NASA's DART mission reveals unexpected asteroid tumbling
NASA's Double Asteroid Redirection Test (DART) successfully altered the orbit of the asteroid Dimorphos more than expected, but scientists were puzzled by the discovery that the impact caused the moonlet to start tumbling. The mission, which involved crashing a spacecraft into Dimorphos in September 2022, aimed to test planetary defense techniques. Observations from ground-based telescopes confirmed the surprising rotational change.
In a groundbreaking experiment for planetary defense, NASA's DART spacecraft slammed into the asteroid moonlet Dimorphos on September 26, 2022, at a speed of about 6 kilometers per second. The target was part of the binary asteroid system with the larger Didymos, approximately 160 meters in diameter and orbiting its parent body every 11 hours and 55 minutes before the impact.
Initial results, announced in 2023, showed that the impact shortened Dimorphos's orbital period by 32 minutes and 12 seconds, far exceeding the predicted 7-minute change. This demonstrated the effectiveness of kinetic impactors in deflecting near-Earth objects. However, new analysis from the James Webb Space Telescope and other observatories revealed an unanticipated outcome: Dimorphos is now tumbling chaotically rather than rotating smoothly.
"The tumbling was completely unexpected," said Andy Rivkin, a planetary scientist at Johns Hopkins Applied Physics Laboratory and DART investigation lead. "We had models for orbital changes, but not for this kind of rotational disruption." The tumbling complicates future deflection strategies, as it affects how momentum is transferred during impacts.
Background context underscores the mission's importance. With over 30,000 known near-Earth asteroids, NASA aims to develop methods to prevent potential collisions with Earth. DART was the first full-scale test of such a technique, launched in November 2021 from Vandenberg Space Force Base. The European Space Agency's Hera mission, set to arrive at the system in 2026, will provide closer inspection to study the impact site's boulder ejections and the moonlet's altered shape.
Scientists note that while the orbital shift succeeded, the tumbling raises questions about the ejecta plume's role in amplifying the effect. "The unexpected outcome doesn't invalidate the test; it enhances our understanding," Rivkin added. This discovery highlights the complexities of asteroid dynamics, informing refined models for defending against cosmic threats.
No immediate risks to Earth arise from this event, as Didymos and Dimorphos will not approach closely until 2123. The findings, published in journals like Nature Astronomy, emphasize the need for continued observation and simulation to predict asteroid behavior accurately.