Comments on: 100 Years Since Tunguska

By: Steven Aftergood

Steven Aftergood — Wed, 02 Jul 2008 13:03:52 +0000

The 1994 Air Force estimate of a Tunguska-like “impact” once every hundred years now appears to be overstated, based on surveys of near-Earth objects that have been performed since that time.

According to Alan Harris of the Space Science Institute writing in Nature (26 June 2008, p. 1178), “an object that might cause a Tunguska-like event — roughly 50 meters in diameter — should collide with Earth only about every 1,500 years.”

On the other hand, writes astronomer Duncan Steel in the same issue of Nature (p. 1159), “50 meter objects are too small to spot far in advance of their impact. So although another Tunguska coming out of the blue is not a likely event in any given June, it is not out of the question.”

By: Henry M

Henry M — Wed, 02 Jul 2008 12:45:14 +0000

If explosions like Tunguska “occur about once in one hundred years,” then why have no others been recorded?

Just asking.

By: Steven Aftergood

Steven Aftergood — Sat, 28 Jun 2008 12:18:29 +0000

Thanks for this. All of these numbers are estimates, but several of the numbers in the Tass news report are wrong (as indicated above), and the JPL estimates are presumptively more reliable.

By: jhm

jhm — Sat, 28 Jun 2008 12:06:23 +0000

The email I received from JPL this morning contradicts some of the items here:

It is estimated the asteroid entered Earth’s atmosphere traveling at a speed of about 33,500 miles per hour. During its quick plunge, the 220-million-pound space rock heated the air surrounding it to 44,500 degrees Fahrenheit. At 7:17 a.m. (local Siberia time), at a height of about 28,000 feet, the combination of pressure and heat caused the asteroid to fragment and annihilate itself, producing a fireball and releasing energy equivalent to about 185 Hiroshima bombs.

[...]

Yeomans and his colleagues at JPL’s Near-Earth Object Office are tasked with plotting the orbits of present-day comets and asteroids that cross Earth’s path, and could be potentially hazardous to our planet.

Yeomans estimates that, on average, a Tunguska-sized asteroid will enter Earth’s atmosphere once every 300 years.

Little boy , according to Wikipedia, yielded 13 to 16 kilotons, making this less than three megatons, no?