On this day in space! Aug. 3, 2004: NASA launches MESSENGER spacecraft to orbit Mercury

On August 3, 2004, NASA launched the MESSENGER spacecraft on a groundbreaking mission to orbit Mercury. The mission's name, MErcury Surface, Space ENvironment, GEochemistry and Ranging, encapsulates its scientific objectives. After a six and a half year journey aboard a Delta II rocket launched from Cape Canaveral Space Force Station in Florida, MESSENGER finally reached Mercury's orbit in 2011.

Mercury, the closest planet to the sun, poses unique challenges for space exploration. Its proximity to the sun and subsequent high gravitational pull necessitated MESSENGER to utilize gravitational assists from Venus and Mercury to slow down and avoid falling into the sun. The spacecraft completed 15 orbits around the sun before successfully entering Mercury's orbit.

Despite the difficulties, MESSENGER made significant discoveries about Mercury. The planet, with its harsh conditions, holds the promise of water ice in its permanently shadowed polar craters. MESSENGER's findings revealed that Mercury's core is unusually large, comprising about 85% of its radius, which is larger than Earth's core. The planet is also remarkably flat, with fewer elevation changes than those observed on Earth's moon and Mars.

The most tantalizing discovery, however, was the presence of "radar-bright" deposits in Mercury's polar craters. These deposits could potentially harbor pockets of water ice, making Mercury a crucial target for future space exploration.

MESSENGER's primary mission concluded in 2012, but it was extended twice due to its successful performance. In 2015, NASA intentionally crashed the spacecraft into Mercury to conclude its mission. Today, another spacecraft is on its way to Mercury. The BepiColombo mission, a joint project between Japan and the European Space Agency, launched two orbiters in 2018 and is scheduled to arrive at Mercury in November.