Astro 13
Current techniques can measure stellar motion to less than
walking speed
If every star had an Earth-like planet in an Earth-like orbit, how many could be detected by a transit?
1 in 200
Which of the following statements is not true about the planets so far discovered around other stars?
Photographs reveal that most of them have atmospheres much like that of Jupiter.
How do we think the ʺhot Jupitersʺ around other stars were formed?
They formed as gas giants beyond the frost line and then migrated inwards.
The reason that most extrasolar planets are found close to their parent stars is
the amount and frequency of the starʹs motion are both higher.
About how many extrasolar planets have been discovered (as of 2008)?
between 100 and 1,000
How do we expect that the first Earth-sized extrasolar planets will be discovered (if they exist)?
by the transit technique from an observatory in space
The Doppler technique only provides a measure of the minimum mass of a planet because
only the motion of star toward the observer is measured, not the full motion.
The astrometric technique looks for planets with careful measurements of a starʹs
position in the sky
As of 2008, most known extrasolar planets have been discovered by
the Doppler technique
Viewed from afar, the transit of Earth would cause the Sunʹs brightness to dim by approximately one part in
10,00
Suppose you are using the Doppler technique to look for planets around another star. What must you do?
Compare many spectra of the star taken over a period of many months or years.
A planetʹs density can be measured by combining
Doppler and transit observations
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 is a consequence of the discovery of hot Jupiters for understanding our own Solar System?
It shows that we do not fully understand the formation of our Solar System.
How will the Kepler mission (scheduled for 2008 launch) look for planets around other stars?
It will look for slight changes in a starʹs brightness that repeat at regular intervals.
Which new idea has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?
Jovian planets can migrate from the orbits in which they are born.
Planets detected via the Doppler technique have been mostly
Jupiter-mass, in very close orbits.
How are the orbits of extrasolar planets different from the orbits of planets in our solar system?
Many extrasolar planets travel on very eccentric orbits.
Which planet can we see occasionally transit across the face of the Sun?
Mercury
Based on everything you have learned about the formation of our solar system, which of the following statements is probably not true?
Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation.
Assuming that our ideas about how ʺhot Jupitersʺ ended up on their current orbits are correct, why didnʹt 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.
All the following statements about known extrasolar planets are true. Which one came as a surprise to scientists who expected other solar systems to be like ours?
Some of the planets orbit their star more closely than Mercury orbits the Sun.
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.
You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every four 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 planetʹs ʺminimum massʺ?
The size of the Doppler shift that we detect depends on whether the planetʹs orbit is tilted.
Why is it so difficult to take pictures of extrasolar planets?
Their light is overwhelmed by the light from their star.
Why are many of the newly detected extrasolar planets called ʺhot Jupitersʺ?
Their masses are similar to Jupiter but they are very close to the central star and therefore hot.
Current evidence suggests that many massive jovian planets orbit at very 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, weʹve found very 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.
How much brighter is a Sun-like star than the reflected light from a planet orbiting around it?
a billion times brighter
In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star?
a massive planet that is close to its star
What is an extrasolar planet?
a planet that orbits a star that is not our own Sun
Approximately how many other planetary systems have been discovered to date?
a thousand
The first planets around other Sun-like stars were discovered
about a decade ago
By itself, the Doppler technique provides a measure of a planetʹs
all of the above
Which detection techniques can find the planetʹs orbital distance (assuming we know the mass of the star)?
all of these techniques
Most of the planets discovered around other stars
are more massive than Earth and orbit very close to the star.
The transit method of planet detection works best for
big planets in edge-on orbits around small stars.
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 starʹs spectrum
Which of the following methods has not yet detected planets around other stars?
detection of reflected light by the planet
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
When is the soonest we are likely to have images and spectra of Earth-like planets around other stars?
in a decade or two, through space missions now in the early planning stages
Which of the following is not expected for a ʺhot Jupiterʺ that orbits 0.05 AU from its star?
intense volcanism
Suppose a planet is discovered by the Doppler technique and is then discovered to have transits. In that case, we can determine all the following about the planet except
its rotation period
Based on available data, what kind of objects in our solar system do most of the known extrasolar planets resemble?
jovian planets
The astrometric technique of planet detection works best for
massive planets around nearby stars.
What is astrometry?
measuring the positions of the stars on the sky
What is the closest that extrasolar planets have been found to their stars?
nearer to their stars than Mercury to our Sun
In essence, most of the extrasolar planets discovered to date have been found by
observing a star carefully enough to notice that it is experiencing a gravitational tug caused by an unseen planet.
What do models suggest make up the clouds on ʺhot Jupitersʺ?
rock dust
The composition of a planet can be determined by
spectra
The size and shape of a planetʹs orbit can be determined by
the Doppler technique
The composition of a planetʹs 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 shape of the periodic velocity pattern tells us
the orbital eccentricity of the planet.
A planet is detected via the Doppler technique. The repeating pattern of the stellar motion tells us
the orbital period of the planet.
What information does the Doppler technique give about an extrasolar planet?
the planet's minimum mass
The depth of the dip in a starʹs brightness due to the transit of a planet depends most directly on
the planet's size
A planet is detected via the Doppler technique. The velocity change of the star is a measure of
the planetʹs mass and orbital distance.
Which planet search technique is currently best suited to finding Earth-like planets?
transit
