Mystery Moon of Mars Discovered During Asteroid Probe Flyby
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The Hera probe made a dazzling swing around Mars, leveraging the planet's gravitational pull to propel itself towards its asteroid target. This brief rendezvous with the Red Planet granted Hera an unprecedented glimpse of Mars' lesser-known, tidally locked moon as it orbited its home planet.
On October 7, 2024, the European Space Agency (ESA) launched its Hera mission with a grand objective: inspect the aftermath of NASA's DART mission that impacted an asteroid to alter its orbit. Hera is on track to meet its asteroid target in 2026, but during its Mars flyby on Wednesday, it offered a perfect opportunity to put its science tools into action for the first time since its departure from Earth (1).
The spacecraft approached Mars to within 3,106 miles (5,000 kilometers), allowing the planet's gravity to reposition Hera's trajectory toward its target as it cruised through the cosmos. In the course of this flyby, Hera activated a treble of instruments to image the Red Planet's surface and its moon Deimos.
"Our spacecraft's instruments have been put to the test for the first time during Hera's Mars flyby, and they've proven themselves exemplary. This demonstrates their remarkable capabilities!" ESA's Hera mission scientist, Michael Kueppers, declared in a statement (1).
Mars boasts two moons: Phobos and Deimos. The latter is minuscule, with a diameter of merely 7.7 miles (12.4 km). It plausibly broke off from Mars following a colossal impact or it could be a small asteroid ensnared by the planet's gravity. Deimos takes 30 hours to complete a single orbit around Mars.
Besides capturing images of the slightly distorted moon, Hera also partook in joint observations of Deimos with ESA's Mars Express, which has stayed in Mars' orbit for over two decades (2).
Hera's target binary asteroid system is barely one-fourth the size of Deimos. Dimorphos, a 558-foot-wide (170-meter) space rock, orbits its larger 2,625-foot-wide (800-meter) companion, Didymos. In September 2022, NASA's 1,340-pound spacecraft collided with Dimorphos, intending to slightly adjust its orbit as an experiment in planetary defense. The mission was a triumph, establishing that kinetic impactors can effectively redirect dangerous asteroids should one potentially threaten Earth. Preliminary data from ground-based optical and radio telescopes indicates that Dimorphos' orbital period around Didymos has shortened from 11 hours and 55 minutes to 11 hours and 23 minutes post-collision (3).
Ground-based observations alone are insufficient. That's where Hera comes in, conducting a comprehensive, post-impact survey from space. Hera is set for a subsequent maneuver in February 2026, followed by a series of thruster firings starting in October 2026 to fine-tune its trajectory and reach the Didymos system in December 2026 (4).
"This has been our team's initial taste of exploration, but it won't be our last," ESA Hera mission manager Ian Carnelli stated in a declaration. "In 21 months, the spacecraft will reach our target asteroids, and initiate our in-depth analysis of the only object in our Solar System to have had its orbit significantly altered by human action."
(1) ESA, Hera mission scientists share knowledge about Mars and asteroids, press release
(2) ESA's Mars Express Orbiter, NASA website
(3) NASA's DART mission demonstrates planetary defense technology, NASA press release
(4) ESA's Hera mission website, ESA website
- The success of Hera's Mars flyby in December 2024 demonstrated the spacecraft's science tools' capabilities, providing a key stepping stone towards future space missions, such as asteroid redirection technology.
- In December 2026, Hera is set to reach its asteroid target, the binary asteroid system of Didymos and Dimorphos, which were altered by NASA's DART mission in 2022, marking a significant milestone in the advancement of science and technology.
- Deimos, Mars' minuscule moon, offers a unique scientific opportunity for future studies, as its origin remains uncertain, whether it broke off from Mars or is an asteroid captured by its gravitational pull.
- The Hera mission, launched by the European Space Agency in 2024, will not only inspect the aftermath of NASA's DART mission but will also contribute to the broader scientific understanding of asteroids and the potential for future asteroid redirection, a key aspect of planetary defense.
