Mars opposes Earth?
It's not really a rivalry. About every 26 months planet Earth passes between the Sun and sister planet Mars. It's also a time when the two worlds are closer together than normal. Because the orbits of the planets are not perfectly circular, the date of opposition and the date of closest approach aren't usually the same and the distance at its closest also varies.
This year the closest approach of Earth and Mars will take place on December 18 when they will be just shy of 55 million miles apart. Opposition takes place December 24 and Mars will be at its brightest for Earth-bound viewers. The close approach and brightness makes viewing the Red Planet its best during opposition and near-opposition periods.
Find Mars on your own: Mars, now at the "feet" of constellation Gemini, rises in the eastern sky around sunset, reaches its highest point in the sky around midnight, and sets in the west near sunrise. The brightest star-like object in its neighborhood, Mars will be easy to spot. To the unaided eye the planet will look like an extremely bright red star; it will look about the same through binoculars. Using a good telescope running at at least 150X, however, a clear viewing night will reveal some surface markings including polar ice. Continuing through January 2008 astronomers around the world will have their best shot at seeing the mysterious desert world. Be on the lookout for viewing opportunities at area observatories, astronomy clubs, and nature centers. The two worlds will rapidly part company and, as February winds down, Mars will be rapidly shrinking and its telescopic viewing season will come to an end. This time around won't be an unusually close approach but it will be another 10 years before Earth and Mars are so near each other. It's time to take a look!
The orbital movements of Earth relative to Mars also make opposition season an excellent time to launch spacecraft destined to land there. On August 4 NASA successfully launched the Phoenix spacecraft which is currently in interplanetary cruise mode. Given a successful landing on May 25, 2008, Phoenix will study a Martian polar region. The lander does not have the ability to move about in the way the highly-successful Mars Exploration Rovers do. Among other tasks, it will use a robot arm and a sophisticated onboard chemical laboratory to analyze soil and ice samples it gathers.
Scientists hope to learn: can the Martian arctic support life, what is the history of water at the landing site, and how is the Martian climate affected by polar dynamics? Phoenix was named for the mythic bird because it rose from the "embers" of two previous failed missions using much of their backup hardware and instrumentation. One of those missions was the ill-fated 1999 Mars Polar Lander that apparently crashed on that planet and has never been located.
The Phoenix is about 18 feet long with the solar panels deployed. The central body itself is about 5 feet in diameter. From the ground to the top of its sensor mast, the lander measures about seven feet tall. It weighs 772 pounds. Scientists and engineers don't expect Phoenix to operate much beyond its 90-day mission. Because Phoenix is solar powered and cannot move to brighter areas, the lander will cease functioning when its power runs out and the extreme cold (around -200 degrees) of the Martian winter sets in "killing" the electronics system. By then, however, it is hoped that valuable new information about our neighbor world will have been returned.