EDUCATOR’S PAGE
A Visit to the Red Planet
Michael J. Urban, MEM-1910
Mars intrigues us. Next to the Earth and moon, it is the most heavily studied and frequently visited (by spacecraft) obect in the entire solar system. To say it piques our scientific curiosity is per- haps an understatement; it fascinates us, captivating our imagination with its possibilities. Not only is Mars home to the largest volcano in the solar system, but it also houses a reservoir of water (ice, vapor, and maybe liquid at times), and who knows, maybe one day we will discover that it harbors life too.
Exploration History
There have been some 20 successful missions to Mars since Mariner 4 left Earth in the year 1964[1]. Included among them are four surface travelers sent by the National Aeronautics and Space Administration (NASA): Pathfinder, the twin Spirit and Opportunity exploration rovers, and the Mars Science Laboratory Curiosity. The latest NASA visitor to Mars reached orbit in September of 2014: the Mars Atmospheric and Volatile Evolution (MAVEN) orbiter[2]. While Curiosity still roams the surface of the Red Planet in search of additional evi- dence of water, the MAVEN probe investi- gates Mars’ atmosphere and interactions with the solar wind[3]. NASA’s next tentatively planned mission will place a lander on Mars to study its interior; the Interior Explorations using Seismic, Geodesy and Heat Transport (InSight) mission is scheduled to lift off during the next launch window with Mars in May of 2018[4]. The orbital configuration of Mars and Earth align for optimal distance every 26 months, explaining why mis- sions are initiated about every two years.
General Characteristics
Mars is the fourth planet from the sun, orbiting at a distance of approxi- mately 225 million kilometers (com- pared to Earth’s 150 million km average distance). Mars is a terrestrial planet with a diameter about half the size
of the Earth’s; its gravitational acceleration is a third of the Earth’s and twice that of Earth’s moon. The atmosphere of Mars is primarily composed of carbon dioxide gas (95%), with lesser amounts of nitrogen (2.7%) and argon (1.6%), and trace amounts of water vapor (210 ppm). The thin envelope of gases surround- ing the planet produces a mere 6 millibars (mb) of atmospheric pressure on average (Earth’s average pressure is 1015 mb) – far too low for sustaining standing bodies of liquid water. Average temperatures on Mars linger around -60°C. (All specific values obtained from NASA’s Mars Fact Sheet[5].)
Despite being an alien world very different from Earth, Mars shares some interesting similarities: a 24-hour rotational period, an axial tilt of 25° (compared to Earth’s 23.5° tilt) causing seasonality, and polar ice caps of water and carbon dioxide. Mars also experiences surface winds, and at times, the entire planet’s surface can be shrouded by dust from powerful wind storms. In 1971, when Mariner 9 entered orbit around Mars, the first photographs sent back to Earth revealed nothing of the Martian surface due to a veil of dust – only the top of Olympus Mons (the larg- est volcano in the solar system, tower- ing 25 km above the surface) protruded through the dust along the spacecraft’s orbital path[6]. Summer afternoons will routinely produce dust devils. These fas- cinating twisters resemble those found on Earth, but are many times larger, some observed with kilometer-wide bases and heights of 10 km[7].
Clouds are not uncommon on Mars, and diurnal heating patterns occasion- ally produce water-ice clouds surround- ing volcanic mountains. Carbon dioxide snowfall has even been detected at the planet’s southern hemisphere[8]. Water
Photo credit NASA.
is much more abundant on Mars than previously thought. Although only min- ute traces are found in the atmosphere, there is water-ice permafrost in some of the soil on Mars and the maority of the 4 km thick north polar cap is composed of water-ice[9]. During its past, extensive flooding events occurred on Mars[10], and ust a few months ago, NASA announced finding evidence for liquid water flowing on Mars’ surface in ephemeral streams (likely fostered by the presence of dis- solved salts and subsequent lowering of the melting point of water ice)[11].
Geologic Context
In May of this year, Mars made its closest approach to Earth (75 million km distant), shining bright red in the sky. Its vivid red color – causing it be aptly called the “red planet” – is due to the abundance of iron oxide at its surface. The crust of Mars is primarily basaltic, and therefore rich in iron-laden minerals like olivine and pyroxene. The mineral hematite, an iron oxide, is a weather- ing product of basalt, and fine grains of hematite dust cover much of the planet’s surface[12].
www.aipg.org
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56