Published by the Students of Johns Hopkins since 1896
December 8, 2021

MESSENGER begins revealing Mercury's secrets

By Julia Zhang | November 19, 2009

Lately, the discoveries made about the solar system have been astronomical, especially concerning the smallest and inner-most planet, Mercury.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging, or MESSENGER, spacecraft was designed by the Hopkins Applied Science Laboratory to collect data about Mercury's core structure, magnetic field, high density, geological history, atmosphere and poles, and ultimately transmit the information back to Earth.

Scientists were also looking for evidence to support several theories, including one theory that the planet is gradually shrinking. These ideas originated when the first probe to ever visit Mercury (the Mariner 10) brought back images of gigantic scarps, faults in the planet's crust, in 1975.

MESSENGER has made three fly-bys around Mercury, two of which occurred this year. In addition, the spacecraft previously made one Earth fly-by and two Venus fly-bys, all in preparation for entering into orbit around Mercury in 2011. To orbit a planet, a man-made object must strategically accelerate and decelerate until it becomes an artificial satellite of a larger body.

In the second fly-by around Mercury, large flux transfers were observed in the planet's magnetosphere, behavior that differed greatly from what was observed during the first fly-by. This brings attention to how solar and wind interactions with a planet's magnetic field can influence occurrences in the magnetosphere, especially, as in this case, when the planet is so close to the sun.

During the third and final fly-by completed on Oct. 6 of this year, MESSENGER unveiled a never-before-seen thirty percent of Mercury's surface.

Technology played a key role in these new findings. Whereas the Mariner 10 was equipped with cameras only capable of resolving images up to .99 miles across, MESSENGER's cameras could resolve images up to 59 feet, allowing much more accurate conclusions to be drawn from photos.

From over 1,200 images taken in the most recent fly-by, scientists observed that Mercury's surface is very different from other planets', with its large craters and extensive bright regions surrounding irregular depressions that could be volcanic plains.

The Mercury Laser Altimeter (MLA) allowed high-resolution analysis of the planet's topography, for the first time ever. These measurements will give scientists the ability to better interpret Mercury's surface geology.

An instrument called the Magnetometer was used to observe Mercury's magnetosphere. It was discovered on the third fly-by that Mercury's internal magnetic field is highly symmetric. Before, most of the available data was only on the planet's eastern hemisphere but this time, the western hemisphere was also covered. The Mercury Atmospheric and Surface Composition Spectrometer analyzed Mercury's exosphere and detected traces of magnesium there for the first time while also noting that the distributions of sodium, calcium and magnesium differ from area to area, and from time to time. The dynamic changes in the exosphere are considered "seasonal effects" caused by proximity to the sun. Mercury's surface was also discovered to have much higher average iron and titanium compositions than expected.

Currently, scientists have images of about 95 percent of Mercury's surface and have made quite a few significant discoveries about the planet. There are still observations to make and theories to examine, but, overall, the future of MESSENGER looks bright.

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