The European Space Agency's Hera spacecraft has photographed the asteroid Didymos and its small moon Dimorphos as two separate objects for the first time, marking the start of its approach to the only celestial body whose orbit humans have measurably changed. Hera took the image with its Asteroid Framing Camera on Oct. 18 from about 1,280 kilometers (795 miles) away, ESA announced on Oct. 27.

In that first frame, Dimorphos covers only about one pixel. ESA plans to release the first detailed images of Dimorphos on Nov. 25.

The stakes are practical — Hera will turn NASA's 2022 asteroid impact from a dramatic one-time test into a measured technique, telling scientists how hard they would need to hit a dangerous asteroid to push it aside if one is ever found on a collision course with Earth.

First Light From the Didymos System

Two thruster firings a week apart slowed Hera to 20 meters per second relative to the asteroids, ESA said. Didymos is about 780 meters (2,560 feet) across, while Dimorphos is about 151 meters (495 feet), roughly the size of a large stadium. The pair orbit an average of 1.15 kilometers apart, and Dimorphos circles its parent at about 18 centimeters per second.

ESA project scientist Michael Küppers said the image marked a milestone. "With this image, the smaller Dimorphos asteroid becomes visible for the first time," Küppers said. Hera mission manager Ian Carnelli called it the first view of the double asteroid system "through Hera's own eyes."

The Didymos system was about 197 million kilometers (122 million miles) from Earth at the time of ESA's announcement. Neither asteroid poses any threat to Earth, which is one reason it was chosen as a safe test target.

DART Changed an Orbit and Raised New Questions

On Sept. 26, 2022, NASA's Double Asteroid Redirection Test (DART) spacecraft deliberately crashed into Dimorphos at 6.1 kilometers per second, or about 13,600 mph. The impact sent a plume of debris across 10,000 kilometers of space and shortened Dimorphos's 11-hour-55-minute orbit around Didymos by about 33 minutes, according to ESA. NASA's first estimate after the impact was 32 minutes, later refined to about 33.

That made Dimorphos the first object in the solar system whose orbit was measurably changed by human action. But the result also created a puzzle. ESA asks which properties of Dimorphos explain a deflection so much greater than impact simulations predicted.

The likely answer lies in the debris — material blasted off the surface acted like a rocket exhaust, adding extra push beyond the spacecraft's own momentum. How much extra depends on Dimorphos's mass and internal structure, which DART could not measure because it was destroyed on impact.

Mass, Crater and Interior Measurements Ahead

Hera's main job is a crash site investigation. Its primary objective is to measure the mass of Dimorphos, which lets scientists calculate exactly how efficiently DART's momentum was transferred, according to a NASA technical summary of the mission. That number, known as the momentum enhancement factor, is what future defense planners would use to size an impactor.

Hera will also map the impact crater, or determine whether DART reshaped Dimorphos without leaving a classic crater, and measure the shape and surface of both asteroids. Its instruments include two framing cameras, a laser altimeter, a hyperspectral imager and a thermal infrared camera.

Two shoebox-sized CubeSats will extend the survey. Milani will study surface composition and dust, while Juventas carries a small low-frequency radar that ESA describes as the first radar to probe the interior of an asteroid. Radar soundings could reveal whether Dimorphos is a solid body or a loose rubble pile held together by weak gravity, which strongly affects how it responded to the impact. The mission plan ends with a landing attempt.

Planetary Defense Beyond the Image Release

Planetary defense depends on two steps: finding dangerous asteroids early, then knowing how to move them. Telescopes have catalogued most large near-Earth asteroids, and none of the known large objects poses a significant impact risk in the coming century. Smaller asteroids, including some large enough to devastate a region, remain harder to detect.

DART and Hera together form the first full test of the kinetic impactor method, which needs years of warning to work. A small nudge applied far in advance can grow into a miss distance of thousands of miles by the time an asteroid reaches Earth's orbit. Hera's data will show how reliable that nudge would be for a body like Dimorphos.

The Nov. 25 release should show Dimorphos's surface in detail for the first time since DART's final images and Italy's LICIACube flyby in 2022. Hera is expected to spend about six months studying the system, according to the German Aerospace Center (DLR), a mission partner.

For most people, the payoff is reassurance rather than immediate change. No asteroid deflection mission is planned against a real threat, and none is needed now. But the data will help space agencies decide how much warning time, spacecraft mass and speed would be required, and whether a single impact would be enough or a backup would be needed for a rubble-pile target. Nature World News will report on the first close-up images once ESA publishes them.

What Readers Want to Know

What did Hera photograph? Didymos and its moon Dimorphos as two separate objects for the first time, from about 1,280 kilometers away on Oct. 18, 2026.

What did DART do to Dimorphos? DART struck Dimorphos at 6.1 kilometers per second in 2022 and shortened its orbit around Didymos by about 33 minutes.

When will detailed images be released? ESA plans to release the first detailed images of Dimorphos on Nov. 25.

What will Hera measure? The mass of Dimorphos, the impact crater or reshaping, surface composition, and internal structure, using its cameras and two CubeSats.

Is Didymos a threat to Earth? No. The system was chosen as a safe target for testing asteroid deflection.

Why does this matter for planetary defense? Hera's measurements will show how effectively a spacecraft impact can move an asteroid, informing how a real deflection mission would be designed.