ESA's Hera Probe Splits Double Asteroid Didymos Into Two Worlds for the First Time
From 1,280 km away, the planetary-defense spacecraft separated Didymos from its moonlet Dimorphos, the only object in the solar system whose orbit humans have measurably shifted.
A European spacecraft built to inspect the aftermath of humanity's first asteroid-deflection test has seen its targets with its own eyes, and the picture shows two objects where, until now, there was one point of light.
The European Space Agency's Hera spacecraft resolved the two asteroids of the Didymos system separately for the first time, revealing the system's binary nature. The pair is currently about 197 million km (122 million miles) from Earth. Hera imaged Didymos and its small companion Dimorphos with its monochromatic Asteroid Framing Camera on the evening of Oct. 18, from 1,280 km (795 miles) away. At that distance Dimorphos shows up as roughly a single pixel.
The image followed the success of Hera's braking maneuvers earlier this month. A pair of thruster firings a week apart slowed the spacecraft to just 20 meters per second (45 miles per hour) relative to the asteroid pair, letting it close the distance gradually and on a fine-tuned approach.
"For the first time we are seeing through Hera's own eyes the double asteroid system that the mission was designed and built for," said mission manager Ian Carnelli. "Our views will grow much sharper as Hera comes closer. We will unveil the first detailed images of Dimorphos, the first object in the solar system to have had its orbit measurably shifted by human action, on Nov. 25."
That orbital shift came from NASA's DART probe, which slammed into Dimorphos on purpose to test whether a spacecraft could redirect an asteroid. The impact shortened the moonlet's orbital period around Didymos by about 33 minutes. DART gave scientists the result from afar, through telescope observations. What it could not do was show them what the collision did to the asteroid itself.
Hera is meant to fill that gap. Over the coming months it will carry out a close-up "crash site investigation" of Dimorphos, using multiple instruments and deploying a pair of shoebox-sized CubeSats for a still closer survey, eventually progressing to landing. The mission aims to measure Dimorphos's mass and internal structure and document the changes the impact caused. Those numbers decide how well the technique, known as kinetic deflection, would work against a real threat, since the push an asteroid receives depends on what it is made of and how loosely it is held together.
For now, the milestone is a proof that the spacecraft's camera, navigation and braking all work as planned. The detailed first look at Dimorphos is scheduled for Nov. 25.
