ESA Advances Hera Mission to Investigate DART Asteroid Impact

Europe's Hera spacecraft is approaching the Didymos asteroid system to investigate the consequences of NASA's 2022 collision with Dimorphos, a small asteroid moon. The European Space Agency (ESA) launched the mission in October 2024 to determine how the impact changed the asteroid and improve calculations of how effectively a spacecraft can divert a potentially hazardous object.

NASA's Double Asteroid Redirection Test (DART) spacecraft struck Dimorphos in September 2022 at approximately 6.1 kilometers per second, or nearly 22,000 kilometers per hour, according to Swissinfo.ch and Bluewin. The collision shortened Dimorphos' orbital period around its larger companion, Didymos, from 11 hours and 55 minutes to approximately 11 hours and 22 minutes, a reduction of about 33 minutes.

However, researchers still need to establish how extensively the collision reshaped Dimorphos and how much of DART's energy and momentum the asteroid absorbed. Hera's close-range observations are intended to provide evidence needed to answer those questions.

Martin Jutzi, an astrophysicist at the University of Bern involved in the mission, explained that the investigation will help researchers assess the relationship between an asteroid's mass and the energy required to change its trajectory.

"The results will provide a better basis for determining how much energy and momentum are needed to deflect an asteroid of a certain mass. This will allow us to determine how efficiently we can actually deflect an asteroid by colliding with it."

Jutzi told the Keystone-SDA news agency that the findings will improve estimates of kinetic-impact effectiveness. Determining Dimorphos' mass remains particularly important because researchers need that measurement to quantify the momentum transferred during DART's collision.

A research team involving Jutzi and John Wimarsson of the University of Bern, alongside Sabina Raducan of the International Space Science Institute in Bern, previously simulated the collision using computer models. Their calculations suggested that Dimorphos consists of loosely bound debris rather than a single solid mass.

Based on those simulations, the researchers predicted that DART might have substantially deformed the asteroid moon instead of simply excavating a crater. Hera's observations are expected to help establish whether that prediction matches the actual aftermath.

As reported by Swissinfo.ch, Hera's arrival phase requires carefully coordinated spacecraft maneuvers. The mission's braking sequence began in October 2026, with ESA confirming that the first braking maneuver, BRM-1, completed its planned 93-minute burn within the required parameters on October 16, according to the mission update summarized by neoteo.com.

ESA scheduled the second braking maneuver, BRM-2, for October 22, 2026. The planned burn was expected to last approximately 31 minutes, followed by three smaller transition maneuvers toward the end of October as Hera continued its approach.

The spacecraft's planned Early Characterisation Phase in November will bring it to approximately 30 kilometers from Dimorphos, enabling researchers to obtain the first usable close-range images. By December, the planned observing distance is expected to decrease to around 10 kilometers, according to Swissinfo.ch and Bluewin.

The Didymos system consists of the larger asteroid Didymos, approximately 780 meters in diameter, and Dimorphos, which measures about 160 meters, according to the supplied mission reports. Dimorphos orbits Didymos, making the pair a useful natural laboratory for examining the effects of a deliberate kinetic impact.

Hera's investigation also has implications for planetary defense. Astrophysicist Martin Jutzi said asteroids do not present an immediate impact threat in the context of the mission, but collisions with Earth remain a realistic possibility depending on an object's size.

According to Jutzi, objects measuring 10 to 20 meters across strike Earth statistically every few decades. Larger objects measuring 100 to 200 meters across may hit Earth every 10,000 to 20,000 years, potentially causing devastating regional or global consequences.

Hera's measurements are intended to help scientists determine how accurately a kinetic-impact mission can redirect an asteroid of known mass. The mission follows DART's successful orbital change experiment and will provide more detailed information about the physical response of a small asteroid to a high-speed collision.