CAPE CANAVERAL, Fla. (AP) -- The only spacecraft ever to orbit Mercury ended its four-year tour with a crash landing Thursday.
NASA's Messenger plunged from orbit as planned and slammed into the sun's closest planet at about 8,750 mph (14,081 kph), creating a crater an estimated 52 feet (16 meters) across.
Messenger became the first spacecraft to orbit hot, little Mercury, in 2011. It circled the solar system's innermost planet 4,105 times and collected more than 277,000 images.
"Today we bid a fond farewell to one of the most resilient and accomplished spacecraft ever to have explored our neighboring planets," said lead scientist Sean Solomon, director of Columbia University's Lamont-Doherty Earth Observatory.
NASA Messenger Mercury
Doomsday at Mercury: NASA craft falls from orbit into planet
A view of the planet Mercury from the MESSENGER spacecraft, which stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
This artist's rendering provided by NASA shows the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft around Mercury. On Thursday, April 16, 2015, NASA announced that after years of orbiting the planet, the spacecraft will crash into the planet at the end of the month. (NASA/JHU APL/Carnegie Institution of Washington via AP)
Ten years ago, on August 3, 2004, NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft blasted off from Cape Canaveral, Florida, for a risky mission that would take the small satellite dangerously close to Mercury’s surface, paving the way for an ambitious study of the planet closest to the Sun. (Photo via NASA)
A solar flare erupted on the far side of the sun on June 4, 2011, and sent solar neutrons out into space. (Photo via NASA/STEREO/Helioviewer)
South America and portions of North America and Africa are shown in this false-color image from NASA's MESSENGER spacecraft, taken on an Aug. 2, 2005 Earth flyby to adjust the spacecraft's path to Mercury. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
This artist's rendering provided by the Johns Hopkins University Applied Physics Laboratory shows the sunshade on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (Messenger) around the planet Mercury. The sunshade shields the spacecraft's instruments from heat and solar radiation. (Johns Hopkins University Applied Physics Laboratory via AP) Image converted using ifftoany
This Oct. 6, 2008 image provided by NASA shows previously unseen terrain on Mercury as the Messenger spacecraft approached the planet during its second flyby. In the foreground is a region of rough, heavily cratered terrain with a large, ancient two-ring impact basin at the bottom center of the image. In the distance is a region of younger, tectonically modified smooth plains that have been pockmarked by small craters. (NASA, Johns Hopkins University Applied Physics Laboratory, Carnegie Institution of Washington via AP)
This color image, taken on May 1, 2013 by the Wide Angle Camera (WAC) instrument aboard NASA's MESSENGER spacecraft orbiting Mercury, features Hovnatanian crater, named for Armenian painter Hakop Hovnatanian. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
This Oct. 6, 2008 photo provided by NASA shows Mercury during the Messenger spacecraft's second flyby of the planet. (NASA, Johns Hopkins University Applied Physics Laboratory, Carnegie Institution of Washington via AP)
This new, high-resolution view of Cunningham crater was recently acquired by MESSENGER. What you can't see in this image, which shows striking details of the crater's interior, is the extensive set of rays associated with Cunningham. The bright rays of Cunningham indicate that the crater is relatively young, having formed on Mercury likely within the last billion years. In this new view, the preserved terraces of the crater walls, the well-defined central peak, and the limited number of overlying small craters are also all signs of Cunningham's relative youth. (Photo via NASA/Johns Hopkins University Applied Physics)
In this undated photo provided by NASA, technicians with The Johns Hopkins University Applied Physics Laboratory in Titusville, Fla., prepare the MESSESNGER spacecraft for a move to a hazardous processing facility in preparation for loading the spacecraft's hypergolic propellants. (NASA via AP)
This colorful view of Mercury was produced by using images from the color base map imaging campaign during MESSENGER's primary mission. These colors are not what Mercury would look like to the human eye, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up Mercury's surface. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
The crater at the center of this scene is named for choreographer George Balanchine, as the beautiful swath of diffuse blue ejecta emanating from the crater might remind one of the famous blue tutus in one of Balanchine's most well known ballets, Serenade. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
This image of Mercury, acquired by the Mercury Dual Imaging System (MDIS) aboard NASA's MESSENGER mission on April 23, 2013, allows us to take a step back to view the planet. Prior to the MESSENGER mission, Mercury's surface was often compared to the surface of Earth's moon, when in fact, Mercury and the moon are very different. (Photo via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
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Solomon noted in a statement that Messenger set a record for planetary flybys - once past Earth, twice past Venus and three times past Mercury before entering Mercury's orbit - and survived "both punishing heat and extreme doses of radiation" to surpass expectations.
Flight controllers managed to keep the spacecraft going a few extra weeks by using helium gas not originally intended as fuel. But the gas tank finally emptied and gravity's relentless tug did Messenger in.
Mercury is the last of the rocky inner planets in our solar system - also counting Mars and Venus - to be littered by mankind.
Thursday's crash occurred on the side of Mercury facing away from Earth and telescopes. Several minutes passed before NASA received confirmation. Controllers received no signal from Messenger when it was supposed to be back in the coverage zone - a sign that the spacecraft, measuring 10 feet solar wingtip to wingtip, had, indeed, succumbed to gravity.
"Well I guess it is time to say goodbye," the Messenger Twitter feed stated as the end drew near.
Then after the impact: "On behalf of Messenger, thank you all for your support. We will continue to update you on our great discoveries. We will miss it."
Astronomers who used Messenger to detect Mercury's frozen water-covered poles and significantly off-center magnetic field called it an end of an era. Other discoveries: volcanic deposits that are evidence of the planet's eruptive past, and noticeable global shrinkage.
"It has been an amazing journey of discovery," said the University of British Columbia's Catherine Johnson, a senior scientist at the Planetary Science Institute. Data analyses will continue for at least another year.
Messenger's $427 million mission began with a launch from Cape Canaveral, Florida, in 2004. Johns Hopkins University handled everything for NASA.
Until Messenger, the only spacecraft to visit Mercury was NASA's Mariner 10 back in the 1970s. That was only a fly-by mission.
The Europeans and Japanese are teaming up for Mercury's next guests, a pair of satellites known as BepiColombo. They're scheduled for launch in 2017 and arrival in Mercury's orbit in 2024.