Videoing Jupiter isn't an uncommon astronomical technique. Although on any given night you wouldn't expect to see much action from the massive planet, the individual frames of a video are processed by astronomical imaging software and the individual frames are stacked to produce a high-resolution final image. This technique is used to remove the haze and turbulence caused by atmospheric effects. But very occasionally, these videos can capture the odd transient event, like a meteor flash.
ANALYSIS: Impact Observed in Jupiter's Atmosphere
Although seeing a bright flash across millions of miles of interplanetary space may give the impression that Jupiter was hit by something pretty big, as Plait mentions in his blog, the impactor wasn't likely more than a few tens of meters wide. As Jupiter has a more powerful gravitational field than Earth, objects will hit the Jovian atmosphere around five-times faster than they hit Earth's atmosphere. Greater velocity means more energy, so (from the kinetic energy equation E=1/2mv2) we'd expect an object hitting Jupiter to be carrying 25 times more energy than a comparable object hitting Earth's atmosphere. This means 25 times more energy will be released on impact, producing a way bigger flash.
If you're experiencing a little deja vu right now, you're right, this certainly isn't the first time amateur astronomers have witnessed Jupiter flashing.
In 2009, a significant impact was witnessed by amateur astronomer Anthony Wesley in Australia that, after some detective work, was found to be an asteroid impact. Then in 2010, Wesley was again looking in the right place at the right time to spot another large impact and confirmed by Philippines-based amateur astronomer Christopher Go.
ANALYSIS: Why Did Jupiter Flash?
But the biggest cometary carnage event in recorded history was chronicled by the Hubble Space Telescope when Comet Shoemaker-Levy 9 fought with Jupiter's gravity in July 1994, but ultimately got shredded, peppering the Jovian atmosphere with huge chunks of icy debris.
These impact events are critical for planetary scientists to understand just how often planets get hit by asteroids and comets, particularly Jupiter. Some theories suggest that Jupiter is Earth's protector in some ways; its gravitational well prevents potential Earth-impacting asteroids or comets from causing mayhem. But other theories hint that Jupiter's gravity may actually redirect some near-Earth object orbits into Earth's path.
In this case it seems that Jupiter was being our defender, and amateur astronomers - once again - were key to this impact event's discovery.
Source: Bad Astronomy