Nasa spacecraft orbits Mercury
For the first time, Nasa has put a spacecraft in orbit around the solar system's smallest planet, Mercury.
Nasa said a spacecraft called Messenger successfully veered into orbit on Thursday night after a six and a half-year trip and 4.9 billion miles.
The desk-sized spacecraft fired its engine for 15 minutes before entering an egg-shaped orbit.
The mission required some tricky manoeuvring to fend off the gravitational pull of the sun.
"It was right on the money," Messenger's chief engineer Eric Finnegan said.
Messenger is in orbit that brings it as close as 120 miles above the planet's surface.
"This is as close you can possibly get to being perfect. Everybody was whooping and hollering; we are elated," Mr Finnegan said. "There's a lot of work left to be done, but we are there."
Messenger was launched in 2004. Next month it should start transmitting pictures from as close as 120 miles above the surface of Mercury, a strange planet of extremes.
Messenger will investigate Mercury's mysterious magnetic field and the possibility of ice in craters, even though it is the closest planet to the sun.
A Nasa Twitter account under Messenger's name gave play-by-play accounts as it arrived at the small planet. This "Messenger" "exchanged tweets" with Voyager 2, one of Nasa's oldest and most-distant spacecraft. Voyager 2, launched in 1977 and now at the edge of the solar system, tweeted good luck and Messenger "answered" with a tweet: "Many thanks! Cold out there? Kinda warm where I am."