Before and after: how DART reshaped Dimorphos

From a boulder-strewn oblate spheroid to a flattened, possibly tumbling moonlet — what the impact did to Dimorphos itself.

Published 2026-10-23

Dimorphos's name means “having two forms,” and DART gave it exactly that: a before and an after.^[5]

Before: a boulder-covered moonlet

Before the impact, Dimorphos was shaped like an oblate spheroid — slightly squashed — with a surface covered in boulders but virtually no craters.^[5] DART's final images showed an egg-shaped body strewn with rocks, suggesting a rubble pile held together by weak gravity.^[5] Its surface is young, less than 0.3 million years old.^[5]

The impact

On September 26, 2022, DART hit Dimorphos at about 6.1 km/s.^[1] The 610 kg spacecraft carried no science instruments; its camera, DRACO, guided it to the center of the moon and provided the only detailed views of the surface.^[6] DART's last complete image was taken about 12 km away, two seconds before impact.^[1]

After: a new orbit

Dimorphos's 11.92-hour orbit around Didymos was shortened by 33 minutes.^[5][1] The momentum transferred was about 3.6 times what DART alone could deliver, because the ejecta acted like a rocket blast.^[6] More than 1,000,000 kg of dusty debris flew off, forming a tail at least 30,000 km long.^[6]

After: a new shape

Studies indicate the impact changed Dimorphos from a roughly symmetrical oblate spheroid into a flatter oval — a triaxial ellipsoid.^[5] It was predicted to have resurfaced the whole moon and left a crater several tens of meters across.^[5]

After: tumbling?

Brightness changes suggest Dimorphos may now be tumbling chaotically. If so, tidal forces from Didymos should gradually return it to a tidally locked state within several decades.^[5] ESA's Hera, arriving in November 2026, will see the “after” form up close.^[3]

Numbered citations link to the sources list on the Dimorphos overview page.