“It’s an object from 160 meters to 11 million kilometers. It’s like hitting a golf hole… on the Moon”

NASA’s Double Asteroid Redirection Test (DART) spacecraft has almost reached its destination. This probe, about 19 meters long and weighing 580 kilograms, is destined to collide with Dimorphos, the moon of the asteroid Didymos.

After its launch at the end of NovemberDART has sailed through space and until a few days ago we could not finally see the first images Dimorphos, about 160 meters in diameter, and Didymos, 780 meters in diameter.

And now alone? you have to hit your target: being 11 million kilometers away from Earth, and making that last journey autonomously, the end of the mission is that dart hit like a dart in the target, crashing at a speed of approximately 27,760 kilometers per hour -6.6 kilometers per second- on the small asteroid moon Dimorphos, which orbits Didymos.

Scientists hope that this impact will change the orbit of the asteroidprobably leaving a crater in it for posterity.

After the impact, the Hera mission of the European Space Agency (ESA) will fly to the receiving body of the impact to carry out a in-depth analysis of the crater formedthe mass of the asteroid and many more elements, extracting from this important experiment data on a controlled and repeatable planetary defense technique.

To find out a little more, at 20BITS we have interviewed Adriano Campo Bagatin, physicist with a doctorate in Astronomy involved in the DART mission through the University of Alicante.

Recreation of DART reaching its target.
POT

What is the involvement of Spanish teams and institutions in DART?

On the one hand, the Institute of Astrophysics of the Canary Islands participates with a group of people who, above all, take care of the observations of the event, both in the days before and in the days following. Keep in mind that at the time of impact this object can only be seen from the southern hemisphere of Africa. In the following weeks it will be possible to observe it in the northern hemisphere, so the Roque de los Muchachos Observatory (ORM) in La Palma will be a very important enclave.

There is also another team Center for Astrobiology (CAB) from Madrid what does experimental work on crater formationso their involvement will be to a greater extent after the impact, based on the data obtained.

Finally, for our part, we have been involved for a long time in both DART and Hera, the part of the mission led by ESA.

DART spaceship illustration.
DART spaceship illustration.
POT

What kind of previous research is being done by your team?

What we do are numerical models for try to understand what the propagation of energy will be like after the crash of the ship on the asteroid Dimorphos and if this collision can cause a shake away from the point of impact that could generate a dust output at a higher speed than it should.

Likewise, and more regarding the Hera mission, from my team tWe also studied the part of the internal structure of both Didymos, the main asteroid, and Dimorphos, as well as the formation mechanism of these binary systems. We start from the hypothesis that these bodies can be classified under the type ‘rubble pile’ –rubble-pile in English-, a type of asteroid formed by rocks of different sizes united only by self-gravity or by small cohesive forces, that is, they are formed, most likely, from the remains of a collision between asteroids. Really knowing the type of structure of the asteroid will be essential to understand the result of the collision.

Finally, we also try to know if it is possible that there is a cloud of dust around the binary asteroid system because Didymos is rotating very quickly: it makes a complete turn, a turn on itself, in just two and a quarter hours, which is just at the limit of instability, that is, if it rotated more fast could not hold together. Because of this, there may be dust or even large stones that have become loose from the asteroid’s equatorial zone and may be in orbit around the body.

Asteroid Dimorphos to scale with the Colosseum in Rome.
Asteroid Dimorphos to scale with the Colosseum in Rome.
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What consequences would there be if there was a lot of dust? And find wild rocks? Would this prevent us from observing the event?

Presumably the cloud would not be so dense that we would not be able to observe the impact, but it is something to which we are exposed, because we do not know at this time if that situation is happening or not. We can only see something when we get very close to the object in the minutes before the collision.

As far as getting damaged, the DART probe, with its speed and size, if it finds dust particles it would have no problem. nothing would happen to him.

With the information we have, what is most likely to happen?

First, we hope to hit the asteroid [se ríe]. Being able to hit Dimorphos. Keep in mind that this is an experiment, a demonstration of space technologyso the result could be that we show that we have not been able to get it right… after all, we are talking about an object of 160 meters and a body that at the moment of impact will be 11 million kilometers from Earth. It’s like hitting a golf hole… on the Moon. Also, there’s another complication, which is the fact that the last four hours of DART’s navigation is autonomous, meaning it has an algorithm that has to follow the target and hit the target.

If we get it right, the impact has to deflect the orbit of the asteroid Dimorphos, Didymos’s satellite, and later we will measure that deviation. How? Thanks to ground-based telescopes: we know from measurements made from the earth how long it takes Dimorphos to make a complete revolution around Didymos before impact, we will have to observe after the collision how long it takes him to do this same maneuver. The time difference will offer us as a result to know how the impulse that DART has delivered to the asteroid has been..

Explanation of the DART mission.
Explanation of the DART mission.
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How are we able to calculate this?

We know the speed of the probe -27,760 kilometers per hour or 6.6 kilometers per second- and its mass -580 kilograms-. Knowing this, we will see what change in the speed of the asteroid we are capable of causing.

What is this mission going to do?

It will be fundamental to be able to tare all the collision models that already exist. Thus, in the event that there is a potential future threat, in the first place, we would already know what the effect of an impact of this type would be, so we could scale the mass, speed and the rest of the parameters according to need – depending on the size, distance and speed of the asteroid approaching Earth. You could even have a series of probes ready and all you need to do is upload them to a rocket and point them at the target..

Therefore, knowing this potential threat at least a couple of years in advance, it might be possible to avoid it.

What if we don’t achieve the mission objective?

Although there is European participation, this is a mission of POT…so if things don’t go as planned, it would be NASA who would assess the circumstances and the situation and make the appropriate decisions on how to proceed.

What is the worst thing that we can find when going to make the impact?

Perhaps the most pathological case would be that when we reach the moments before the impact we find that a rock has been dislodged from the asteroid the size of a room or a car that is right in the path of DART… It is true that people win the lottery, but we would only have one ticket [se ríe]. It would be a very unlikely case.

It is important to emphasize that we really do not know what these objects are like, in fact, we do not know the exact shape of Dimorphos with certainty, we have made an ellipsoid-type model, but we do not know the reality because we have not yet been able to observe it. We also do not know what the surface is like or what is below the surface. We don’t know if we are going to hit it perpendicularly or in an area where there is a hill, for example, and then we would hit it sideways… The models made by the teams in charge of studying the impact say that a crater could be generated after the impact, but could also be deformed. There are still many issues that we cannot resolve until after observing the event..

The ship already has the asteroid Didymos and its satellite Dimorphos in sight, against which it will impact.
First images of the asteroid Didymos and its satellite Dimorphos.
POT

And if everything goes well… what would be the next step? Would we try again?

That is a good question. Neither NASA nor ESA have planned for now to do another experiment of this type. I think the current strategy is to see how this one comes out and see how much we understand from this. In my opinion, I believe that what should be done afterwards is that if there are critical parameters that remain unclear, propose another mission to clarify them.

In addition, this is an object of a certain type, made mostly of rocks, but not all bodies near Earth are the same, some are more porous, made of rocks with a higher percentage of carbon and therefore lighter. In these, perhaps the reaction and the result of an impact was different.

Being realistic, it is very possible that we will have to do another experiment.

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