This image shows the moon, Earth's only natural satellite, at center with the limb of Earth near the bottom transitioning into the orange-colored troposphere, the lowest and most dense portion of Earth's atmosphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue-colored atmosphere. The silvery-blue noctilucent clouds extend far above Earth's troposphere. Image credit: NASA
Mariner 10 took this first close-up photo of Venus using an ultraviolet filter in its imaging system on Feb. 5, 1974. The photo is color-enhanced to bring out Venus's cloudy atmosphere, as the human eye would see it. A thick veil of clouds high in carbon dioxide perpetually blankets Venus, and its surface temperature approaches 900 degrees Fahrenheit. Image credit: NASA
This color image of the planet Mercury was generated by combining three separate images taken through the MESSENGER spacecraft's wide angle camera filters sensitive to light in different wavelengths. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Earth's atmosphere is critically important to all of us. In addition to providing us with air to breathe, it protects us from temperature extremes, harmful space radiation, and vast numbers of incoming meteoroids. The atmosphere is a very complex system that we are only beginning to understand. Gaining a better understanding of the atmosphere, how it protects us, and how we can protect it is in all of our interests.
In order to understand Earth's atmosphere and how it works, it is essential to study atmospheres under a wide range of conditions beyond Earth. Examining atmospheres on other planets allows this. For example, by studying the atmosphere of Venus, we learned about the role of carbon dioxide as a greenhouse gas, and saw how it drives the temperature on Venus as high as 860 degrees Fahrenheit (460 degrees Celsius).
The moon has a type of atmosphere scientists call a surface boundary exosphere. This very thin atmosphere may actually be the most common type of atmosphere in our solar system. Yet despite occurring so frequently, surface boundary exospheres largely remain a mystery. The moon, Mercury, larger asteroids, many moons orbiting the solar system's giant planets and even some of the distant Kuiper Belt Objects beyond Neptune, all have surface boundary exospheres.
To fully understand atmospheres and how they work, we also need to understand the most common type. Fortunately, the moon is in our own celestial "backyard," and NASA's Lunar Atmosphere and Dust Environment Explorer's (LADEE) observations of the lunar atmosphere and surface conditions will provide us with insights we can apply to many worlds.