Hera Spacecraft Achieves First Light by Resolving Didymos and Dimorphos as Separate Asteroids — General science

The European Space Agency's Hera mission has captured its first distinct images of the binary Didymos system, successfully separating the parent asteroid from its smaller companion, Dimorphos, at a distance of 1280 km.

The European Space Agency's Hera spacecraft has achieved a significant milestone in planetary defence by resolving its two target asteroids as separate entities for the first time. This breakthrough reveals the binary nature of the Didymos system, which is currently located approximately 197 million kilometers from Earth. The historic images were captured on the evening of October 18 using the spacecraft's monochromatic Asteroid Framing Camera while Hera was positioned 1280 km away from the asteroid pair.

Michael Kueppers explained that prior to this acquisition, the Didymos system appeared as a single dot to the spacecraft. In this initial image, the smaller Dimorphos asteroid is visible for the first time, appearing as roughly one pixel but clearly separated from its parent body. This imaging success followed successful braking maneuvers earlier in the month, where two thruster firings spaced a week apart slowed Hera to just 20 m/s relative to the asteroids, allowing for a gradual and fine-tuned approach.

The two celestial bodies differ significantly in size. Dimorphos measures 151 meters across, comparable to the Great Pyramid of Giza, while the parent asteroid Didymos has a diameter of 780 meters, slightly smaller than Dubai's Burj Khalifa. The pair orbits an average distance of 1.15 km apart, with Dimorphos circling its parent at a speed of about 18 cm/s. Mission manager Ian Carnelli noted that this marks the first time the double asteroid system, for which the mission was specifically designed, is being viewed through Hera's own eyes.

Sharper views are expected as Hera draws closer, with the first detailed images of Dimorphos scheduled for release on November 25. Dimorphos holds a unique place in history as the first object in the Solar System to have its orbit measurably shifted by human action. On September 26, 2022, NASA's DART spacecraft impacted Dimorphos at a velocity of 6.1 km/s. The collision generated a debris plume spanning 10,000 km and slowed the asteroid's orbit by approximately 33 minutes.

Despite this success, key unknowns remain regarding the effectiveness of the kinetic impact method for planetary defence. Scientists still need to determine the precise makeup, structure, and mass of Dimorphos, as well as understand whether the impact left a crater or reshaped the body entirely. These factors are crucial for explaining why the deflection was significantly greater than impact simulations had predicted. Over the coming months, Hera will conduct a close-up investigation of the crash site using multiple instruments and deploying two shoebox-sized CubeSats for an even closer survey before eventually attempting a landing.

Sources: ESA Space News.