Hera — ESA's Planetary Defense Mission

Hera | Impact Simulations

Hera is an ESA-led planetary defense mission, developed as part of a larger international endeavor, the Asteroid Impact and Deflection Assessment (AIDA) collaboration. In the first part of AIDA, NASA's DART mission impacted Dimorphos, the small moon of the double-asteroid Didymos system, to change its orbit around the larges Didymos primary. Now, Hera will visit this asteroid pair to gather additional data on Dimorphos, to help turn this 'kinetic impact' planetary defense method into a well-understood and potentially repeatable technique. The University of Bern is involved in the Hera Science Team, primarily in the Impact Physics Working Group, which is concerned with simulations to model impacts and collisions between asteroids, comets, or planets

UPCOMING MISSION HIGHLIGHTS

November 2026

The first mission to make a rendezvous with a binary asteroid, Hera is scheduled to arrive at Didymos in November, four years after DART, to begin six months of investigation over five phases lasting between two and six weeks each.

Following its arrival in November, Hera will begin the 'Early Characterization' phase of the mission, which is set to last six weeks. From December 2026 to January 2027, Hera will go more into depth with a 'Detailed Characterization' phase. In January 2027 it will also release the two CubeSat satellites, which will support Hera in the 'Multi-Point Investigation of Dimorphos' phase lasting from February to April 2027. In that time period, Hera will also be engaged in 'Autonomous Proximity Operations', 'Detailed Crater Investigation' and 'Low-Altitude Detailed Investigation'. From March to April 2027, the two CubeSat satellites will land on Dimorphos. Finally, the 'Experimental Phase' will take place from May to June 2027, after which Hera may bring its own mission to an end by attempting a landing on Didymos, to further study Dimorphos from its surface.

LATEST MISSION HIGHLIGHTS

22 October 2026

Following Hera's first glimpse of its destination on October 07, the spacecraft now began its braking maneuver on its approach to the binary asteroid system and its ultimate target, Dimorphos. With reduced velocity, Hera can begin observing in November.

Hera performed a brief test burn on October 02 in preparation for the initial braking maneuver on October 15, which lasted 93 minutes. On October 22, the spacecraft performed a second braking maneuver at a distance of 2'300 km from Didymos, reducing its velocity by 70 m/s relative to the target system. By the time Hera begins its 'Early Characterization Phase' in November, it will only be approximately 30 kilometers away from Dimorphos.

This pair of maneuvers will be followed by three smaller 'transition' maneuvers towards the end of the month that will reduce Hera's relative velocity with respect to the Didymos system down to near zero. Read more about Hera's arrival and mission in the Keystone-SDA interview with PD Dr. Martin Jutzi at swissinfo.ch here.

18 October 2026

Following a first braking maneuver and a bit over a week after capturing a first image of Didymos, Hera resolved its two target asteroids separately for the very first time, revealing the binary nature of the Didymos system.

At the moment, the Didymos system is approximately 197 million km away from Earth. Now at a distance of 1280 km away from the asteroid pair, Hera imaged Didymos and Dimorphos with its monochromatic Asteroid Framing Camera. Read more on the ESA website here.

07 October 2026

Exactly two years after its launch, Hera caught its first glimpse of its destination, the binary asteroid system Didymos. The spacecraft imaged its target from 236'500 km away, where it is only visible as a single pixel.

By combining multiple images and performing photometric analysis, the Hera mission team was able to identify Didymos against the background star field, seen in visible light, smaller than an individual pixel but sufficiently bright to be detected by the camera. Read more on the ESA website here.

Hera at the University of Bern

The University of Bern is involved in Hera's Investigation Team, which is composed of the Mission PI, the Mission Advisory Board, the Working Group Chairs as well as Instrument Leads. PD Dr. Martin Jutzi, researcher at the Space Research and Planetary Sciences Division (WP), and Dr. Sabina Raducan, formerly also at WP and now Science Program Manager at ISSI, are co-chairs of the Impact Modeling Working Group. Additionally, John Wimarsson, recent PhD graduate at WP, is part of the Dynamics Working Group. Jutzi and Raducan are also members of the Data Analysis, Exploitation and Interpretation Working Group, focused on Geomorphology and Mechanical Properties.

Within the framework of the Hera mission, the work at the University of Bern is concerned with simulations and modeling of impacts, using the "Bern Smoothed Particle Hydrodynamics" (SPH) code. The University of Bern is a global leader in the numerical modeling of impacts and the method was also used to simulate the collision of NASA's DART spacecraft with the asteroid Dimorphos.

Smoothed Particle Hydrodynamics

The Bern SPH code was developed at the Uni Bern over two decades. It enables high-resolution computer simulations in which colliding bodies are broken down into millions of particles, whose behavior during impact is controlled by the interaction of various reconfigurable variables such as gravity and density.

More about the mission

Hera is the first spacecraft developed by the European Space Agency in the frame of planetary defense, and is part of a larger international collaboration project, originally devised in the 1990s by Prof. Andrea Milani at the Pisa University. The 'Asteroid Impact and Deflection Assessment' (AIDA) collaboration was officially set up in 2013 by scientists supported by NASA and ESA, and aims to test the kinetic impact method as a suitable way to deflect asteroids which pose significant danger to Earth. In a first part, NASA's Double Asteroid Redirect Test (DART), was launched on November 24, 2021, and journeyed on to the binary asteroid Didymos, where it collided with its satellite Dimorphos on September 26, 2022, and successfully altered the rotation of Dimorphos around Didymos.

The second phase of the AIDA project, ESA's Hera spacecraft will study the Didymos system and specifically the effects of the DART spacecraft on Dimorphos in detail, and contribute to the validation of the kinetic impact method to change the trajectory of near-Earth asteroids that would otherwise collide with Earth. The main objective of the mission is to fill in vital missing information about the asteroid system and the DART impact, and provide a detailed post-impact survey of the asteroids to turn this experiment into a well-understood and repeatable technique for planetary defense.

Together with its payload, the two CubeSat satellites Juventas and Milani, Hera will study the surface characteristics, internal porosity, and internal structure of the two asteroids. They will map Dimorphos in its entirety with a spatial resolution of a few meters and the vicinity of the impact with a resolution of 10 centimeters, and estimate its mass with high accuracy. Through these investigations, Hera will determine a) how much momentum transfer depends on density, porosity and characteristics of the asteroid's surface and internal structure, and b) what proportion of the kinetic energy is transferred in the fragmentation and restructuring of the asteroid or in the kinetic energy of the ejected materials.