In observing Dimorphos, the small asteroid that the probe DART impacted in September 2022, researchers as well as students at a California high school have discovered unexpected orbital changes.

Recent observations have indicated the asteroid is tumbling since the impact. However:

Dimorphos also appeared to be continuously slowing down in its orbit for at least a month after the rocket impact, contrary to NASA’s predictions. California high school teacher Jonathan Swift and his students first detected these unexpected changes while observing Dimorphos with their school’s 2.3-foot (0.7 meter) telescope last fall. Several weeks after the DART impact, NASA announced that Dimorphos had slowed in its orbit around Didymos by about 33 minutes. However, when Swift and his students studied Dimorphos one month after the impact, the asteroid seemed to have slowed by an additional minute — suggesting it had been slowing continuously since the collision. “The number we got was slightly larger, a change of 34 minutes,” Swift told New Scientist. “That was inconsistent at an uncomfortable level.”

Swift presented his class’s findings at the American Astronomical Society conference in June. The DART team has since confirmed that Dimorphos did indeed continue slowing in its orbit up to a month after the impact — however, their calculations show an additional slowdown of 15 seconds, rather than a full minute. A month after the DART collision, the slowdown plateaued.

One explanation proposed for this slowdown points at the spray of rocks and boulders that surrounded Dimorphos after DART’s impact. When some of those boulders fell back onto the asteroid, they might have caused the orbital slowdown, and as the number of new impacts dropped, the slowdown stabilized.

Now that a full year has passed since the impact, it is possible to assess the full orbital changes to the asteroid. Thus, a new report is expected shortly.