For the first time, a comet has been seen to change both its speed and direction of rotation, thanks to new analyses of images from the Hubble Space Telescope. The unexpected reversal was caused by "gas ejection" jets that blasted an icy mixture of gas and dust into the solar system, according to a new study.
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The comet, known as 41P Tuttle–Giacobini–Kresák (or simply 41P), was originally discovered by American astronomer Horace Parnell Tuttle in 1858, before being rediscovered by French astronomer Michel Giacobini in 1907 and again by Slovak scientist Ľubor Kresák in 1951 (hence its long name). 41P likely originated in the Kuiper Belt — a region beyond the orbit of Neptune that includes asteroids, comets, and dwarf planets — and for most of its long life orbited the Sun in cycles lasting from decades to centuries.
However, about 1,500 years ago, its path was altered by a close gravitational interaction with Jupiter. Today, it moves in a much tighter orbit, completing one orbit around the Sun every 5.4 years. When it approaches its closest point to the Sun, known as perihelion, it also passes close to Earth and becomes visible with a telescope. Its last approach to the Sun occurred in 2022, and it was also studied extensively in 2001, 2006, 2011, and 2017.
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During the 2017 flyby, astronomers noticed that the spin rate of 41P slowed significantly as the comet passed close to Earth — something scientists had initially attributed to a common gas ejection phenomenon. The Hubble Space Telescope also captured extensive photographic footage of the flyby, but it was archived without being studied in depth.
In a new study published March 26 in The Astronomical Journal, an astronomer reanalyzed Hubble images from 2017 and found that the sudden slowdown was followed by a previously unknown acceleration episode. Nearly all known comets have been observed to exhibit “gas ejections” at some point in their lives. This phenomenon occurs when ice, gas, and dust from the comet’s interior are ejected through small cracks in its core — usually due to increased proximity to the Sun, which allows solar radiation to sublimate the material inside and crack its icy shell.
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Experts are not sure whether 41P's extreme gas ejection was caused by multiple jets or a single massive outburst. However, if similar events occur during subsequent perihelion passes, the icy comet could break up, as happened with comet C/2025 K1 (ATLAS), which spectacularly disintegrated in late 2025.
