Collision in deep space – the science

Israeli scientists participated in the DART asteroid interception project

The asteroid dimorphs before and after the DART impact (left). Photo: Hubble Space Telescope, NASA, ESA

Weizmann Institute of Science scientists this week witnessed an extraordinary event: the first intentional collision of a NASA spacecraft with a near-Earth asteroid intended to change its trajectory. The unmanned NASA spacecraft was launched in November 2021 and hit on Tuesday, September 27, at 2:00 a.m.: 15:00 am Israel time, in the asteroid Dimorphos, which moves in orbit around a larger asteroid – Didymus. The interception is part of NASA’s DART program, designed to give the American space agency the ability to divert celestial bodies from their orbits that may collide with Earth. The institute’s scientists are part of an international scientific team of the agency that follows the trajectory of Dimorphos and is entrusted with evaluating the effectiveness of the experiment.

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The observations of the institute’s scientists – Prof. Eran Ofek from the Department of Particle Physics and Astrophysics and Dr. David Polishuk from the Department of Physics Research Infrastructures – showed a clarification as a result of the spread of a cloud of dust and fragments that were thrown into space following the collision at a speed of tens of meters per second. These observations are important not only for understanding a change in trajectory the asteroid, but also to understand the physics of these asteroid collisions with each other.

Prof. Ofek and Dr. Polishok observed and measured the collision using six 11-inch aperture telescopes that are part of the telescope array of the Banaut Smeder Institute in the Arava, and through another telescope located at the Shem Weiz Observatory near the Ramon Observatory.

Dimorphos, which is about 160 meters in diameter, and Didymus, which is 780 meters in diameter, circle in their orbit at a distance of about 11 million kilometers from the Earth. None of them were on a collision course with the Earth and they do not pose a danger even after the collision.

Like other astronomers in longitudes close to Israel’s, the institute’s scientists were able to observe the event, since it occurred for them after dark. Now, they and other teams are checking if the collision will indeed lead to the expected shift: a reduction of about 1% in the asteroid’s orbit, which is reflected in a shortening of about ten minutes in the time Dimorphos orbits Didymus, which was 11 hours and 55 minutes before the impact.

“To know how much the asteroid did change its trajectory, we need to wait for the dust cloud to disperse – some will disperse in space, some will sink back,” said Dr. Polischuk and estimated that it would take between one and four weeks to be able to make the necessary observations.

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