A spacecraft took off Monday to investigate the scene of a cosmic crash.
The European Space Agency’s Hera spacecraft took off on a two-year journey to a small and innocuous asteroid hit by NASA two years ago as part of a dress rehearsal for the eventuality a killer space rock would threaten Earth. This is the second part of a planetary defense test that could one day help save the planet.
SpaceX’s Falcon rocket quickly disappeared with Hera into the clouds late in the morning. An hour later, applause broke out in the control center in Germany as the spacecraft separated from the rocket’s upper stage and contacted base. “It’s an incredible day,” the space agency’s director general, Josef Aschbacher, later celebrated.
The 2022 crash of NASA’s Dart spacecraft shortened the orbit of the asteroid Dimorphos around its larger companion, demonstrating that if a dangerous rock was headed toward the blue planet, there’s a chance it could can be deviated from its trajectory with sufficient notice.
Scientists are eager to take a close look at the aftermath of the impact to learn exactly how effective Dart was and what changes might be needed to protect Earth in the future. “The more detail we can gather, the better, because it could be important for planning a future diversion mission if it becomes necessary,” Derek Richardson, an astronomer at the University of Maryland, explained before the launch.
Researchers want to know whether Dart (short for Double Asteroid Redirection Test) left a crater or even reshaped the 150-meter asteroid. It looked like a flying saucer before Dart’s impact and might now resemble a kidney bean, said Richardson, who participated in the Dart mission and is helping with Hera’s.
Dart’s arrival caused boulders to fly off Dimorphos, giving an extra boost to the momentum of the impact. The debris trail stretched for months for more than 10,000 kilometers.
An unknown environment
Some rocks and other debris could still be lying around the asteroid, posing a potential threat to Hera, flight director Ignacio Tanco warned.
“We really don’t know the environment we’re going to be operating in very well,” Tanco said, “but that’s the whole point of the mission: to go out there and find out what’s going on.”
European officials describe the US$400 million mission as a “crash scene investigation.”
Hera “returns to the scene of the crime and recovers all the scientific and technical information,” summarized project manager Ian Carnelli.
Equipped with a dozen scientific instruments, the small Hera, the size of a car, will have to pass near Mars in 2025 to benefit from gravitational acceleration before arriving near Dimorphos by the end of 2026. The asteroid is actually a small moon of Didymos, twin in Greek, a fast-spinning asteroid five times larger. When Hera arrives, the asteroids will be 195 million kilometers from Earth.
Hera will attempt to orbit the rocky pair, with flyby distances gradually decreasing from 30 kilometers to 1 kilometer. The spacecraft will monitor the small moon for at least six months to determine its mass, shape and composition, as well as its orbit around Didymos.
Before impact, Dimorphos circled its larger companion at a distance of just over 1 kilometer. Scientists believe that the orbit is now tighter and oval-shaped, the small moon could even be tipping.
Two shoebox-sized cubic nanosatellites will detach from Hera for even closer, drone-style inspections. One of them will use radar to scan the small moon’s rock-strewn surface. Scientists suspect that Dimorphos formed from material discarded by Didymos. Radar observations should help confirm whether Didymos is indeed the mother of the small moon.
The cubic nanosatellites will attempt to land on the small moon once their study is complete. If it tilts, the exercise will be more complex. Hera could also end her mission with a precarious landing on the larger Didymos.
Neither asteroid poses a threat to Earth, either before or after Dart’s appearance. That’s why NASA chose the pair for humanity’s first asteroid deflection demonstration.
Leftovers from the formation of the Solar System 4.6 billion years ago, asteroids mainly orbit the Sun between Mars and Jupiter in the so-called main asteroid belt, where millions of asteroids are found between them. They become near-Earth objects when they are expelled from the belt and come closer to Earth.
The number of near-Earth objects identified by NASA currently exceeds 36,000, almost all asteroids, but also a few comets. More than 2,400 of them are considered potentially dangerous for the Earth.
