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. For a QuickTime
animation [1.1 MB] of the orbits of Earth and Mars and their relative
positions through 2000 and 2001 click here.
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. For a QuickTime animation [1.5
MB] of this view of Mars through the years 2000 and 2001 click here.
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. For a QuickTime animation
[2.6 MB] of the predicted Mars meteorology over a one-year period click here.
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. For more information on
Martian water, see the Mars water
page. For a 2.5 MB QuickTime animation of the Martian water column
predictions for 2000 and 2001 click here.
The statistics printed below the image indicate the apparent diameter of Mars (in seconds of arc); the angle between the Sun and the Earth as viewed from Mars (in degrees); an angular measure of the season in the Martian northern hemisphere (Ls= 0 at the vernal equinox, 90 at the summer solstice, 180 at the autumnal equinox, and 270 at the winter solstice); the sub-solar latitude in degrees (another indicator of the season); the longitude of the sub-Earth point in the image; and the latitude of the sub-Earth point.
Click here to display the full GIF or JPEG image. Both images are about 170 kB in size.
You can also display the classical 4-panel Mars Today poster (about 120 kB).
View a 600 kB Mpeg or a 3.3 QuickTime animation of the full MarsToday poster through 2000 and 2001.
