ESA’s Hera got its first look at the asteroids DART crashed into, with close-ups due Nov. 25

ESA’s Hera spacecraft has separated the two halves of its target for the first time. An image taken on the evening of Oct. 18 from 1,280 km away shows Didymos and its moon Dimorphos as distinct objects, where earlier frames showed a single point of light. The first detailed pictures of Dimorphos, the body NASA’s DART spacecraft struck in 2022, are scheduled for release on Nov. 25.

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Dimorphos fills about one pixel in the new frame, so no crater or boulder is visible yet. The picture settles the geometry of the pair and leaves the geology for later.

The Asteroid Framing Camera and the 1,280 km frame

The image came from Hera’s black-and-white Asteroid Framing Camera, ESA reported on Oct. 27, with the asteroid pair roughly 197 million km from Earth. Michael Kueppers, quoted in the agency’s account, said the smaller asteroid becomes visible for the first time with this image. Ian Carnelli, Hera’s mission manager, said the frame is the first time anyone is seeing the double asteroid system through Hera’s own eyes. ScienceDaily republished the ESA text on Nov. 3.

Two thruster firings a week apart in early October slowed Hera to 20 m/s relative to the asteroids, which allows a gradual, fine-tuned approach. Didymos measures about 780 m across, slightly smaller than the Burj Khalifa is tall, and Dimorphos about 151 m, comparable to the Great Pyramid of Giza. Dimorphos circles Didymos at an average separation of 1.15 km, moving at roughly 18 cm/s.

What DART changed and what Hera must measure

NASA’s DART struck Dimorphos on Sept. 26, 2022, at about 6.1 km/s. In an October 2022 NASA release, the agency reported that the moon’s orbit around Didymos shortened by 32 minutes, from 11 hours 55 minutes to 11 hours 23 minutes, with an uncertainty of about 2 minutes. NASA had set a minimum success benchmark of 73 seconds, and DART beat it by more than 25 times. The release put the impact speed at about 22,530 km per hour and said neither asteroid posed a hazard to Earth before or after the hit. ESA’s account says the views will sharpen as Hera moves closer, and gives no specific arrival date. ESA and DLR cite about 33 minutes, so the 2022 figure and the later wording differ by a minute.

Debris from the impact was thrown as far as 10,000 km, and the deflection came out larger than computer simulations predicted. Hera’s job is to find out why. ESA describes Dimorphos as the first object in the Solar System whose orbit has been measurably shifted by human action. ESA’s open questions include whether DART left a crater, whether it altered the moon’s overall shape, and what the mass, composition and internal structure of Dimorphos turn out to be.

DLR’s page adds context on the hardware that made the 2022 test possible. DART weighed about half a tonne, and DLR calls the mission the first experiment to use the kinetic impact method to deflect an asteroid, describing it as successful. Earth-based observations, not DART itself, produced the orbit-period measurement, because the spacecraft was destroyed on impact. Hera is the follow-up that can measure the result up close.

Nov. 25 close-ups, two CubeSats and a landing

ESA says the Nov. 25 release will carry the first detailed images of Dimorphos and opens a crash site investigation running over the coming months. DLR’s mission page says Hera is expected to arrive in the Didymos system at the end of 2026, and no source read this run gives a firmer arrival date.

Hera also carries two small CubeSats. According to ESA’s CubeSat page, Milani, built by Tyvak in Italy, carries the ASPECT hyperspectral imager to map surface minerals and the VISTA instrument to detect dust and volatiles such as water. Juventas, built by GomSpace in Luxembourg, will perform the first radar sounding of an asteroid’s interior, probing up to 100 m into Dimorphos with its JURA radar, and can land to measure gravity with its GRASS gravimeter. ESA’s account says Hera itself will eventually attempt a landing.

Nancy Chabot of Johns Hopkins APL, DART’s coordination lead, said in 2022 that the mission had returned fascinating data about both asteroids and had shown how effective a kinetic impactor can be as a defense technology. Hera’s measurement of Dimorphos’s mass is what would let engineers turn that single result into a repeatable method, and DLR describes the aim as a reproducible planetary defence technique. Lori Glaze, director of NASA’s Planetary Science Division, called the 2022 result one important step toward understanding the full effect of DART’s impact, and Johns Hopkins APL built and operated the spacecraft for NASA’s Planetary Defense Coordination Office. ESA also runs a public companion platform for the mission at hera.esa.int, where questions about the approach can be posted. Whether the Nov. 25 images show a crater remains to be seen.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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