We are experts of the European Space Agency ESA working on Near Earth Objects such as asteroids, their detection and deflection and the respective activities like ESA’s proposed Asteroid Impact Mission (AIM) – ask us anything!

Happy Asteroid Day! 1. How often do the trajectories of Near Earth Objects line up in a collision course with Earth? If I were to take a wild guess, somewhere around once every 4-5years? xD

1. What's the most elegant solution we, as humans, have come up to deal with asteroids coming our way?

2. Probably off-topic, but does the ESA host educational visits for overseas students? Perhaps as part of outreach programmes, similar how CERN does it.

Thank you! :)

(SB) ESA's Advanced Concepts Team, an Agency thinktank, has looked into various alternatives to the standard 'kinetic impact' method that ESA's AIM and NASA's DART missions will (if approved) test out in 2022. For instance, to tether an asteroid with an electric thruster to 'spin it up' until it crumbles due to centrifugal force - http://www.esa.int/gsp/ACT/mad/projects/AsteroidsAndNEOs/centrifugalfragmentation.html Or simply shining reflected sunlight on an incoming asteroid using mirrored mini-satellites to divert its path - http://www.esa.int/gsp/ACT/doc/ARI/ARI%20Study%20Report/ACT-RPT-MAD-ARI-08-4301-MirrorBees-Glasgow_v3.pdf or using a 'gravity tractor' spacecraft whose own mass influences the asteroid's course - http://www.esa.int/gsp/ACT/doc/MAD/ACT-RPR-MAD-2010-GravityTractorOCP.pdf The general rule is that the earlier an asteroid is detected, the lower the energy scale needed to divert it.

As for international visits, if you are at Uni in a Member State there are opportunities (check with ESA Education Office), there are also some international opportunities. Check also with bodies such as the International Space University

First of all, that sounds like an amazingly cool place to work.

How do you guys feel about movies such as Armageddon and Deep Impact being the most common exposure that the public has had to the work you're doing? Does they help with raising the level of awareness or cause problems by producing an expectation of everything being like a Hollywood blockbuster?

(VP) It is! I still pinch myself sometimes.

All publicity is good publicity, even if suspension of disbelief is required for most of them! Please don't get me started on Interstellar! Anyway, apart from Warp engines being a few decades down the line (a man can dream), I don't think anyone can ever feel let down from the real side of Space Engineering! These are arguably the most complex machines we've ever come up with as a species and if you ever see one up close, it will awe you! Not to mention actually being part of building something like that!

(SB) In Armageddon especially they launched very quickly in response to the threat - using two Space Shuttles at once! In the actual space industry even the highest priority missions would still take time. That's one aim of monitoring programmes such as that undertaken by ESA's Space Situational Awareness, to identify risks early enough that plenty of options stay on the table

What asteroid that hit Earth had the most diverse composition of materials? Anything truly mysterious?

(MK says)

Many meteorites are rich in organic material, which can be highly complex, even up to nucleobases, the building blocks of life. However, much of this fragile material gets destroyed by the heat of entry. Also, we don't know to which extent complex organic chemistry found in meteorites may have entered it while it was already on Earth, as a contamination.

Arguably, the most tantalizing scientific question is how life on Earth first formed. Material from space may have played a major role. But to understand more about that, we need to study pristine asteroid material - that hasn't been through the intense heat of atmospheric entry and then lay on the Earth surface for a long time subject to Earth microbes and erosion.

Scientists need to study the real thing, and the only way to find that is out there in space - we need to get some material before it falls on Earth, while it is still pure. Even a few hundreds of grams would be very valuable.

Heya! Thanks for doing this.

My questions:

• What's the usual size of Asteroids coming our way?
• How many 'close' misses are there per year?
• What's the size from which we should be starting to get worried?

[CR] Answer to question three: Q: What's the size from which we should be starting to get worried? A: The Chelyabinsk asteroid that injured about 1500 people (no one died) in February 2013 was around 20 m in diameter so anything in that size regime can be cause for concern. Smaller asteroids will only cause very localized damage (such as in Chelyabinsk) and here of course the impact location would matter. The same asteroid coming in over an ocean would not cause any harm, for instance. On the other hand, asteroids that are few kilometres in diameter could have global consequences such as what likely happened to the dinosaurs.

https://en.wikipedia.org/wiki/Chelyabinsk_meteor

What's the usual size of Asteroids coming our way?

[CR] Great question! I will start with the first question: Q: What's the usual size of Asteroids coming our way? A: There is an excellent reference with title “The population of near-Earth asteroids” by Harris and D’Abramo you can find here In there, Figure 4 shows the relationship of how many NEOs are there of a given size. Basically, there are asteroids in sizes varying from sand corn sized to many kilometres in diameters. The rule of thumb is that there are many more small sized asteroids and fewer bigger ones. The relationship actually follows a power law. This is demonstrated by the fact that you can look up in the night sky and see harmless shooting stars that are caused by very small asteroids (small particles) and that big asteroids impacts are not part of our every day experience. Sorry if the reference is behind a pay wall but you might be able to find the source if you do some smart googling….I will try to find it free in the meantime as well.

If the public knew an asteroid was on a collision course with Earth there would be widespread hysteria and a breakdown of civil society. If you knew of a credible asteroid threat, when would you release the information if at all?

[CR] So far, all information on potential asteroid threats is available publicly on risk lists (webpages) that are maintained by ESA and NASA. Here is ESA's and here is NASA's. On this list you find all sorts of information including estimated asteroid size and impact probability (IP).

Hey! Thanks for hosting this AMA.

What kind of systems do we currently have to deflect asteroids coming our way?

(MK says):

I would like to add to the answer given by my colleagues by asking you to think ahead a bit. Say, not to 2020 or 2030, but rather to 2080, 2090, or why not, 2116.

There will still be a threat by asteroids then, but human space capability will have evolved dramatically by then.

The best we can do currently or even in the near future will be no more than addressing an immediate threat. That might work, or it might not. If it works, it might work less well than hoped. Or it might reduce the impact risk at one Earth encounter, but increase the risk at some later encounter.

Even a slightly deflected asteroid will still be a risk. It will still be there, and its (slightly changed) orbit will still cross the Earth orbit. The real solution is to take an asteroid apart - breaking it down into small parts that no longer constitute a danger.

That may not be possible with current technology, but it also is not an unsurmountable problem. Most asteroids are just rubble piles a few hundreds of meters across. Surely there will be technologies later in this century that allow humanity to take care of a few hundreds of meters of loosely piled rocks!

We have many ideas on how a deflection system would look like. Clearly the final choice would depend on the kind of threat, in particular the collision epoch and the asteroid size.

Since it is envisioned that the most likely threat is posed by asteroid of small size (say 50-400m diameter) I will give here three main "deflection" options one could/would consider:

1 - The kinetic impactor

2 - The gravity tractor

3 - Laser ablation (from space)

Now, this list is not exhaustive as scientists have been very creative in the last years and considered many advanced proposals. But as far technological requirements, I would argue the three method above are the ones that are the most feasible using current technologies.

In the case of the kinetic impactor, we at ESA actually made a number of preliminary trajectory computations showing the viability of such a concept, for example, on the case of the scenario where the asteroid Apophis needed deflection prior to its 2029 close Earth encounter.

One must also understand that the actual decision on which way to go is a delicate interplay between the time available to actually plan the mission and the assessed risk of collision. The more one waits the better the risk estimate, but the more costly/drastic the deflection option.

DI

How does an asteroid first 'get on your radar'? How far is that limit, and how long do you have to monitor it before you realize it is an asteroid?

[CB/PC] Telescopes are generally used to discover and track near-Earth objects (NEOs). The majority 1km-sized NEOs are mapped and is now increasing the number of objects tracked to cover those of 140m and larger. This is a continuous process. A NEO has a closest approach to the sun of 1.3 astronomical units (1AU is the distance from the Earth tot the sun) They are discovered once they reflect enough Sun light to be visible by our telescopes; the distance at which this happens depends mostly by the size of observed object: the bigger the farthest, usually some AU from us but for small ones sometimes much closer. Simulations are run on the basis of such first observations, depending on the quality of those observations and position in space may take just one night to conclude on the nature of the object and its orbit for next decades, in other cases more observations are needed and may take up to few months.

Hey ESA,

Do you think that we are too scared of Asteroid impacts because of movies etc or is the chance of the earth getting hit by an asteroid really so high for the next 50-100 years that we should be highly concerned about it?

The risk of an asteroid actually hitting the Earth causing vast regional damage is indeed small but not negligible. The Tunguska event is often mentioned as an example (or the less dramatic Chelyabinsk event). That happened 100 years ago and caused a rather significant damage on a relatively inhabited area of Siberia. A frequency on the magnitude of hundreds of years is commonly estimated for those types of events.

So, in a nutshell, we do not think that an asteroid of the size of Km will hit us and wipe human kind (as you see in movies), rather we are concerned and focussed on smaller asteroids and the regional damage they could possibly cause.

DI

How often does an object cross the earth's orbit at a time when it threatens to impact the moon more than the earth? Has deflection of these objects been considered, too?

The Moon is a much smaller body with respect to Earth. Asteroid impacts on the moon are therefore extremely rare and as we struggle to compute impact risks for the Earth, the ones for the Moon would be subject to even larger uncertainties.

That I know of, the scenario you envisage has not been seriously considered so far (for the reasons explained above)

(SB) Lunar asteroid impacts are seen periodically from Earth:, eg http://www.space.com/24789-moon-meteorite-impact-brightest-lunar-explosion.html As for deflection, there are plenty of craters already on the Moon, another one would not make much difference...

(MK says):

Once we have determined the orbit of an asteroid through space, which requires observing it repeatedly at different times, we can start predicting its future orbit. This is called numerical propagation, which is a big word for using a computer to compute how all kinds of perturbations are going to be changing the orbit of the asteroid at any later point in time.

Such perturbations may be caused by the gravity of the Earth, the Moon and other bodies, but also by the small but constant pressure exerted by sunlight, or by the heat which is radiated off a\an asteroid surface. With time, even small things make a difference.

If the threat of an impact and the effectiveness of a deflection are considered (the latter luckily has not been necessary so far, but one day, it will be). this numerical propagation is vital, so we have to get it right!

(PC) on top of already provided answers... have in mind that there is no atmosphere protecting the moon surface from small-size objects, therefore so many sign of impacts there.

Not to mention no erosive processes of any kind!

Are we currently capable of stopping a 1 km-wide asteroid aiming right for NYC with 12 months notice?

(MK says):

No. Much more warning time is required

I would say that the chances of that happening are zero. We do have a rather satisfactory knowledge on the orbit of objects of that size (they are big) and no threats are foreseen.

But lets play along and assume your scenario would become concrete. No "gentle" deflection methods would then be feasible nor could be considered (see MK reply), except perhaps a number of perfectly timed nuclear explosions happening in space with a carefully planned geometry. Even so, it would be extremely hard to guarantee what would actually happen to the asteroid trajectory and if the deflection would be accomplished.

DI

Happy Asteroid Day everybody!!

I have an impression that globally general public have not enough been informed or "educated" about reality of asteroid (or comet or whatever) impact, and I feel it's more important to know about it in advance than such people know (or think of) today. Probably especially kids. Then, I think humans can make better decision on how to use our money, resources, knowledge etc. So along with developing better technology to detect smaller bodies in any directions, how do you think about informing/educating globally about reality of such impact?? Is it going well or don't you satisfy with current status?? Thank you very much!!

(SB) ESA is partnering with international Asteroid Day because it is a good initiative to educate the general public about both the potential threat and the future promise of asteroids, in terms of resource availability, scientific value and so on. Look up into the night sky and in a short while you'll see a shooting star, as a dust-sized mote burns up in the atmosphere. So items are incoming all the time - their scale being governed by probability. This kind of outreach is about filling in a gap in the current popular view of Earth and the Solar System, getting to know the local neighbourhood better. Work is being done to more accurately model asteroid risks, to put them on the same yardstick as other natural disasters: http://www.esa.int/Our_Activities/Space_Engineering_Technology/Asteroid_day/Asteroids_assessing_the_risk

Hi! Thank you so much for taking our questions! You guys are amazing in taking the time to do so :)

my question may be silly but do you get the chance to do research on what asteroids are composed of before reflecting them? If not, is it because you already know or for other reasons? If so, what are asteroids composed of and have you found anything that was unexpected?

(MK says):

In general, we can learn some about the composition of asteroids by studying the sunlight that is reflected off them, using a technique called spectroscopy. This allows learning something about the composition even from afar. Unfortunately, this technique may lead to inaccurate or ambiguous results, and also, it would not tell us what is below the surface or whether asteroids are made up of solid chinks a]or whether they contain large voids internally, which is possible if they are made up of loosely packed rubble.

So the question is not just what they are made up of, but also what their internal structure is.

[BGG] Actually that is one of the objectives of the Asteroid Impact Mission, to further improve our understanding of what the asteroids are composed of and how they react to impacts. Several missions have already visited asteroids/comets trying to gather this information and compare it to that acquired from Earth using different types of telescopes. Only by doing so we can better predict what types there are from Earth and their behaviour in case we really need to deflect any on Earth collision trajectory. Typically composition of asteroids include rock-forming minerals, metals, sulphides, clays, and organic compounds. The structure and composition though can vary a lot from one to another.

That is amazing! Thank you both for answering my question! Is it possible to find out where these asteroids originated from given their trajectory then? That is amazing that you can also see what the internal structure of these asteroids are like, have there been any asteroids where their structure is questionable?

[BGG] This is very tricky question, they are mostly left overs of the planetary formation... but planets themselves are believed to have gone through interactions (mostly due to Jupiter and Saturn) dramatically changing their orbits. There is though ways to catalogue them indeed based on their orbits and composition. Regarding their internal structure, little is known yet. This is where missions like Asteroid Impact Mission could help answering lots of questions. So far ESA has done it with a comet thanks to Rosetta and Philae, AIM will do it for the first time ever with Didymos asteroid.

Hi thank you for doing this AMA and Happy Asteroid Day!

How do you detect the path of an asteroid and if it were to be projected at Earth what must we do to brace for an impact?

(MK says):

None of the thousands if Earth crossing asteroids currently known pose a concrete impact risk. But the problem is that we don't know even close to all of the Earth crossing asteroids that are big enough t cause massive, perhaps even global damage. What needs to be done right now is to go on looking and to chart the orbit of every new body that is found. This is called a sky survey. Then we need to understand much more about their interior composition. We really do not understand these small bodies very well. The more we learn, the better our chances are of our winning out against a hazardous asteroid, should one be found.

Asteroid trajectories are computed from (mainly) optical observations from ground and space based telescopes.

In case an asteroid was to be detected in an Earth collision course our options would depend on the advance time we have before the impact. In a likely scenario we would have some years to plan a deflection option.

DI

(PC) Usually the path is derived on the basis of optical observations of moving objects in stars fields. Background stars are used as reference of angular motion of an object and repeating such observation over time create a series of angular positions with respect to Earth. Software simulations are run to find an orbit compatible with such series of angular positions and as a result we understand the absolute position (including distance from Earth). Further observations, sometimes over a time span of months, will help in reducing the uncertainty of orbit propagation. This means that we can predict with higher accuracy where the object will be at some point in future. The level of accuracy in our propagation give us the confidence for an actual impact and if so... this is what we are discussing all day today.

When last time I saw the graphic of MASCOT2 lander, the solar arrays are on the flipside of the top panel of the 6-panelled square-shaped body. I suspect that when try to hop, the top panel should be closed, right?? If so, does that mean you can open & close the top panel again & again & again whenever you want & power is available??

[CB says] Nice question! When MASCOT2 is deployed from the AIM spacecraft at an altitude of 200m above the surface of Didymoon, it will drift towards the surface with its deployable solar array stowed. If, once it has stopped bouncing (something we expect), it is upside down or in another way blocking the deployment of the array, there is an activator to make MASCOT2 do a small hop. This it can repeat until the attitude is good, without the need to deploy the arrays. Once it is safe the top panel opens and the radar can be operated.

(VP) Great question!

Due to the specific requirements of the Low-frequency radar (which will study the deep interior of the asteroid) and the need to have the antenna pointing upwards, the MASCOT-2 needed a very well defined top and bottom. By comparison to the LFR, the other payloads on-board MASCOT-2 consume much less power and can be fed from the undeployed top panel. The plan currently is to hop around and avoid bad spots, then when we're happy, we deploy the top panel and start using the LFR! Currently, we are not thinking of moving MASCOT-2 again: the whole point of being able to move around is just to make sure we don't land on an undesirable spot like Philae did.

Hi guys! Two questions: how much information about an asteroid are you able to get from the ground/satellites without sending a probe out? Other than size,rotation, albedo,etc.

In that vein: what's the most interesting asteroid studied/discovered in your opinion?

(VP) Besides Didymos, I specially like 6671 Concari. Ask Paolo Concari why!

/u/ESAAsteroidDayAmA Why? :⁾

(VP) Paolo is an amateur astronomer and he's got that asteroid named after him! See kids? Learn your science and you can get your own asteroid!

[BGG] Indeed from ground you can get size and shape, rotation speed and axis orientation, and some albedo reflectivity properties, but also by using spectrometry the composition of their surface. In case of binary asteroids, such as Didymos (Asteroid Impact Mission's targeted asteroid), you can also get their mass from the time it takes to rotate around each other... a so their density. Using satellites, on top of increasing accuracy and certainty on the measures, it is possible to study the sub-surface and deep interior using high and low frequency radars respectively.

(PC) Ground observations are based mostly on optical observations, the so called spectrometry gives hints on the external compositions and the so called astrometry gives information on the positions. This is sufficient to define the type of asteroid. Curves of lights can be used, and in some rare cases also radar measurements, can gives information on the shape and spin axes. But all the research done on top of the basic position knowledge is limited to large sized objects due to the limited amount of light reflected and received on Earth.

(artificial) Satellite being way closer to the object under study can provide more accurate information also for minor objects and can also carry instruments that sounds the interior of the structure (radar), measures the magnetic fields, makes a thermal model and perform experiments to precisely determine the mass of the object, increasing further the knowledge of the inner structure. Satellites can even carry, as Rosetta did with Phileae and proposed AIM with MASCOR2, landers that perform in-situ science, impossible from Earth.

The most interesting one? I have not an answer for that, sorry, but 6671 (1994 NC1) looks cool to me ;-)

This may be a little off-topic, but here it goes:

You all have very different job titles. It would be cool to hear from each of you what a day at ESA looks like.

So, what do each of you do in a typical day at ESA?

(VP) We're mostly in the Netherlands, so the average day looks rainish grey :)

I am a Systems Engineer at the Systems and Concurrent Design Section. My main duties are thus supporting both missions already in industry (AIM, where I coordinate the intefaces between platform and payload teams) and the preliminary mission design we do at the CDF (see the link below). Preliminary studies I have done were for example the next generation of Science spacecraft or mission architecture planning for the Moon. I am also involved with CleanSat, an initiative to foster green technology in space, and OCDT, a Model-based Systems Engineering software that allows you to virtually design a spacecraft.

http://www.esa.int/Our_Activities/Space_Engineering_Technology/CDF

http://www.esa.int/Our_Activities/Space_Engineering_Technology/Clean_Space

Hey awesome people!

A bit off topic, but lets say i am a mechanical engineer in mechatronics, what masters will be most likely to land me in ESA and how does that happen ??

[CR] If you already have a mechatronics degree, that should serve the purpose quite well. The backgrounds at ESA are quite diverse: engineers (mechanical, electronic, computer, radio, optics, ...), scientists, and other positions are usually sought after. You should really go into the field that fascinates you. If you are still at university, there is the opportunity of internships (called stagiaires), if you relatively fresh out of uni, you can apply to a Young Graduate Trainee position, and otherwise just go via ESA's job portal. It might be necessary/beneficial to be a citizen of one of the ESA member states (different from EU, for example Canada is in).

Since it impacts all of Earth, who/what government makes the final call on approving plans and funding for any big plans to prevent a asteroid hitting Earth?

[CR] This is a tricky one and the question is still very much open. This is what we have so far: You are exactly right, that the asteroid impact threat is inherently international because any nation on Earth can be affected. That is why the United Nations, as a “club of the global community”, has taken up the task of figuring out what the best response procedure to a given asteroid threat is. To accomplish this task, two groups have been set up: The International Asteroid Warning Network (IAWN) and the Space Mission Planning and Advisory Group (SMPAG). IAWN’s task is to foster collaboration between partners (nations) who can detect asteroids and to warn if there is a credible threat. SMPAG, on the other hand, is concerned with the response action and this ranges from what action to take if IAWN identifies a threat, to identify who calls the shots (coming back to your question here), and to facilitate the design and implementation of a deflection mission. Because these questions are not only technical in nature but very political, the answer to them is not straight forward. With a deflection mission, you can essentially move the impact point of an incoming asteroid and you can imagine that nations that don’t like each other will not agree on which direction the impact point should be moved to in order to get it off the Earth. Anyways, working on it and you can follow the progress in the meeting protocols on the SMPAG webpage if you fancy some deeper digging. Personally, I would expect that some form of international collaboration emerges out of this process.

Hi! Two questions from me:

1. Is there anything that particularly excites you about AIM? Any ideas for what will come after AIM?

2. What is your perfect Sunday?

[CR] AIM (and AIDA in general) is the coolest science mission on the horizon at the moment. Here is an excellent 6 min video explaining the mission. For Planetary Defense, it will, for the first time, deflect an asteroid and measure the outcome of this deflection. One effect that is very unclear at the moment is the so called impulse enhancement factor (usually beta) that comes into play during a kinetic impactor mission. The kinetic impactor is the most likely deflection technology to be used and it is essentially a block of metal that will be collided with the target asteroid at high speed (kilometers per second). Now, a simple way to think about the impulse interaction here is like in a game of billiard - the change in speed for the target is dependent on linear momentum transfer due to the collision of the impactor. However, the impactor will likely throw a lot of material out into space because it explodes upon impact due to its high speed and this ejecta will cause an extra push on the target body, thus enhancing the impulse delivered by the impactor. Unfortunately, we don't really know how strong this enhancement is and the AIDA mission will deliver crucial data on this. Beyond Planetary Deflection, AIM will deepen our understanding of the nature of asteroids and by extension the solar system. It is also a technology demonstrator mission deploying CubeSats in deep space (not done to date), utilizing deep space inter satellite communication network, using a laser telecommunication module from deep space and more. I think that it is really a great mission.

Are asteroids the reason there are so many pot holes in the road?

[CR] excellent question with a short answer: If you live on the Moon, yes. If you live on Earth, no.

how realistic was Independence Day: Resurgence? Wouldn't the alien ship become a sphere due to its enormous mass? Could the aliens have simply dropped an asteroid on the earth to wipe it clean? Wouldn't the moon's orbit have been skewed? Why weren't there massive hurricanes and winds as the alien ship touched down on Earth and zillions of tons of air got displaced? Why do the aliens harvest planets for energy when a single star would give them more than they could possibly use? And why not harvest planets devoid of life, there are plenty?

[CR] just watched it and thought it was fun. All your questions have a point though.

I hear asteroids can be worth trillions of dollars if mined. What's the chances of lassoing one of those bad boys during a close-earth encounter and pulling it into a safe orbit for later use?

(VP) It's all about delta V: how much amount of speed change do you need to get something from one place to another (ELI5ed). Considering that, it might just be easier to go to an asteroid in quasi-orbits around Earth than it would be to catch and pull a close-earth encounter.

Opinions on Brexit and how it'll effect ESA?

(VP) ESA is a separate organisation from the European Union, so in principle nothing changes. However, there are collaboration programmes ESA-EU, and GB is one of the leading partners for Galileo for instance. It remains to be seen what might happen there.

On a personal note, ESA is an organisation of European Unity and yes, last friday was felt as a sad day.

Is there a scenario where we would be blind to an incoming threat until too late? e.g. low albedo objects thanks

[CR] anything coming roughly from the direction of the Sun will be invisible because the Sun would blind our sensors if we point them at it. Chelyabinsk was such a scenario.

Low albedo would also make it tougher to detect. However, some proposed missions (B612's Sentinel and JPL's NEOCam) want to implement infrared sensors and are, thus, not dependent on reflectivity of the asteroid but on thermal radiation which is easier to detect in such a scenario.

When people talk about asteroids and space exploration, many times they talk about resources. What would the impact on our ecosystem be if we brought in billions of billions of litres of water or lots of oxygen? Is that a smart move, even if possible?

(SB) Asteroid resource utilisation is generally considered in terms of supplying extraterrestrial bases, to supply water, rocket fuel etc. The cost of getting supplies off the Earth makes such extraterrestrial resource utilisation at least theoretically competitive, using orbital resource depots etc. To actually return air and water to Earth rather than say the Moon or high orbit would be incredibly expensive. Much cheaper to build desalination plants or produce oxygen through standard industrial processes...

Hi ESA! I know that many people think our next big step in space exploration should be getting humans to Mars. Is this a near-term goal for ESA? And if not, what ARE the biggest upcoming goals?

EDIT: I realize me question might be a bit broad considering you are asteroid specialists, so I understand if you don't have an answer!

(VP) There are ongoing discussions with the international partners of the ISS (NASA, JAXA, Roscosmos) about how to proceed forward. While getting humans to Mars is what everyone agrees should be the next big step, ESA is currently more keen on using the Moon (or rather cislunar space) extensively as our first stepping stone.

(MK says):

There are many missions to near-Earth asteroid that can be accomplished within a year - going there, studying the asteroid for some weeks, and coming back. In fact, asteroid mission would be the perfect preparation for a manned Mars mission. You can study many aspects of long-duration manned interplanetary flight at a significantly reduced risk and cost, compared to a manned Mars mission.

odds of earth getting hit my a major asteroid?

An excellent resource monitoring those chances is http://newton.dm.unipi.it/neodys/index.php?pc=0

If by "major" you mean anything able to cause vast regional damage, then as you can see from the list of the current risks, we do not have reasons to be concerned.

If by "major" you mean anything like the Chelyabinsk meteor, then the chances are quite important.

DI

[CR] You should take a look at the so called NEO risk list (one is maintained by ESA and one by NASA). Click on "Full Risk List" and it will show all NEOs that we currently know of that have a non-zero chance of impacting the Earth in the next 100 years. You get information like name, size, date of first possible impact and impact probability (IP).

Are any major space agencies or private companies considering either mining asteroids for resources or attempting to land human beings on one? What are the technological challenges that we need to overcome to be able to mine asteroids or land humans on them?

Thank you for doing this AMA. Space exploration is always a fun topic to discuss!

(PC) Very recently (early June this year) the Grand Duchy of Luxembourg has made a step promising within 2017 a legal framework that will help the development of space mining at investor level. Seems science fiction but may be it's coming...

More can be found on vacuous specialized/generic online websites.

(SB) There are companies including Planetary Resources and Deep Space Industries and ESA's former Director General Jean-Jacques Dordain is advising the Luxembourg government on this topic, because Luxembourg intends to become a leader in the sector: http://spacenews.com/luxembourg-to-invest-in-space-based-asteroid-mining/ Right now, the only proposed manned mission to an asteroid is NASA's Asteroid Retrieval Mission, which would first retrieve a small asteroid and place it in lunar orbit, for a follow-on manned mission using Orion and SLS. ESA is proposing the (unmanned) Asteroid Impact Mission, which would study the smaller of the two Didymos binary asteroids in great detail, ahead of a NASA spacecraft impacting it. The hope is AIM can gather data on asteroid surface characteristics and experience of operating in very low gravity conditions, by putting down a microlander, which might serve to build up experience for follow-on resource utilisation etc. One big challenge for asteroid missions is that they have only brief launch windows relative to Earth and can involve months of travel time to reach.

Logic dictates that in the event of a credible asteroid threat being detected by a government space agency, the public would be kept int the dark. Organizing an international conference under the guise of a "hypothetical" asteroid threat however would allow international co-operation without raising suspicion even among participants who would be unaware of the true value of their contributions. Isn't this what the IAA planetary defense conference actually is? Didymos isn't the target of the 2020 asteroid redirect/impact mission is it?

[CB says] Thanks for the questions. Starting with the last one first, I can say with absolute certainty that Didymos is most definitely the target of the observation/impact mission (AIM/DART) I am following! As for the first question, the Earth gets hit by objects every day, but they are mostly so small that they just burn up in the atmosphere. The few that do get through to the surface (meteorites) are generally also very small. However, larger objects such as the Tunguska air burst which devastated a large area in Siberia, happen only every 100 years or so. If a space agency such as ESA detected that such an object would be slamming into Los Angeles next week, don't you think that Los Angelinos would like to be evacuated in time?

(VP) Just to add to this: each spacecraft heading to an interplanetary destination must be tailored to that destination! We are talking about trajectories, launchers, thermal subsytems, power subsystems, and much much more! So while we could relatively quickly change the design to face a real threat, I highly doubt any of us could be tailoring it to any place other than Didymos right now without any of the other ones knowing!

(MK says):

Asteroid 65803 Didymos certainly is the target of the 2020 asteroid impact mission, or rather, the small moon of the asteroid is - because this is a binary asteroid. You must understand that we know very little about the internal structure of small asteroids, so we don't know much about how their orbits can be changed by a redirection manoeuvre. The DART mission is a scientific mission that sill help us to understand asteroids a little bit better. Didymos in itself is not considered a threat. But it's a good place to conduct this interesting experiment of a high velocity crash to see how a small asteroid reacts.

Let's be real here guys. The question everyone wants the answer to is, "Are we in for some Armageddon stuff anytime soon?".

(VP) Hopefully not! We are doing everything we can to keep Bruce Willis safely on Earth.

(MK says)

Armageddon was about an asteroid as large as Texas. The short answer is that there is no near Earth asteroid that comes even close to that size. The largest "Earth Crossers" are a few tens of km in size, and most are much smaller, a "kilometre" or less. So Armageddon was invoking a lot of artistic license, to say the least.

However, there will be a NASA mission called DART that will include a high velocity crash of a spacecraft on an asteroid, albeit a small one. This will be in 2022. ESA will contribute to this mission in form of a spacecraft that watches the crash from nearby. A lot less dramatic than Armageddon, and certainly not incurring any danger to the Earth, but still rather cool, I'd say.

Can we call asteroids rocks? Why?? And does the theory that explains how earth water came from asteroids still available and working? Also do you think it is worthy to spend a lot of the space agencies's budget to explore an asteroid?

[CB] Whether asteroids can be considered as rocks is a good point! In fact, that's one of the main things we want to send AIM and DART to Didymos to find out. At the moment it is not entirely clear whether they are really solid in nature, like a lump of granite, or more like aggregated smaller rocks. Scientific simulations seem to suggest the latter since it seems likely that the binary Didymos system formed by a single larger asteroid losing material to form the secondary one. The low-frequency radar on the MASCOT-2 lander will send radio waves through the smaller asteroid so that we will be able to determine the internal structure. However, we do not believe that there is any water on or in the asteroids. Comets consist largely of water ice and one the objectives of ESA's Rosetta mission was to check whether the isotopes of that water matched that in our oceans. In fact, the answer to that question was negative, so it does not look as though our ocean water came from comets.

As far as whether it is worth spending money on doing this, well, firstly I would have to say that AIM is a relatively cheap mission. Secondly, expanding our scientific knowledge of the universe is something that it is very difficult to put a price on. In addition, the AIM mission is a technology demonstrator with an optical downlink, deployable cubesats with intersatellite-link capability two types of planetary radar, optical sensors etc. Much of this kind of technology would be needed for a potential human mission to Mars, say. Finally, if we do work out what asteroids are made of and what happens when we hit one with a projectile, this will definitely help us in the future should we need to deflect one away from Earth in the future.

(MK says):

Asteroids contain lots of different materials. Certainly lots of metals and metal compounds, as well as silicates and organic matter. So calling them "rocks" isn't wrong.

Water ice and other volatile material is probably very rare on asteroids, certainly on asteroids whose orbits are close to the Earth orbit, because these will have been "baked out" over the millennia.

There is however an enormous amount of water ice, carbon dioxide ice and carbon monoxide ice and other volatile on comets. Comets are on quite different orbits than most asteroids, but there is a kind of grey area. Some objects that look like asteroids may in fact be comets, or "old comets" that have fizzled out, so to speak.

Investigating asteroids certainly is a worthwhile endeavour. Much of the material there is still very pristine, despite the baking out and the exposure to harsh radiation. We simply cannot find such material on Earth. It would have eroded or been destroyed or changed long ago. We need to go out there and find it if we want to learn about what made up the Earth as it formed out of gas and dust, 4.6 billion years ago.

Ceplecha was still refining an orbital prediction for the great daylight fireball of 1972(using military radar data) 7 years after the event and predicted a possible impact event in August 1997. Who in astronomy circles was worrying about this potentially regionally devastating and undoubtedly dangerous asteroid? STS-85 was orbiting the Earth at the time with an infrared camera but no mention is made of this object. Did the ESA and NASA look for it in August 1997? Was NASA and the ESA really asleep at the wheel or are they just hiding the truth? This object is not listed as a NEO. Where is it now?

Not sure, but as far as I can see on scientific studies, that asteroid was estimated to be rather small (~15m) and got smaller after the atmospheric passage. So no devastating regional damage was risked.

Asteroid that small are likely to "just" create entertaining fireworks.

DI