Mars Today, created by Howard Houben of the Mars Global Circulation Model group, is a poster produced daily by the Center for Mars Exploration at NASA's Ames Research Center. The poster depicts current conditions on Mars and its relationship to Earth in four panels.
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.
At the present time, however, Mars is near opposition (almost directly
opposite the sun in the sky) and can be observed throughout the night.
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 the present season of northern spring,
Mars's north pole is tilted slightly towards the Sun (and the
Earth), with the north polar cap visible.
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.
The lower right hand 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. At the current
season, Mars's southern hemisphere is dominated by strong westerly
winds while there is much eddy activity in the northern hemisphere.
Strong cross-equatorial flow at low altitudes
(a component of the Hadley circulation) gives rise to the pattern of
easterlies in the tropics of the winter hemisphere and westerlies in the
tropics of the summer hemisphere.
Because the image is built daily, the one you download will actually show today's position of and conditions on Mars. Keep watching this page. In the near future we will try to give you access to the images for the past year.
Note: Clicking the following will display the file automatically.
.gif)
Mars Today [116k]
http://cmex-www.arc.nasa.gov/MarsImages/MarsToday/MarsToday.html
Return To Space Menu.