"A step forward" for "planetary defense": NASA succeeds in deflecting the trajectory of an asteroid around the Sun

Four years ago, NASA crashed a spacecraft into a small asteroid to try to deflect its trajectory, a maneuver worthy of a science fiction novel that aimed to learn how to protect humanity from a possible future threat.

Named Dart, this unprecedented test mission targeted a small, harmless asteroid called Dimorphos, a moon of a larger asteroid, Didymos. The impact of the spacecraft caused Dimorphos to adopt a shorter, faster trajectory around Didymos, around which it orbits.

But it also propelled this duo into a slightly different orbit around the Sun, according to a study published this week in the journal Science Advances.

Plan for "planetary defense"

These additional analyses thus provide solid data for establishing a "planetary defense" plan should an asteroid threaten to strike Earth in the future, point out the international researchers behind this study.

Their detailed observations document the effects of the 2022 Dart mission and show that for "the first time" a "human-made object has measurably altered the trajectory of a celestial body around the Sun," NASA noted in a statement.

Data that is difficult to track

To do this, the researchers studied stellar occultations, that is, the moments when an asteroid passes in front of a star and causes a brief dimming of its brightness, explains the study's lead author, Rahil Makadia, to AFP. These occultations allowed them to obtain ultra-precise measurements of the asteroid's position, speed, and shape.

However, they are difficult to track. The team therefore relied on amateur astronomers from around the world, who recorded 22 of these stellar occultations. Using this data, along with years of additional observations, they were able to measure Didymos's orbit around the Sun with great precision, explains Rahil Makadia. "We were able to measure the exact order of this change" and perform calculations that could aid future "planetary defense efforts," he continues. The calculated change in the orbit was minuscule, with the orbital period changing by only 0.15 seconds. Although minimal, this change is enough to make a difference, the scientists assert. "Given enough time, even a minimal change can result in a significant deflection," notes Thomas Statler, a NASA scientist, in a statement. "The incredibly precise measurements taken by the team confirm once again the effectiveness" of this planetary defense technique, and show how a binary asteroid system—that is, a system composed of two asteroids like Dimorphos and Didymos—"could be deflected by striking only one of the two asteroids that compose it."