Report by: Kristen Reband
After the 1980’s it became clear that most planets and some moons had permanent and substantial atmospheres. These atmospheres have been divided in to three large family groups based on what the atmospheres are primarily composed of. The three family groups are Nitrogen, Carbon dioxide and Hydrogen/Helium. Earth, Titan, Triton and Plato are in the Nitrogen family group. Mars and Venus are in the Carbon dioxide family while Jupiter, Saturn, Uranus, and Neptune are included in the Hydrogen/Helium family.
A planet that does not have a permanent and substantial atmosphere is Mercury. Mercury’s atmosphere has been measured to have small amounts of Helium 1000 km above its surface. However, it is believe that these readings are likely due to solar wind and Mercury's crust breaking down. Solar wind is a stream of partials which are ejected from the upper atmosphere of a star.
While many Earth-based observations and spacecraft missions, along with theoretical models, have given an unprecedented understanding of planetary atmospheres some of their fundamental properties are still not understood or not understood very well. One of these fundamental properties is called atmospheric energy balance. Questions needed to be answered to understand atmospheric energy balance of a planet’s or moon’s atmosphere are as follows:
What are the sources of energy incident upon an atmosphere?
How is this energy redistributed internally?
How much of that energy is lost back into space?
Of course the most common source of energy in our solar system is the Sun, transmitted by means of radiation or via solar wind. Energy is also stored in each planetary body as thermal, chemical or rotational energy.
Most of the physical processes that control Earths energy balance also act on other planets. For example, there are many uncertainties about Earth’s CO2 cooling rate which is controlled by excitation of CO2 through collisions with atomic oxygen. By observing Mars or Venus simultaneously with Earth helps to better determine the CO2 cooling rate. Mars has been found to be half as responsive as Earth to changes in solar forcing (solar variations). Mars has also been found to be four to seven times as responsive as Venus.
Another example is that the atmospheres drag on satellites orbiting Earth and Mars gives measurements of how variations in solar radiation intensity affect atmosphere densities.
At any given altitude heating of the atmosphere will result in an enhancement of densities and stronger atmospheric drag on a satellite. Measuring these drag variances allows deviation of at a spirit temperature changes and thereby of the effects of solar forcing.
These studies are prime examples of how other planets in our solar system can be used as laboratories to better understand the complexity of our own atmosphere.
 Ingo C.F. Muller-Wodarg, “Exploring Other Worlds to Learn More about Our Own,” Perspectives, Jun., pp1319-1320, 2006.
 Calvin J. Hamilton, “Mercury,” [online document] 1997, [2007 Jan 25], Available at HTTP:www.solarviews.com/eng/mercury.htm