After several years of service studying Mercury, the closest planet to the sun, the NASA MESSENGER spacecraft has run out of fuel and will fall to Mercury’s surface this afternoon, sometime around 3:30pm EDT, officials from the US space agency have confirmed.
The probe is scheduled to crash at speeds of more than 8,750 miles per hour (3.91 kilometers per second) and will leave an impact crater that engineers estimate could be up to 52 feet (16 meters) wide, forever becoming part of the world that it spent so much time analyzing for afar.
Bringing light and intricacies
The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) probe has travelled around Mercury more than 4,100 times since entering the orbit around the planet on March 18, 2011, becoming the first spacecraft ever to do so and only the second to get a close-up look at the smallest world in the solar system (Mariner 10 was the other).
“MESSENGER brought to light the intricacies of an intriguing world,” NASA said.
“The mission discovered a surface rich in diverse chemistry,” the agency recalled. “It sensed a bizarrely offset magnetic field. It photographed strange ‘hollows’ where material seems to have boiled away into space under the scorching sun. It mapped vast volcanic deposits, found that the entire planet has shrunk by as much as 7 kilometers in radius, and… uncovered deposits of water ice in the depths of polar craters where the sun never shines.”
A word from MESSENGER:
I want to send out a big thank you to everyone who has worked on my mission and has followed my story!!
— MESSENGER (@MESSENGER2011) April 30, 2015
Drastically changing understanding
MESSENGER launched on August 3, 2004, traveling 4.9 billion miles (7.9 billion kilometers) and completing flybys of Earth, Venus, and Mercury before finally beginning what was supposed to be a one-year science orbit around its target in March 2011. However, as it started collecting data, scientists found themselves left with more questions than answers, leading NASA to grant a pair of mission extensions for a total of three additional years of research.
Over the course of its lifespan, the spacecraft has drastically changed scientists’ understanding of Mercury, according to deputy principal investigator Larry Nittler from the Carnegie Institution of Washington. Geochemical measurements conducted by MESSENGER revealed that the planet’s surface had little iron but was rich in moderately volatile elements like sodium and sulfur, ruling out existing theories used to explain why the planet had a higher density than other worlds.
Elemental maps also revealed that the planet was highly heterogeneous, chemically speaking, and that Mercury’s surface was shaped by volcanic activity. MESSENGER also discovered a series of unique geological structures that were shaped by the loss of volatile materials, as well as confirmed the presence of considerable water ice that was sheltered from the sun’s heat in a series of permanently shadowed impact craters near the planet’s polar regions.
“We have found that the complex interplay of the interplanetary magnetic field with that of Mercury results in a remarkably dynamic electromagnetic environment surrounding the planet, including unexplained bursts of electrons and highly variable distributions of different elements in the thin exosphere,” Nittler said last year while marking the probe’s 10th anniversary.
Officials from the Johns Hopkins University Applied Physics Laboratory unveiled a list of their “Top 10” MESSENGER science results – discoveries which include field-aligned currents running from its magnetosphere to low altitudes along magnetic field lines, bursts of energetic electrons in the planet’s magnetosphere, seasonal variations in its exosphere and the fact that the planet is getting smaller, having contracted by as much as seven kilometers in radius.