The Messenger spacecraft will end a 10-year mission orbiting the planet Mercury, as the vehicle will crash into the planet on April 30.
The spacecraft, which arrived at Mercury in March 2011, will soon run out of fuel and crash into the solar system's innermost world. Currently, the vehicle is skimming just above the surface of the planet.
Messenger launched on Aug. 3, 2004, on a circuitous route to Mercury that carried the spacecraft around the sun 15 times over the course of 7 years. This was only the second mission to Mercury, following the Mariner 10 mission of 1974 and 1975. The spacecraft has exceeded its expected mission lifespan by three years.
"A lot of people didn't give this spacecraft much of a chance of even getting to Mercury, let alone going into orbit and then gathering data for four years instead of the original scheduled one-year mission. In the end, most of what we considered to be gospel about Mercury turned out to be a little different than we thought," William McClintock of the Laboratory for Atmospheric and Space Physics at Colorado University-Boulder said.
One of the biggest surprises of the Messenger mission involved the tenuous atmosphere, known as an exosphere, which surrounds Mercury. Most astronomers believed this layer, generated by micrometeorite impacts, would be highly variable over time and impossible to predict. Instead, researchers discovered the exosphere experiences regular patterns, similar to seasons on Earth.
During its four years orbiting Mercury, Messenger also noted a massive iron core within the planet, carbon from comets layered on the planet's surface. The mission also revealed evidence that over a million tons of ice may be hiding in craters on the planet despite surface temperatures as high as 800 degrees Fahrenheit. Some of these craters were once filled with lava, astronomers discovered from data collected by Messenger.
Engineers have performed regular adjustments to the orbit of Messenger to delay its final descent. The last of these is planned for April 24.
"Following this last maneuver, we will finally declare MESSENGER out of propellant, as this maneuver will deplete nearly all of our remaining helium gas. At that point, the spacecraft will no longer be capable of fighting the downward push of the sun's gravity ... MESSENGER's final act will be to leave an indelible mark on Mercury, as the spacecraft heads down to an inevitable surface impact," Daniel O'Shaughnessy a mission systems engineers from the Johns Hopkins University Applied Physics Laboratory, said.
The exact method through which Messenger will meet its end is still uncertain. The vehicle could finally drag to a halt on the surface of Mercury, or it may strike a scarp — tall cliff-like features formed by cooling of the planet during the formation of the solar system.
