How do we know if the DART impact actually moved the asteroid?

A few minutes after 1:00 a.m. Spanish time, the DART probe crashed into its target, the small asteroid Dimorpho, fulfilling the planned program almost in a second. At the speed of a bullet fired from a 44 Magnum, against a rock 160 meters in diameter, 11 million kilometers from Earth, he hit the target.

The images transmitted by the probe’s camera during the last minutes of its trajectory were truly spectacular. First the set of the main asteroid, Didymus, and its satellite, Dimorpho, could be seen. Then, as DART approached at more than 6 kilometers per second, the first one moved out of the field of view, while Dimorph increased in size step by step.

The last six or seven images focus on this asteroid, which in a few moments went from being a simple point of light to showing some superficial details and, finally, to some detailed close-ups that made the entire control team scream with satisfaction Of flight.

Unlike other astroids, which alternate between rough areas and almost smooth expanses of dust, Dimorph is literally studded with rocks. In the last image, which could only be transmitted in part due to the destruction of the probe, details of less than an inch can be seen. And then, fade to red: “We have impact!”

Has the goal of moving Dimorpho slightly out of its original orbit been achieved? That is the question that observatories around the world, from Chile to La Palma, will have to answer in the coming weeks. There is an extensive observation program underway in this regard, made up of a large network of space and ground telescopes that observe both asteroids in detail before, during and after the impact. It is expected that in the next few hours, days or weeks they will be able to confirm if Dimorfo has deviated and how much.

The Didimo-Dimorph system is essentially a clock. Until now, the small body made a complete revolution around its parent in 11 hours and 55 minutes. The impact was rear facing, so it should have caused a slight change in height, to a lower orbit, and a reduction of about 73 seconds in the time it takes to complete each revolution. Now him clock should advance.

This asteroid was chosen because, apart from its dual nature, from Earth it looks of singing: Approximately every twelve hours, Dimorpho’s trajectory leads him to hide behind his partner and reappear shortly after. Giant telescopes can photograph it, while others can measure the difference in brightness as it enters and exits the eclipse. Even some radar systems are also capable of detecting it. Now, the astronomers’ job will be to measure the interval between each two successive appearances. It should be about a minute shorter than before. If confirmed, this will be the best proof that for the first time in history a celestial body has been moved.

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