NASA to Crash Two GRAIL Probes Into the Moon at 5:28 p.m. EST, Monday

NASA will end its latest moon mission Monday by crashing two probes into the moon.

The two probes, called Ebb and Flow, have been circulating the moon and measuring its gravity. They will crash into a mountain near the Goldschmidt crater at approximately at 3,760 miles an hour at 5:28 p.m. EST. Ebb will be the first to hit the moon and Flow will be approximately 20 to 30 seconds behind.

"We are not expecting a big flash or a big explosion" Maria Zuber, GRAIL principal investigator at the Massachusetts Institute of Technology, stated last week. "These are two small spacecraft, we use the term apartment-size washer/dryer-size spacecraft with empty fuel tanks. So we are not expecting a flash visible from Earth."

Prior to crash landing, Ebb and Flow will fire their main engines until their propellant tanks empty. The purpose of this exercise is to better predict the fuel consumption needs of future missions.

The two probes were part of $500 million mission called the Gravity Recovery and Interior Laboratory (GRAIL), which started in September 2011. The probes have been orbtiing the moon since January 1, 2012. During the course of their mission, Ebb and Flow collected gravity maps between March and May 2012 which revealed that the moon's crust is far more shallow and fractured than previously expected.