Four years after NASA purposefully crashed a spacecraft into the asteroid Dimorphos to alter its orbit by approximately 33 minutes, the European Space Agency‘s (ESA) Hera asteroid mission has arrived to inspect the cosmic wreckage. The probe is undertaking precise orbital braking manoeuvres to pull within 30 kilometres (20 miles) of the binary asteroid system, offering scientists their first close-up look at how kinetic impact planetary defence reshapes a celestial body.
The mission marks a critical shift from experimental theory to post-impact forensic science. While Earth-based radar and space telescopes confirmed that the Double Asteroid Redirection Test (DART) successfully shifted the asteroid’s path around its larger partner, Didymos, researchers still do not know the exact scale of the crater left behind or the full structural consequences of the smash.
The Cosmic Crime Scene: What DART Left Behind
When the half-tonne DART impactor slammed into Dimorphos at hyper-velocity on 26 September 2022, it kicked up massive plumes of rocky debris into deep space. The primary goal was simple: prove that humanity could deflect a hazardous asteroid should one ever threaten Earth. Yet, the physics that unfolded during and after the impact proved far more intricate than initial computer simulations suggested.
“Hera wants to be the detective, like Inspector Colombo, going back to the crash scene,” said Patrick Michel, a planetary scientist at the French National Centre for Scientific Research (CNRS) and principal investigator of the Hera mission.
Telescopic monitoring after the impact revealed unexpected mechanical reactions across the binary system. Planetary scientists discovered that Dimorphos’s orbital period continued to subtly fluctuate up to six months after the collision, hinting that the asteroid may now be tumbling uncontrollably in its orbit.
On a starry background, a small yellow crosshairs centers on a small dot
Challenging the ‘Solid Rock’ Misconception
A widespread misconception is that asteroids are solid, impenetrable boulders gliding through the vacuum of space. In reality, smaller bodies like Dimorphos are frequently “rubble piles” β loose aggregates of boulders, gravel, and dust bound together only by tenuous gravity.
Because of this fragile composition, researchers suspect DART did not merely carve out a neat circular crater. The collision likely deformed the entire structure of the space rock, shifting massive boulders across the surface and potentially transferring debris onto Didymos.
A cube-shaped spacecraft wrapped in foil floats on a black background
Hera’s Operational Approach and Deployment
Hera will conduct three critical thruster burns to settle into proximity with the Didymos system. After closing in to roughly 30 kilometres in November, the spacecraft will navigate closer in December to construct ultra-high-resolution 3D maps of both asteroids.
- Three-stage braking phase: The mother craft reduces relative velocity during October to gently match the trajectory of the asteroid pair.
- Close reconnaissance: Approaching within 30 kilometres (20 miles) to commence photographic mapping and thermal analysis.
- CubeSat release: Deploying two piggyback nanosatellites directly into the orbit of the target.
- Radar sounding and landing: Probing internal structures with low-frequency radar before
- attempting low-gravity surface landings.
A timeline beginning in october 2024 with an illustration of a rocket, ending in a small satellite with two wing-like solar panels around two large asteroids in april 2027
Comparing the Deflector and Detective Missions
While NASA demonstrated the brute force needed to alter a celestial trajectory, ESA provides the precision measurements required to turn a single success into a repeatable defence protocol.
| Mission Attribute | DART (NASA) vs Hera (ESA) |
|---|---|
| Primary Objective | Kinetic redirection of target asteroid |
| Key Payload | Kinetic impactor with optical navigation camera |
| Follow-Up Hardware | Milani (mineralogy) & Juventas (radar) CubeSats |
| Orbital Change Recorded | Shortened Dimorphos orbit by ~33 minutes |
| Operating Timeline | Impacted 2022; Hera operates through 2027 |
Internal Scans and CubeSat Landings
In the new year, Hera will release two shoe-box-sized CubeSats to perform the mission’s riskiest manoeuvres. The first, dubbed Milani, carries a hyperspectral imager to identify the mineral composition of the asteroids and assess the dust kicked up by the collision.
The second probe, Juventas, will employ low-frequency radar to peer deep underneath Dimorphos’s surface. This will represent the first time scientists have directly sounded the interior of a space rock to assess its internal cohesion, ending its operational run with an intentional touchdown on Dimorphos.
“We know that there was a lot of material kicked up,” said Angela Stickle, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory. “We know that we probably left a pretty significant mark on Dimorphos.”
The findings gathered by the trio of spacecraft through 2027 will establish whether kinetic deflection can reliably protect the planet from near-Earth objects of all structural types.
π‘ Planetary defence depends on knowing whether an incoming object will shatter or absorb kinetic energy during an interception.
π As Hera inches closer, its sensors will reveal whether human hands have permanently altered Dimorphos into an elongated, tumbling world.
π Leave your thoughts in the comments below: do you believe kinetic impactors are our best defence against hazardous space rocks?
