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A European spacecraft and two shoebox-size satellites are about to launch to survey the aftermath from NASA’s DART mission, which intentionally slammed into an asteroid named Dimorphos and altered its orbit two years ago.
The European Space Agency’s Hera mission is expected to lift off aboard a SpaceX Falcon 9 rocket at 10:52 a.m. ET on Monday from NASA’s Kennedy Space Center in Florida. If Hera doesn’t launch on Monday, there are opportunities until October 27, according to the ESA.
The spacecraft and its two CubeSat companions are slated to arrive at the asteroid Dimorphos, and the larger asteroid it orbits named Didymos, in late 2026. Together, the three spacecraft will conduct a “crash scene investigation” to solve the remaining mysteries about the double-asteroid system, according to ESA scientists.
NASA planned the DART, or Double Asteroid Redirection Test, mission to carry out a full-scale assessment of asteroid deflection technology on behalf of planetary defense. The agency wanted to see whether a kinetic impact — such as crashing a spacecraft into an asteroid at 13,645 miles per hour (6.1 kilometers per second) — would be enough to change the motion of a celestial object in space.
Neither Dimorphos nor Didymos poses a danger to Earth. Still, the double-asteroid system was a perfect target to test deflection technology because Dimorphos’ size is comparable to asteroids that could threaten Earth.
Astronomers have used ground-based telescopes to monitor the impact’s aftermath since the collision in September 2022, and they determined that the DART spacecraft successfully changed the way Dimorphos moves, shifting the moonlet asteroid’s orbital period — or how long it takes to make a single revolution around Didymos — by about 32 to 33 minutes.
But many questions remain, including whether the DART spacecraft merely left behind a crater or if its momentum completely reshaped Dimorphos. And determining the exact composition of the double-asteroid system, as well as the consequences of the DART mission, could help space agencies further refine the technology that could deflect asteroids from affecting Earth in the future.
“Hera will close the loop by providing us in detail the final outcome of the DART impact,” said Patrick Michel, director of research at the National Centre for Scientific Research in France and principal investigator of the Hera mission.
Embarking on a two-year journey
When the Hera spacecraft, about the size of a small car, reaches the double-asteroid system in October 2026, it will be 121 million miles (nearly 195 million kilometers) from Earth. Didymos is a mountain-size asteroid with a diameter of 2,559 feet (780 meters), while Dimorphos is similar in size to the Great Pyramid of Giza, with a diameter of 495 feet (151 meters).
But first, Hera will swing by Mars in mid-March 2025, which will provide the spacecraft with the extra momentum needed to reach Didymos and Dimorphos two years after launching.
In addition to testing out its suite of 11 instruments, Hera will fly within 3,728 miles (6,000 kilometers) of the Martian surface. Hera will also observe one of Mars’ two moons, named Deimos, from a distance of 621 miles (1,000 kilometers).
Scientists think that both of Mars’ small, lumpy moons may be asteroids that were captured from the main asteroid belt, located between Mars and Jupiter. Hera’s flyby will capture data for Japan’s Martian Moons eXploration probe. That mission, launching in 2026, will survey both of the red planet’s moons and land a small rover on Phobos, collecting samples of that Martian moon that can be returned to Earth.
Then, Hera will arrive in orbit around the Didymos system in October 2026, spending six weeks observing both asteroids to ascertain more details about their shapes, masses, and thermal and dynamic flybys while identifying points of interest for future, closer flights.
After the six-week survey, Hera will release its two CubeSats named Juventas, the Roman name for a daughter of Hera, and Milani. Milani was named in honor of Andrea Milani, a professor of mathematics at Italy’s University of Pisa who died in 2018. Milani is known for creating the first automated system to compute probabilities that an asteroid could impact Earth in the future.
Juventas is equipped with a radar instrument that will be able to peer deep beneath the surface of the space rocks, while Milani has a multispectral imager to map minerals and dust on both asteroids. The instrument can capture a wider range of colors than the human eye can see to determine the composition of individual boulders and the dust environment around them.
The CubeSats, which have their own propulsion systems, will use inter-satellite links to communicate with Hera and relay their findings back to Earth, Michel said.
Over 10 weeks, Hera will carry out observations that bring it closer to the surface of the asteroids, eventually coming within 0.6 miles (1 kilometer). Multiple flybys are expected of the impact location created by DART on Dimorphos.
Eventually, Hera may land on Didymos, which could serve as the end of its mission or a limited extension if it survives the landing, while the CubeSats could both make similar experimental landings on Dimorphos. None of the spacecraft is specifically engineered for landing but will slow down enough to operate cameras and instruments on the asteroids after landing, according to the agency.
Surveying the aftermath
Humanity’s most detailed glimpses of the double-asteroid system has been brief.
The images captured by DART and a small satellite named LICIACube, which separated from the spacecraft to capture footage of the collision and the resulting debris cloud, have fueled much of the impact-related research released since September 2022.
But when Hera visits Dimorphos, it could look very different, Michel said.
“What is the most exciting for me is that although we have superb images of Didymos, Dimorphos and its surface taken by the DRACO camera aboard the DART spacecraft before its collision, we already know that the same bodies and surface areas will have nothing to do with what those images showed us when Hera takes new images,” Michel said. “It still feels like discovering new worlds. And the cool thing is that we will know why they are new or different, as DART gave us all the initial conditions that led to their transformation.”
Data collected by the mission could help scientists understand the internal structure of each asteroid. When DART slammed into Dimorphos, a plume of debris extended more than 6,213 miles (10,000 kilometers) into space and persisted for months — enough to create the first human-made meteor shower that may be visible on Mars and Earth in the future.
Scientists are eager to know if Dimorphos is a rubble pile asteroid, held together by gravity with large voids inside, or a solid core surrounded by boulders and gravel, Michel said.
Understanding every possible aspect of Dimorphos is crucial, mission scientists say, because if an asteroid of its size ever hit Earth, it could destroy an entire city.
While the DART mission was an “amazing success,” Michel said, Hera is necessary to understand the final outcome of DART’s deflection test and measure its efficiency.
“I hope this can offer a source of inspiration for other missions devoted to planetary defense and solar system exploration,” he said.
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