The upper left panel diagrams the current positions of Mars and Earth in their orbits around the Sun. Note that Mars has a highly elliptical orbit compared to the Earth. For much of the time, Mars is too close to the Sun (as viewed from Earth) to be observed by Earth-based telescopes. The panel also shows the interplanetary trajectory of Mars Global Surveyor. That spacecraft entered Mars orbit in 1997. Much information on the Martian surface and atmosphere was being gathered by the Global Surveyor which began the mapping phase of its mission in spring 1999.
The upper middle panel shows two views of the positions of Mars and Earth from vantage points near the ecliptic (the plane of the Earth's orbit). This allows visualization of the tilts of the rotation axes of the planets that are responsible for the seasons. Two views are necessary because Mars and Earth are tilted in nearly orthogonal directions. At this time, late spring in the Earth's northern hemisphere, the north pole is pointed towards the sun. It is also late spring in the northern hemisphere of Mars and that planet's north pole is pointed towards the sun at a similar angle. The changes in seasons on the Earth and Mars can be visualized in a 1.2 MB QuickTime animation of this panel through 2000 and 2001.
The panel on the upper right compares the apparent size of the Martian disc as viewed from Earth with the size of Earth's disc as viewed from Mars. (Since the diameter of Mars is about half that of the Earth, Mars appears to be about half the size of the Earth when viewed from the same distance.) Both of these discs are compared to a circle 25 seconds of arc in diameter. This circle represents the largest possible apparent size of Mars as viewed from Earth (which is achieved only on those very rare occasions when the planets are both favorably positioned at the nearest points in their orbits). Even at these times, Mars -- a very difficult telescopic object to observe in detail -- is only about half the apparent size of the much more distant, but much larger planet Jupiter.
The lower left hand panel displays a simulated image of Mars as it would appear at the present time to a very high resolution Earth-based telescope. At this time, (late northern spring), an extensive carbon dioxide frost cap is growing in the southern hemisphere. Sharp brightness contrasts have allowed telescopic observers to follow Martian surface features for many years. Unlike the Earth, the Martian atmosphere is usually free of obscuring clouds. One exception is the cold region surrounding the winter pole that may be covered by a polar hood of water or even carbon dioxide clouds. Another exception occurs during periods of widespread dust storm activity, usually in southern spring and summer.
The lower middle panel shows a model prediction of the meteorology at the present time (from the Ames Mars Climate Model). Daily average temperatures in the lower atmosphere are color coded, while predicted wind speeds and directions are indicated by the arrows. In the equatorial regions near the surface, the atmospheric flow is dominated by the Hadley circulation that transports air from the cold winter hemisphere southwards across the equator. Because the equator rotates at a faster speed than other parts of the planet, this leads to a tradewind-like pattern of easterlies in the winter hemisphere and westerlies in the summer hemisphere. Strong westerlies are also apparent in the region of the polar night while light easterlies are prevalent in the vicinity of the summer pole.
The lower right panel shows model predictions of the atmospheric water vapor column on Mars. At the present season -- late northern spring -- there is a nearly uniform distribution of water vapor over the low latitude regions of Mars best observed from Earth. The atmospheric inventory of water should continue to increase for several months as water sublimes off the permanent northern polar ice cap.
The upper middle panel shows two views of the positions of Mars and Earth from vantage points near the ecliptic (the plane of the Earth's orbit). This allows visualization of the tilts of the rotation axes of the planets that are responsible for the seasons. Two views are necessary because Mars and Earth are tilted in nearly orthogonal directions. At this time, late spring in the Earth's northern hemisphere, the north pole is pointed towards the sun. It is also late spring in the northern hemisphere of Mars and that planet's north pole is pointed towards the sun at a similar angle. The changes in seasons on the Earth and Mars can be visualized in a 1.2 MB QuickTime animation of this panel through 2000 and 2001.
The panel on the upper right compares the apparent size of the Martian disc as viewed from Earth with the size of Earth's disc as viewed from Mars. (Since the diameter of Mars is about half that of the Earth, Mars appears to be about half the size of the Earth when viewed from the same distance.) Both of these discs are compared to a circle 25 seconds of arc in diameter. This circle represents the largest possible apparent size of Mars as viewed from Earth (which is achieved only on those very rare occasions when the planets are both favorably positioned at the nearest points in their orbits). Even at these times, Mars -- a very difficult telescopic object to observe in detail -- is only about half the apparent size of the much more distant, but much larger planet Jupiter.
The lower left hand panel displays a simulated image of Mars as it would appear at the present time to a very high resolution Earth-based telescope. At this time, (late northern spring), an extensive carbon dioxide frost cap is growing in the southern hemisphere. Sharp brightness contrasts have allowed telescopic observers to follow Martian surface features for many years. Unlike the Earth, the Martian atmosphere is usually free of obscuring clouds. One exception is the cold region surrounding the winter pole that may be covered by a polar hood of water or even carbon dioxide clouds. Another exception occurs during periods of widespread dust storm activity, usually in southern spring and summer.
The lower middle panel shows a model prediction of the meteorology at the present time (from the Ames Mars Climate Model). Daily average temperatures in the lower atmosphere are color coded, while predicted wind speeds and directions are indicated by the arrows. In the equatorial regions near the surface, the atmospheric flow is dominated by the Hadley circulation that transports air from the cold winter hemisphere southwards across the equator. Because the equator rotates at a faster speed than other parts of the planet, this leads to a tradewind-like pattern of easterlies in the winter hemisphere and westerlies in the summer hemisphere. Strong westerlies are also apparent in the region of the polar night while light easterlies are prevalent in the vicinity of the summer pole.
The lower right panel shows model predictions of the atmospheric water vapor column on Mars. At the present season -- late northern spring -- there is a nearly uniform distribution of water vapor over the low latitude regions of Mars best observed from Earth. The atmospheric inventory of water should continue to increase for several months as water sublimes off the permanent northern polar ice cap.
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