150Lec26(1)-1

150Lec26(1)-1 - Lecture #26: Extraterrestrial Volcanism and...

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Lecture #26: Extraterrestrial Volcanism and Faults Be familiar with the bolded terms. Several planets and moons in our Solar System show evidence of volcanism and quakes. There are now eight recognized planets in the Solar System, which are listed from closest to farthest from the Sun : Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , and Neptune (Abbott, 2008: Figure 17.4, p. 469; Table 17.2, p. 470; know the order of the planets from the Sun ). Recently, astronomers decided that Pluto really isn't a planet. The American and Russian space programs have allowed us to view the planets and some of their moons in greater detail. Mercury Mercury is the closest known planet to the Sun. The planet is slightly larger than the Moon. Like the Moon, Mercury has many craters and essentially lacks an atmosphere. Mercury’s low mass and close proximity to the Sun are probably responsible for its virtually nonexistent atmosphere. Because of its short distance from the Sun and lack of a heat-retaining atmosphere, surface temperatures range from –177°C at night to 427°C during the day (Busch 2000, p. 14). The landscape of Mercury may be divided into highlands and lowland plains (Vilas 1999, p. 88–89). The highlands are heavily cratered. The lowland plains have fewer craters and consist of basalt plains that result from eruptions billions of years ago. Volcanic structures have only been recently discovered on Mercury. Thrust faults up to 500 km long and 2 km high cross part of Mercury’s surface. The faults may have resulted from contractions in the planet’s diameter as the mantle and core cooled (Vilas 1999, pp. 88– 94). Venus Venus, the second planet from the Sun, is slightly smaller than Earth. The planet is covered with a thick atmosphere consisting almost entirely of carbon dioxide . Venus has about 92 times the surface pressures of Earth (Busch 2000, p. 15). The carbon dioxide produces a greenhouse effect that results in surface temperatures above 400°C, or hot enough to melt lead (Busch 2000, p. 15; Abbott, p. 293). Volcanism on Earth releases large amounts of carbon dioxide. However, rather than being retained by the Earth's atmosphere, the compound is largely absorbed by ocean water, converted into carbonates to form rocks (such as limestones ) or stored as organic carbon in organisms (Saunders 1999, p. 98). Because Venus has no oceans or life, the carbon dioxide accumulates in
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150Lec26(1)-1 - Lecture #26: Extraterrestrial Volcanism and...

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