Interstellar comet 3I/ATLAS reveals weird wobbling jets in rare sun-facing tail
3I/ATLAS may have moved away from Earth as it makes its way out of the solar system, but this interstellar intruder continues to delight and surprise astronomers.
(Center) A white light of the comet 3I/ATLAS is surrounded by a blue glow against a black backgroundHubble Space Telescope captured interstellar comet 3I/ATLAS in November. (Corners) Images of the coma of 3I/ATLAS (Image credit: NASA, ESA, STScI, D. Jewitt (UCLA). Image Processing: J. DePasquale (STScI)/ Serra-Ricart, Licandro, and Alarcon)
It may be on its way away from Earth and heading out of the solar system, but interstellar invader comet 3I/ATLAS still has some surprises for researchers.
New research reveals that jet structures in the sun-facing "anti-tail" of this comet, estimated in some observations to stretch up to 620,000 miles (1 million kilometers), were wobbling every 7 hours and 45 minutes as 3I/ATLAS approached the sun. Of course, comets are famous for their tails and haloes, comprised of gas and dust that is blown from their nucleus as radiation from the sun heats them. However, these tails generally face away from the sun and the influx of solar radiation. A rare anti-tail is a cometary tail that points toward the sun, rather than away from it.
"Characterizing jets in 3I thus represents a rare opportunity to investigate the physical behavior of a pristine body formed in another planetary system," the researchers behind this discovery wrote in a paper published on the paper repository site arXiv.
The team discovered the wobbling jets in the coma of 3I/ATLAS after observing the comet across 37 nights between July 2 and Sept. 5, 2025, with the Two-meter Twin Telescope (TTT), a robotic facility located at the Teide Observatory in Tenerife, Canary Islands.
These observations allowed the researchers to track how the comet's coma evolved from a sun-facing fan of dust before August, to a pronounced antisolar tail. They attribute this transformation to the increasing influence of solar radiation on dust with the coma as 3I/ATLAS headed toward a close approach to the sun on Oct. 30, 2025, when it came to within around 130 million miles (210 million km) of our star.
The jet structure appeared within the anti-tail of 3I/ATLAS on 7 nights between Aug. 3 and Aug. 29, and its wobble or precessional motion implied to the team that the icy heart of this interstellar invader is rotating around once every 15 hours and 30 minutes. This is a shorter rotational period for 3I/ATLAS than has previously been estimated.