In 1994, comet Shoemaker-Levy 9 was ripped into pieces by Jupiter's gravity and struck the gas giant, creating a spectacle across it's atmosphere. In a more recent finding, comet 240/P has been observed to have broken into pieces, but this time, the reason is not because of Jupiter's immense gravity, but something else. A study published by David Jewitt and collaborators investigates why 240/P may have broken apart with different conditions from the famous comet of 1994.
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Astro Brief is a podcast collaboration between KSMU, the Missouri Space Grant, and MSU's Department of Physics, Astronomy and Materials Science. Hosted by Dr. Mike Reed, Astro Brief focuses on astronomical events, the field of astronomy, and astronomy-related guests. It airs Thursdays at 9:45 am on KSMU.
Transcript
Perhaps some of our listeners will remember the infamous comet Shoemaker-Levy 9 of 1994, but for those who don't — likely most of you — I will recap.
The Comet was discovered in 1993, just before passing near to Jupiter, and as it passed by Jupiter, that planet's strong gravity ripped the comet into 20 major fragments and several smaller ones. Those fragments then swung around the Sun, and in July of 1994, one by one, they plunged into Jupiter at roughly 130,000 miles per hour. Each fragment exploded in the pressure of Jupiter's atmosphere, creating dark blotches the size of Earth. It was a very exciting event — especially for myself, an undergraduate student at the time. But in a few weeks, the dark blotches were gone, as was Comet Shoemaker-Levy 9.
That was over 25 years ago, so why am I bringing it up now?
Because I want to talk about another interesting comet, 240P/Neat. Comet 240P is not going to hit Jupiter anytime soon, but it has been affected by the gravity of that giant planet. And just as a reminder, Jupiter's mass is 318 times that of Earth and more than two and a half times that of all the other planets combined. So its gravity has an oversized effect on objects within our solar system, and that's where Comet 240P comes into it.
This comet most likely originated in a region of our solar system called the Kuiper Belt, named after Gerard Kuiper, who predicted its existence in 1951. It is a doughnut-shaped region of our solar system beginning at Neptune's orbit of 30 AU — or Earth-Sun distances — and extending out to around 50 AU. That region contains Pluto and thousands upon thousands of icy rocky objects smaller than a few miles across.
Comet 240P came from that area, but somehow Jupiter's gravity disturbed its orbit and probably quite recently.
It was discovered in 2002 when its closest approach to the sun — or perihelion distance — was two and a half AU. Already, its orbit was under eight years and so to be discovered only in 2002, it was likely a recent addition to our inner solar system. Its furthest distance from the sun — or aphelion — is now only 5.6 AU, just past Jupiter's orbit. And so on its first pass after discovery — nearest to Jupiter in 2007 — its perihelion shrank to just 2.1 AU. So obviously Jupiter is continuing to affect this comet.
During 2018 and 2019, there were several instances where the comet had a burst of brightness likely related to elevated mass loss.
And then in June of 2025, a fainter object was detected moving along with 240P. This prompted Dr. David Jewitt of UCLA and collaborators to monitor 240P using the Nordic Optical Telescope on the island of La Palma. They observed monthly, beginning in October 2025 through its perihelion in December and until April of 2026 and they confirmed that the second object was in fact a piece of comet 240P.
They published their findings in The Astronomical Journal in July.
They measured the major piece of the comet at 0.6 miles in diameter, and the smaller piece likely is just over a quarter of a mile in diameter. Possibly when attached, it would have looked like a smaller version of comet 67P, which was visited by the Rosetta space mission. That comet was shaped roughly like a rubber duck, with the body portion being a couple miles across and the smaller head portion about half that size. The two pieces of comet 240P are moving apart at just over 2 miles per hour, which means the comet split not too much over three years before their observations. Because of outgassing — which can change their motions a bit — Dr. Jewitt and collaborators can't be sure exactly when it happened. And it makes me wonder if it happened during the 2018-2019 Brighton events, but there's no way to know for certain.
What David Jewitt and collaborators were interested in is why the comet split into two pieces, and because of 240P's special orbit and their longer observations, they can make a determination.
The comet has not been significantly close to Jupiter or any other planet since 2008, so unlike the spectacular comet Shoemaker-Levy 9, it did not break because of gravity from a planet. Since its orbit takes it above and below the asteroid belt, it did not have a collision, and since they measured the dust loss rates, they can conclude that it cannot be due to some kind of gas pressure like a geyser within the comet. They conclude that it must have been caused by spin accelerated by outgassing. The current spin rate of the larger portion is not known, but if it could be measured, then the theory could be proven or disproven.
Now the challenge is to make that measurement.