An artist’s impression of comet 41P as it approached the sun and shot material off into space
NASA, ESA, CSA, Ralf Crawford (STScI)
A small comet has been observed reversing its rotational direction, marking the first time astronomers have documented such an occurrence. Understanding these changes could provide insights into the internal structure of comets, offering clues about the early solar system’s makeup.
Known as Comet 41P/Tuttle-Giacobini-Kresák, or 41P, this comet measures approximately 1 kilometer in diameter and completes an orbit around the sun roughly every 5.4 years. It becomes visible only when it enters the inner solar system and passes close to Earth, with its last appearance recorded in 2017.
During March of that year, the comet was spinning once every 20 hours. By May, observations showed it had significantly slowed to completing one rotation every 46 to 60 hours. Recently, David Jewitt from the University of California, Los Angeles, reviewed Hubble Space Telescope data from December 2017, revealing that the comet’s rotation had accelerated to one spin approximately every 14 hours.
This phenomenon might be explained by the comet’s rotational speed decreasing until it halted and then began spinning in the opposite direction, gaining speed. Sunlight may have caused ice on the comet’s surface to transform into gas, acting like a jet. If this jet propulsion opposed the initial spin direction, it could decelerate and eventually reverse the comet’s rotation.
“It is the first detected ‘fast’ change of the rotation direction for a celestial body,” states Dmitrii Vavilov at the University of Washington in Seattle. Typically, significant shifts in the rotation of celestial bodies, even small comets, occur over decades or centuries.
John Noonan from Auburn University in Alabama anticipates that observing 41P during its next appearance in late 2027 or early 2028 will be compelling. “I’d be keen to see if these comets are more likely to fracture as well, due to the stress.” If 41P’s spin becomes too rapid, its nucleus might disintegrate.
Jewitt noted, “I expect this nucleus will very quickly self-destruct,” in a statement. The disintegration may have already occurred. If so, it presents a valuable chance to study the interior of a comet that solidified during the solar system’s formation. Analyzing this ancient ice could offer vital insights into the early solar system’s chemical composition and serve as a reference for understanding how those chemicals evolved over time.
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