On Thursday, NASA will launch two unmanned spacecrafts to the moon, nearly forty-two years after US astronaut Buzz Aldrin planted an American flag on the lunar surface.

The US space agency's twin GRAIL spacecrafts will embark on its fact-finding lunar mission from Florida's Cape Canaveral. The satellites will sit atop a United Launch Alliance Delta II rocket which will blast off to space as early as 8:37 am Thursday (1237 GMT). Live launch coverage will start at 6am Eastern on NASA TV. However, clouds and thunderstorms are expected to linger near Florida's Space Coast for the next few days making a delay more likely than not. However, the sky is expected to clear by Saturday or Sunday, GRAIL launch weather officer Joel Tumbiolo said.

On entering the lunar orbit, the two spacecrafts will fly 34 miles above the lunar surface and spend three months measuring lunar gravity and will conduct other experiments to determine the structure of the lunar interior from crust to core that will not only help us understand the origin (the popular belief is that when a planet-sized object crashed into the Earth, it flung a load of material into space that eventually became the moon) and thermal evolution of the moon better but also may help scientists learn a lot about how the other big planets in the inner solar system — Mercury, Venus, Earth and Mars — formed and evolved as well. Most importantly, the mission will help unlock many secrets of our planet's lonely and mysterious satellite as it will map the far side of the moon which humans have never explored.

Start the slideshow to find out more about NASA's GRAIL spacecrafts and mysteries of the moon

NASA handout image of the GRAIL missions twin spacecraft in orbit around the moon
NASA handout image shows an artist's concept of the Gravity Recovery and Interior Laboratory (GRAIL) mission's twin spacecraft in orbit around the moon. REUTERS/NASA
NASAs GRAIL twin spacecraft stand side by side as they are prepared for testing and processing in the Astrotech payload processing facility in Titusville
NASA's Gravity Recovery and Interior Laboratory, or GRAIL, twin spacecraft stand side by side as they are prepared for testing and processing in the Astrotech payload processing facility in Titusville, Florida in this May 21, 2011 photograph from NASA. NASA's GRAIL spacecraft is set to launch to the moon aboard a United Launch Alliance Delta II rocket on September 8, 2011 REUTERS/NASA
NASA handout image of the GRAIL missions twin spacecraft in orbit around the moon
NASA handout image shows an artist's concept of the Gravity Recovery and Interior Laboratory (GRAIL) mission's twin spacecraft in orbit around the moon. The GRAIL mission will fly the spacecraft, in the same orbit, over areas of greater and lesser gravity, caused both by visible features such as mountains and craters and by masses hidden beneath the lunar surface, they will move slightly toward and away from each other. An instrument aboard each spacecraft will measure the changes in their relative velocity very precisely, and scientists will translate this information into a high-resolution map of the moon's gravitational field. The mission is scheduled to launch on September 9, 2011 REUTERS/NASA
NASA handout photo of the Gravity Recovery and Interior Laboratory-A GRAIL-A lunar probe in Titusville
NASA's Gravity Recovery and Interior Laboratory-A (GRAIL-A) lunar probe is lifted from its workstand and across the clean room towards the spacecraft adapter ring (L) where GRAIL-B is already secured at the Astrotech Space Operation's payload processing facility in Titusville, Florida in this NASA handout photo dated August 10, 2011. The two Gravity Recovery and Interior Laboratory (GRAIL) spacecraft will orbit the moon in formation to determine the structure of the lunar interior from crust to core and to advance understanding of the thermal evolution of the moon. GRAIL's launch is scheduled for September 8, 2011 REUTERS/NASA
NASA LRO image of Apollo 17 landing site
The twists and turns of the last tracks left by humans on the moon crisscross the surface in this LRO image of the Apollo 17 site. In the thin lunar soil, the trails made by astronauts on foot can be easily distinguished from the dual tracks left by the lunar roving vehicle, or LRV. Also seen in this image are the descent stage of the Challenger lunar module and the LRV, parked to the east. NASA
Combination photos of NASAs twin GRAIL spacecraft set for launch on September 8, 2011
These undated NASA images show the various stages of pre-launch preparations of NASA's twin GRAIL spacecraft at Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida, which were released September 7, 2011. NASA's GRAIL spacecraft is set to launch to the moon aboard a United Launch Alliance Delta II rocket on September 8, 2011. REUTERS/NASA
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