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[Table] Asteroid Day AMA – We’re engineers and scientists working on a mission that could, one day, help save humankind from asteroid extinction. Ask us anything!

Source
There are several people answering: Paolo Martino is PM, Marco Micheli is MM, Heli Greus is HG, Detlef Koschny is DVK, and Aidan Cowley is AC.
Questions Answers
Can we really detect any asteroids in space with accuracy and do we have any real means of destroying it? Yes, we can detect new asteroids when they are still in space. Every night dozens of new asteroids are found, including a few that can come close to the Earth.
Regarding the second part of the question, the goal would be to deflect them more than destroy them, and it is technologically possible. The Hera/DART mission currently being developed by ESA and NASA will demonstrate exactly this capability.
MM
I always wanted to ask: what is worse for life on Earth - to be hit by a single coalesced asteroid chunk, or to be hit by a multiple smaller pieces of exploded asteroid, aka disrupted rubble pile scenario? DVK: This is difficult to answer. If the rubble is small (centimetres to meters) it is better to have lots of small ones – they’d create nice bright meteors. If the rubble pieces are tens of meters it doesn’t help.
Let’s say that hypothetically, an asteroid the size of Rhode Island is coming at us, it will be a direct hit - you’ve had the resources and funding you need, your plan is fully in place, everything you’ve wanted you got. The asteroid will hit in 10 years, what do you do? DVK: I had to look up how big Rhode Island is – a bit larger than the German Bundesland ‘Saarland’. Ok – this would correspond to an object about 60 km in diameter, right? That’s quite big – we would need a lot of rocket launches, this would be extremely difficult. I would pray. The good news is that we are quite convinced that we know all objects larger than just a few kilometers which come close to our planet. None of them is on a collision course, so we are safe.
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Why are you quite convinced that you know all object of that size? And what is your approach in finding new celestial bodies? DVK: There was a scientific study done over a few years (published in Icarus 2018, search for Granvik) where they modelled how many objects there are out there. They compared this to the observations we have with the telescopic surveys. This gives us the expected numbers shown here on our infographic: https://www.esa.int/ESA_Multimedia/Images/2018/06/Asteroid_danger_explained
There are additional studies to estimate the ‘completeness’ – and we think that we know everything above roughly a few km in size.
To find new objects, we use survey telescopes that scan the night sky every night. The two major ones are Catalina and Pan-STARRS, funded by NASA. ESA is developing the so-called Flyeye telescope to add to this effort https://www.esa.int/ESA_Multimedia/Images/2017/02/Flyeye_telescope.
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Thanks for the answer, that's really interesting! It's also funny that the fist Flyeye deployed is in Sicily, at less than 100km from me, I really had no idea DVK: Indeed, that's cool. Maybe you can go and visit it one day.
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What about Interstellar objects however, like Oumuamua? DVK: The two that we have seen - 'Oumuamua and comet Borisov - were much smaller than the Saarland (or Rhode Island ;-) - not sure about Borisov, but 'Oumuamua was a few hundred meters in size. So while they could indeed come as a complete surprise, they are so rare that I wouldn't worry.
Would the public be informed if an impending asteroid event were to happen? And, how would the extinction play out? Bunch of people crushed to death, knocked off our orbit, dust clouds forever? DVK: We do not keep things secret – all our info is at the web page http://neo.ssa.esa.int. The ‘risky’ objects are in the ‘risk page’. We also put info on really close approaches there. It would also be very difficult to keep things ‘under cover’ – there are many high-quality amateur astronomers out there that would notice.
In 2029 asteroid Apophis will fly really close to Earth, even closer than geostationary satellites. Can we use some of those satellites to observe the asteroid? Is it possible to launch very cheap cube sats to flyby Apophis in 2029? DVK: Yes an Apophis mission during the flyby in 2029 would be really nice. We even had a special session on that topic at the last Planetary Defense Conference in 2019, and indeed CubeSats were mentioned. This would be a nice university project – get me a close-up of the asteroid with the Earth in the background!
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So you’re saying it was discussed and shelved? In the conference we just presented ideas. To make them happen needs funding - in the case of ESA the support of our member countries. But having something presented at a conference is the first step. One of the results of the conference was a statement to space agencies to consider embarking on such a mission. See here: https://www.cosmos.esa.int/documents/336356/336472/PDC_2019_Summary_Report_FINAL_FINAL.pdf/341b9451-0ce8-f338-5d68-714a0aada29b?t=1569333739470
Go to the section 'resolutions'. This is now a statement that scientists can use to present to their funding agencies, demonstrating that it's not just their own idea.
Thanks for doing this AMA! Did we know the Chelyabinsk meteor in 2013 (the one which had some great videos on social media) was coming? Ig not, how comes? Also, as a little side one, have there been any fatalities from impact events in the past 20 years? Unfortunately, the Chelyabinsk object was not seen in advance, because it came from the direction of the Sun where ground-based telescopes cannot look.
No known fatalities from impacts have happened in the past 20 years, although the Chelyabinsk event did cause many injuries, fortunately mostly minor.
MM
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How often do impacts from that direction happen, compared to impacts from visible trajectories? In terms of fraction of the sky, the area that cannot be easily scanned from the ground is roughly a circle with a radius of 40°-50° around the current position of the Sun, corresponding to ~15% of the total sky. However, there is a slight enhancement of objects coming from that direction, therefore the fraction of objects that may be missed when heading towards us is a bit higher.
However, this applies only when detecting an asteroid in its "final plunge" towards the Earth. Larger asteroids can be spotted many orbits earlier, when they are farther away and visible in the night side of the sky. Their orbits can then be determined and their possible impacts predicted even years or decades in advance.
MM
There must be a trade-off when targeting asteroids as they get closer to Earth, is there a rule of thumb at what the best time is to reach them, in terms of launch time versus time to reach the asteroid and then distance from Earth? DVK: Take e.g. a ‘kinetic impactor’ mission, like what DART and Hera are testing. Since we only change the velocity of the asteroid slightly, we need to hit the object early enough so that the object has time to move away from it’s collision course. Finding out when it is possible to launch requires simulations done by our mission analysis team. They take the strength of the launcher into account, also the available fuel for course corrections, and other things. Normally each asteroid has its own best scenario.
Do you also look at protecting the moon from asteroids? Would an impact of a large enough scale potentially have major impacts on the earth? DVK: There are programmes that monitor the Moon and look for flashes from impacting small asteroids (or meteoroids) - https://neliota.astro.noa.g or the Spanish MIDAS project. We use the data to improve our knowledge about these objects. These programmes just look at what is happening now.
For now we would not do anything if we predicted a lunar impact. I guess this will change once we have a lunar base in place.
Why aren't there an international organisation comprised of countries focused on the asteroid defence? Imagine like the organisation with multi-billion $ budget and program of action on funding new telescopes, asteroid exploration mission, plans for detection of potentially dangerous NEA, protocols on action after the detection - all international, with heads of states discussing these problems? DVK: There are international entities in place, mandated by the UN: The International Asteroid Warning Network (http://www.iawn.net) and the Space Mission Planning Advisory Group (http://www.smpag.net). These groups advise the United Nations. That is exactly where we come up with plans and protocols on action. But: They don’t have budget – that needs to come from elsewhere. I am expecting that if we have a real threat, we would get the budget. Right now, we don’t have a multi-billion budget.
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There is no actual risk of any sizable asteroids hitting earth in the foreseeable future. Any preparation for it would just be a waste of money. DVK: Indeed, as mentioned earlier, we do not expect a large object to hit is in the near future. We are mainly worried about those in the size range of 20 m to 40 m, which happen on average every few tens of years to hundreds of years. And where we only know a percent of them or even less.
President Obama wanted to send a crewed spacecraft to an asteroid - in your opinion is this something that should still be done in the future, would there be any usefulness in having a human being walk/float on an asteroid's surface? DVK: It would definitely be cool. I would maybe even volunteer to go. Our current missions to asteroids are all robotic, the main reason is that it is much cheaper (but still expensive) to get the same science. But humans will expand further into space, I am sure. If we want to test human exploration activities, doing this at an asteroid would be easier than landing on a planet.
this is another reply Yes, but I am slightly biased by the fact that I work at the European astronaut centre ;) There exist many similarities to what we currently do for EVA (extra vehicular activities) operations on the International Space Station versus how we would 'float' around an asteroid. Slightly biased again, but using such a mission to test exploration technologies would definitely still have value. Thanks Obama! - AC
I've heard that some asteroids contains large amounts of iron. Is there a possibility that we might have "space mines" in the far away future, if our own supply if iron runs out? Yes, this is a topic in the field known as space mining, part of what we call Space Resources. In fact, learning how we can process material we might find on asteroids or other planetary bodies is increasingly important, as it opens up the opportunities for sustainable exploration and commercialization. Its a technology we need to master, and asteroids can be a great target for testing how we can create space mines :) - AC
By how much is DART expected to deflect Didymos? Do we have any indication of the largest size of an asteroid we could potentially deflect? PM: Didymos is a binary asteroid, consisting of a main asteroid Didymos A (~700m) and a smaller asteroid Didymos B (~150m) orbiting around A with a ~12 hours period. DART is expected to impact Didymos B and change its orbital period w.r.t. Didymos A of ~1%. (8 mins)
The size of Didymos B is the most representative of a potential threat to Earth (the highest combination of probability and consequence of impacts), meaning smaller asteroids hit the Earth more often but have less severe consequences, larger asteroids can have catastrophic consequences but their probability of hitting the earth is very very low.
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Why is there less probability of larger asteroids hitting earth? DVK: There are less large objects out there. The smaller they are, the more there are.
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Is there any chance that your experiment will backfire and send the asteroid towards earth? PM: Not at all, or we would not do that :) Actually Dimorphos (the Didymos "moon") will not even leave its orbit around Didymos. It will just slightly change its speed.
I'm sure you've been asked this many times but how realistic is the plot of Armageddon? How likely is it that our fate as a species will rely on (either) Bruce Willis / deep sea oil drillers? Taking into consideration that Bruce Willis is now 65 and by the time HERA is launched he will be 69, I do not think that we can rely on him this time (although I liked the movie).
HERA will investigate what method we could use to deflect asteroid and maybe the results will show that we indeed need to call the deep sea oil drillers.
HG
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So then would it be easier to train oil drillers to become astronauts, or to train astronauts to be oil drillers? I do not know which one would be easier since I have no training/experience of deep see oil drilling nor becoming an astronaut, but as long as the ones that would go to asteroid have the sufficient skills and training (even Bruce Willis), I would be happy.
HG
If budget was no object, which asteroid would you most like to send a mission to? Nice question! For me, I'd be looking at an asteroid we know something about, since I would be interested in using it for testing how we could extract resources from it. So for me, I would choose Itokawa (https://en.wikipedia.org/wiki/25143_Itokawa), which was visited by Hayabusa spacecraft. So we already have some solid prospecting carried out for this 'roid! - AC
this is another reply Not sure if it counts as an asteroid, but Detlef and myself would probably choose ʻOumuamua, the first discovered interstellar object.
MM
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Do we even have the capability to catch up to something like that screaming through our solar system? That thing has to have a heck of a velocity to just barrel almost straight through like that. DVK: Correct, that would be a real challenge. We are preparing for a mission called 'Comet Interceptor' that is meant to fly to an interstellar object or at least a fresh comet - but it will not catch up with it, it will only perform a short flyby.
https://www.esa.int/Science_Exploration/Space_Science/ESA_s_new_mission_to_intercept_a_comet
After proving to be able to land on one, could an asteroid serve as a viable means to transport goods and or humans throughout the solar system when the orbit of said asteroid proves beneficial. While it is probably quite problematic to land the payload, it could save fuel or am I mistaken? Neat idea! Wonder if anyone has done the maths on the amount of fuel you would need/save vs certain targets. - AC
PM: To further complement, the saving is quite marginal indeed because in order to land (softly) on the asteroid you actually need to get into the very same orbit of that asteroid . At that point your orbit remains the same whether you are on the asteroid or not..
can the current anti-ballistic missiles systems intercept a terminal phase earth strike asteroid? or it is better to know beforehand and launch an impacting vehicle into space? DVK: While I do see presentations on nuclear explosions to deflect asteroids at our professional meetings, I have not seen anybody yet studying how we could use existing missile systems. So it's hard to judge whether existing missiles would do the job. But in general, it is better to know as early as possible about a possible impact and deflect it as early as possible. This will minimize the needed effort.
How much are we prepared against asteroid impacts at this moment? DVK: 42… :-) Seriously – I am not sure how to quantify ‘preparedness’. We have international working groups in place, mentioned earlier (search for IAWN, SMPAG). We have a Planetary Defence Office at ESA, a Planetary Defense Office at NASA (who spots the difference?), search the sky for asteroids, build space missions… Still we could be doing more. More telescopes to find the object, a space-based telescope to discover those that come from the direction of the Sun. Different test missions would be useful, … So there is always more we could do.
Have you got any data on the NEO coverage? Is there estimations on the percentage of NEOs we have detected and are tracking? How can we improve the coverage? How many times have asteroids been able to enter earths atmosphere without being detected beforehand? Here’s our recently updated infographics with the fraction of undiscovered NEOs for each size range: https://www.esa.int/ESA_Multimedia/Images/2018/06/Asteroid_danger_explained
As expected, we are now nearly complete for the large ones, while many of the smaller ones are still unknown.
In order to improve coverage, we need both to continue the current approach, centered on ground-based telescopes, and probably also launch dedicated telescopes to space, to look at the fraction of the sky that cannot be easily observed from the ground (e.g., towards the Sun).
Regarding the last part of your question, small asteroids enter the Earth atmosphere very often (the infographics above gives you some numbers), while larger ones are much rarer.
In the recent past, the largest one to enter our atmosphere was about 20 meters in diameter, and it caused the Chelyabinsk event in 2013. It could not be detected in advance because it came from the direction of the Sun.
We have however detected a few small ones before impact. The first happened in 2008, when a ~4-meter asteroid was found to be on a collision course less than a day before impact, it was predicted to fall in Northern Sudan, and then actually observed falling precisely where (and when) expected.
MM
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DVK: And to add what MM said - Check out http://neo.ssa.esa.int. There is a ‘discovery statistics’ section which provides some of the info you asked about. NASA is providing similar information here https://cneos.jpl.nasa.gov/stats/. To see the sky which is currently covered by the survey telescopes, you need to service of the Minor Planet Center which we all work together with: http://www.minorplanetcenter.org, ‘observers’, ‘sky coverage’. That is a tool we use to plan where we look with our telescopes, so it is a more technical page.
Are there any automatic systems for checking large numbers of asteroids orbits, to see if the asteroid's orbit is coming dangerously close to Earth, or is it done by people individually for every asteroid? I ask it because LSST Rubin is coming online soon and you know it will discover a lot of new asteroids. Yes, such systems exist, and monitor all known and newly discovered asteroids in order to predict possible future impacts.
The end result of the process is what we call "risk list": http://neo.ssa.esa.int/risk-page
It is automatically updated every day once new observational data is processed.
MM
What are your favourite sci-fi series? DVK: My favorites are ‘The Expanse’, I also liked watching ‘Salvation’. For the first one I even got my family to give me a new subscription to a known internet streaming service so that I can see the latest episodes. I also loved ‘The Jetsons’ and ‘The Flintstones’ as a kid. Not sure the last one counts as sci-fi though. My long-time favorite was ‘Dark Star’.
this is another reply Big fan of The Expanse at the moment. Nice, hard sci-fi that has a good impression of being grounded in reality - AC
this is another reply When I was a kid I liked The Jetsons, when growing up Star Trek, Star wars and I also used to watch with my sister the 'V'.
HG
When determining the potential threat of a NEA, is the mass of an object a bigger factor or size? I'm asking because I'm curious if a small but massive object (say, with the density of Psyche) could survive atmospheric entry better than a comparatively larger but less massive object. The mass is indeed what really matters, since it’s directly related with the impact energy.
And as you said composition also matters, a metal object would survive atmospheric entry better, not just because it’s heavier, but also because of its internal strength.
MM
What are your thoughts on asteroid mining as portrayed in sci-fi movies? Is it feasible? If so would governments or private space programs be the first to do so?What type of minerals can be found on asteroids that would merit the costs of extraction? Certainly there is valuable stuff you can find on asteroids. For example, the likely easiest material you can harvest from an asteroid would be volatiles such as H2O. Then you have industrial metals, things like Iron, Nickel, and Platinum group metals. Going further, you can break apart many of the oxide minerals you would find to get oxygen (getting you closer to producing rocket fuel in-situ!). Its feasible, but still needs alot of testing both here on Earth and eventually needs to be tested on a target. It may be that governments, via agencies like ESA or NASA, may do it first, to prove the principles somewhat, but I know many commercial entities are also aggresively working towards space mining. To show you that its definitely possible, I'd like to plug the work of colleagues who have processed lunar regolith (which is similar to what you may find on asteroids) to extract both oxygen and metals. Check it out here: http://www.esa.int/ESA_Multimedia/Images/2019/10/Oxygen_and_metal_from_lunar_regolith
AC
Will 2020's climax be a really big rock? DVK: Let's hope not...
Considering NASA, ESA, IAU etc. is working hard to track Earth-grazing asteroids, how come the Chelyabinsk object that airburst over Russia in 2013 came as a total surprise? The Chelyabinsk object came from the direction of the Sun, where unfortunately ground-based telescopes cannot look at. Therefore, it would not have been possible to discover it in advance with current telescopes. Dedicated space telescopes are needed to detect objects coming from this direction in advance.
MM
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Is this to say that it was within specific solid angles for the entire time that we could have observed it given its size and speed? Yes, precisely that. We got unlucky in this case.
MM
Have any of you read Lucifer's Hammer by Larry Niven? In your opinion, how realistic is his depiction of an asteroid strike on Earth? DVK: I have – but really long ago, so I don’t remember the details. But I do remember that I really liked the book, and I remember I always wanted to have a Hot Fudge Sundae when reading it.
I was thinking about the asteroid threat as a teen and came up with this ideas (Hint: they are not equally serious, the level of craziness goes up real quick). Could you please comment on their feasibility? 1. Attaching a rocket engine to an asteroid to make it gradually change trajectory, do that long in advance and it will miss Earth by thousands of km 2. Transporting acid onto asteroid (which are mainly metal), attaching a dome-shaped reaction chamber to it, using heat and pressure to then carry out the chemical reaction to disintegrate asteroids 3. This one is even more terrible than a previous one and totally Dan Brown inspired — transporting antimatter on asteroid, impacting and causing annihilation. Thank you for this AMA and your time! DVK: Well the first one is not so crazy, I have seen it presented... the difficulty is that all asteroids are rotating in one way or another. So if you continuously fire the engine it would not really help. You'd need to switch the engine on and off. Very complex. And landing on an asteroid is challenging too. Just using the 'kinetic impactor' which we will test with DART/Hera (described elsewhere in this chat) is simpler. Another seriously proposed concept is to put a spacecraft next to an asteroid and use an ion engine (like we have on our Mercury mission BepiColombo) to 'push' the asteroid away.
As for 2 and 3 I think I will not live to see that happening ;-)
What is the process to determine the orbit of a newly discovered asteroid? The process is mathematically quite complex, but here's a short summary.
Everything starts with observations, in particular with measurements of the position of an asteroid in the sky, what we call "astrometry". Discovery telescopes extract this information from their discovery images, and make it available to everybody.
These datapoints are then used to calculate possible trajectories ("orbits") that pass through them. At first, with very few points, many orbits will be possible.
Using these orbits we can extrapolate where the asteroid will be located during the following nights, use a telescope to observe that part of the sky, and locate the object again.
From these new observations we can extract new "astrometry", add it to