In a technological feat that gives scientists their first opportunity to dig into a remnant of the early solar system, the European Space Agency’s Rosetta mission successfully placed a small spacecraft on the surface of a speeding comet on Wednesday.

With this achievement, a comet is no longer a mysterious and sometimes frightening spray of light across the night sky, but another member of the solar system to be explored, like the moon and Mars. The technology of landing on a comet, with its wisps of gravity, could be applied to future efforts to mine asteroids.

The agency’s director general, Jean-Jacques Dordain, described the touchdown on Comet 67P/Churyumov-Gerasimenko, a 2.5-mile-wide ball of rock, ice and dust moving faster than 40,000 miles an hour, as “a big step for human civilization.”

“Our ambitious Rosetta mission has secured another place in the history books,” Mr. Dordain said at a news conference. “Not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a probe to a comet’s surface.”