MESSENGER Mission Floats Over Mercury

Scientists at the MESSENGER mission control at NASA’s Jet Propulsion Lab raised the spacecraft’s orbit around Mercury, to give it a little more time to continue low level observations of the planet’s surface features and magnetic field. MESSENGER is due to run out of fuel soon and will free fall into Mercury’s atmosphere when that happens. By slowing down the spacecraft’s descent, mission scientists are hoping to gain some unprecedented close-up observations.

Yesterday’s maneuver raised MESSENGER’s orbit from 3.4 miles above the planet’s surface to 17.1 miles, by increasing its velocity. The final stage of the mission is being extended by a series of orbit-correcting maneuvers (OCMs), which raise its orbital height and increase its velocity to counterbalance the pull of the gravitational fields of Mercury and the sun.

The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft was launched in 2004 and entered orbit around Mercury in 2011. The mission was always a dangerous one, bringing the spacecraft very close to Mercury’s surface and to the sun, where it is subject to intensely high temperatures and complex interplanetary magnetic fields. Messenger is only the second spacecraft sent to Mercury after Mariner 10, which flew by in 1974 and 1975.

MESSENGER has mapped the surface, geology and planetary environment of Mercury, producing many surprises for scientists. Mercury’s anomalously high density among inner solar system planets is not due to the presence of high amounts of iron, as previously thought. Instead, its surface is high in volatile elements like sodium and sulphur.

MESSENGER has shown that Mercury’s internal composition is very homogenous. This offers clues to the history of the planet’s geological formation. MESSENGER also found that Mercury’s surface was shaped by volcanic activity, and that there are large amounts of ice permanently frozen inside the craters at the planet’s poles. Even though temperatures at Mercury’s surface can reach as high as 840F, the deep shadows inside the craters keep the water from boiling off.

The tradition of innovation in MESSENGER’s design and execution continues till the final stages of the mission. The OCMs allow it to use the remaining fuel to float over Mercury’s surface, to continue collecting data until the inevitable end.