This week, researchers with NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission held a bit of a wake. On or about April 30, the spacecraft is expected to impact the surface of Mercury at almost 9,000 miles per hour. The researchers spent some time discussing some of the hi-lights, discoveries and innovations of the mission which originally launched on August 3, 2004.
It took six and a half years for the MESSENGER spacecraft to arrive and enter orbit around Mercury, where it has been since March of 2011.
Originally, the mission was supposed to last for one year (earth time) and answer six questions. Those included inquiries into Mercury’s density, geological history and the structure of Mercury’s core and magnetic field.
However, as frequently happens when something new to science is being examined, the early observations of Mercury raised new questions. The MESSENGER mission was granted two extensions for a total of three years and, through an innovative use of fuel, squeezed in an extra month allowing it to collect a final set of low-altitude data.
However, the spacecraft is now almost out of fuel and caught in Mercury’s gravitational pull. No matter how much scientists may wish for more in just over two weeks, the mission will end.
Sean Solomon, director of Columbia University’s Lamont-Doherty Earth Observatory and MESSENGER Principal Investigator summarized the mission’s incredible success.
“MESSENGER had to survive heating from the Sun, heating from the dayside of Mercury, and the harsh radiation environment in the inner heliosphere, and the clearest demonstration that our innovative engineers were up to the task has been the spacecraft’s longevity in one of the toughest neighborhoods in our Solar System. Moreover, all of the instruments that we selected nearly two decades ago have proven their worth and have yielded an amazing series of discoveries about the innermost planet,” said Solomon in a statement.
“Although Mercury is one of Earth’s nearest planetary neighbors, astonishingly little was known when we set out. MESSENGER has at last brought Mercury up to the level of understanding of its sister planets in the inner Solar System. Of course, the more we learn, the more new questions we can ask, and there are ample reasons to return to Mercury with new missions,” he continued.
In a briefing at NASA headquarters, scientists listed some of the remarkable discoveries made by MESSENGER. Most notably, the discovery that the barren planet, closest to the sun contains large amounts of water ice and other frozen materials.
“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. Those same impacts also likely delivered the material in the dark layer discovered by MESSENGER to cover most polar deposits and interpreted, on the basis of its sublimation temperature and low reflectance, to be carbonaceous. By this interpretation, Mercury’s polar regions serve as a witness plate to the delivery to the inner solar system of water and organic compounds from the outer solar system, a process that much earlier may have led to prebiotic chemical synthesis and the origin of life on Earth. MESSENGER’s findings have made Mercury an even more interesting body for future exploration than before our mission,” said Solomon.
The team also discussed the technical advances made by the MESSENGER mission. Especially important were the technologies used to keep the spacecraft cool and operational at such close proximity to the sun.
“The front side of the sunshade routinely experiences temperatures in excess of 300 degrees Celsius (570 degrees Fahrenheit), whereas the majority of components in its shadow routinely operate near room temperature (20 degrees Celsius or 68 degrees Fahrenheit). The sunshade is extremely effective at isolating most of the vehicle from the Sun’s radiation, but reflected infrared radiation from Mercury greatly influences the temperatures of MESSENGER’s components behind the sunshade. The influence of Mercury is effectively managed with careful selection of vehicle orientation, to balance heating across the spacecraft, as well as an intricate system of heat pipes and radiators,” said Helene Winters, the MESSENGER Project Manager.
On April 24, MESSENGER’s controllers will send it instructions for one final maneuver, simultaneously exhausting the last of its fuel and setting it on a path toward its final impact.
