One of the most fascinating happenings in scientific history took place precisely 100 years ago. This was the Tunguska event, a cosmic collision that devastated 2,000 square kilometers of a (fortunately) remote and lightly populated area of Siberia. The force of the blast was estimated at 200 kilotons of TNT. When scientists finally got to the site, they were puzzled. They had assumed it was a meteorite or perhaps a comet, but there was no impact crater. Over the decades, this would lead to speculation as wild as antimatter, mini-black holes, and alien spaceships. It's now generally thought the cause was a stony meteorite that vaporized with explosive force 5-10 km above the ground, although some researchers still think a comet was more likely.
COMMENT: Whatever the Tunguska object was, it reminds us our existence on this planet is fragile. That's an important thought to keep in mind as we consider dangers from other Near Earth Objects (NEOs) that may appear in the future.