Phobos

Credit: Malin Space Science Systems/NASA

Mars, of course, has two moons, Phobos (“Fear”) and Deimos (“Panic”). The photo above is of Phobos, the innermost and larger of the two moons, taken by the Mars Global Surveyor on August 19, 1998. Phobos and Deimos were discovered in 1877 by the American astronomer Asalph Hall. He had been on the verge of giving up his search to discover if Mars had any moons, but his wife, Chloe Angeline Stickney Hall, persuaded him to continue. As a result, when he did discover Phobos and Deimos, the largest crater on Phobos (visible above) was named after her, using her maiden name, Stickney.

The crater Stickney is about ten kilometers (six miles) in diameter. Individual boulders are visible on the near rim of the crater, and are presumed to be ejecta blocks from the impact that formed Stickney. Some of these boulders are enormous -- over 50 meters (160 feet) across. Also crossing at and near the rim of Stickney are shallow grooves that was originally thought to have been formed when the crater was made; however, further research from data by the Mars Express spacecraft have revealed that the grooves are independent of Stickney and are deposits of material thrown into space by impacts on the Martian surface.

The far wall of the crater shows lighter and darker streaks going down the slopes. The presence of material of different brightness on the far crater slopes, and in some of the grooves, shows that the satellite is made from different types of materials.

Cerberus

Credit: USGS, The Viking Project, NASA

One more hemispherical view of Mars to present, this being of Cerberus. Like the previous two pictures, this photo mosaic was taken by the Viking 1 Orbiter in February 1980 when Mars’ northern hemisphere was in the early summer. The view is from 2,000 kilometers above the surface. In this picture, there are thin white clouds scattered above the northern hemisphere.

Some of the prominent features in this image include the large dark area left of the image center known as Cerberus. The Elysium Planitia volcanic region shows as a bright yellow area north of Cerberus, with several well defined channels radiating from the flanks of this volcano. Just to the right of the center of the image is the crater Tettit, with its peculiar dark "tail" extending to the southwest. The arcuate markings on the upper right of the image are in the south-west Amazonis plains and are thought to be extended sand drifts. The three bright spots north of Cerberus, upper left of image, are volcanoes partially veiled by thin clouds.

Syrtis Major

Credit: USGS, The Viking Project, NASA

Yesterday, we showed part of the western hemisphere of Mars. The western hemisphere is dominated by several major geological features: Valles Marineris and the Tharsis bulge, upon which are four of the largest volcanos in the solar system: Olympus Mons (not visible in the picture) and the three Tharsis Montes (Ascraeus Mons (northern most), Pavonis Mons and Arsia Mons (southern most)). Alba Patera, an enormous shield volcano, is also in the western hemisphere, but is not visible in the picture.

Today, we show the Syrtis Major hemisphere; once again, this is a photo mosaic by the Viking 1 Orbiter in February 1980, when the season was early summer in the northern hemisphere. The viewer’s distance is 2,000 kilometers above the surface of the planet (for yesterday’s photo, the distance was 2,500 kilometers high).

The large bright colored area, located in the upper left area of the image is known as Arabia Terra. The dark area to the right of Arabia, called Syrtis Major Planus, is a low-relief volcanic shield of probable basaltic composition. Bright white areas to the south, including Hellas Planitia, an impact basin, at extreme lower right, are covered by carbon dioxide frost. Regions to the west and south of Syrtis Major are heavily cratered and relatively old. The dark feature coming around the western horizon is known as Sinus Sabaeus.

Welcome to Areology

Credit: USGS, The Viking Project, NASA

This is a new blog I'm creating that will focus on the planet Mars. I'm a big fan of two astronomy-oriented photoblogs, Astronomy Picture of the Day and LPOD - Lunar Photo of the Day, and I hope to do something similar for Mars. I'm not a professional areologist (who is? ;) ), but I'm very interested in the subject and perhaps we can learn a few things about Mars together. Should I make any mistakes, please let me know; corrections are always welcome.

The above photo of part of the western hemisphere of Mars (click to enlarge) is a compilation mosaic of over 100 photos taken by the Viking 1 Orbiter in February 1980.