Hubble Space Telescope: Comet spin reversal observed for the first time
Approaches to the sun can dramatically change comets. However, their reversal of rotation has never been observed – at least not until now.
Artistic representation of a comet with a gas jet
(Image: NASA, ESA, CSA, Ralf Crawford (STScI))
About nine years ago, the Hubble Space Telescope first found indications that a comet had reversed its direction of rotation after passing the sun. David Jewitt of the University of California, Los Angeles, determined this from archival images, as NASA reports. These and data from the NASA Swift space telescope show that comet 41P/Tuttle-Giacobini-Kresák first rotated slower in May 2017 and much faster in December of the same year. The simplest explanation is that its rotation was slowed by outgassing and eventually reversed. Finally, it rotated once on its axis within 14 hours, after previously taking 46 to 60 hours for a rotation in the opposite direction.
Comet nearing its end?
Comet 41P takes about 5.4 years to orbit the sun and has been known since the mid-19th century. The data from the Hubble Space Telescope dates from its closest approach to the sun (perihelion) in spring 2017, when it was also observed with the Swift telescope. According to NASA, the data shows that its activity had significantly decreased. Compared to 2001, it had emitted significantly less gas. Nevertheless, this was apparently enough to reverse its direction of rotation. The measurement data also show that the comet has a diameter of about one kilometer, making it relatively small. This allows the outgassing to influence its movements more easily.
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Although comets are among the shorter-lived celestial bodies, changes in their structure normally occur over centuries or longer, NASA explains. The sun is responsible for this, especially when they come particularly close to the sun on their orbit. With each of these approaches, comets lose mass because volatile material is torn away. However, the rapid reversal of rotation now indicates major changes in such a celestial body, which are occurring on a timescale understandable to humans. Jewitt even assumes that the comet will be destroyed soon. 41P will next pass the sun in 2028. The research work has been published in The Astronomical Journal.
(mho)
