Yohkoh Solar Observatory

This animation shows the multi-layered nature of the solar atmosphere. It was built from three images, a white-light image of the photosphere, a red-light image of the chromosphere, and an X-Ray image of the corona, the outermost layer. These images were captured on the same day by the telescope aboard the Yohkoh Solar Observatory satellite. The satellite was launched from Japan in August of 1991 and is used to investigate X-Rays and Gamma rays from the Sun. Yohkoh is Japanese for sunbeam.

Layers of the Solar Atmosphere

The Sun is a giant ball of gas; there is no hard surface on the Sun to stand on. However, there is a surface through which we cannot see called the photosphere. The location of the photosphere is defined to be where the gas is so dense that it becomes opaque. The photosphere is about 330 kilometers thick and lies 696,000 kilometers from the center of the Sun. Above the photosphere is the chromosphere, about 2,000 kilometers thick, where the temperature rises from the 5,800-Kelvin-photosphere to tens of thousands of Kelvin. Beyond the chromosphere is the corona, where the density of the gas is very low and tenuous. The corona is difficult to observe and is only seen on Earth during a total solar eclipse.

Ellen Cohen

The Arizona State University TES Team

The Mars Global Surveyor began mapping Mars in 1999. The Thermal Emission Spectrometer instrument on board Surveyor maps the temperature and, hence, the amount of dust in the atmosphere. Beginning in mid-June, 2001, a region of increased dust abundance appeared in the Hellas Basin, an impact basin in the southern uplands that is about 1,800 kilometers in diameter and 6 kilometers deep. This continued for two weeks when the storm intensified and expanded. This is the largest storm Surveyor has seen since it began mapping the planet.

Video: 444 kB, Animated GIF

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Effects of dust storms on Mars

A dust storm of this magnitude has significant impact on the Martian climate. Dust in the atmosphere is warmed by the Sun and heats the atmosphere by 20° C. This warm air rises and moves into the Northern Hemisphere, warming the Northern Hemisphere and causing planet-wide climate variability.

Ellen Cohen

Phil James (University of Toledo), Todd Clancy (STScI), Steven Lee (University of Colorado), and NASA/STScI

These images appear to have been taken from above the Martian pole, but they were taken with the Hubble Space Telescope from Earth orbit. Each frame in this animation was constructed from three separate images taken in October 1996 and in January and March of 1997. The first image corresponds to early spring in the Northern Hemisphere when the polar ice cap extends to about 60° north latitude. The second image was taken in mid-spring and shows a smaller ice cap resulting from increasing atmospheric warming. The final image from early summer on Mars shows a vastly reduced polar cap; much of the carbon dioxide ice has sublimated, revealing the terrain beneath.

Martian Seasons

Mars has a cycle of seasons that is similar to Earth. The reason for this is that both planets are similarly tilted on their rotational axes: a 23.5° tilt for Earth and a 25.2° tilt for Mars. Because Mars takes about twice as long to orbit the Sun, each Martian season is about twice as long as the corresponding season on Earth. In addition, the Martian atmosphere is much thinner than Earth's atmosphere, so there is little insulation to protect the Martian atmosphere from temperature shifts due to changes on the surface or in the Mars-Sun distance.

The Mars-Sun distance

The Mars-Sun distance changes by 20 percent over the course of the year. When Mars is closest to the Sun, it is summer in the Southern Hemisphere and temperatures are up 35° F, producing dust storms that swirl around the planet and absorb sunlight, further heating the atmosphere. When Mars is farthest from the Sun, water-ice clouds reduce atmospheric temperatures. The dust particles in the atmosphere seed these clouds, then fall to the ground. Competition between cloud cooling and dust heating drives annual as well as short-term climate changes on Mars.

Ellen Cohen