The asteroids – fragments left over from the formation of the inner planets – are objects that arouse great curiosity on the part of those who want to get to know the constituent elements of the Solar System and trace the chemistry of life. In addition, humans are considering extracting metals from them, but one of the main reasons scientists study these ancient space debris is the likelihood that they will cause damage to Earth. For this reason, for 2022 NASA is planning a planetary defense mission that includes sending a spacecraft to collide with a nearby asteroid in order to see if it would be possible to deflect it in case its trajectory leads it to collide with this planet.
Naomi Murdoch, a 36-year-old Scottish scientist specializing in the geophysical evolution of asteroids in the Higher Institute of Aeronautics and Space ISAE-SUPAERO from France is part of a follow-up mission of the European Space Agency. Murdoch explains to the magazine Horizon that, after the impact, the mission will determine the characteristics of the asteroid to design strategies with which to deal with any asteroid that could threaten the Earth. Although the scientist warns there is no danger that a large rock debris will kill life on Earth, but there is a danger that one causes considerable damage.
Question. What is the interest in asteroids?
Answer. Asteroids contain clues to how our Solar System formed. Your physical makeup and makeup can also help answer the big question of how life came about.
P. How many have we identified, and what are they made of?
R. So far we have identified more than a million asteroids, but in space there are dozens, if not hundreds of millions that we are unaware of. This is because, unlike stars, asteroids do not emit their own light, but only reflect sunlight, so many of the smaller ones are difficult to distinguish. Their composition depends on where they formed in the Solar System. Those that made it closer to the Sun are those that have suffered the most from the effects of heat, which has caused them to lose matter that could have been very interesting to study. But the most abundant are the C-type asteroids (carbonaceous), probably composed of clay and siliceous rocks, which formed in the area furthest from our star and are among the oldest objects in the solar system. However, they are difficult to detect due to their relatively dark color.
“There are many, many more small asteroids than large asteroids, and due to their size, they are difficult to detect and track.”
Then we have brighter variants. Those of type M (metallic), composed mainly of iron, are found mainly in the intermediate section of the asteroid belt (located more or less between Mars and Jupiter). The S type [stony, es decir, rocosos], which contains siliceous materials and nickel-iron, is generally found in the interior of the asteroid belt.
Most meteorites [un pequeño fragmento de un asteroide o de un cometa que sobrevive al viaje a través de la atmósfera terrestre] found on Earth are metallic or rocky. The carbonaceous type is more difficult to find on the Earth’s surface, unless the asteroid was quite large, since it has to survive our planet’s atmosphere without undergoing total combustion. In short, the types of meteorites that we find on earth do not have to be representative of the type of asteroids that could collide with our atmosphere.
P. What kind of asteroids are scientists worried about because of the danger they pose?
R. In principle, an asteroid of any size could hit us, but the largest are easy to detect. Most of us have identified them and they do not pose a danger. There are far more small asteroids than large asteroids, and because of their size, they are difficult to detect and track. We have to look for them several times to determine their orbit and to know where they will be in space.
Our focus is on small asteroids, which measure between 100 and 500 meters. This size range is probably the most dangerous, because it could cause significant damage to the Earth, for example on a regional or national scale. But we still don’t know where they all are. That is why asteroids of this size range are key to the defense of the Earth, since there is a danger that one day we will discover that one that we did not know existed is heading towards us.
Space scientists are trying to improve our ability to detect these smaller asteroids and then assess whether they pose a threat and ultimately whether we have to try to deflect the object.
As part of the NEO-MAPP project, we are contributing to the preparation of these planetary defense missions, improving the space instruments related to the measurement of the properties of the surface, subsurface and internal structure of asteroids, since these parameters will be what determine the success or failure of a diversion mission. Another objective is to generate greater knowledge about landing on an asteroid, the consequences of the low-gravity environment of these objects, and how to interpret the data recorded during interactions on the surface.
“The asteroids that could hit us are fundamentally in the range of between 100 and 500 meters in size
P. Once you have detected an asteroid that you want to explore, how do you go about landing on it?
R. Before the first space missions, it used to be believed that asteroids were nothing more than bland chunks of rock, but we are beginning to realize that they are actually much more interesting. They have their own evolutionary history, which is very important for understanding the Solar System in general.
The only way to check the mechanical and physical properties of an asteroid is to touch it and interact directly with it, but we do not know well the real surface of these objects, behind which there is a low-gravity environment. It is a truly strange place, usually covered in granular matter such as sands, rocks, and boulders, depending on the type of asteroid and its size. Everything indicates that, in this low-gravity environment, this granular material behaves much more like a fluid than the same material would behave on Earth.
For this reason, the landings of previous missions have had different degrees of success, so now we are studying what happens when landing in gravitational conditions similar to those of these asteroids.
P. You are part of the European Space Agency’s Hera mission, which will be the continuation of NASA’s DART mission to a binary asteroid system. What do you hope to achieve with them?
R. DART is a future planetary defense mission designed to collide with a near-Earth asteroid called Dimorphos that orbits like a moon around the larger asteroid Didymos. The idea is to check if the orbit of Dimorphos can be deviated. In the days that follow we will know if the deviation has been successful or not. Hera will then study and characterize the asteroid pair and the resulting crater.
Hera’s main ship will not touch the surface, and will conduct the investigations by orbiting the asteroids. However, minisatellites called cubesats they will land on the moon. One of them, for example, will orbit to study the asteroid (its main instrument is a radar to explore its interior), and then it will descend to the surface. The landing part of the mission is an “extra” for science (since it is not necessary to fulfill the mission objectives), but extremely interesting to characterize the physical properties of the asteroid.
The idea of these missions is to test a key deflection method, and to understand the target they are targeting. Although Dimorphos does not pose a threat to Earth, its size is about the same as that of asteroids that could pose a danger. What we want is to have a well-characterized large-scale experiment that we can use to extrapolate to any other potential asteroid threat. To do this we have to gain knowledge about our targets, including their shape and density, the size of the impact crater, and the level of debris generated after the collision.
By measuring the physical properties and characterizing the target in detail, we will be able to calibrate our mathematical models of the impact. If one day a potentially threatening asteroid crosses our path, we can use these models to predict what might happen if we try to deflect it.
Another part of Hera is the plan to take a look inside the moon. I think it will be very exciting to see what is there, because that will tell us a lot about the history of the asteroid pair.
“The only way to check the mechanical and physical properties of an asteroid is to touch it and interact directly with it, but we do not know well the real surface of these objects.
P. In other words, we are preparing to deal with any asteroid that could cause damage to the Earth. But how likely is an asteroid to wipe us out?
R. Small asteroids, including bodies tiny enough to call them space dust, collide with our atmosphere every day. They are the shooting stars. The probability of an asteroid causing large-scale damage is very small. The size range between 100 and 500 meters is the most dangerous. That is why scientists are working on it. In general, we can sleep soundly knowing that it is extremely unlikely that an asteroid is going to wipe us out.
Translation of NewsClips.