There is great deal of media interest in tomorrow’s flyby of asteroid 2012 TC4, which will make an unusually close pass to Earth at a distance of just 43,780 km at 07:41 CEST – that’s well inside the orbit of the Moon and indeed, closer than some satellites. The chunk of space rock is about as big as the famous 2013 Chelyabinsk object (in the range of 10-20 m diameter) but despite the near approach, there is no risk that it will hit Earth.

Below, we’ve put together a few general outline Q&As provided by Detlef Koschny, responsible for Near-Earth Object (NEO) activities in ESA’s Space Situational Awareness (SSA) programme office.

UPDATE 12 Oct 10:10 CEST – Post-flyby comments from ESA’s Detlef Koschny

Q. Did any telescope to see the asteroid?

Yes, many telescopes observed 2012 TC4. Some nice images and animations were done also by amateurs:

Near-Earth Asteroid 2012 TC4 extremely close encounter: online observations – 11 and 12 Oct. 2017

Not all telescopes worked as planned due to technical issues, which can happen. One large, important asset is the big radar system in Arecibo, Puerto Rico – which was not functioning due to damage from the recent hurricane there. Luckily another US-based radar system could be used a couple of nights ago. This is exactly why we do this exercise – to not be surprised by these things.

Q. How did the tracking and response exercise go?

I consider it a big success! Basically, we pretended that this is a ‘critical’ object with a high risk of impacting Earth (which it was/is not) and exercised our communication channels and used telescopes and radar systems for observations. The main thing we at ESA have already learnt: We were well prepared and most observations and communications worked as planned. The international asteroid community also got valuable experience; via regular telecons and email exchanges we distributed information and had discussions.

What did we learn? The initial size estimates were roughly 10-30 m. After radar observations, it looks like the object is on the smaller end of that, at about 10-12 m. This means it must be very bright and reflects about 40% of the light that hits it. This was also the case for asteroid Steins, which was observed by ESA’s Rosetta spacecraft in 2008.

This object is rotating once every approximately 12 min, which is quite fast. We are still looking at data trying to better understand, or limit, it’s composition.

We now need to determine the position, or orbit, of the object again with high accuracy after today’s Earth flyby. This will allow us to update our predictions of the fly-by distances during future Earth flybys. Currently, we have a computed a possibility of roughly a 1/15000 (<0.1 %) chance that it enters Earth’s atmosphere in 2079. I expect this number to change dramatically now that the object has passed Earth’s gravitational influence.

(Original blog post continues below)  

Q. What are the basic details on this flyby?

We’ve posted a PDF Factsheet in ESA’s NEO Coord Centre website: Asteroid 2012 TC4 Factsheet (PDF) .

Q. Is ESA working with any other agencies on watching for this or other asteroids?

We work very closely with, for example, NASA. I am right now at a meeting of the Space Mission Planning Advisory Group (SMPAG), where today we are discussing legal issues related to planetary defense. ESA is chairing this UN-mandated group, and we have colleagues from around the world workign with us: NASA, ASI (Italy), CNES (France – they are the host this time, and we are in Toulouse), DLR (Germany), JAXA (Japan) and CSA (China). SMPAG brings together space agencies to discuss what we could do to mitigate an asteroid impact threat.

Another important UN-mandated group is the International Asteroid Warning Network (IAWN), which is a network of all agencies/organisations that can detect and follow asteroids in space, generate impact warnings, and model possible impact effects.

ESA’s Rüdiger Jehn, co-manager of near-Earth object activities under ESA’s Space Situational Awareness (SSA) programme, explains why asteroids and other NEOs pose a risk and how Europe is working to contribute to the global asteroid hunt.

Q. The flyby of 2012 TC4 is being used by NASA to test our ability to identify and then track asteroids that come close to Earth. If one were to head directly toward us, are there any practical steps we can take to deflect an asteroid, and do we have the capability to do that now?

Yes, we are using this asteroid flyby to test our systems. Responding to media queries is part of the exercise, as this helps agencies like ESA and NASA to better know what kind of information journalists and their audiences will want to have answered.

So, we are using 2012 TC4 as an exercise; we are pretending that it is an impactor, and asking, what would we do? Indeed the first part of any response is to observe any detected object. We at ESA, working with the European Southern Observatory (ESO), actually ‘recovered’ this asteroid – meaning we spotted it again and got a good fix on its orbit after it had been previously spotted but then lost –  in July this year.

At our meeting here in Toulouse, we are discussing how to best deflect the object. ESA, together with NASA, is preparing a demonstration mission called AIM to test the ‘kinetic impactor’ method of deflecting an asteroid.

Fireball from the Chelyabinsk meteor airburst, as recorded by a Russian driver's 'dashcam' during the the morning of 15 February 2013. Credit: Semni Istiqlal

Fireball from the Chelyabinsk meteor airburst, as recorded by a Russian driver’s ‘dashcam’ during the the morning of 15 February 2013 (click for video). Credit: Englishrussiatv

If the object were as as small as 2012TC4, we don’t need to deflect it (it will explode and be destroyed in our atmosphere).

But in that case we would need to inform the public to, for example, stay away from windows – it was the shock wave from the Chelyabinsk object in 2013 that damaged many windows, causing injuries due to flying glass.

For that, we at ESA’s SSA programme are actively setting up interfaces and modes of communication to European national emergency response agencies/offices.

Q. Would we would need a lot of time to respond to mount an effective response?

2012TC4 is small enough that it doesn’t need to be deflected.

To distribute the warning message I mentioned above would only take hours to a few days. So we would have been fine in this case [if 2012 TC4 was an Earth impactor].

For larger objects, above about 40 m diameter, we indeed may want to deflect it, and for that we’d need to launch a space mission. That indeed would take some time; for example, a kinetic impactor would need to hit the asteroid a few years before the potential Earth collision, the reason being that the potential deflection (due to kinetic energy) of a satellite impact is only very small, so it would take a few years for the orbit shift to accumulate enough distance to avoid an Earth impact.

Q. So, if there were to be an impact, in practical terms, it would be a case of working out where the asteroid might hit and then taking appropriate measures – for example, evacuation if a populated area were to be affected?

Yes – but it really depends on the object’s size. If it were under 40 m, we would warn or evacuate. If over 50 m, we’d want to start thinking about deflection. The decision criteria agreed by IAWN and SMPAG, which ESA supports, are here: (See Section 7.1).

Q. What impact would an asteroid the size of 2012 TC4 have if it were to hit? Would it be similar to Tunguska?

It’s smaller than Tunguska, only about 10-20 m (we just got some radar observations last night). So it’s more like Chelyabinsk in 2013. So, there would be a shock wave possibly shattering windows; possibly a few meteorites falling down. It’s not really such a big one.

Note: More details via Asteroid 2012 TC4 at ESA NEO Coord Centre