Why is there no atmosphere on the Moon?

It is well known that the higher the temperature of a gas, the faster its atoms and molecules move. For example, at 0 degrees Celsius, the average speed of hydrogen and helium molecules is 1.84 and 1.31 km/s (kilometers per second). If the temperature of the gases is increased to 100 degrees Celsius, then the average speed of these gas molecules will increase by almost 20%. <img alt="" src="https://miro.medium.com/v2/resize:fit:700/1*ZWGfTNHyqXEHdmRPTygQhw.png" style="height:396px; width:700px" /> A gas molecule on the Moon can overcome its gravity and leave our satellite if its speed exceeds the Moon’s second cosmic velocity. The second cosmic velocity for the Moon is 8639.99 km/h or about 2.4 km/s. However, since gas molecules have varying speeds, some faster than average and some slower, they can leave the Moon not only when their average speed is greater than the second cosmic velocity but also in cases where it is even half of it. This process would occur more slowly, as only the fastest molecules, whose speed exceeded the second cosmic velocity, would leave the Moon. Even at room temperature, the speeds of hydrogen, oxygen, and other gas molecules are more than half of the Moon’s second cosmic velocity. Therefore, the Moon cannot retain them due to its relatively weak gravity. <a href="https://medium.com/@deep.space/why-is-there-no-atmosphere-on-the-moon-4f0ddcdfdce0">Read More</a>