On Feb. 15, a hunk of space rock 50 feet across and weighing some 7,000 tons screamed into our atmosphere at 40,000 miles per hour over Chelyabinsk, Russia, about 9:20 a.m. local Russian time.
The rocky meteorite shattered from the pressure of moving at such supersonic speeds at an altitude of 12 to 15 miles. The explosion was equivalent to a 500-kiloton nuclear weapon, several times smaller than the nuclear bombs dropped in World War II.
Ironically, the last time anything of any significant size hit Earth from space, it also exploded over Russia.
On June 30, 1908, a 150-foot-wide, rocky meteorite slammed into our atmosphere over the Tunguska Forest region of Siberia.
The explosion knocked down some 80 million trees over an area of 830 square miles.
It is estimated that the shock wave from the air blast measured 5.0 on the Richter scale. That one released an energy equivalent of 7,700 kilotons of explosive energy.
Meteorite impacts on this scale are considered a once-a-century event. Smaller events occur much more frequently. In fact, a bit of a space rock just entered our atmosphere. Whoops, there goes another. And another. They come in at a rate of about one per second. Some 50,000 tons of stuff from space comes to Earth every year. The vast majority are no bigger than a grain of sand or a dust mote. At night, we see them as shooting stars. We don't see them at all during daylight hours, unless, like that one over Russia, they happen to be big enough to glow brighter than the daylight sky.
Impact events occur with increasing rarity with larger sizes. Space rocks massive enough to destroy a city may happen only once every few thousand years and most will hit over ocean.
Asteroids with the power to destroy a state- or country-sized region — plus the economy of our planet — happen with million-year frequencies.
Rarely, only a few times in all of geologic history, a species-killing asteroid smacks Earth.
The last time was 65 million years ago.
How bad was that one? Ask the next dinosaur you meet on the street. I'm sure he'll have a few horror stories to tell.
We look for these things. Hopefully we'll see it coming years, better still, decades, before it arrives. That would give us a fighting chance to deflect it away from a deadly date with our precious planet.
At 6:01 a.m. on the morning of March 20, the sun, having spent the last six months visiting the Southern Hemisphere, crosses over into the Northern Hemisphere, marking the middle of the long sunset for Antarctica and the equally long sunrise for the Arctic. For us in Oklahoma, it denotes the beginning of spring.
When something of a cosmic nature is heading our way, we'll let you know in the Kirkpatrick Planetarium's daily presentation of “Tonight's Sky.” Call 602-3761 or check out our Web page at www.sciencemuseumok.org for more information.
The Oklahoma City Astronomy Club meets at the Planetarium on March 8 at 6:45 p.m. Guests are free and welcome. Go to www.okcastroclub.com for more information.
Planet visibility report: At the beginning of the month, Jupiter is high in the east at sunset. Saturn rises around 10 p.m. All of the other three visible planets, Mercury, Mars and Venus are lost for the month. New moon occurs on Monday with full Moon following on March 27.
Wayne Harris-Wyrick is director of the Kirkpatrick Planetarium at Science Museum Oklahoma. Questions or comments may be emailed to firstname.lastname@example.org.