Rocks taken out from NASA's experiment to change the orbit of an asteroid may collide with Mars in the future. Space Portal website |

NASA's (National Aeronautics and Space Administration) Asteroid Orbit Adjustment Mission, which investigated whether it was possible to intentionally alter the asteroid's orbit.Arrow“, the satellite of the asteroid that became the target.”Dimorphos“It successfully changed its orbit. The experiment also yielded some unexpected results, including the ejection of boulders several meters across.

The research team consists of Marco Finucci from NEOCC (Near-Earth Object Coordination Center) and Albino Carbognani from INAF (Italian National Institute of Astrophysics).By tracking the paths of 37 rocks observed flying 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 asteroid's orbit

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

NASA's mission to change the asteroid's orbitArrow“It was a mission carried out to find out if exactly this way was possible. In the DART mission, the Didymos satellite orbits the asteroid No. 65803 Didymos.”DimorphosWe collided with the main body of the spacecraft and checked whether it was possible to reduce its orbit.

On September 26, 2022, DART collided with Dimorphos. Observations conducted in space and on Earth revealed some unexpected consequences of the collision. For example, the orbital period was expected to shorten by about 10 minutes due to orbital downsizing, but in reality it was more than three times as high, to about 33 minutes. The reason for this discrepancy in expectations is thought to be that Dimorphos is not a single mass of rock, but rather consists of countless small, loosely connected rocks. With such a structure, it is difficult to accurately estimate the impact after collision through simulation.

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Another unexpected result is rocks being blown off Dimorphos. Through observations made by the Hubble Space Telescope,A total of 37 boulders with diameters ranging from 1 to 7 m were traced from Dimorphos.(※1). It was not expected in advance that such a large number of large rocks would fly. It is believed that these rocks were not thrown directly by the energy of the impact, but by reaction when the entire dimorphos, which consists of loosely connected rock fragments, were shaken by the impact of the impact.

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

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・Multiple boulders several meters wide were detected ejected from “Dimorphos” and the target of the “DART” impact experiment (August 8, 2023)

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

Finucci and Carbognani's research team estimated changes in the rock's orbit over the next 20,000 years to determine the fate of the rock ejected from DART. It is usually impossible to accurately estimate the orbit of such a small celestial body. However, in this case, this research is 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 the 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 MarsAt 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.

*2…The closest approach will be about 3 million kilometers in about 2500 years.

If a rock several meters in diameter hits the Earth, it will either completely burn up in the Earth's atmosphere or leave only small fragments behind. However, Mars has an atmosphere that is only 0.75% thinner than Earth's, so it would likely fall with little resistance. The researchers also examined this effect: If a rock is relatively strong, it will fall to the surface without losing much of its mass;A crater with a diameter of 200 to 300 meters is formed.I expected. However, it is not clear whether the dimorphos rock is solid or not. If it is more fragile than expected, it may break in the air, and there may be no visible impact on the ground.

Although no life has been found on Mars yet, there is a good chance that humans will establish a base on Mars within a few thousand years. It is difficult to detect small asteroids like these, with a diameter of several meters. Although this is a distant future, bases on Mars that do not have adequate protection from the atmosphere would be at risk of collisions 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 bodies falling to Earth. Tens of thousands of celestial objects 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 was assumed that these meteorites originated from asteroids in the asteroid belt between Mars and Jupiter.

But as observational capabilities improved, it became clear that there are “near-Earth asteroids” that pass very close to 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 it fell, originally originated from the fourth asteroid “Vesta” in the asteroid belt, but subsequent research led to a The theory is that the origin may be asteroid No. 454100 (2013 BO73), a near-Earth asteroid with a diameter of about 500 metres.

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

According to one study, it is estimated that when a small celestial body with a diameter of about 1 meter collides with an asteroid with a diameter of about 100 meters, some of the fragments scattered by the collision fall to the Earth and are sometimes found in the form of meteorites on the surface of the Earth. Some say they make up about 4% of fireballs, while others say they make up about 40% or even 70% of meteorites discovered.

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

With current technology, it is difficult to detect an asteroid alone, even if it is about 100 meters in diameter. Moreover, the DART mission is actually the first time that we have been able to detect a small celestial body with a diameter of about 1 meter and predict its orbit accurately.(※3). The long-range rock path predictions made this time may have an impact on estimating the origin of meteorites found on Earth.

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

source

• M. Finucci and A. Carbognani. “Long-term orbital evolution of dimorphos rocks and their implications for the origin of meteorites”. (Monthly Notices of the Royal Astronomical Society)
• Filip Hlubek and Juraj Toth. “Orbital evolution and possible parent asteroids of 40 meteorites instrumentally observed”. (Planetary and space sciences)
• a. Carbognani and M. Finucci. “Identifying the parent bodies of meteorites among near-Earth asteroids.” (Monthly Notices of the Royal Astronomical Society)
• E. Peña Asencio, et al. “Identifying meteorite drops among clusters of bright ‘scattered’ fragments imaged by the Spanish Meteor Network during the spring of 2022.” (Monthly Notices of the Royal Astronomical Society)
• Peter Jeniskens, et al. “Impact and recovery of asteroid 2018 LA”. (Meteorites and Planetary Science)

Text / Riri Ayaka Editing / sorae editorial department