The planet Mars in astronomy

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The Planet Mars in astronomy

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Mars is of great interest to earthlings because it is the only terrestrial planet (Mercury, Venus, Earth and Mars) whose surface can be observed directly from Earth. Mercury is never further than 28° (its "elongation") from the Sun, so Earth-based observation of that planet is severely hampered by the Sun's glare. Venus' 48° elongation offers better viewing from Earth than Mercury, and Venus is slightly closer to us than Mars, but its surface is constantly shrouded in thick clouds. And the four gas giants Jupiter, Saturn, Uranus and Neptune don't even have a sold surface.



Schiaparelli's Mars' map

Map of Mars by Giovanni Schiaparelli




In 1877 when Mars was at an opposition (when opposed to the Sun Mars is closest to the Earth, visible all night, and most fully illuminated) the Italian astronomer Giovanni Schiaparelli observed "canali" in the equatorial regions of the planet, which he drew above. Canali is Italian for "channels" which Schiaparelli took to be natural configurations on Mars' surface; but a mistranslation of canali into "canals" as artificial constructs gave rise to a mythos with a life of its own. Canals on Mars was picked up and embellished by astronomer, businessman, author and mathematician Percival Lowell (founder of Lowell Observatory who began an effort leading to Pluto's discovery) who went so far in his drawings that even Schiaparelli thought Lowell's details were imaginary. When the great 33"/83 cm. refractor at Meudon, France (with 4 times the resolution and 14 times the light-gathering power of Schiaparelli's 8.6"/22 cm. refractor) was turned on Mars 32 years later during its 1909 opposition and no canals were seen, the idea of canals on Martian began to lose favor. The arrival of Mariner 4 on Mars in 1965 finally put it to rest.

Fourth from the Sun at 1˝ times Earth's distance, Mars' surface (ground or soil) temperature ranges from about -225° (-143° C) at the poles in winter to almost 81° F (27° C) on rare summer days at the equator. On the other hand, the air temperature measured by the Viking Landers about five feet above the surface varies between -178° F (-107° C) in the winter to about 1° F (-17° C) in the summer. Though the closest planet to Earth in seasons and temperature, at its thickest Mars' atmosphere is comparable to the Earth's 22 miles above the surface (Everest is less than six miles high), with only traces of oxygen and water. Mars also lost its magnetosphere four billion years ago, stripping its atmosphere and leaving poor insulation against the harmful effects of the solar wind and UV radiation. All these facts together make the Martian surface a deadly place for human beings, yet a walk in the park compared to the Planet of Love's (Venus') lead-melting surface temperature, sea-bottom air pressure and sulfuric acid clouds. On the lighter side Mars' diameter is only half that of Earth's, so on Mars you would weigh only 38% of what you do here. You could skip about joyfully until the other factors sobered you up.

The striking photograph above appears in higher resolution on page 134 in You and the Universe.  At its center is the largest canyon in the solar system, Valles Marineris. Ten times as long and four times as deep as the Grand Canyon, it goes one-fifth of the way around Mars. At the left of the photograph are three huge volcanoes on a big bulge called the Tharsis Ridge. Scientists think Valles Marineris is a large crack in the Martian crust that formed as the planet cooled, later widened by erosion. Near its eastern flanks are channels that may have been formed by water. Similar outflow channels tens of kilometers wide, hundreds long, and up to a kilometer deep suggest that an immense reservoir of water was present during much of Mars’ history. It is conservatively estimated that Mars had the equivalent of a global ocean half a mile deep when they formed, which today may be buried as subsurface groundwater. Mars’ axial tilt varied from 0° to 60° in just the last ten million years, an extraordinary amount probably leading to immense planet-wide climactic changes! If so, this buried groundwater could have been vaporized and driven into the atmosphere.

The immense Tharsis bulge on the left horizon of Mars’ globe above is a volcanic dome located on Mars’ equator 2,500 miles across and 6.2 miles high. Tarshish was the Biblical name (1 Kings 10:22) given to a remote place across the sea in Solomon’s time. Later, Giovanni Schiaparelli gave the Greek form of this name, Tharsis, to a region on Mars. The Tharsis plateau is in fact so massive that it may have caused a smaller bulge, Arabia Terra, on Mars’ opposite side. Tharsis has had a tremendous impact on Martian history. Surrounded by a ring-shaped depression called the Tharsis trough, great quantities of CO2 and water vapor could long ago have been outgassed from Tharsis magma, forming a CO2atmosphere with 150% of Earth’s sea-level pressure, and enough water to cover the entire planet to a depth of 400 feet.

Also on the left horizon (and from left to right) are the great shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons. The largest Tharsis volcano and tallest mountain in the solar system, Olympus Mons, three times taller than Everest, is not shown. Between the Tharsis bulge and Valles Marineris' westernmost extension is what appears to be a bunch of scratches on Mars' surface; this is as a maze of canyons, valleys and grabens known as Noctis Labyrinthus—"the labyrinth of the night".

This Planet-Mars-in-Astronomy page and much of this 600-page website are excerpted from the personalized Fine Art Book You and the Universe.

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© Carl Woebcke: The Planet Mars in Astronomy, 1991-2017. All rights reserved.