New research has found that rocky debris blown off the small asteroid Dimorphos when NASA's DART spacecraft deliberately collided with it in 2022 could trigger the first human-made meteor shower, known as the Dimorphids.
The space agency planned the Double Asteroid Redirection Test (DART) mission to conduct a large-scale evaluation of asteroid-deflection technology for planetary defense. NASA wanted to see if a kinetic impact - such as crashing a spacecraft into an asteroid at 13,645 miles per hour (6.1 kilometers per second) - would be enough to alter the motion of a celestial body in space.
Neither Dimorphos nor the large space rock it orbits, Didymos, pose a threat to Earth. Still, the binary asteroid system was a perfect target to test deflection technology, since Dimorphos's size is comparable to that of asteroids that could pose a threat to our planet.
Astronomers used ground-based telescopes to monitor the aftermath of the impact for nearly two years. They found that the DART spacecraft successfully changed the way Dimorphos moves. The lunar asteroid's orbital period (the time it takes to make one revolution around Didymos) has shifted by about 32 to 33 minutes.
But scientists also estimate that the deliberate collision generated more than 2 million pounds (nearly 1 million kilograms) of rocks and dust - enough to fill about six or seven train cars. Where exactly in space all that material will end up is still an open question.
Now, new research suggests that fragments of Dimorphos could arrive near Earth and Mars within one to three decades, with the possibility that some debris could reach the Red Planet within seven years. Small debris could also reach Earth's atmosphere within the next 10 years. The Planetary Science Journal has accepted the study for publication.
"This material could produce visible meteors (often called shooting stars) as they enter the Martian atmosphere," said study lead author Eloy Peña Asensio, a postdoctoral researcher in the Deep-space Astrodynamics Research and Technology group at the Polytechnic University of Milan in Italy. "Once the first particles reach Mars or Earth, they could continue to arrive intermittently and periodically for at least the next 100 years, which is the duration of our calculations."
Predicting space debris
The individual pieces are small, ranging from grains of sand to fragments the size of smartphones, so Peña Asensio says the debris poses no risk to Earth.
"They would break up in the upper atmosphere by a process known as ablation, caused by friction with the air at hypervelocity," he said. "There is no way that a Dimorphos material would reach the Earth's surface."
However, it is more difficult to determine when the debris reaches Earth. For this, it is necessary to estimate the velocity of the fragments.
When the spacecraft crashed into Dimorphos, it was not alone. A small satellite called LICIAcube separated from the spacecraft before impact to capture images of the collision and the debris cloud that formed afterward.
"These crucial data have enabled and continue to enable a detailed analysis of the debris generated by the impact," said Peña Asensio.
The research team used LICIACube data and the supercomputing facilities of the Consortium of University Services of Catalonia to simulate the trajectory of 3 million particles that the impact created. The computer modeling measured different possible paths and velocities of the particles through the solar system and how radiation released by the sun could affect the movement of the particles.
Previous research prior to the impact suggested that Dimorphos particles might reach Earth or Mars, Peña Asensio said. For the new study, however, the team reduced the simulations to a single set so that they matched the LICIACube data after the impact.
The results of the study confirm that if the debris were ejected from Dimorphos at a speed of 1,800 kilometers per hour (500 meters per second), some fragments could reach Mars, while other, smaller and faster-moving debris could reach Earth at a speed of 5,770 kilometers per hour (1,600 meters per second).
The team said there were still uncertainties about the nature of the debris, but they concluded that the fastest-moving particles could reach Earth in less than 10 years.
The study authors consider the possibility of the Dimorphids meteor shower reaching Earth unlikely, but they can't rule it out, Peña Asensio said. And if it did happen, it would be a small, weak meteor shower.
"The resulting meteor shower would be easy to identify on Earth, as it would not coincide with any known meteor showers," he said by email. "These meteors would be slow-moving, with peak activity expected in May, and would be visible mainly from the Southern Hemisphere, apparently originating near the constellation Indus."
Although the researchers did not explore this possibility in their paper, their studies suggested that debris from Dimorphos could reach other, nearby asteroids.
A visit to the aftermath
Debris was expected to be ejected from the impact, but the possibility of the material reaching Earth or Mars could only be calculated after the collision, said study co-author Michael Küppers, a planetary scientist at the European Space Astronomy Centre.
"Personally, I was initially surprised to see that even though the impact occurred close to Earth (about 11 million kilometers away), it is easier for the impact ejecta (debris) to reach Mars than Earth," Küppers said by email. "I think the reason is that Didymos crosses the orbit of Mars, but stays just outside the orbit of Earth."
Particles can be ejected by near-Earth asteroids like Phaethon, which is responsible for the Geminid meteor shower that peaks in mid-December each year. Studying what was released by the DART impact could help predict when such material could reach Earth or Mars, said Patrick Michel, an astrophysicist and research director at the National Centre for Scientific Research in France. Michel was not involved in the study.
"This study attempts to quantify this possibility and confirms that it can happen, even if it is based on models that have their own uncertainties," Michel said.
Future observations could help researchers refine the debris' mass measurements and determine how fast it is moving, allowing them to calculate expected meteor activity, Peña Asensio said.
These observations will be carried out by the Hera mission. The European Space Agency mission is expected to be launched in October to observe the aftermath of the DART impact and will arrive at the asteroid system by the end of 2026. Together with a pair of CubeSats, the spacecraft will study the composition and mass of Dimorphos and its transformation by the impact. Hera will also determine how much momentum was transferred from the spacecraft to the asteroid.
"Is there an impact crater, or was the impact so big that Dimorphos was reshaped globally?" said Küppers, who is also the project scientist for the Hera mission. "We have some evidence for the latter from ground data. Hera will definitely tell us. We will also see if the impact left Dimorphos (tumbling)."
Overall, the mission will allow astronomers to understand the dynamic evolution of debris "produced by an impact in such a complex system of double asteroids," Michel said.
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