Chapter 7 Astronomy 110

What changed in out understanding of the moon and moon-Earth system as a result of humans landing on the moons surface?

By landing on the surface of the moon, we were able to collect surface samples and then use radiocarbon dating techniques to determine the age of the Moon. We were able to conclude that the moon is dead geologically.

How do terrestrial and giant planets differ?

Closer to sun, smaller, higher densities, silicates and metals. Giants have low densities, far from sun, larger, no solid surface, more moons.

What is the difference between a differentiated body and an undifferentiated body, and how might that influence a body's ability to retain heat for the age of the solar system?

A differentiated body is one that has been heated to the point where it is liquid, and heavier, denser materials sink to the center of the planet, and the lighter elements rise to the outer layer. The concentration of materials helps to retain heat in the interior of a planet. Undifferentiated bodies were never heated enough for the elements to separate; they cool quickly and are typically smaller in size.

How do asteroids and comets differ?

Asteroids are composed primarily of rock and metal and reside in the inner part of the solar system. Comets are typically icy objects that come from the outer and become visible as they approach the sun ice sublimates, asteroids have greater densities

Venus rotates backward and Uranus and Pluto spin about an axis tipped nearly on its side. Based on what you learned about the motion of small bodies in the solar system and the surfaces of the planets, what might be the cause of these strange rotations?

Collisions were frequent in the early solar system, so it is not unlikely that these strange rotations are due to collisions of these planets with significantly large objects during their formation or subsequent evolution.

What is comparative planetology and why is it useful to astronomers?

Comparative planetology is the study of how planets work and evolve by comparing them and the processes that have influenced their development. This method allows us to learn about the origin and evolution of the entire solar system, instead of each planet as a discrete object in space.

What is the difference between a meteor and a meteorite?

Meteoroids that collide with Earth's atmosphere are called meteors. If the object makes it through the atmosphere and lands on the surface of Earth, then it is called a meteorite.

Describe how we use radioactive elements and their decay products to find the age of a rock sample. Is this necessarily the age of the entire world from which the sample comes?

Radioactive elements decay in a systematic way. The half life measures the amount of time it takes half of a sample to decay. The world melts and this time is only for the last time it was melted.

Which type of planets have the most moons? Where did these moons likely originate?

The giant planets have the most moons, especially Jupiter and Saturn. Many of them are thought to have been captured from the small-body population during the formation of the solar system.

What does a planet need in order to retain an atmosphere? How does an atmosphere affect the surface of a planet and the ability of life to exist?

The gravity of a planet helps to determine whether an atmosphere can be retained. Mars has a shallow atmosphere compared to Earth, but it is also only 1/3 the size of Earth. Venus and Earth are about the same size and both have atmospheres. A dense atmosphere insulates the surface of a planet so that more heat is retained; however, the composition of the atmosphere is also important. Certain gases lead to a greenhouse effect, allowing the planet to be warmer than you would expect from its position around the Sun. Life as we know it requires temperatures and pressures at which water is liquid.

What was solar nebula like? Why did the sun form at its center?

The solar nebula was a huge cloud of material made up of gas and dust. The sun formed at the center due to gravitational forces, caused that material to stick together, and once the mass and density increased sufficiently, nuclear fusion caused a star to form: the sun.

Explain our ideas about why the terrestrial planets are rocky and have less gas than the giant planets

The terrestrial planets and the gas planets are thought to have formed under different conditions. The inner planets are made of elements that can survive the heat of the Sun; gases would have evaporated. The giant planets are far enough away that gases could accumulate around the planet cores and remain there for the age of the solar system.

What characteristics do the worlds in our solar system have in common that lead astronomers to believe that they all formed from the same "mother cloud" nebula?

They generally rotate and revolve in the same direction and their orbits lie roughly in the same plane. The chemical makeup of the giant planets is similar to the sun.