Astronomy 6
Directly detecting an Earth-size planet around one of the nearest stars (besides the Sun) is roughly equivalent to trying to take a picture of a ball point from a pen at a distance of about ________ kilometers.
4000
Choose the correct statement describing the astrometric method and the GAIA mission.
Astrometric method uses very precise measurements of stellar side-to-side positions in the sky to look for the slight motion caused by orbiting planets. The GAIA mission was launched by the European Space Agency with a goal of measuring the positions of a billion stars to unprecedented accuracy.
The size and shape of a planet's orbit can be determined by
the Doppler technique
The first planets around other Sun-like stars were discovered
about a decade ago.
The Doppler technique for planet detection has found Earth-like planets around nearby Sun-like stars.
f
Assume that the light curve shown below represents data from repeated transits by one planet in your sample. Which of the numbered points represents the time when the planet is directly in front of its star as viewed from Earth?
3
Today, the leading hypothesis for the existence of hot Jupiters is that they formed in their outer solar systems and then migrated inward. Why did this hypothesis gain favor over alternative ideas?
Computer models that simulate planetary formation show that interactions between young planets and other material in the surrounding disk can cause planetary migration.
Which of the following is a consequence of the discovery of hot Jupiters for understanding our own Solar System?
It has been modified to allow for planets to It shows that we do not fully understand the formation of our Solar System
Which of the following is a consequence of the discovery of hot Jupiters for the nebular theory of solar system formation?
It has been modified to allow for planets to migrate inwards or outwards due to gravitational interactions
Which of the following best explains why Kepler 10b is called a "super-Earth"?
It has similar composition to Earth, but is more massive.
Why is our Jupiter not a "hot Jupiter"?
It is likely that in our system the nebular gas cleared out before it could have much migratory effect on the planet.
Suppose that, overall, your 3-year transit program detects planets orbiting about 1% of the stars that you are monitoring. What should you conclude?
It is likely that most stars in your survey are orbited by planets.
What is planetary migration, and how may it account for the surprising orbits of many extrasolar planets?
Many extrasolar planets are much closer to their stars than we had expected. In fact, our formation model does not allow jovian planets to form that close to their stars. However, we think that it is possible for planets to migrate through their disks because of interactions with the gas in the disk.
Which method of planetary detection works only for planets that happen to orbit their star with an orientation that causes them to pass directly in front of the star as seen from Earth?
The Transit Method
Choose the correct statement describing the Doppler method.
The Doppler technique watches for movement in stars by looking for periodic Doppler shifts. It's best for detecting massive planets with close-in orbits. It detects planets in all orbit orientations except face-on. It requires large telescopes, and it provides only minimum mass when orbital inclination to Earth is unknown.
A planet is detected via the Doppler technique. The repeating pattern of the stellar motion tells us
The orbital period of the planet
Consider the planet that causes the stellar motion shown in Plot 2 (be sure you have clicked the "Plot 2" button in the lower window of the animation). What can be said about a different planet orbiting the same star with an orbital period of 500 days?
The planet must be closer to the star.
Suppose that for one of the planets detected by the transit method in your program, you conduct follow-up observations using the Doppler method. What key additional information will you learn?
The planet's mass and average density.
Which of the following properties can be inferred from the star's orbital period?
The planet's orbital radius
Notice that the planets with the largest radii all fall in the category of "hot Jupiters," which means Jupiter-like planets that are hot because they orbit close to their stars. Which of the following best explains why these planets are large in radius?
Their high temperatures make their atmospheres expand to larger radii.
Why are many of the newly detected extrasolar planets called "hot Jupiters"?
Their masses are similar to Jupiter but they are very close to the central star and therefore hot.
The discovery of hot Jupiters led scientists to reconsider the nebuar theory. Which of the following best explains why the nebular theory(as it stood before the discoveries of extrasolar planets) had not predicted the existence of hot Jupiters?
There are no hot Jupiters in our solar system.
Choose the correct statement explaing what was the Kepler mission?
Used the transit method to search for Earth-size planets in Earth-like orbits.
By itself, the Doppler technique provides a measure of a planet's
all of the above
The transit method of planet detection works best for
big planets in edge-on orbits around small stars.
Which one of the following can the transit method tell us about a planet?
its size
Our modern theory of solar system formation—the nebular theory—successfully accounts for all the major features of our own solar system. However, when the first hot Jupiters were discovered, their existence seemed inconsistent with the nebular theory because this theory predicts that __________.
jovian planets can form only in the cold, outer regions of a solar system
Planets detected via the Doppler technique have been mostly
jupiter-mass, in very close orbits
The astrometric technique of planet detection works best for
massive planets around nearby stars.
Most of the planets discovered around other stars are more massive than Jupiter.
t
Multiple planets have been identified around other stars via the transit technique.
t
The signature of a planet is largest in transit measurements when the planet and star are lined up along the line of sight to the telescope.
t
Based on the model types shown in Figure 13.16 in the textbook, a planet made almost entirely of hydrogen compounds would be considered a
"water world"
Three planets are circled on the planetary mass-radius diagram shown at left. Rank these planets, along with Earth and Jupiter, in order of mass, from highest to lowest. Rank from highest mass to lowest mass. To rank items as equivalent, overlap them.
(HIGHEST) COROT-14b, Jupiter, HAT-P-32b, Kepler 10b, Earth (LOWEST)
Consider the same set of planets as in Part A, but without Earth. Rank these planets in order of average density, from highest to lowest. Rank from highest density to lowest density. To rank items as equivalent, overlap them.
(HIGHEST) Kepler 10b, COROT-14b, Jupiter, HAT-P-32b (LOWEST)
Consider the same set of planets as in Part A. Rank these planets in order of radius, from largest to smallest. Rank from largest radius to smallest radius. To rank items as equivalent, overlap them.
(LARGEST) HAT-P-32b, COROT-14b, Jupiter, Earth, Kepler 10b (SMALLEST)
Choose the correct statement representing the evidence that the planet orbiting 51 Pegasi is a hot Jupiter.
51 Pegasi is a planet whose orbital period is so short (4 days) that it must lie incredibly close to its star. Furthermore, the size of the stellar Doppler wobble is so large that it must be caused by a planet with at least a mass of 0.6 MJ.
Suppose you monitor a large number (many thousands) of stars over a period of 3 years, searching for planets through the transit method. Which of the following are necessary for this program to detect an extrasolar planet around one of these stars?
1) As seen from Earth, the planet's orbit must be seen nearly edge-on (in the plane of our line-of-sight) 2) You must be able to precisely measure variations in the star's brightness with time. 3) The planet must have an orbital period of less than about 1 year.
In analyzing the data from your program, you discover one star that dims by about 0.1% for about two hours on every 63rd day. Assuming the dimming is caused by a single planet, what would you conclude about this planet?
1) It has an orbital period of 63 days. 2) Its size (area of disk) is about 0.1% of the star's mass.
Assume that the migration hypothesis is the correct explanation for the hot Jupiters. In that case, the revised nebular theory looks just like the old theory, except that it now allows for the possibility of migration. Which of the following statements are consistent with this revised theory?
1. Jovian planets can migrate inward and disrupt the orbits of terrestrial planets. 2. Jovian planets always form in the cold, outer regions of their star system. 3. Terrestrial planets always form in the warm, inner regions of their star system.
Approximately how many other planetary systems have been discovered to date?
a thousand
A planet's density can be measured by combining
Doppler and transit observations
Which method(s) are based on the gravitational tug a planet exerts on its star and hence can tell us about a planet's mass?
Doppler method Astrometric method
What's the best explanation for the location of hot Jupiters?
They formed farther out like Jupiter but then migrated inward.
Choose the correct statement representing how does the transit method work.
We monitor the brightness of a star as the planet passes in front of the star's disk. The star's light dims slightly because the planet blocks some of the star's visible light. This technique works only in the rare cases when the planet's orbit is nearly edge-on as seen from Earth. So we can only detect a small fraction of the existing planets.
Is it possible to determine the planet's mass from the star's velocity curve?
Yes, by measuring both the star's orbital period and its change in velocity over the orbit
How much brighter is a Sun-like star than the reflected light from a planet orbiting around it?
a billion times brighter
Which of the following methods has led to the most discoveries of massive planets orbiting near their parent stars?
detecting the gravitational effect of an orbiting planet by looking for the Doppler shifts in the star's spectrum
How do we think the "hot Jupiters" around other stars were formed?
they formed as gas giants beyond the frost line and then migrated inwards
What is astrometry?
measuring the positions of stars on the sky
To determine a planet's average density, we can use
transit and doppler methods together
Based on what we know about our own solar system, the discovery of hot Jupiters came as a surprise to scientists because these planets are __________.
so close to their stars
Astronomers have discovered more planets around other stars than in our Solar System.
t
The reason that most extrasolar planets are found close to their parent stars is
the amount and frequency of the star's motion are both higher
The composition of a planet's atmosphere be measured during a transit by analyzing
the excess absorption of starlight at specific wavelengths
A planet is detected via the Doppler technique. The velocity change of the star is a measure of
the planet's mass and orbital distance
The depth of the dip in a star's brightness due to the transit of a planet depends most directly on
the planet's size
