Europe's Hera probe arrives this month at the asteroid NASA rammed in 2022; first close-ups due Nov. 25
Hera's camera has already split the target into two asteroids, a half-mile-wide one and its football-stadium-size moon. Its job is to find out what the 2022 crash did to the moon.
The European Space Agency's Hera spacecraft arrives this month at Dimorphos, the small asteroid NASA deliberately crashed a spacecraft into in 2022, ESA said Tuesday. Its first detailed pictures of the impact site are due Nov. 25.
What it's visiting
Dimorphos is a 151-meter (495-foot) chunk of rock, about the size of Egypt's Great Pyramid, that orbits a bigger asteroid, Didymos. Didymos is 780 meters across, about half a mile, and spins once every two hours and 15 minutes. The two are about 1.15 km (0.7 mile) apart, and Dimorphos moves at about 18 centimeters per second, slower than half a mile per hour. The pair is about 197 million km (122 million miles) from Earth, so a radio command takes about 11 minutes to reach Hera.
Why go back to a crash site
On Sept. 26, 2022, NASA's DART spacecraft, about 550 kg (1,200 pounds), hit Dimorphos at 6.1 km per second, about 13,600 mph. It knocked loose an estimated 16 million kg (35 million pounds) of rock and dust, about 0.5% of the asteroid, and shortened Dimorphos's orbit around Didymos by about 33 minutes, far more than simulations predicted. It was the first time humans measurably changed the path of an object in the solar system.
What nobody knows is what the crash did to Dimorphos itself: whether it left a crater or reshaped the whole asteroid, what it is made of and how much it weighs. ESA says its mass is still uncertain by tens of percent. Those answers would tell planners how hard to hit a dangerous asteroid someday. Hera is ESA's first planetary defense mission.
What Hera has seen so far
On Oct. 18, from 1,280 km (795 miles) away, Hera's black-and-white Asteroid Framing Camera caught the two asteroids as separate dots for the first time; Dimorphos filled about one pixel. It is "clearly well separated from its parent body," said Michael Kueppers, ESA's Hera mission scientist. By our arithmetic, Didymos looked from there about one-fifteenth as wide as the full moon looks to us. Braking burns in October slowed Hera to about 20 meters per second (45 mph) relative to the asteroids, and three smaller burns planned for late October were to bring it nearly to a stop alongside them.
The spacecraft
Hera, about the size of a small car and weighing up to 1,214 kg (2,680 pounds) fully fueled, launched from Cape Canaveral, Fla., on Oct. 7, 2024, and swung past Mars in spring 2025. It carries two shoebox-size satellites, Juventas and Milani, to be released early next year. Juventas carries the smallest radar ever flown in space to look inside Dimorphos for hidden voids, and Hera's mission plan ends with a landing attempt. The pair is far too faint to see with a backyard telescope.
Source: European Space Agency, "10 asteroid mysteries that Hera will explore" (Nov. 3, 2026), "First light: Hera resolves two asteroids instead of one" (Oct. 27, 2026), "Braking news! Time for ESA's Hera asteroid mission to go slow" (Oct. 7, 2026), Hera mission and spacecraft pages; NASA/JPL Small-Body Database (Didymos). Drafted by AI for San Jose from ESA material, in our own words.
- ESA: 10 asteroid mysteries that Hera will explore (Nov. 3, 2026)
- ESA: First light: Hera resolves two asteroids instead of one (Oct. 27, 2026)
- ESA Multimedia: Hera's first view of the separate Didymos and Dimorphos asteroids (credit ESA, ESA Standard Licence)
- ESA: Braking news! Time for ESA's Hera asteroid mission to go slow (Oct. 7, 2026)
- ESA: The Hera Spacecraft (mission facts)
- NASA/JPL Small-Body Database: 65803 Didymos