[meteorite-list] MESSENGER Spacecraft Achieves Unprecedented Success Studying Mercury

[Ron Baalke]

April 16, 2015
     
NASA Spacecraft Achieves Unprecedented Success Studying Mercury

After extraordinary science findings and technological innovations, a NASA 
spacecraft launched in 2004 to study Mercury will impact the planet's 
surface, most likely on April 30, after it runs out of propellant.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging 
(MESSENGER) spacecraft will impact the planet at more than 8,750 miles per 
hour (3.91 kilometers per second) on the side of the planet facing away from 
Earth. Due to the expected location, engineers will be unable to view in real 
time the exact location of impact.

On Tuesday, mission operators in mission control at the Johns Hopkins 
University Applied Physics Laboratory (APL) in Laurel, Maryland, completed 
the fourth in a series of orbit correction maneuvers designed to delay the 
spacecraft's impact into the surface of Mercury. The last maneuver is 
scheduled for Friday, April 24.

"Following this last maneuver, we will finally declare the spacecraft out of 
propellant, as this maneuver will deplete nearly all of our remaining helium 
gas," said Daniel O'Shaughnessy, mission systems engineer at APL. "At 
that point, the spacecraft will no longer be capable of fighting the downward 
push of the sun's gravity."

Although Mercury is one of Earth's nearest planetary neighbors, little was 
known about the planet prior to the MESSENGER mission.

"For the first time in history we now have real knowledge about the planet 
Mercury that shows it to be a fascinating world as part of our diverse solar 
system," said John Grunsfeld, associate administrator for the Science 
Mission Directorate at NASA Headquarters in Washington. "While spacecraft 
operations will end, we are celebrating MESSENGER as more than a successful 
mission. It's the beginning of a longer journey to analyze the data that 
reveals all the scientific mysteries of Mercury."

The spacecraft traveled more than six and a half years before it was inserted 
into orbit around Mercury on March 18, 2011. The prime mission was to orbit 
the planet and collect data for one Earth year. The spacecraft's healthy 
instruments, remaining fuel, and new questions raised by early findings 
resulted in two approved operations extensions, allowing the mission to 
continue for almost four years and resulting in more scientific firsts.

One key science finding in 2012 provided compelling support for the 
hypothesis that Mercury harbors abundant frozen water and other volatile 
materials in its permanently shadowed polar craters.

Data indicated the ice in Mercury's polar regions, if spread over an area the 
size of Washington, would be more than two miles thick. For the first time, 
scientists began seeing clearly a chapter in the story of how the inner 
planets, including Earth, acquired water and some of the chemical building 
blocks for life.

A dark layer covering most of the water ice deposits supports the theory that 
organic compounds, as well as water, were delivered from the outer solar 
system to the inner planets and may have led to prebiotic chemical synthesis 
and, thusly, life on Earth.

"The water now stored in ice deposits in the permanently shadowed floors of 
impact craters at Mercury's poles most likely was delivered to the 
innermost planet by the impacts of comets and volatile-rich asteroids," 
said Sean Solomon, the mission's principal investigator, and director of 
Columbia University's Lamont-Doherty Earth Observatory in Palisades, New 
York. "Those same impacts also likely delivered the dark organic 
material."

In addition to science discoveries, the mission provided many technological 
firsts, including the development of a vital heat-resistant and highly 
reflective ceramic cloth sunshade that isolated the spacecraft's 
instruments and electronics from direct solar radiation - vital to mission 
success given Mercury's proximity to the sun. The technology will help 
inform future designs for planetary missions within our solar system.

"The front side of the sunshade routinely experienced temperatures in 
excess of 300 Degrees Celsius (570 Degrees Fahrenheit), whereas the majority of 
components in its shadow routinely operated near room temperature (20 Degrees C or 
68 Degrees F)," said Helene Winters, mission project manager at APL. "This 
technology to protect the spacecraft's instruments was a key to mission 
success during its prime and extended operations."

The spacecraft was designed and built by APL. The lab manages and operates 
the mission for NASA's Science Mission Directorate. The mission is part of 
NASA's Discovery Program, managed for the directorate by the agency's 
Marshall Space Flight Center in Huntsville, Alabama.

For a complete listing of science findings and technological achievements of 
the mission visit:

http://www.nasa.gov/messenger


-end-

Dwayne Brown
Headquarters, 
Washington
202-358-1726
dwayne.c.brown at nasa.gov 

Paulette Campbell
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
240-228-6792
paulette.campbell at jhuapl.edu