NASA is bidding farewell to its Mercury-orbiting spacecraft, Messenger, that will end its 11-year mission. It will plunge into Mercury and crash on the surface of the planet at about 8,750 miles per hour.

The half-ton spacecraft was launched by NASA atop a Delta II rocket in August 2004. The main objectives of the Messenger mission were to study magnetic field, geology and chemical composition of Mercury. NASA scientists hoped that the spacecraft will take about 2,500 images of Mercury. However, Messenger ended up taking over 270,000 pictures of the planet.

Messenger made a few flybys of Mercury in 2008 and in 2009 before finally entering the planet's orbit in August 2011 and became the first spacecraft to orbit Mercury.

Now, after spending over a decade in space and around four years orbiting the Mercury, the Messenger mission will finally come to an end on Thursday, April 30. The spacecraft is out of fuel and is expected to plunge on the surface of the planet at about 3:25 p.m and 3:30 p.m. ET.

The high speed collision of Messenger on Mercury's surface is mainly due to the absence of thick atmosphere on the planet. Normally, atmosphere burns and reduces the speed of incoming objects. Scientists suggest that the collision will happen three times faster than the speed of sound.

The impact will result in the creation of a crater 52 feet wide on Mercury's surface.

Mercury is the inner-most planet of the solar system and the nearest to the Sun, which makes the surrounding region extremely hot. It was a challenging task for NASA scientists to build a spacecraft that would survive in the extreme space conditions.

"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," says Sean Solomon the Principal Investigator of NASA's Messenger mission.

Solomon added that instruments selected for Messenger about two decades ago proved their worth and lasted for a long time.

In the recent decades a lot of attention has been diverted to the exploration of Mars. However, the Messenger mission has been very important as it made significant discoveries about Mercury in less than two decades.