Phys 105 Astronomy Ch. 13 Study Set

What are the two major approaches to detecting extrasolar planets indirectly?

1. Observing the motion of a star to detect the subtle grav-itational effects of orbiting planets. 2.Observing changes to a star's brightness that occurwhen one of its planets passes in front of the star asviewed from Earth.

Why are extrasolar planets hard to detect directly?

A Sun-like star is about a billion times brighter than the sunlight reflected from its planets, and trying to see it at that distance is like being in San Francisco and trying to see a pinhead 15 meters from a grapefruit in Washington, D. C.

Summarize the key features shown in figure 13.16, and briefly describe the nature of planets that would fit each of the model curves shown on the graph.

Graph compares planetary radius and mass of extrasolar planets to those of Earth and Jupiter. Most planets are centered around 1.0 to 10 times Jupiter's mass and are .8 to 1.6 times Jupiter's radius.

Overall, does the nebular theory seem adequate for describing origins of other planetary systems? Explain.

It is fine, but we need to modify it slightly because of new data.

Briefly describe the Kepler mission and how it meets three key challenges posed by the transit method.

It is searching for terrestrial planets from one half to twice the size of Earth. It solves the challenge of watching constantly as it orbits the sun, avoiding blocking that Earth based telescopes face from the planet. It monitors a large amount of stars to compensate for the fact that only a small number will be detectable by the transit method from Earth and the solar system. It is also very precise.

Briefly describe the Doppler method and its strengths and limitations.

It looks for back and forth motion that can be measured from Doppler Shifts in a star's spectrum. It was used to discover the first extrasolar planet. It is better at finding massive planets, and not small ones like Earth. The planet found has to be close to it's sun.

How do the orbits of known extrasolar planets differ from those of planets in our solar system? Why are these orbits surprising?

Many planets orbit closer than Mercury orbits our sun. None orbit as far from their sun as the Jovians do in our's. Their orbits are also very eccentric. They are surprising because scientists were forced to reconsider the nebular theory, as it was/is thought that large planets had to form far out from the sun.

Why does the Doppler method generally allow us to determine only minimum planetary masses? in what cases can we be confident that we know precise masses? Explain.

Only the minimum mass can be found through this method, because we can only see motion along one direction, and so we have no way of knowing at what angle the system is tilted relative to Earth's orbit. If it is tilted so that the planet(s) cross almost directly in front of the star, then the mass that is calculated is the planet's true mass. However, if the system is tilted so that the system would look like a dartboard to us, then the mass calculated is much smaller than the actual mass.

Briefly describe the astrometric method and its strengths and limitations.

Precise measurements of stellar positions in the sky are used to look for the slight motion caused by orbiting planets. It works best for detecting binary star systems, but planet searches can be difficult using this method. It is also hard to use the method as the side to side wobble is very small at distance. The other issue is the time it takes to confirm the wobble as planets can take years to centuries to complete their orbits.

How can gravitational tugs from orbiting planets affect the motion of a star? Explain how alien astronomers could deduce the existence of planets in our solar system by observing the Sun's motion.

The planets cause the star to wobble around on the point of the system's center of mass. Someone observing our solar system could use this method called the astrometric method to detect Earth and the other planets.

Why do scientists suspect that planetary migration is behind the close-in and eccentric orbits of many extrasolar planets? How might this migration have occurred?

There are a lot of extrasolar planets that are Jovian planets orbiting close to their system's sun, contrary to nebula theory. Planets moving through the disk of the solar nebula could create gravitational waves that would cause matter to clump and build up, exerting a gravitational pull back on the planet, drawing it closer to the star. The planets moving closer causes orbital resonances which affect the orbits and close encounters that throw one planet out of the system and the other into an eccentric orbit.

Briefly describe how Kepler, GAIA, and direct observations should improve our understanding of extrasolar planets in coming years.

They will provide us with a better ability to determine what planets exist in other systems and whether Earth type planets are common or rare.

How does the transit method work? Could we use this method to find planets around all stars that have them? Why or why not?

This method only works for star-planet systems that have orbits aligned in such a way that, as seen from Earth, the planet travels between us and the star and temporarily blocks some of the light from the star once every orbit. The planet has to be on the larger size usually and close, otherwise detecting a planet blocking enough light from Earth is difficult as it is not that noticable.

Briefly describe what we can learn from careful study of a planet that undergoes transits and eclipses.

We can learn atmospheric composition and temperature. We can do this by seeing how much light and is what wavelengths are blocked by the planet's upper atmosphere.

Summarize the current state of knowledge about extrasolar planet masses and sizes. Based on the evidence, is it likely that smaller planets or larger planets are more common?

We can mainly see large planets because of our methods of detection, however based models we know that small planets are more common. When the data is adjusted for the fact that our observations are skewed by the methods we use, we find that statistically small worlds are more common.

Briefly summarize the planetary properties we can in principle measure with current detection methods, and state which methods allow us to measure each of these properties.

We can measure orbital eccentricity and inclination using the Doppler method data, in the future the astrometric data may also provide similar info. We use also use these two to get info on planetary mass, Doppler data is the main method once again. Planetary size is provided by transit observations. Planetary Density can be gotten from transit method-discovered planets by using the Doppler method.

How can scientists account for the fact that extrasolar planets seem to come in a wider range of types than the planets of our own solar system?

We need to factor in the fact that planets in other systems have hotter or cooler suns, which will change how the planets made of the same material appear in different systems.