This is the first time that the two famous space telescopes have been used to simultaneously observe the same celestial object: an asteroid located 11 million kilometers from Earth, the target of the world’s first planetary defense test. The James-Webb and Hubble telescopes, the most powerful space observatories, revealed detailed views of NASA’s DART probe impact on an asteroid on Thursday, October 29, images that will help scientists understand the expected process of modification of the orbit.
On Monday evening, the probe deliberately crashed into the surface of Dimorphos, a small moon 160 meters in diameter orbiting a larger asteroid, in an attempt to deflect its orbit.
It will be necessary to wait between a few days and a few weeks before the scientists can confirm that its trajectory has indeed been altered, and manage to locate it in relation to its original position. But soon after the collision first images – taken by ground-based telescopes and the onboard LICIACube nano-satellite – showed a vast cloud of dust around Dimorphos, stretching for thousands of kilometres.
A cloud on which the James-Webb and Hubble telescopes, operating in space, were able to “zoom in more finely”, told AFP Alan Fitzsimmons, an astronomer at Queen’s University in Belfast, involved in ground observations of Project Atlas, a network of four telescopes controlled from Hawaii. These images show “clearly how this material is shattered after the explosive Dart impact, it’s quite spectacular”he welcomes.
A compact core surrounded by “plumes of material”
“The impact seems much greater than expected”, comments for his part Ian Carnelli, head of the European Hera mission, intended to inspect the damage to the surface of Dimorphos in four years. Hera had counted on a crater about 10 meters in diameter, but in view of the images taken by LICIACube 50 kilometers from the star, confirmed by those of space telescopes, it could be much larger… “If there is a crater, because maybe a whole piece of Dimorphos was just torn off. »
The James-Webb’s NIRCam camera, working in the near infrared, observed the impact for several hours after the collision. Its ten images reveal a compact nucleus surrounded by “material plumes” like expanding filaments, “moving away from the center of the place where the impact took place”describes a joint statement from the European Space Agency (ESA) and the teams of the two telescopes.
The images of the Hubble telescope, taken by a wide-angle camera twenty-two minutes, five hours and eight hours after the crash, show in visible light the movement of the ejecta, that is to say the material torn from the star. The latter appear in the form of rays, with a gradual increase in luminosity, but which stabilized eight hours after the impact, which “intrigues astronomers”according to the press release.
The importance of the amount of material ejected
The James-Webb telescope, which has been observing 1.5 million kilometers from Earth since last July, and Hubble, in service for more than thirty years, will soon reveal how much material has been ejected, its nature (large pieces or fine dust?) and at what speed.
This information will help scientists to “understanding the efficiency with which a kinetic impact can modify the orbit of an asteroid”, according to the press release. The kinetic impact technique experimented by NASA consists in colliding with an asteroid in order to ” to push “ slightly, and thus deviate its trajectory. A bit like playing pool in space.
The more material ejected, the more the trajectory has a chance of being altered. “How quickly astronomers will be able to measure the deviation will depend on the effectiveness of DART”emphasizes Alan Fitzsimmons.
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