An unseen comet or possibly an icy asteroid apparently crashed into Jupiter's atmosphere near the giant planet's south pole sometime during the last few days, creating a "gargantuan" blemish easily visible from Earth.
The presumed impact, discovered by Australian amateur astronomer Anthony Wesley July 19 and confirmed by NASA's Infrared Telescope Facility at Mauna Kea, Hawaii, came almost 15 years to the day after multiple fragments of Comet Shoemaker-Levy 9 crashed into Jupiter in 1994.
"We're not sure how large this fragment could have been," Leigh Fletcher, a researcher at the Jet Propulsion Laboratory in Pasadena, Calif., told CNET.
"But it certainly had the energy and the momentum that was sizable enough that when it hit the upper atmospheric layers of Jupiter, it created a kind of splash of material that lofted aerosols and gases and various other particulates to really high altitudes."
The scar left in Jupiter's atmosphere is roughly the size of an atmospheric feature known as the "little red spot," a long-lasting storm nearly the size of Earth.
"The size of this impact scar is extremely large and it does bear all the hallmarks of one of the intermediate collisions that occurred in the Shoemaker-Levy 9 impact," Fletcher said. "It's not as big as some of the largest ones, but it's certainly more dramatic than some of the smaller impacts of Shoemaker-Levy 9.
"We've compared it in size to the little red spot on Jupiter, you can see the two are roughly a similar order of magnitude in size," he said. "It's smaller than Earth-sized, but it's certainly gargantuan by earthly proportions."
Over the next few days and weeks, the Hubble Space Telescope, other space-based telescopes, and observatories around the world will focus on the impact site to learn as much as possible about what might have hit Jupiter and how the impact affected the planet's atmosphere.
Looking at Jupiter in infrared light, the Infrared Telescope Facility in Hawaii confirmed an impact point near the south pole with a visible scar and "bright upwelling particles in the upper atmosphere," according to a NASA statement.
But it will be difficult confirming the nature of the impactor.
"It's going to be really hard to tell," Fletcher said in a telephone interview. "I've been using the analogy of throwing a stone into a pond. The stone disappears and you see all of the splash that comes back from it. We're going to have to do some really detailed modeling and get a real good understanding of the splash before we can tell you about the stone. It certainly wasn't seen and it wasn't tracked by any means from Earth. So we didn't see it before the collision."
But the solar nebula from which Jupiter and the outer planets formed is believed to have been rich in ice material.
"And so it's expected that whatever impacted with Jupiter, if it comes from a local population of impact bodies, is probably going to be icy in origin," Fletcher said.
In high-velocity collisions like this one, so much energy is released that "shock chemistry" occurs, creating "chemical reactions that otherwise would not occur in the atmosphere of Jupiter," Fletcher said.
"The last time this happened with Shoemaker-Levy 9, we detected lots of materials," he said. "One in particular was hydrogen cyanide, or HCN, which was observable in Jupiter's atmosphere for many years after the collision (of Shoemaker-Levy 9).
"What we're hoping to discover in the next few days as we turn the telescopes and spectrometers of the world towards Jupiter is that maybe that HCN has been replenished by whatever impact body it was."