Our Solar System • the Sun • the eight planets • more than 130 satellites of the planets • a large number of small bodies (the comets and asteroids) • and the interplanetary medium • (There are probably also many more planetary satellites that have not yet been discovered)
The Sun • Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy. • Diameter: 1,390,000 km • Mass: 1.989 x 1030 kg • Temperature: 5800 K (surface) 15,600,000 K (core)
The Sun • The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System • (Jupiter contains most of the rest)
The Sun • It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it. But there are many more smaller stars than larger ones; the Sun is in the top 10% by mass. • The median size of stars in our galaxy is probably less than half the mass of the Sun.
The Sun • The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. • This changes slowly over time as the Sun converts hydrogen to helium in its core.
The Sun • The Sun's energy output (386 billion billion megawatts) is produced by nuclear fusion reactions. • Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons of energy in the form of gamma rays
Mercury • Orbit: 57,910,000 km (0.38 AU) from Sun • Diameter: 4,880 km • Mass: 3.30 x 1023 kg • Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K
Mercury • Mercury has a small magnetic field whose strength is about 1% of Earth's • Mercury has no known satellites
Mercury • Mercury has been visited by only one spacecraft, Mariner 10. • It flew by three times in 1974 and 1975. • Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). • A new discovery-class mission to Mercury, MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys
Venus • Orbit: 108,200,000 km (0.72 AU) from Sun • Diameter: 12,103.6 km • Mass: 4.869 x 1024 kg • Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar: • Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass). • Both have few craters indicating relatively young surfaces. • Their densities and chemical compositions are similar.
Venus • Because of these similarities, it was thought that below its dense clouds Venus might be very Earthlike and might even have life. • But, unfortunately, more detailed study of Venus reveals that it may be the least hospitable place for life in the solar system.
Venus • The pressure of Venus' atmosphere at the surface is 90 atmospheres. • That’s about the pressure at a depth of 1 km of below ocean!! • It is composed mostly of carbon dioxide. • There are several layers of clouds many kilometers thick composed of sulfuric acid
Venus • The dense atmosphere produces a greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead) • Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun.
Earth • Orbit: 149,600,000 km (1.00 AU) from Sun • Diameter: 12,756.3 km • Mass: 5.972 x 1024 kg • It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet!!
Earth • The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. • Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. • We know most of this only from seismic techniques.
Crust divided into several plates • Plates float on top of mantle • Surface recreated every 500,000,000 years • Oldest rocks 4 billion years old • Rocks older than 3 billion are rare • Oldest fossils are 3.9 billion years old (algae)
Earth • 71 Percent of the Earth's surface is covered with water • The Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water
Earth • Earth has a modest magnetic field produced by electric currents in the outer core. • The interaction of the solar wind, the Earth's magnetic field and the Earth's upper atmosphere causes the auroras!! (Northern Lights)
First landed on moon in July 1969 • Last went to moon in 1972 • Less than 10 people have ever walked on the moon
Moon • Orbit: 384,400 km from Earth • Diameter: 3476 km • Mass: 7.35 x 1022 kg
Moon - Tides • The gravitational forces between the Earth and the Moon cause some interesting effects. • The most obvious is the tides. The Moon's gravitational attraction is stronger on the side of the Earth nearest to the Moon and weaker on the opposite side.
Moon - Tides • Since the Earth, and particularly the oceans, is not perfectly rigid it is stretched out along the line toward the Moon. • From our perspective on the Earth's surface we see two small bulges, one in the direction of the Moon and one directly opposite.
Mars • Orbit: 227,940,000 km (1.52 AU) from Sun • Diameter: 6,794 km • Mass: 6.4219 x 1023 kg • Temperature: 140 K (-207 F) at the pole in winter, 300 K (80 F) at equator in summer. • Has two moons - Phobos & Deimos
Mars • The first spacecraft to visit Mars was Mariner 4 in 1965. • Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. • Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 1997 July 4. • In 2004 the Mars Expedition Rovers "Spirit" and "Opportunity" landed on Mars sending back geologic data and many pictures; they are still operating after more than a year on Mars.
Mars • Three Mars orbiters (Mars Global Surveyor, Mars Odyssey, and Mars Express) are also currently in operation.
Olympus Mons--78,000 ft high, about the area of Arizona • Valles Marineris--System of canyons, 4000 km long, 2-7 km deep
Several hundred thousand known asteroids • 26 larger than 200 km wide • Total mass of all asteroids less than mass of moon • Largest: 1 Ceres--988 km in diameter, accounts for 25% of all asteroid mass in solar system. • Asteroid belt exists between Mars and Jupiter, about 2-4 AU from sun