Heavy hitter (Image: George Hall)

A bright flash spotted early yesterday in Jupiter’s swirling atmosphere was most likely due to a hit by a comet or asteroid, astronomers say. Although the impact is the fourth one seen in just over three years, the uptick does not mean Jupiter is getting hit more often, only that more people are looking.

“Jupiter has been taking hits like this for a long time,” says Franck Marchis of the SETI Institute in Mountain View, California. “It’s just that now, amateur astronomers have the capabilities to detect them.”

With the speed of digital communication, the army of enthusiasts scanning the skies can connect with professional astronomers to follow up on an observation almost instantly.


Seeing real-time impacts and studying the scars left on Jupiter will give scientists unique windows into the gas giant’s atmospheric properties. The events can also tell astronomers more about the impacting objects themselves, giving a better picture of the sizes and numbers of bodies swarming through the solar system.

“This is a remarkable tool for us professional astronomers,” Marchis says. “We cannot observe Jupiter continuously. But now when something like this happens, we can see it.”

Cameras rolling

Amateur astronomer Dan Peterson of Racine, Wisconsin, first saw a bright flash near Jupiter’s equator through a telescope but didn’t manage to catch it on camera. One report was not enough to confirm the flash as an impact, so Peterson emailed a description of what he saw to other astronomers.

Astrophotographer George Hall of Dallas, Texas, had been filming Jupiter that night with a small telescope and a web camera.

“Had [Peterson] not recognized the event and issued the alert, I would never gone back and reviewed my videos in enough detail to see the impact,” Hall told New Scientist in an email. Sure enough, Hall had captured a four-second video of a bright flash at Jupiter’s eastern rim.

In July 2009 a dark cloud of debris heralded an impact by what astronomers now think was a 500-metre-wide asteroid. Before that, the only observed impact was in 1994, when fragments of comet Shoemaker-Levy 9 rained down on Jupiter’s atmosphere.

Two more hits were spotted in June and August 2010, but the last one wasn’t large enough to leave a lasting mark.

This most recent impact seems to be similar to both 2010 events in terms of brightness, according to an analysis by Ricardo Hueso of the University of the Basque Country in Bilbao, Spain.

Telescopes will be trained on the planet tonight to see if the impact left a scar. If so, astronomers may decide to follow up with the Hubble Space Telescope to determine the object’s trajectory and how deep it penetrated into Jupiter’s atmosphere.

Gravity shield

The recent spate of impacts highlights Jupiter’s role as cosmic street sweeper, clearing up debris that might otherwise hit Earth, says Glenn Orton of NASA’s Jet Propulsion Laboratory in Pasadena, California.

“Jupiter is a big gravitational vacuum cleaner,” says Orton. “We qualitatively know that Jupiter’s protecting the Earth. Without Jupiter we’d have a lot more impacts.”

Catching more of Jupiter’s hits will help provide the first accurate census of bodies 100 metres across and smaller – those too small to see with telescopes – in the outer solar system.

“We’re getting good data on the population of small bodies that are out there. There’s not a lot that’s known about that,” says Mike Wong of the University of California, Berkeley. “This is a pretty new field that kind of just started in 2009.”

Correction: An earlier version of this article stated that the 2009 impact caused a visible flash on Jupiter; it did not. Also, the earlier version stated that the brightness of the new flash was between that of the 2009 and 2010 events; it was actually similar to both 2010 flashes.