slight chance of dust.
But Earth is hit by massive amounts of dust every day. It’s just of geeky interest that it’s possible six months from now that someone might see a shooting star that came from this impact - but would likely not know it 🙂.
They had a choice of asteroids to try hitting, they wanted one with a moon so that they could detect whether the moon’s orbital period around the asteroid changed. The idea is it could help them calibrate the effect of a deflection asteroid impact. They naturally chose an asteroid that would be harmless, couldn’t be diverted into an Earth crossing orbit in any way.
The aim is to keep Earth safe. But to put this in perspective, if we’d had the capability to deflect asteroids at the time of the ancient Egyptian pyramids - we wouldn’t have needed to use it yet.
Also, if there was any risk from any asteroid this would be shared with everyone and we'd be workign together to deflect it in earnest. This isn't a deflection mission, the impactor is far too light for that. They would need half a dozen of our very heaviest spacecraft for a deflection mission.
Astronomers are completely open about asteroids, it is all done in the open, shared observations, shared predictions, very public. It is like weather forecasting. No weather forecaster would ever hide news of a hurricane - it’s their job to warn us of them. They would be out of their job the next day if they did such a stupid thing, and I am pretty sure no weather forecaster in the entire history of weather forecasting has ever hidden news of a hurricane prediction. In the same way no astronomer would ever hide news of an asteroid impact, and they can’t do it either.
With current technology, we could have deflected the Tunguska impact in 1908 or the Chelyabinsk meteorite with enough warning and if we had the technology back then (which we didn’t). But if the aim was to save lives a far easier approach is just to tell people to evacuate the impact point which we’d know exact to 100 metres 6 days before impact. Not much different from an evacuation for a hurricane.
But there have never been any asteroid warnings - they re really rare.
My non techy interface to the CNEOS sentry table for scared people. It's the same thing but with words like "no hazard" instead of the rather cryptic "0" in the "Torino scale" column etc.
. NASA Near Earth Asteroids and Comets Sentry Table - As words instead of techy numbers
NASA NEVER issued any asteroid warning. Advance notice of a few harmless fireballs - that's it. They missed the Chelyabynsk asteroid - a bit larger & they'd have spotted it. Apophis briefly got as far as "of interest to astronomers", now removed.
Why you don’t need to be scared of asteroids - far less risk than lightning or even the very rare risk of death from a giant hailstone
There has never been any NASA asteroid warning.
The smaller asteroid moon can't hit the asteroid
The smaller asteroid is orbiting the larger one, if it were to hit it then the total momentum of the asteroid + moon system would be unchanged.
But a nudge like this just changes the orbit slightly.
It doesn't spiral inwards.
What happens to a circular orbit if you nudge it is it becomes a bit more elliptical. If elliptical it can become more elliptical or circular.
It doesn't spiral. A spiral is not a solution to the equations of gravity.
If you nudge it inwards one side of its orbit the extra momentum from that nudge automatically nudges it away the opposite side of its orbit making it elliptical if it was originally circular.
Orbits don't work like that. They are stable, not unstable.
E.g if you threw a ball out of the ISS then it just goes into a slightly different elliptical orbit.
If you throw a ball towards Earth it won't hit the Earth.
It moves towards the Earth for half its orbit and away for the other half.
Astronauts have done that.
They throw satellites out of the ISS to put them into other orbits as experiments.
Because the ball has the same orbital velocity as the ISS, minus or plus a few meters per second because of throwing it but it's moving at kilometers per second in orbit around Earth.
https://www.quora.com/Can-you-de-orbit-a-tennis-ball-or-baseball-by-hand-from-the-ISS-during-EVAThat explains the physics.
And - even if you could nudge the asteroid moon so much that it hit the asteroid it would still do nothing to it.
Instead of an asteroid with a moon you'd have a slightly larger asteroid without a moon in the same orbit as before.
The centre of mass would be the same so the orbit would be unchanged except potentially small change due to the nudge.
Not possible for this asteroid but if you imagine an asteroid with a moon orbiting so close to it that a tiny nudge would deflect it to hit the asteroid it would make absolutely no change.
The mass would be the same. The orbital velocity of the asteroid + moon would be the same as the orbital velocity fo the new slightly larger asteroid. So the orbit would be the same.
The velocity around the sun that is.
Also - a general point. Scientists care about Earth. They don't do risky experiments. They check that experiments are safe. They deliberately chose this asteroid for the test because there is no risk to Earth.
They knew there was no possible risk from this experiment.
All that could happen are a few harmless shooting stars from dust thrown off from teh collision, six months later it's possible a few of the many shooting stars we get every day is a spec kof dust from this collision.
But that was far more likely if the collision happened on 1st sept.
Later in the month due to its position in the orbit it becomes far less likely.
At 1st oct it's basically impossible, need to be far more high velocity dust form the collision than expected.
But this is about tiny specks of dust. No possibility of anything large.
Only dust is small enough to get enough momentum to reach Earth.
Like if you drop a plate and it breaks, the tiny specks of dust will fly further than the larger pieces.
Or - if you hit a light golf ball with a club you can hit it a long way. If you tried to do the same with a cannon ball it would hardly budge.
If we ever need to deflect an asteroid we would need a far bigger rocket than this one one weighing many tons and likely many of them one after another. E.g. several falcon heavies devoted ot the task.
But they chose an asteroid that is no risk to Earth and can't be deflected to hit us.
In the Planetary Defense Conference Exercise - 2015 delegates practiced a scenario with a hypothetical incoming 365 meter diameter meteorite, how it would play out, with kinetic interceptor spacecraft. They continue to do these exercises every two years.
In this mission six spacecraft are launched, three from the US, and one each from Russia, China and Europe.
Several space-faring nations will launch a total of six kinetic
impactors later this month to deflect asteroid 2015 PDC
- The U.S. will launch 3 missions, using a Delta IV-H, a Falcon
Heavy, and an Atlas V 551. A larger spacecraft to be launched on
NASA’s first SLS had to scrapped because the launch vehicle
could not be completed in time- Europe, Russia and China are ready to launch one kinetic
impactor each, on Ariane 5, Proton, and Long March- The deflections will occur over a 7-day period in early March, 2020
They don’t use nukes because of strong opposition from some Security Council members.
Kinetic Impactor Mission Design
Day 4 here
. Planetary Defense Conference Exercise - 2015
We now have the much heavier Falcon Heavy and the SLS is nearly ready for launch now, and Elon Musk is working on a very heavy lift rocket which would mean we could deflect the asteroid with fewer missions or deflect a larger asteroid with the same number.
In principle we could use nukes to deflect an asteroid. However this would violate the limited test ban treaty which doesn’t have any exceptions for peaceful use.
Of course in an emergency that could be overriden with agrement of all nations - in this simulation however some nations object. They would worry about precedent.
Iin any case there is no way we can test using nukes so this would be an untested method. While we can test using kinetic impacts - I.e. just hitting it with something which is what DART does.
For more about using nukes and many other ways to deflect asteroids see my
. Methods for deflecting asteroids
There are no examples of asteroid impacts large enough to need deflection in all of human written history.
Some asteroids large enough to flatten a small city have hit Earth but only in rremote places.
The most likely scenario is an impact in a remote place like the 1908 impact in Siberia.
Nobody dies even if an asteroid hits a city in worst case scenario if we are following it as we would be able to track where it would hit to within 100 meters, 6 days in advance. We can evacuate cities in much less than 6 days, in a day or two, for a hurricane warning.
That was explored in another excercise in 2021:
Vastly improbable scenario Impact prediction 6 days before impact 100 km region to evacuate We can evacuate for a hurricane in 2 days. Not real - exercise Image from 2021 PDC Exercise Fact Sheet: Final
See my
Most likely we have to wait tens of thousands of years to the next impact on a city large enough to be worth deflecting to save the city.
Even then we could deflect it away from the city to some nearby desert / sea / doesn’t have to completely miss Earth.
It doesn’t actually make sense to set up an asteroid deflection system such as lots of ICBMs ready to fire. Because the wait time would be very long and we have the capability to do it with last minute improvisations.
What if the Egyptians had developed asteroid detection telescopes? They would still be waiting for the first city killer impact
If we did set up an asteroid defence system, some spaceships waiting to launch on a few days notice, say, then this is a likely scenario 8,000 years from now:
Still waiting for city killer asteroid 8,000 years later.
That’s based on an average of 80 years between city killer sized asteroids (20 meters, but many of those would likely only be air bursts and at most blow out some windows) - probably it’s not as often as that. Then it’s based on only 1% of Earth’s surface being urban.
Just based on the area of the Earth for each type of habitat then the next 100 Chelyabinsk or larger asteroids to hit Earth over the next 80,000 years or so would be like this
Just one of them urban or semi urban.
For the rest then we wouldn’t need to deflect - except we likely would as we wouldn’t know until a few weeks before impact where exactly it would hit.
Our deflector spaceships would most likely end up rusted and decayed long before they could be used. Like the old Buran space shuttle.
Photo from here: .Russia to modify Cold War missiles to destroy asteroids - CNNPolitics
But we might use them to deflect Chelyabinsk sized asteroids just on the remote chance of hitting a city.
See also my
Also
My earlier DART redirect article - it has some extra details. But I have also added new stuff to this one.
My article about deflecting asteroids.
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