AS101 Ch. 13 Other planetary systems
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.
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.
What kinds of planets are easiest to detect with each method?
Both techniques are most sensitive to large planets close to their stars.
The planet must be closer to the star than Earth is to the Sun.
Compare spectra obtained before and during an eclipse.
A planet's density can be measured by combining
Doppler and transit observations.
Choose the correct description of advantages gained if a planet can be detected by both methods.
If a planet can be detected by both methods, then we can find its density—an indication of its composition.
Which of the following might explain the lack of "water worlds" (planets made mostly of water or other hydrogen compounds) in our own solar system?
In our solar system, the solar wind did not clear out gas until relatively late.
Assuming that our ideas about how "hot Jupiters" ended up on their current orbits are correct, why didn't our own solar system end up with any hot Jupiters?
Our solar nebula must have been blown into space shortly after the formation of the jovian planets.
Are there certain planets that each method cannot detect, even if the planets are very large? If so, why can't they be detected?
Planets that do not have necessary orbital alignment cannot be detected.
What are the strengths and limitations of the Doppler method?
The Doppler technique has the main advantage of being able to detect planets in a wide range of orbits—as long as the orbit is not face-on. Its disadvantage is that it can yield only the planet's mass and orbital properties.
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.
Choose the correct statement explaing what was the Kepler mission?
The Kepler mission uses the transit method to search for Earth-size planets in Earth-like orbits.
You observe a star similar to our own Sun in size and mass. This star moves slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?
The planet must be closer to the star than Earth is to the Sun.
Why do we say that the Doppler technique gives the planet's "minimum mass"?
The size of the Doppler shift that we detect depends on whether the planet's orbit is tilted.
What are the strengths and limitations of the transit method?
The transit method has the advantage of yielding a planet's size. Its disadvantage is that few planets have the necessary orbital alignment to even be detectable.
How do we use velocity curves (obtained from spectroscopy) to show that some extrasolar planets are close to their host stars?
The velocity curve of the host star shows periods much shorter than a year.
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.Their masses are similar to Jupiter but their composition is similar to Mercury.
Current evidence suggests that some massive jovian planets orbit at close orbital distances to their stars. How do we think these planets ended up on these close orbits?
These planets migrated inward after being born on orbits much farther from their stars.
To date, we've found few planets orbiting their stars at distances comparable to the distances of the jovian planets in our solar system. Why do astronomers think this is the case?
We have not yet been searching for planets at such distances for a long enough time.
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.
What do we mean by a "super Earth"?
a planet made of metal and rock that is larger in mass than Earth
What is an extrasolar planet?
a planet that orbits a star that is not our own Sun
Which detection techniques can find the planet's orbital distance (assuming we know the mass of the star)?
all of these techniques. Doppler, astrometric, transit
Most of the planets discovered around other stars
are more massive than Earth and orbit very close to the star.
Which method could detect a planet in an orbit that is face-on to the Earth?
astrometric method
What are the two main differences between extrasolar planetary systems discovered to date and our Solar System?
extrasolar planet orbits tend to be closer and more eccentric than in our Solar System
The astrometric technique of planet detection works best for
massive planets around nearby stars.
The first confirmed detections of extrasolar planets occurred in
the 1990s
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.
A planet is detected via the Doppler technique. The shape of the periodic velocity pattern tells us
the orbital eccentricity of the planet.
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.
Which of the following properties can be inferred from the star's orbital period?
the planet's orbital radius
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
