NASA’s Swift spacecraft, which has been in operation for 13 years, has managed to capture an unprecedented change in the rotation of a comet. The images, which were taken in May 2017, revealed that comet 41P / Tuttle-Giacobini-Kresák turned three times slower than it did in March, when it was observed by another telescope at the Lowell Observatory in Arizona (EE .UU.). This is a really abrupt slowdown that had never been seen in a body of this type, as explained by the researchers in the latest issue of the journal Nature .(comet stops)
“The previous record in the rotation of a comet was 103P / Hartley 2, which decreased its rotation from 17 to 19 hours for 90 days,” says Dennis Bodewits, associate researcher at the University of Maryland (UMD) in College Park, who presented the findings at the meeting of the American Astronomical Society (AAS) in Washington. “On the contrary, 41P reduced it more than 10 times in just 60 days, so both the scope and speed of this change is something we have never seen before,” he stresses. It went from about 20 to 60 hours.(comet stops)
41P orbits the Sun every 5.4 years, traveling as far as the planet Jupiter, whose gravitational influence has captured it on its current path. It is less than 1.4 kilometers in diameter, so it is among the smallest of the family of comets whose orbits are controlled by the huge planet. Precisely, its small size is what can help explain how it suffered such a drastic change.(comet stops)
When a comet approaches the Sun, the increase in heating causes the ice on its surface to change directly to a gas, producing jets that throw particles of dust and frozen grains into space. This material forms an extended atmosphere, called coma. Water in the coma decomposes rapidly into hydrogen atoms and hydroxyl molecules when exposed to ultraviolet sunlight, a light that the Swift is able to detect.
Terrestrial observations established the initial rotation period of the comet in approximately 20 hours at the beginning of March 2017 and observed its deceleration later in the same month. The comet passed 21.2 million km from Earth on April 1, and eight days later it made its closest approach to the Sun. Swift photographed the comet from May 7 to 9, revealing variations in its light related to material recently. expelled to coma These slow changes indicated that the 41P rotation period had more than doubled, between 46 and 60 hours.(comet stops)
Estimates of 41P water production , along with the small body size, suggest that more than half of its surface contains jets activated by sunlight. That is a much larger active fraction than in most comets, which usually support jets only on 3% of their surfaces.
“We suspect that the jets in the active areas are oriented favorably to produce the torques that slow down the 41P turn,” says Tony Farnham, lead research scientist at UMD. “If the torques continued to act after the May observations, the 41P rotation period could have been reduced to 100 hours or more at this time.”