19/06/2026
In 2022, humanity hit an asteroid on purpose. We're about to find out if it actually worked the way we think it did.
That was NASA's DART mission. A vending-machine-sized spacecraft slammed into a moonlet called Dimorphos at roughly 6 km/s, on a one-way trip with no return ticket.
Ground telescopes confirmed something happened, the moon's orbit around its parent asteroid Didymos got shortened by about 32 minutes (Jaxa) .
Good news. But nobody actually saw the crash up close, and nobody knows exactly how much mass that asteroid has, which means nobody can say for sure how much of the deflection came from the impact itself versus the debris it kicked up.
That's the gap ESA's Hera spacecraft was built to close.
Hera left Earth back in October 2024, swung past Mars in March 2025 to bend its trajectory and test its cameras, and has spent the time since grinding through deep-space burns to line itself up for the real target. Didymos is a mountain-sized rock about 780 meters across, and Dimorphos, the one DART hit is roughly the size of the Great Pyramid of Giza (ESA) , orbiting it.
The plan was to arrive in December 2026. Then the mission team got greedy in a good way. Because the propulsion system performed so well, engineers designed a more aggressive braking maneuver that lets Hera "brake later and harder" on approach (Earth.com) , shaving a month off the schedule. Hera now arrives in November 2026 (New Space Economy) instead.
Once it gets there, Hera won't just take photos and leave. It's going to spend roughly six months in close orbit, dropping down to altitudes under 2 km (Jaxa) , measuring the crater DART left behind, mapping Dimorphos's shape, and critically, finally pinning down its mass. It's also bringing backup: two shoebox-sized CubeSats, Juventas and Milani, will fly even closer and attempt their own landings.
The number everyone's actually waiting on is something scientists call the momentum enhancement factor. basically, how much extra "kick" the asteroid got from flying debris on top of the raw impact. That number becomes the foundation every future planetary defense mission gets measured against (New Space Economy) .
So DART proved we can hit a moving target 11 million km away and physically alter its path. Hera is the part of the experiment that tells us whether we actually understand why it worked
which is the difference between a lucky shot and a method we can trust the next time a real one is heading our way.
Following along for the arrival in November this is the kind of thing you don't want to find out about a week late.
If we actually had to redirect a real asteroid tomorrow, would you trust the data we have right now?
