The Dart probe (English acronym for Double Asteroid Redirection Test) became this Monday (26) the first artifact to impact against a space object with the deliberate aim of altering its orbit. The collision occurred at 20:15 (Brasília time). Which means that, from the point of view of the experiment, everything worked out. It remains to be seen now what the real effect of the intervention was, which will only be known for sure in the coming days and weeks.
NASA’s pioneering planetary defense mission launched on November 24 of last year at a cost of $324 million.
During its final approach, in the last four hours before colliding with the asteroid Dimorph, the spacecraft guided itself automatically, guided by images from the Draco camera, the only instrument on board.
Dimorpho is a moon asteroid about 160 meters in diameter that orbits another larger asteroid, Didymus, at 780 meters. The set revolves around the Sun in a path that is very close to the paths that Earth and Mars make in their solar orbits.
Although classified as a “potentially dangerous asteroid” because of its occasional proximity, Didymus has not had an appointment with our planet for at least a few centuries, which gives NASA comfort in choosing it as a test target.
The deflection strategy adopted in the mission is known as “kinetic impact”. It boils down to colliding with the object and, with that, subtly altering its orbital speed. The impact occurred as predicted, at 21,600 km/h, accompanied “live” (actually a delay of about 50 seconds, to contemplate the capture, processing and transmission of the image along the little more than 11 million km that separate the Earth from the asteroid at the moment) with transmission of images by the probe itself until its fatal kiss on the surface of the object.
The degree of change in the asteroid’s orbit, however, will still need days and weeks to measure. That’s because it’s a job for astronomers on the ground. Using telescopes on Earth and in space, they will measure the Dimorph’s orbital period. Before the collision, it completed a revolution around Didymus every 11:55 minutes. Afterwards, the expectation is that this period has increased (as a consequence of the change in speed imposed by the impact), but this is something that still needs to be measured.
Accompanying Dart on its flight was a small satellite developed by the Italian Space Agency, LICIACube. It recorded what may well have been the moment of impact with the asteroid, but these images are transmitted to Earth at a much slower rate (due to communication limited by the small spacecraft’s antenna capacity) and were not immediately available.
Several space telescopes were also pointed at the star during the impact. Among them, the famous Hubble and James Webb, in addition to the Lucy probe. Thus, astronomers hope to have a pretty complete picture of what happened there in the collision, in terms of the amount of dust raised and the magnitude of the effect obtained by the test.
Details of the transformation of the asteroid’s surface, however, will have to wait for the European mission Hera, which will be launched in 2024 to revisit the star and see the size of the damage left by this valiant attempt to test a strategy that could prove to be crucial for the defense of the planet. For the first time in 4.5 billion years, Earth has this capability that dinosaurs wish they had had. They became extinct 65.5 million years ago by the impact of a celestial bolide about 10 km in diameter against our planet.