Cette image au sol de la comète C/2020 F3 (NEOWISE) a été prise le 16 juillet 2020, depuis l’hémisphère nord. L’image en médaillon, prise le 8 août 2020 par le télescope spatial Hubble, révèle un gros plan de la comète après son passage par le Soleil. L’image de Hubble se concentre sur le noyau de la comète, qui est trop petit pour être visible. On estime qu’il ne mesure pas plus de 4,8 kilomètres de diamètre. A la place, l’image montre une partie de la coma de la comète, la lueur floue, qui mesure environ 11.000 miles (18.000 kilomètres) de diamètre sur cette image. La comète NEOWISE ne traversera pas le système solaire interne avant près de 7 000 ans. Crédit : NASA, ESA, STScI, Q. Zhang (Caltech) ; image terrestre copyright 2020 par Zoltan G. Levay, utilisée avec permission.
Une comète est une masse rocheuse et glacée qui est passée à proximité du Soleil au sein de notre système solaire, et qui s’est ainsi réchauffée et a commencé à libérer des gaz, entraînant la formation d’une atmosphère visible – et parfois d’une “queue”.
Les comètes sont de petits corps célestes qui ont des orbites très excentriques autour de notre Soleil, ce qui signifie que leur trajectoire orbitale les fait passer près du Soleil, puis les projette au plus profond du système solaire, au-delà de Neptune’s orbit. This means that the amount of light that they receive from the Sun varies considerably.
Comets have small cores or “nuclei,” made up of rock, dust, and ice, with diameters between a few hundred meters and a few tens of kilometers. For most of a comet’s orbit, it only comprises its core. However, after a comet has passed close by the Sun, the solar wind causes the ice to warm up and the comet begins to release gases, a process known as outgassing. The gases form a visible atmosphere around the comet which is not bound by gravity. This unbound atmosphere is called a “coma.”
Sometimes, the coma trails behind the comet, forming a distinctive comet tail. Comets can orbit the Sun for millennia, but eventually, the regular process of heating, outgassing, and cooling may cause them to break up.
Une comète est une masse rocheuse et glacée qui est passée à proximité du Soleil au sein de notre système solaire, et qui s’est ainsi réchauffée et a commencé à libérer des gaz, entraînant la formation d’une atmosphère visible – et parfois d’une “queue”. Crédit : ;” data-gt-translate-attributes=”[{” attribute=””>NASA & ESA
In contrast to probes that have to travel vast distances and require years of planning to visit the planets, Hubble is also able to turn its attention quickly to sudden dramatic events occurring in the Solar System. This allowed it to witness the stunning plunge of comet Shoemaker-Levy 9 into Jupiter’s atmosphere in July 1994. Hubble followed the comet fragments on their last journey and delivered high-resolution images of the impact scars, from which important new information on conditions in the Jovian atmosphere was obtained. The consequences of the impact could be seen for several days afterward, and by studying the Hubble data, astronomers were able to gain fundamental information about the composition and density of the giant planet’s atmosphere.
Comet. Credit: ESA/Hubble, NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI)
Hubble has also observed spectacular comet breakups. This includes the breakup of comet 73P/Schwassmann-Wachmann 3 in 2006 as it visited the inner Solar System. The Hubble images uncovered many more fragments than were reported by ground-based observers and provided an unprecedented opportunity to study the demise of a comet nucleus. Hubble also observed the breakup of comet ATLAS in 2020, providing astronomers with the sharpest view yet of the breakup of a comet. The telescope resolved roughly 30 fragments of the fragile comet. These Hubble images provided further evidence that comet fragmentation is probably common and might even be the dominant mechanism by which the solid, icy nuclei of comets die.
Also in 2020 Hubble captured the closest images yet of the popular comet C/2020 F3 NEOWISE, after it passed by the Sun. The telescope’s images resolved the visitor’s coma, the fine shell that surrounds its nucleus, and its dusty output.