Back in 1994. a comet broke apart, slammed into Jupiter and created a visible scar that lasted for weeks. The comet’s discovery was credited to one professional astronomer and two amateurs: Gene and Carol Shoemaker, and David Levy. Hence it became known as Comet Shoemaker-Levy 9.

Since the earliest days of human history, mankind has scoured the heavens. The invention of the telescope in the late 16th century launched a hugely popular backyard hobby that has yielded its fair share of terrific discoveries — made not by scientists, but by amateurs.

Amateur astronomers scored again this year by being the first to observe two asteroid impacts on Jupiter using high-speed video monitoring equipment: one on June 3, 2010 (image and video here), and another on Aug 20.

In the Philippines, Christopher Go was recording observations of Jupiter — in prime viewing position the night of June 3 for backyard astronomers — when he saw a two-second flash of light. Over in Australia, his fellow skywatcher Anthony Wesley saw the same thing while perusing some real-time video from his telescope.

“When Anthony issued the alert, I was just processing the video of Jupiter I just took, so I checked to see what I got,” Go told Ars Technica back in June. “And there it is, I still can’t believe it, wow, it’s just amazing!” (Both men have made similar observations in the past: Go discovered a temporary “junior red spot” on Jupiter in February 2006, while Wesley was first to spy a 2009 collision with Jupiter also picked up by the Gemini Observatory. That Jupiter sure can take a beating!)

Once alerted via email of these observations, professional astronomers got on the case, scouring their own images for signs of an impact. They concluded that the flash of light was most likely a small comet or asteroid burning up in the gas giant’s atmosphere. Until then, scientists didn’t think such a small collision could be directly observed, but Go and Wesley proved otherwise.

A new paper analyzing follow-up observations of the June event by professional astronomers will soon appear in Astrophysical Journal Letters. The lack of thermal disruptions to the usual chemical signatures that would indicate debris from a collision gave them enough information to deduce the likely size of the object: a mass between 1 to 4 million pounds, although the energy released was considerably less (5 to 10 times less) than that of 1908, when the infamous Tunguska meteroid knocked down a huge swath of trees in Russia. (The asteroid is comparable in size to asteroid 2010 RF12, which passed very close to Earth a couple of weeks ago on September 8.)

The object is likely a remnant from 4.5 billion years ago, when the solar system was first being formed, scientists believe, caught in the strong gravitational pull of the gas giant. In fact, one NASA/JPL astronomer, Glenn Orton, memorably described Jupiter as “a big gravitational vacuum cleaner.” It’s now fairly clear that Jupiter takes a punch from such boloids far more frequently that previously assumed. “Scientists are still trying to figure out just how frequently,” Orton admitted.

And the story doesn’t end there. On August 20, two Japanese amateur astronomers, Masayaki Tachikawa and Aoki Kazuo, reported another asteroid collision with Jupiter, lasting a mere 1.5 seconds, and also leaving no debris that might have been detected by a larger telescope.

What gives them an advantage over professional astronomers when it comes to spying these small 10-meter objects? According to co-author Imke de Pater of UC-Berkeley, they can record the night sky for longer periods of time using color video cameras to capture small impacts lasting two seconds or less; professional telescopes can only capture them by chance.

Wesley, for one, isn’t the least bit surprised that these sorts of discoveries keep happening. “More and more amateur astronomers are becoming involved in high-resolution imaging of Jupiter and Saturn, taking advantage of new technology to produce stunning images that are of great value to planetary researchers and enthusiasts everywhere,” he said in the most recent Gemini press release announcing the paper’s publication. “This last year has seen Jupiter monitored and imaged by amateurs more often than every before, a trend that is certain to continue into the future.”