https://arstechnica.com/science/2022/01/an-old-falcon-9-rocket-may-strike-the-moon-within-weeks/SpaceX launched its first interplanetary mission nearly seven years ago. After the Falcon 9 rocket's second stage completed a long burn to reach a transfer orbit, NOAA's Deep Space Climate Observatory began its journey to a Sun-Earth LaGrange point more than 1 million km from the Earth.
By that point, the Falcon 9 rocket's second stage was high enough that it did not have enough fuel to return to Earth's atmosphere. It also lacked the energy to escape the gravity of the Earth-Moon system, so it has been following a somewhat chaotic orbit since February 2015.
Now, according to sky observers, the spent second stage's orbit is on course to intersect with the Moon. According to Bill Gray, who writes the widely used Project Pluto software to track near-Earth objects, asteroids, minor planets, and comets, such an impact could come in March.
This information is important because it will allow satellites presently orbiting the Moon, including NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2 spacecraft , to collect observations about the impact crater. With the LCROSS mission, NASA deliberately impacted a spent rocket upper stage into the Moon in 2009 for this purpose. Although scientists are most keen to understand the presence of ice at the lunar poles, being able to observe the subsurface material ejected by the Falcon 9 rocket's strike could still provide some valuable data.
The dry mass of the Falcon 9's second stage is about 4 metric tons, and it should impact the Moon at a velocity of about 2.58 km/s.