Astronomers using archival data from NASA’s Hubble Space Telescope have discovered that Jupiter-family comet 41P/Tuttle-Giacobini-Kresák reversed its spin direction during its 2017 perihelion pass. The rare phenomenon, driven by unevenly distributed gas jets acting as thrusters on the tiny nucleus, leaves the cosmic snowball unstable and potentially facing self-destruction.
Comets are icy relics of the early solar system that orbit the Sun, shedding bright tails when solar heat evaporates their frozen surfaces. Most comets evolve gradually over centuries, but an unusual celestial visitor has shattered expectations by fundamentally altering its rotation in a matter of months.
How Comet 41P Slowed Down, Stopped, and Reversed
Comet 41P/Tuttle-Giacobini-Kresák is a short-period comet that travels from the distant Kuiper Belt to the inner solar system every 5.4 years. During its closest approach to the Sun in 2017, the comet exhibited behavior never before witnessed by astronomers.
Data captured in May 2017 by the Neil Gehrels Swift Observatory revealed that the comet had slowed its rotation significantly, spinning three times more slowly than it did just two months prior in March 2017. That slowdown set a shocking new record for rotational change in a comet, outpacing previous observations by a factor of 10 over a 60-day window.
However, the slowdown was only the first phase. Archival images captured by the Hubble Space Telescope in December 2017 showed that the comet had started spinning rapidly again. Researchers analyzing the dataset determined that 41P had continued to slow until it nearly stopped completely, only to begin rotating in the near-opposite direction.
Outgassing Jets Acting as Planetary Thrusters
The physical mechanism behind this unprecedented spin reversal lies in the comet’s interaction with solar heat. As 41P approached the Sun, rising temperatures caused surface ice to sublime, forcing gas to vent aggressively into space.
“Jets of gas streaming off the surface can act like small thrusters. If those jets are unevenly distributed, they can dramatically change how a comet, especially a small one, rotates. It’s like pushing a merry-go-round. If it’s turning in one direction, and then you push against that, you can slow it and reverse it.”
David Jewitt, astronomer at the University of California at Los Angeles
The comet’s exceptionally small size made it uniquely vulnerable to these forces. NASA’s Hubble telescope estimates that the central core, or nucleus, of 41P measures only about 1 kilometer or 0.6 miles in diameter. Autoevolution notes the nucleus is approximately 1,440 feet across, roughly three times the height of the Eiffel Tower, making the body small enough for asymmetric gas vents to overpower its rotational momentum.
An Unstable Future and Rapid Surface Evolution
The dramatic rotational shift highlights a much faster evolutionary timeline than scientists typically observe. Archival comparisons reveal that 41P was exceptionally active during its 2001 orbit, but its gas production had diminished substantially by 2017. This drop-off suggests that near-surface volatile materials may be depleting rapidly or sealing beneath insulating dust layers.
Computer models and measured mass-loss rates indicate that continued rotational changes could cause the comet to become structurally unstable. Researchers project that the nucleus could last only another few decades at its current spin rate before centrifugal forces tear it apart, a stark contrast to the typical 1,000-year lifespan of a standard comet.
The Scientific Power of Archival Space Data
The discovery underscores the value of maintaining accessible repositories of deep-space telemetry. Because the spin reversal took place in 2017 and was only detailed in a study published in The Astronomical Journal, the finding highlights how historical observations continue to yield breakthroughs years after collection.
“Observations made years, or even decades ago, can be revisited to answer new scientific questions. In many cases, scientists continue to make discoveries not just with new observations, but by mining the archive built over decades of space exploration.”
NASA, via CBS News
Whether 41P ultimately fragments from its violent rotational forces or survives to yield further surprises during future perihelion passes, the comet has provided researchers with a rare window into the volatile mechanics governing small bodies in the solar system.
