Chapter 10
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
Most of the planets discovered around other stars using the Doppler technique
are more massive than Earth and orbit very close to the star.
To determine a planet's average density, we can use
the transit and Doppler methods together.
Based on the model types shown in the figure above, a planet made almost entirely of hydrogen compounds would be considered a
water world.
How did Dr. Charbonneau's team discover this planet?
Eight 16-inch telescopes called MEarth
What is it really like on this planet, according to Dr. Vogt and his team?
The days are long, perhaps never ending. On the far side of the planet, it is dark and far colder than the day side.
Why didn't one form in our solar system?
Because the nebula must have dispersed shortly after the formation of our jovian planets.
Which two quantities need to be measured in order to determine the density of a planet?
mass and radius
Based on current data, planetary systems appear to be
present around at least 99% of all stars.
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?
- Jovian planets can migrate inward and disrupt the orbits of terrestrial planets. - Jovian planets always form in the cold, outer regions of their star system. - Terrestrial planets always form in the warm, inner regions of their star system.
How can scientists account for the fact that extrasolar planets seem to come in a wider range of types than the planets of our solar system?
- Not all nebulas are alike - _some richer in planet-forming elements than others, and some poorer. - The differences result from migration, which in turn may result from a postponement of the clearing of the solar nebula.
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
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.
What is the chief difficulty in attempting to detect planets around other stars?
Even the largest planets are typically at least a factor of 10 times smaller than their host stars and Planets do not emit visible light. They are typically at least a billion times fainter than their host stars
How do we think hot Jupiters formed?
Hot Jupiters formed beyond the frost line, as in our solar system, and migrated inward due to interaction with the solar nebula.
What are the two primary methods by which planets have been found around other stars in our galaxy? I) Direct images in visible and infrared light II) Indirectly by detecting the motion of the host star III) Indirectly by measuring the drop in brightness of the host star when the planet crosses our line of sight
II and III
What is the most extraordinary feature of the planet discussed in this article?
It likely has water on its surface.
What is the habitable zone?
It the region around a star where liquid water could exist.
What is the significance of the planet described in this article?
It was the first rocky planet discovered in the habitable zone around a star not in our own solar system.
Our sun wobbles mostly due to the gravitational force exerted by jupiter. If our solar system only contained saturn, how would the period of the suns wobble differ?
It would be longer.
Our sun wobbles mostly due to the gravitational force exerted by jupiter. if our solar system only contained saturn, how would the speed of the sun differ?
It would be slower.
Planets detected via the Doppler technique have been mostly
Jupiter-mass, in very close orbits.
Based on current evidence, how common are planetary systems?
Kepler spacecraft had discovered in total several thousand planet candidates during all the time of its operation, most of them are thought to be real planets.
What could happen in planetary systems where the nebular gas is quickly disbursed?
Large ice-rich planetesimals would not be able to gather hydrogen and helium and become gas giants.
What is planetary migration, and how may it account for the surprising orbits of many extrasolar planets?
Migration means the planet gradually moves closer to its parent star. Many extrasolar planets are much closer to their stars than we had expected. We think that it is possible for planets to migrate through their disks because of interactions with the gas in the disk. Migration can lead to resonances, which can make orbits elliptical.
Why don't we see transit events for most stars that have been found to have planets?
Most of the planets orbit the star without ever getting directly in between the Earth and the Star.
The planet HAT-P-32b has more than twice the radius of Jupiter, yet is only the same mass. It orbits its star more than a factor of ten closer than Mercury's orbit around the Sun. Which is the most plausible explanation for its large size?
Planets that are close to a star are heated up and therefore larger.
Match the star's positions at points 1, 2, 3, and 4 in the plot with the descriptions below.
Point 1: farthest from earth Point 2: headed straight toward earth Point 3: closest to earth Point 4: headed straight away from earth
After this article was published, another group reported that they had analyzed the same set data, plus some of their own, and they claim that this result may be false, as described inSeth Shostak's article, Bye Bye to a Lovely Planet. Consider the definition of science. What does this new counter-claim imply for science and reliability?
Science makes progress despite shortcomings of individual scientists because scientists test the claims of other scientists.
What would happen to the planets in a solar system where the central star did not have a strong wind?
The gas in the solar nebula would create a drag on the planets and their orbits would migrate inwards.
The planet COROT-14b is only slightly larger than Jupiter, but is several times more massive. Which is the most plausible explanation for its similar size to Jupiter?
The hydrogen and helium gas compressed even under their own gravity to a higher density than Jupiter.
Overall, does the nebular theory seem adequate for describing the origins of other planetary systems?
The nebular theory with the added processes of migration and resonances accounts for the basic properties of extrasolar planetary systems.
How does this planet compare to the hot Jupiters discovered around other stars?
The new planet is denser than typical hot Jupiters.
How would the plot change if the planet were more massive (but remained at the same orbital distance)?
The peaks and valleys would get significantly larger (greater positive and negative velocities) because of larger gravitational tugs.
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.
A transiting extrasolar planet is observed to block 1% of its host star's light. How does the size of this planet compare to the host star?
The planet's radius is 10% of the host star's radius.
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.
Why does Dr. Vogt and the discovery team argue, based on the discovery of one planet, that such planets must be common?
They found it after only 11 years of looking.
What evidence do astronomers have that the planet is composed mostly of water?
They have an estimate of its size, which is not much bigger than Earth, and its density, which is not as high as the density of rock.
How long does it take the star and planet to complete one orbit around their center of mass?
about 4 days
What maximum velocity does the star attain?
about 50 m/s
The first planets around other Sun-like stars were discovered
about two decades ago.
Approximately how many other planetary systems have been discovered to date?
about two thousand
The transit method of planet detection works best for
big planets in edge-on orbits around small stars.
What type of observation can astronomers use to measure the composition of extrasolar planet atmospheres?
comparisons of spectra when planets are in front of or are eclipsed by their host stars
Which of the following methods has led to the most discoveries of extrasolar planet candidates?
detecting the dip in measured brightness as the planet crosses our line of sight to the star
Which of the following methods has led to the most confirmed 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
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 and astrometric
Why is it very hard to use the doppler shift method of detecting planets to discover a planet like the earth?
earth is too small in mass
The gravitational force exerted on a star by a planet is
equal to that exerted on the planet by the star and in the opposite direction.
What is one reason why it is very difficult to directly take a picture of an extrasolar planet?
extrasolar planets are very close to the star (relative to the distance to earth)
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
The Doppler technique can be used to estimate the semimajor axis of a planet's orbit by
measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law.
The Doppler technique can be used to measure the orbital period of a planet by
measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak.
During a transit event, the absorption lines from the star will be
not shifted at all.
The habitable zone is defined by the distance at which the equilibrium temperature of a planet being between 0 and 100 degrees Celsius. Thinking about what you've learned in class, what other factors affect the average temperature of a planet?
planet density
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
Which of the following properties can be inferred from the star's orbital period?
the planet's orbital radius
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.
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
Which planet search technique is currently best suited to finding Earth-like planets?
transit
