The Great Daylight Fireball, 1972
A space rock that dipped into the atmosphere and flew back out.
Key facts
- When
- 10 August 1972, early afternoon local time
- Where
- Over Utah, Idaho, Montana and Alberta, United States and Canada
- What hit
- probably between about 3 and 14 m across
- Era
- Witnessed, 1908 to 1999
- Location
- 47.50° N, 112.50° W
If it had come straight in, it could have exploded with an energy from a fraction of a kiloton up to around the Hiroshima bomb, depending on its true size.
It never released that energy: it skipped back out to space.
What happened
On a summer afternoon in 1972, a fireball crossed the sky from Utah northwards into Canada in about a minute and a half. Thousands of people saw it, and a tourist in the Grand Teton area of Wyoming filmed it as a bright point with a long trail, above the mountains.
It was a meteoroid on a path that only grazed Earth's atmosphere. At its lowest point it was about 57 km above Montana, low enough to glow but not low enough to be captured. It passed through about 1,500 km of air and then climbed back into space on a changed orbit.
A US military satellite designed to watch for missile launches also recorded it, one of the first fireballs measured from space.
Effects
None on the ground. The meteoroid lost some of its mass and speed and continued around the Sun.
The evidence
Film, photographs, eyewitness reports and satellite data, which together give its path and speed.
Did you know?
Earth-grazing fireballs are rare, but several have been recorded since, including one over Europe in 1990.
The 1972 film is one of the most famous fireball recordings ever made.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.