Astronomers from the University of Maryland (USA) have achieved capture for the first time images of all phases of a comet's natural burst as he approached Earth. They have achieved this thanks to data from the NASA TESS satellite, used to view extrasolar planets, which have captured the explosive emission of dust, ice and gases from the comet 46P / Wirtanen.
He Wirtanen burst It began on September 26, although its closest position to Earth occurred on December 16. He initial burst brightness It occurred in two distinct phases, with a flash of one hour followed by one in the gradual second stage that continued to grow brighter for another 8 hours.
This second stage was probably caused by the gradual spread of the comet's dust from the outbreak, which causes the dust cloud to reflect more sunlight in general. After reach maximum brightnessthe comet gradually faded over a period of more than two weeks. Because TESS takes detailed and composite images every 30 minutes, the team was able to view each phase with exquisite detail.
"With 20 days of very frequent images, we were able to evaluate changes in brightness very easily. That is why TESS was designed to do its main job as an exoplanet surveyor, "said Farnham."We cannot predict when comet kills will occur. But even if we somehow had the opportunity to schedule these observations, we could not have done better in terms of time. The outbreak occurred a few days after the observations began. "
Tony Farnham, lead author of the study published in the magazine The Astrophysical Journal Letters, explained that they used TESS because "almost a month goes by capturing images of a portion of the sky. Without day or night breaks and without atmospheric interference, we have a very uniform and long-lasting set of observations".
"As comets orbit around the Sun, they can pass through the TESS field of vision. Wirtanen It was a high priority for us Due to its close focus at the end of 2018, we decided to use its appearance in TESS images as a test case to see what we could get out of it. We did it and we were very surprised! "
The team has generated an approximate estimate of how much material may have been expelled in the outbreak, around one million kilograms, which could have left a crater in the comet about 20 meters wide. An additional analysis of the estimated particle sizes in the powder tail can help improve this estimate. Watching more comets will also help determine if multi-stage brightness is rare or common in these outbursts in comets.
The TESS images of comet Wirtanen are the first that capture all the phases of a comet's natural burst although on three previous occasions they were about to achieve it: those of comet 17P / Holmes in 2017 started late. During the same year, observations of comet 29P / Schwassmann-Wachmann 1 (SW1) ended early. And finally, although the outbreak of Tempel 1 was captured in maximum detail, it did not occur naturally, but was caused by the impact module of the Deep Impact mission.
The cause of the outbursts is unknown
The normal comet activity is solar powered which vaporizes the ice near the surface of the nucleus, and the exhaust gases drag the dust from the nucleus to form the coma. However, it is known that many comets experience occasional spontaneous explosions which can significantly increase, but temporarily, the activity of the comet.
Currently It is not known what causes the outbursts, but they are related to Comet surface conditions. A series of possible activation mechanisms have been proposed, including a thermal event, in which a heat wave penetrates a bag of highly volatile ice cream, which causes the ice to vaporize rapidly and produce an explosion of activity, and a Mechanical event, where a cliff collapses, exposing fresh ice to direct sunlight. Therefore, the burst behavior studies, especially in the early stages of brightness that are difficult to capture, can help us understand the physical and thermal properties of the comet.