Ch. 8 - Comparative Planetology Part 2

Which three of the following properties of the solar system are thought to be a result of how the solar system formed?

- size of terrestrial planetary orbits versus Jovian planetary orbits - directions and orientations of planetary orbits compared to the Sun's rotation - size and composition of the terrestrial planets versus the Jovian planets

If you start with 0.80 kg of radioactive potassium (40K), how much will remain after 1.3 billion years? How much will remain after 2.6 billion years? How much will remain after 3.9 billion years? How long would you have to wait until there was no 40K remaining?

.40 kg 0.20 kg 0.10 kg forever

Three-quarters of the radioactive potassium (40K) originally contained in a certain volcanic rock has decayed into argon (40AR). How long ago did this rock form?

2.6 billion years ago

How does our current understanding of the formation of the solar system account for the observation that all planetary orbits lie in nearly the same plane?

A rotating disk of material, like the solar nebula, tends to flatten out and become planar

A 1999 new story about the discover of three planets orbiting the star Upsilon Andromedae stated that "the newly discovered galaxy, with three large planets orbiting a star known as Upsilon Andromedae, is 44 light-years away from Earth." What is wrong with this statement?

A star and three planets would constitute a new solar system, not a galaxy

What is meant by accretion?

Accretion is the process in which an object gathers smaller bits of matter to itself through gravitational attraction

The graphite in your pencil is a form of carbon. Where were these carbon atoms formed?

Carbon is formed by nuclear reactions in stars. At the ends of their lives, stars can erupt in novae or supernovae, and these send elements like carbon across the interstellar medium

How did planetesimals give rise to the terrestrial planets?

Collisions between planetesimals generated heat, which welded the planetesimals together to form the terrestrial planets

What can we learn from a transit event?

Combining the observation of a transit event with the radial velocity information from the Doppler effect allows us to determine the mass of an extrasolar planet

In our solar system, the atoms of these elements are found primarily in the molecules CH4 (methane), NH3 (ammonia), and H2O (water). Why is this?

Hydrogen is the most abundant element and is chemically reactive. Carbon, nitrogen, and oxygen are abundant and chemically reactive, so it is not surprising that compounds of these elements with hydrogen are also abundant

If hydrogen and helium account for 98% of the mass of all the atoms in the universe, why aren't the Earth and Moon composed primarily of these two gases?

Neither Earth nor the Moon has sufficient gravity to retain these gases at the temperatures of this part of the solar system

Suppose you were to use the Hubble Space Telescope to monitor one of the protoplanetary disks shown. Over the course of 10 years, would you expect to see planets forming within the disk?

No

What is the evidence that other stars existed before our Sun was formed?

Our Sun is not massive enough and consequently not hot enough to produce heavy elements. Yet heavy elements exist in the Sun, and these must have been formed in an earlier generation of hot, massive stars

How does our current understanding of the formation of the solar system account for the observation that all planetary orbits are nearly circular?

Planetary orbits are nearly circular because non-circular orbits would be unstable due to gravitational perturbations from other solar system objects

What is a planetesimal?

Planetesimals are asteroid-like bodies with diameters of a kilometer or so

How does the interstellar medium become enriched over time with heavy elements?

Supernovae form heavy elements and spew them throughout the interstellar medium when they erupt

Why did the terrestrial planets form close to the Sun whereas the Jovian planets formed far from the Sun?

Terrestrial planets are composed mainly of rock, which means solid at the relatively high temperatures near the Sun. The Jovian planets contain an abundance of light gases like hydrogen and helium, which would have escaped if the temperature had been higher and the average molecular speeds larger

How does our current understanding of the formation of the solar system account for the observation that all planets orbit the Sun in the same direction the Sun itself rotates?

The counterclockwise orbital motion of the planets and the counterclockwise rotation of the Sun descended from the original counterclockwise rotation of the solar nebula

What is the interstellar medium?

The interstellar medium is the rarified material that exists in the space between stars

Why do most of the satellites of Jupiter orbit that planet in the same direction that Jupiter rotates?

The major satellites of Jupiter are thought to have condensed out of a nebula around Jupiter, much like the planets condensed out of the solar nebula. The entire Jupiter nebula was rotating in the same direction

What does it mean for a planet to transit a star?

The planet passes across the face of the star as seen from Earth

Why are terrestrial planets smaller than Jovian planets?

There was far more material available for planet formation in the outer part of the solar nebula (where ices could exist) than in the inner parts. Thus the planets that formed in the outer part were larger

Why are the terrestrial planets denser at their centers than at their surfaces?

When these planets were molten in the early solar system, the denser, iron-rich minerals sank to the centers of the planets, whereas the less dense, silicon-rich minerals floated to their surfaces