NASA’s MESSENGER spacecraft, which has orbited and studied the planet Mercury since 2011, will end its extended mission as it runs out of fuel and crashes into the planet on April 30, 2015. Join Slooh for a live show as we cover this extraordinary event and discuss the achievements of the MESSENGER Mercury mission.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) began its mission when it launched from Cape Canaveral aboard a Delta II rocket on August 3, 2004. A direct flight to Mercury was too difficult because the craft would gain too much speed as it moved closer to Sun. It was impractical to carry enough fuel for braking. And Mercury has no atmosphere for the craft to brake using atmospheric friction. So to manage its speed, MESSENGER took a complex roundabout route to Mercury with a flyby of Earth, two flybys of Venus, and three flybys of Mercury itself. MESSENGER’s flybys of Mercury were the first by any craft since the Mariner 10 mission in 1975.

MESSENGER settled into a highly elliptical orbit around Mercury on March 18, 2011. During its more than 4,000 orbits of the planet over the past four years, the spacecraft mapped and imaged the inner planet, probed its magnetic field and gravity, and discovered a surprising amount of water in Mercury’s exosphere. It also found evidence for past volcanic activity and the possibility that Mercury has a liquid-iron core. Late in 2014, scientists also suggested MESSENGER discovered signs of an annual meteor shower on Mercury.

Because the craft operates so close to the Sun, its orbit slowly degrades as the Sun pulls it closer to the surface of the planet. Early in April, MESSENGER’s orbit will quickly decay as the craft runs out of hydrazine fuel. Engineers will maintain orbit as long as possible using the helium pressurant gas that remains in the fuel tanks. The craft is now orbiting between 6 km and 39 km above the surface of the planet and is collecting more scientific data on Mercury’s exosphere and gravitational field.

As the last bits of pressurized helium run out, the half-ton spacecraft will finally impact the planet at 8,720 mph on April 30. NASA engineers expect MESSENGER will impact Mercury between 19:25 and 19:30 UT, although it may complete one more 8-hour orbit of Mercury before impact. The impact site will not be visible from Earth, but Slooh will have full coverage of the event and a retrospective of the MESSENGER mission.