ASTR-101Section 004

Lecture 8

Introduction to the Solar System

John T. McGraw, Professor

Danielle - Theater Operations

Test 1 Results

• Max Score 76 out of 85.

• Curve set at 78:3 A’s7 B’s8 C’s4 D’s1 F’

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64%

Earthlike and Jupiter-like

The Terrestrial and Jovian Planets• The four inner planets are called

terrestrial planets

• Relatively small (with diameters of 5000 to 13,000 km)

• High average densities (4000 to 5500 kg/m3)

• Composed primarily of rocky materials

• The four giant outer planets are called Jovian planets

• Large diameters (50,000 to 143,000 km)

• Low average densities (700 to 1700 kg/m3)

• Composed primarily of hydrogen and helium gas.

Pluto•Pluto is a special case

• Smaller than any of the terrestrial planets

• Intermediate average density of about 1900 kg/m3

• Density suggests it is composed of a mixture of ice and rock

• Many Pluto-like Kuiper Belt Objects (KBOs) are now known

• Pluto was discovered by Clyde Tombaugh, long-time professor at NMSU. By NM State Law, Pluto remains a “planet!”

Definition of a planet

• The definition of planet set in August 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which:

1. is in orbit around the Sun,

2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and

3. has "cleared the neighborhood" around its orbit.

Dwarf Planets• A dwarf planet is a planetary-mass object that is neither a planet nor

a natural satellite.

• Orbit of a star, is massive enough for its gravity to crush it into a hydrostatically equilibrious shape (usually a spheroid), but has not cleared the neighborhood of other material around its orbit.

Ceres as seen from the Dawnspacecraft. It is the only dwarf planet in the asteroid belt.

Pluto as viewed by New Horizons space probe on July 13, 2015.

Makemake and its moon viewed by the Hubble Space Telescope.

Eris and its moon Dysnomia viewed by the Hubble Space Telescope.

Small chunks of rock and ice orbiting the Sun

• Asteroids are small, rocky objects, while comets and Kuiper belt objects are made of dirty ice

• All are remnants left over from the formation of the planets

• The Kuiper belt extends far beyond the orbit of Pluto

• Pluto can be thought of as the first member of the Kuiper belt

~ 5

AU

L4

L5

L3

Seven large satellites are almost as big as the terrestrial planets

The abundances of the chemical elements