Download Physics 127 Descriptive Astronomy Homework #8 Key (Chapter 4

Physics 127 Descriptive Astronomy
Homework #8 Key (Chapter 4)
Winter 2015
4-1. What are the two agreed upon defining characteristics of a planet?
The two defining characteristics or a planet are: (1) It is a (non-stellar) object orbiting a star. (2) It is sufficiently massive
that its gravity has shaped it (approximately) into a sphere.
4-2. Compare the characteristics of a terrestrial planet to those of a Jovian planet.
A table is an efficient way to summarize the most obvious differences:
Characteristic
Location
Temperature
Composition
Relative Size
Rings?
Moons
Rotation
Density
Atmosphere
Surface
Associated Debris
Class Members (descending size order)
Terrestrial Planets
Inner solar system
Warm to hot
Rocky
Small
No
Few to none
Slow (P ~ days)
High (𝜌 ~ 3.3 𝑡𝑜 5.5 g/cm3 )
Thin (CO2, N2, O2)
Cratered/Volcanic/Mountainous
Asteroids
Earth, Venus, Mars, Mercury, Moon
Jovian Planets
Outer solar system
Cold to very cold
Gaseous (mostly H and He)
Large
Yes
Many
Fast (P ~ hours)
Low (𝜌 ~ 0.7 𝑡𝑜 1.7 g/cm3 )
Thick (H2, He, CH4, NH3)
Gaseous, not well-defined
Kuiper Belt, Comets
Jupiter, Saturn, Uranus, Neptune
4-6. What are the asteroid belt, the Kuiper belt, and the Oort cloud? Where are they located? How do
the objects found in these three regions compare?
These are three groups of debris in the solar system, mainly solar nebula material that did not coalesce into planets or
their moons. The asteroid belt is a belt of rocky debris, mainly confined to a region between the orbits of Mars and
Jupiter and roughly confined to the ecliptic plane orbiting about the sun in the same direction as the planets. The
Kuiper belt is a belt of icy objects with rocky impurities, also roughly in the ecliptic plane, orbiting in the same
direction as the planets and asteroids, beyond the orbit of Neptune. The Oort cloud is a much larger cloud of icy debris
with rocky impurities well outside the Kuiper belt. It is thought to be roughly confined to a thick spherical shell, and
not confined to the ecliptic plane.
4-8. What is the connection between comets and the Kuiper belt? What is the connection between
comets and the Oort cloud?
Most, perhaps all, comets are believed to be objects that either originated in the Kuiper Belt or the Oort cloud, the
orbits of which now penetrate the inner solar system. Most Kuiper Belt comets are believed to be fragments produced
in collisions between Kuiper Belt objects. These typically have periods of thousand to tens of thousands of years. Oort
cloud comets are believed to have been perturbed into elongated orbits by passing stars. Typical periods are millions of
years. Both comet types are made primarily of ices and embedded dust and rocks.