A NASA spacecraft that made surprising discoveries of ice and other materials on Mercury will crash on the planet around April 30, scientists said on Thursday.

The Mercury Surface, Space ENvironment, GEochemistry, and Ranging, or MESSENGER, probe has been circling the innermost planet of the solar system for more than four years, the first close-up studies of Mercury since NASA's Mariner 10 spacecraft made three flybys in the mid-1970s.

Out of fuel and losing altitude, MESSENGER is expected to make a high-speed crash near the planet's north pole at around 3:25 EDT (1925 GMT) on April 30, flight controllers told reporters during a webcast news conference.