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Something Large Just Smashed Into Jupiter

17 SEPTEMBER 2021

Poor old Jupiter. It's just hanging out there, being a gas giant, shepherding trojans, minding its own business, and boom. Smacked upside by a stray space rock.

That's not necessarily unusual for Jupiter, actually. What is unusual is that someone happens to be looking and filming at just the right time - and this month, that happened, with sky-watchers around the globe catching an explosion in the planet's upper atmosphere.

 

On 13 September 2021, at 22:39 UT, amateur astronomers recorded the bright flash of what appeared to be a Jupiter impact - namely Harald Paleske from Germany, who was recording the shadow of Io as it passed in front of the planet, and José Luis Pereira from Brazil.

Others included Simone Galelli in Italy, and Jean-Paul Arnould and Michel Jacquesson in France. Thibaut Humbert, Stéphane Barré, Alexis Desmougin and Didier Walliang of the Société Lorraine d'Astronomie in France also managed to film the putative impact.

If confirmed, the event will only be the eighth impact event observed on Jupiter since the impact of comet Shoemaker-Levy 9 in 1994, which broke apart due to Jupiter's tidal forces, and produced a string of impacts.

These were actually on the planet's far side, but a 2.2-meter telescope in Hawaii photographed the heat signatures of these impact sites as they orbited into view, and Hubble captured the dark smears left behind on the clouds, known as a scar.

It's unknown precisely how often Jupiter gets smacked by something large or fast enough to produce an impact flash visible from Earth, but it's thought to be fairly often - somewhere between 20 and 60 times per year. Jupiter is large and has a huge gravitational field, which accelerates meteorites to generate much more energetic events than we experience on Earth.

 

But we don't see them as often as they're predicted to occur, for multiple reasons. The most recent capture of an impact event on Jupiter was over two years ago.

"It's a very fleeting event, it's a few seconds," astronomer Jonti Horner from the University of Southern Queensland in Australia told ScienceAlert at the time.

"It wouldn't be so obvious, if you were looking through the eyepiece of the telescope. A lot of the time these things will go unnoticed and unobserved. Half of them will happen on the far side of the planet. So there's a lot of things working against seeing these events."

Nevertheless, the rate at which we detect them seems to be increasing. This will be of great benefit to astronomers hoping to understand Jupiter's role as a cosmic vacuum cleaner protecting Earth from rocks that might have otherwise headed our way.

 

Some analysis suggests that this may have been exaggerated, but, either way, understanding it more accurately can help us model the chances for life in other planetary systems that have or don't have Jupiter-like gas giants.

The object that smacked Jupiter in 2019 turned out to be an object 12 to 16 meters in diameter (40 to 50 feet), with a mass of about 450 tons and a stony-iron composition.

We're going to have to wait for an in-depth analysis of the flash, and subsequent observations looking for an impact scar, to see what hit Jupiter this time around. But with so much material to work with, we're excited to see what astronomers find.