Rocks ejected from NASA’s experiment to change the orbit of an asteroid may collide with Mars in the future | sorae Space portal site

NASA’s (National Aeronautics and Space Administration) asteroid orbit modification mission, which verified whether it is possible to intentionally change the orbit of an asteroid.DART”, the satellite of the asteroid that became the target object “Dimorphos” successfully changed its orbit. The experiment also had some unexpected results, one of which was the ejection of several meters wide boulders.

The research team of Marco Fenucci from NEOCC (Near Earth Object Coordination Center) and Albino Carbognani from INAF (Italian National Institute of Astrophysics)By tracking the trajectories of 37 rocks observed to have flown out during the DART mission, researchers found that four of them have the potential to collide with Mars in the future.The results of this analysis may be important in considering the origin of small celestial bodies that collide with Earth and Mars.

■“DART” mission to intentionally change the orbit of an asteroid

The most likely theory is that the mass extinction at the end of the Cretaceous period, which occurred approximately 66 million years ago, was caused by an asteroid impact. If a similar celestial collision were to occur, the current civilization would suffer catastrophic damage, so even if it is not an urgent issue, the search for ways to avoid celestial collisions continues. One of the most practical methods with current technology is to collide an artificial object with an asteroid at high speed and use its kinetic energy to change its orbit.

NASA’s asteroid orbit change mission “DART” was a mission carried out to find out if exactly this method was possible. In the DART mission, the satellite “Didimos” orbiting around the asteroid No. 65803 “Didimos”DimorphosWe collided the main body of the spacecraft with “ and verified whether it was possible to reduce its orbit.

On September 26, 2022, DART collided with Dimorphos. Observations conducted both in space and on the ground revealed some unexpected results of the collision. For example, it was expected that the orbital period would be shortened by about 10 minutes due to the reduction of the orbit, but in reality it was more than three times as long, to about 33 minutes. The reason for such a discrepancy in predictions is thought to be that Dimorphos is not a single block of rock, but is made up of countless small rocks that are loosely connected. With such a structure, it is difficult to accurately estimate the impact after a collision through simulation.

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・Reconfirming better-than-expected results Verifying NASA’s asteroid orbit change mission “DART” (March 15, 2023)
・The shape of “Dimorphos” may have changed significantly due to the collision with “DART” (March 27, 2024)

Another unexpected result is rocks flying off Dimorphos. Through observations by the Hubble Space Telescope,A total of 37 rocks with diameters ranging from 1 to 7 meters were traced from Dimorphos.(*1). It was not predicted in advance that so many large rocks would fly out. It is thought that these rocks were not ejected directly by the energy of the collision, but by the reaction when the entire Dimorphos, which is made up of loosely connected rock fragments, was shaken by the impact of the collision.

*1…However, due to limitations in observation ability, the minimum diameter that can be accurately estimated is 4m.

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・Multiple rocks several meters wide ejected from “Dimorphos” were observed Target object of the collision experiment “DART” (August 8, 2023)

■It turns out that a protruding rock may collide with Mars

Fenucci and Carbognani’s research team estimated changes in the orbit of the rock over the next 20,000 years to determine the fate of the rock that ejected from DART. It is normally impossible to accurately estimate the orbit of such a small celestial body. However, in this case, this research was made possible because we have a clear reference point called Dimorphos and we know the exact time it flew from there, allowing us to calculate a more accurate orbit.

After repeating simulations for 37 rocks, taking into account errors, we found that they will not collide with Earth for at least the next 20,000 years.(*2). But on Mars,At least 4 rocks can collideI understand that.Two of them are likely to collide in about 6,000 years, and the remaining two in about 15,000 years.there is.

*2…The closest approach will be approximately 3 million km in approximately 2,500 years.

If a rock several meters in diameter were to collide with Earth, it would either burn up completely in Earth’s atmosphere or leave only small fragments. However, Mars has an atmosphere that is only about 0.75% thinner than Earth’s, so it is possible that it will fall with little resistance. The authors also examined this effect: If a rock is relatively strong, it will fall to the surface without losing much mass;A crater with a diameter of 200 to 300 m is formed.I predicted. However, it is not clear whether the Dimorphos rock is solid. If it is more brittle than expected, it may break apart in the air, and there may be no obvious impact on the ground.

Although no life has been found on the surface of Mars so far, there is a good chance that humans will set up a base on Mars in a few thousand years. Small asteroids like this, only a few meters in diameter, are difficult to observe. Although this is a distant future, bases on the surface of Mars that are not protected by a sufficient atmosphere will be at risk of collision with even small celestial bodies.

■Research into the origin of meteorites found on Earth

The results of this study also provide interesting insights into the origin of celestial objects that fall to Earth. Tens of thousands of celestial bodies fall to Earth every day, and it is estimated that between 10 and 50 of them reach the earth’s surface as meteorites. Traditionally, it has been assumed that these meteorites originated from asteroids in the asteroid belt between Mars and Jupiter.

However, as observational capabilities improve, it becomes clear that there are “near-Earth asteroids” that pass very close to the Earth.Could debris from a near-Earth asteroid fall as a meteorite?A theory has emerged. For example, “2018 LA” (meteorite name “Motopi Pan Meteorite”), one of the rare asteroids discovered in space before falling, originally originated from the fourth asteroid “Vesta” in the asteroid belt. However, subsequent research has led to a theory that the origin may be asteroid number 454100 “2013 BO73”, a near-Earth asteroid with a diameter of approximately 500 m.

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・Did the meteorite that fell in Botswana in 2018 come from the asteroid Vesta? (May 3, 2021)

According to one study, it is estimated that when a small celestial body with a diameter of about 1 m collides with an asteroid with a diameter of about 100 m, some of the fragments scattered by the impact fall to the earth and are sometimes found as meteorites on the earth’s surface. Some say it accounts for about 4% of fireballs, while others say it’s about 40% or even 70% of discovered meteorites.

On the other hand, in the DART mission, the main body of the probe, which has a mass of about 570 kg, collided with Dimorphos, which has a diameter of about 170 m and a mass of about 4 million tons, at a speed of about 6.6 km per second, resulting in multiple rocks several meters in diameter being scattered. The energy at this time is about 1/16 of the situation in which a small celestial body about 1 m in diameter collides with an asteroid about 100 m in diameter, but it shows that a sufficiently similar situation can still occur.

With current technology, it is difficult to discover an asteroid alone, even with a diameter of about 100 meters.Furthermore, the DART mission is actually the first time that we have been able to discover a small celestial body with a diameter of about 1 m and accurately predict its orbit.(*3). The long-term trajectory predictions of rocks made this time may have an impact on estimating the origin of meteorites found on Earth.

*3…Some asteroids that have come very close to Earth or collided with it are estimated to have a diameter of several meters. However, the number of observations of these asteroids is limited, and their orbits can only be predicted very roughly, making it difficult to estimate their origin.

Source

• M. Fenucci & A. Carbognani. “Long-term orbital evolution of dimorphos boulders and implications on the origin of meteorites”. (Monthly Notices of the Royal Astronomical Society)
• Filip Hlobik & Juraj Tóth. “Orbital evolution and possible parent asteroids of 40 instrumentally observed meteorites”. (Planetary and Space Science)
• A. Carbognani & M. Fenucci. “Identifying parent bodies of meteorites among near-Earth asteroids”. (Monthly Notices of the Royal Astronomical Society)
• E. Peña-Asensio, et al. “Identifying meteorite droppers among the population of bright ‘sporadic’ bolides imaged by the Spanish Meteor Network during the spring of 2022”. (Monthly Notices of the Royal Astronomical Society)
• Peter Jenniskens, et al. “The impact and recovery of asteroid 2018 LA”. (Meteoritics & Planetary Science)

Text/Riri Ayaka Edit/sorae Editorial Department