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- NASA's DART test shortened Dimorphos' orbit from 11 hours 55 minutes to 11 hours 23 minutes, proving deliberate orbit change.
- Ground-based observations have about a 10% residual uncertainty; Hera will measure the asteroid's mass and orbit shift far more accurately.
- Hera performed braking maneuvers and will approach within 20 miles to begin close flybys and gather detailed impact data.
- Hera will spend at least six months surveying Didymos, deploying cubesats Milani and Juventas to study composition and interior.
In September 2022, a NASA spacecraft violently smashed into a tiny asteroid as a test of planetary defense. Now, a new probe is ready to check out the wreckage by rendezvousing with the space rock for a closer look.
The European Space Agency (ESA) launched its Hera mission on October 7, 2024, as a crucial follow-up to NASA’s DART (Double Asteroid Redirection Test), a first-of-its-kind attempt to redirect the orbit of an asteroid. The small, car-sized spacecraft recently pulled off a braking maneuver to slow it down as it approaches the binary asteroid system before it makes its first close flyby in early November.
Hera is set to perform a detailed, post-impact survey with the aim of turning a one-time, space experiment into a well-understood planetary defense mechanism. The mission could also help scientists learn more about how asteroids form.
Collision ahead
For the DART test, NASA sent a 1,340-pound spacecraft (607 kilograms) and smashed it into Dimorphos, a 558-foot-wide (170-meter) space rock that orbits its larger 2,625-foot-wide (800-meter) companion, Didymos. Ground-based observations revealed that, following the collision, Dimorphos’s orbital period around Didymos shortened from 11 hours and 55 minutes to 11 hours and 23 minutes.
The mission was deemed a success, demonstrating that a spacecraft could deliberately alter an asteroid’s motion. But successfully hitting an asteroid and understanding exactly what that impact did are two different things. To understand the full consequences of the impact, scientists needed a closer investigation.
That’s where Hera comes in, armed with a suite of science instruments to inspect the asteroid after the collision and investigate whether DART’s success can be turned into a dependable strategy for protecting Earth.
Enter, Hera
Ground-based observations are estimated to be stuck with a 10% residual uncertainty with their measurements, and models of the impact still haven’t been able to calculate the mass and makeup of Dimorphos, according to ESA.
Once it reaches Dimorphos, Hera will not only investigate the scene of the crime, it will also measure the asteroid’s mass, as well as its shifted orbit in a far more accurate way. Hera will also conduct the most detailed survey of a binary asteroid system, which make up about 15% of all known asteroids, yet none have ever been studied up close before.
Earlier this month, Hera got its first look at its target. The spacecraft imaged the Didymos binary asteroid system from an approximate distance of 146,954 miles (236,500 kilometers) away. On October 15, Hera performed a braking maneuver to fine-tune its trajectory toward the pair of space rocks and fired its thrusters to come close to matching the asteroids’ velocity.
In early November, the spacecraft will come within 20 miles (30 kilometers) of the asteroids and begin gathering data. Hera will continue to move in closer to the asteroid system before it deploys a pair of shoebox-sized cubesats, named Milani and Juventas, in January 2027. Milani is tasked with identifying the composition of materials on and around Dimorphos while Juventas will use a radar to peer inside the interior of the asteroid.
After a two-year journey through space, Hera is expected to spend at least six months surveying the Didymos asteroid system, examining the aftermath of NASA’s DART impact and gathering data to advance planetary defence.
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