Planetary scientists call the thin gaseous envelope around the Moon as the _______.

lunar exosphere

The correct answer is Option (3) - lunar exosphere

The term "lunar exosphere" refers to the extremely thin and tenuous layer of gases surrounding the Moon. Unlike Earth, which has a substantial atmosphere composed of various gases, the Moon has a very limited exosphere, which is primarily made up of gases released from the lunar surface itself.

The lunar exosphere is composed of various elements and compounds, including helium, hydrogen, neon, argon, and trace amounts of other gases. These gases are released from the Moon's surface due to a variety of processes, such as the bombardment of solar wind particles, micrometeoroid impacts, and the outgassing of volatile compounds from the lunar regolith (surface layer).

Due to the Moon's low gravity and lack of a significant atmosphere, the gases in the exosphere are not held in place by gravitational forces to form a distinct layer like Earth's atmosphere. Instead, they exist as individual atoms and molecules that are continuously escaping into space or being replenished from the lunar surface.

The study of the lunar exosphere provides valuable insights into the geology, chemistry, and dynamics of the Moon's surface and its interaction with the space environment. Understanding the composition and behavior of the exosphere helps scientists unravel the processes shaping the lunar environment and can inform future exploration missions to the Moon.