Bob Doyle, Columnist
Last Feb. 15, there was a brilliant point of light flying across the dawn skies of Chelyabinsk in southwestern Russia.
As it reached the end of its flight, the object was brighter than the sun. Then it dimmed, leaving behind a striking trail. Three minutes later, its shockwave hit the ground, shattering thousands of windows and injuring more than 1,600.
After detailed analysis by both Russian and NASA scientists, it was estimated that the object was an asteroid about 60 feet across that exploded with a force of 500,000 tons of TNT.
Last October, Russian scientists found a 1,250 pound fragment of this asteroid that had fallen into a nearby lake.
In November, researchers led by Canadian scientist Peter Brown analyzed the last two decades of impact data. Their conclusion: that space rocks the size of the Chelyabinsk asteroid may hit the Earth several times each century.
Last year, there was a timely book by astronomer Donald Yeomans, who works at the Jet Propulsion Laboratory in California. “Near-Earth Objects: Finding Them Before They Find Us” was published by the Princeton University Press with ISBN 978-0-691-14929-5.
It would be helpful to first define the terms: meteoroid, asteroid, comet and meteorite. All are cosmic intruders that may come our way.
A meteoroid is a space rock smaller than one meter or 3.3 feet across. An asteroid is a space rock larger than one meter across. A comet is a space object that’s mostly frozen ices (water, carbon dioxide or ammonia ) whose outer layers turn to gases as they approach the inner solar system.
A meteorite is a fragment of a meteoroid or asteroid that reaches Earth’s surface. (Most meteorites fall in the ocean.)
Each day it is estimated that one hundred tons of meteoric or asteroidal material falls to Earth. About once a day a basketball sized meteoroid impacts the Earth’s atmosphere; its collisional speed is high enough that most of the object is burned up, producing much meteoric dust.
A mini-asteroid the size of VW Beetle likely strikes the Earth every six months. Such a space rock flattened the back end of a 1980 Chevy Malibu on the evening Oct. 9, 1992.
The streaking space rock was seen over a large area of Pennsylvania and New York. To make a long story short, Michelle Knapp of Peekskill, N.Y., owner of the Malibu, sold both her car and the meteorite to a group of collectors for $69,000!
The greatest meteor fall in recorded history occurred in the early morning of June 30, 1908, in an uninhabited area of Tunguska, Siberia.
The object exploded at five miles altitude with an energy of 4 million tons of TNT, producing a shock wave that leveled about 800 square miles of forest (larger than the area of Allegany County).
A Russian farmer, who was sitting on a porch of a trading post 40 miles from the impact, was blown off his feet when the pressure wave reached him. The estimated size of the asteroid was about 100 feet across. Such impacts would likely strike the Earth every few centuries.
Closer to home, there is strong evidence of an asteroid from 2 to 3 miles across impacting the Cape Charles area (Virginia) near the southern end of the Delmarva Peninsula.
The collision occurred 35 million years ago. This event produced a crater about 53 miles in diameter and a tremendous tsunami that swept over the Atlantic coast.
The evidence is shocked quartz obtained from cores drilled in the Chesapeake Bay area. Molten material was hurled into Western Maryland.
The heat from the impact would have set many forests on fire. (My next column will deal with the detection of these rogue asteroids and what could be done if we had sufficient warning of a probable collision.)
SKY SIGHTS AHEAD: The planet Venus has reappeared in the southeastern dawn and is easily seen by 6 a.m. The crescent moon will appear near Venus on Jan. 29 at dawn. Brilliant Venus will be a dawn object until mid-September.
This week, planet Mercury can be seen at dusk, setting in the southwest about 6:55 p.m.
Bob Doyle invites any readers comments and questions. E-mail him at firstname.lastname@example.org . He is available as a speaker on his column topics.