D/1770 L1, popularly known as Lexell's Comet after its orbit computer Anders Johan Lexell, is discovered by the great French astronomer Charles Messier in June 1770.

It is notable for having passed closer to the Earth than any other comet in recorded history, approaching to a distance of only 0.0146 astronomical units (2,184,000 kilometers, or 1,360,000 miles).

The comet has not been seen since 1770 and is currently considered lost.