NASA's Messenger spacecraft will be ending its mission with a crash landing on April 30, 2015, but that's exactly as it should be. Four years ago, it made history by entering into orbit around Mercury and the mission will end by making history yet again when it becomes the first man-made object to impact the surface of the planet.
The spacecraft exhausted its supply of propellant after a series of orbital maneuvers on April 24, 2015 and is scheduled to hit the surface of Mercury at about 3:25pm ET
NASA estimates that the space vehicle will hit the planet's surface at more than 8,700 MPH, leaving a crater more than 50 feet wide. Since the impact is set to be on the side of Mercury that faces away from Earth, it will not be possible to see it via any space telescopes, however scientists believe future orbital missions might be able to spot the crater the impact will create.
"After studying the planet intently for more than four years, Messenger's final act will be to leave an indelible mark on Mercury," Daniel O'Shaughnessy, Messenger's mission systems engineer at Johns Hopkins University's Applied Physics Laboratory, said in a statement on Thursday.
Messenger was launched in 2004, and during 2008 and 2009 it conducted three flybys of Mercury. From there it went into orbit around the planet is 2011 and has been sending back data ever since. There has only been one other probe to study the planet closest to sun, NASA's Mariner 10, however that was decades ago in 1974 and 1975 when it flew by three times, but never entered Mercury's orbit.
While the name Messenger evokes images of a satellite sending and receiving communications, it is actually the shortening of an acronym that stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. It was intended not as a communication tool, but as a mapping vehicle to survey the geological surface of Mercury as well as the composition of is atmosphere. The mission was able to confirm that the planet contained deep deposits of brimstone as well as metric tons of water and ice from comet and asteroid impacts.
"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 Messenger principal investigator Sean Solomon, who is also director of Columbia University's Lamont-Doherty Earth Observatory.
According to a NASA statement, the Messenger team was impressed by both the scientific knowledge the mission gathered as well as the spacecraft's ability to weather intense heat. Temperatures routinely rose above 570 degrees Fahrenheit, coming from the sun and the dayside of the planet.
Originally scheduled to last only one year, the team was able to conserve enough propellant for years worth of observations, including a final low altitude observation of the planet's surface.
Although Messenger is the first spacecraft to orbit Mercury, it won't be the last: A European-Japanese will launch in 2017 and put two spacecraft into Mercurial orbit in 2024.