Mars swings to within 99 million kilometers of our fair planet this week, making its closest approach until 2012. Get your telescope out, or simply look up and gaze at the steady orange-red glow of the Red Planet. It rises in the east in the constellation Cancer just after sunset. You can’t miss it. At magnitude -1.3, Mars almost shines as bright as Sirius, the brightest star in the sky.

The particulars of Red Planet:

Diameter: 3400 km (about 0.53x Earth)
Mass: 6.4 x 10^23 kg (about 0.1x Earth)
Orbital Period: 687 Earth days
Rotation period: 24 hours 37 minutes (a “Mars day” is called a “sol”)
Axial Tilt: 25 degrees (similar to Earth’s 23.5 degrees)
Orbit size: 1.67 astronomical units at aphelion, 1.38 at perihelion (Mars has a highly elliptical orbit; remember the average Earth-sun distance is 1.0 astronomical unit)
Opposition Frequency: Mars is at “opposition” when it’s opposite the sun as seen on Earth, as it is this week. Oppositions occur every 780 days, on average.
Atmospheric composition: 95.7% carbon dioxide, 2.7% nitrogen, 0.2% oxygen)
Surface temperature: -90 C to -5 C, approximately
Satellites: Two natural satellites, Phobos and Diemos; both are likely captured asteroids

While Venus is nearly the same shape and size as the Earth, Mars has a surface that's much more familiar. Mars has broad deserts that look a little light some deserts on Earth. Again somewhat like Earth, Mars has polar caps of frozen water and carbon dioxide which grow and shrink with the planet's seasons. Mars also has a thin atmosphere, which means it has wind and weather and clouds and even massive dust storms that engulf large parts of the planet.

Mars also has a number of large volcanoes, including the immense Olympus Mons which rises 27 km above the surface of the planet, dwarfing Earth's Mount Everest. Unlike Earth, Mars did not develop plate tectonics. That means Martian volcanoes sit permanently over hot-spots in the crust and grower larger over time. Most volcanoes lie on a large, elevated bulging area of the planet's surface called Tharsis, which is six miles high and as large as North America. No one knows for sure what caused this massive bulge.

Unlike Earth, Mars presently has no liquid surface water. But there are large canyons thought to be carved into the surface by ancient flows of liquid water a couple of billion years ago. The largest canyon, Valle Marineris, puts Earth's Grand Canyon to shame. Valle Marineris has a width of 200 km in some parts, a depth of 7 km, and stretches to a length of 4,000 km… roughly the width of the continental United States.

Mars gets its reddish color from the sand of its deserts. But even a small telescope shows darker continent-size features once thought to be areas of vegetation. These dark features are simply crater fields where darker sub-surface material has been ejected and scattered by the wind.With a small telescope, you can see the dark surface features, polar caps, and occasional dust storms. But since it presents a small disk, even at its closest approaches to Earth, Mars is not easy to observe.

v s/AASTRO

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