Discovery of an asteroid only 150 feet across less than 4 million miles from Earth by a University of Hawaii telescope is a significant event, considering the violent origin and history of the solar system when impacts and collisions formed and cratered the planets.

An object that small would not seem to present much of a threat to a planet 6,000 miles in diameter.

Objects of 150 feet or less across normally incinerate by friction with the atmosphere, but they can still be capable of significant damage.

In 1908 an object estimated to be about that size exploded five miles high in the atmosphere over Tunguska, Siberia, with a force equal to 1,000 Hiroshima bombs. Although only the shock wave from the explosion struck the surface, it was powerful enough to snap trees a foot in diameter like toothpicks five miles from the epicenter. Imagine the disastrous effects if this were to happen near a populated area today.

A Tunguska-like event probably occurs somewhere on Earth’s surface only every 1,000 years or so, so why the concern? Ask the victims of a 200-year flood if a low occurrence event is something to be concerned about.

The UH telescope, the Pan-STARRS PS1, is a prototype connected to the world’s largest digital camera. The telescope is small, only 6 feet in diameter, but the camera is a monster 1,400-megapixel device that can cover an area of the sky as large as 36 full moons. A single photo printed at 300 dpi would cover a basketball court, and PS1 takes an image every 30 seconds, enough to fill a DVD every 2.5 seconds, 1,000 DVDs per night.

For a long time geologists and astronomers thought the chaotic collisions that formed the planets were finished long ago. This began to change with the verification only 50 years ago that the astrobleme now called Meteor Crater was indeed the result of an impact by a solid, nickel-iron meteorite about the same size as the one PS1 just discovered.

In the past three decades, it has become increasingly clear that cosmic impacts have played and will continue to play an important role in Earth history as they are now linked to several mass extinctions, including the demise of dinosaurs.

Although here has not been a calamitous impact in recorded history, the next event is sure to be a matter of when and not if.

So far, nearly 800 near Earth objects, or NEOs, more than half a mile wide have been identified by existing discovery teams, which is thought to be about 90 percent of the total. But less than 5 percent of NEOs 150 feet or larger have been located. PS1 and its planned four-camera progeny have a lot of work to do.