Astronomy chapter 13

The first planets around other Sun-like stars were discovered

about a decade ago

Approximately how many other planetary systems have been discovered to date?

a thousand

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

Which of the following methods has not yet detected planets around other stars?

detection of reflected light by the planet

Most of the planets discovered around other stars

are more massive than Earth and orbit very close to the star

How much brighter is a Sun-like star than the reflected light from a planet orbiting around it?

a billion times brighter

What is astrometry

measuring the positions of stars on the sky

By itself, the Doppler technique provides a measure of a planet’s

minimum mass, orbital radius, orbital eccentricity

Planets detected via the Doppler technique have been mostly

Jupiter-mass, in very close orbits

Current techniques can measure stellar motion to less than

walking speed

A planet’s density can be measured by combining

Doppler and transit observations

The composition of a planet can be determined by

spectra.

The size and shape of a planet’s orbit can be determined by

the Doppler technique

The astrometric technique of planet detection works best for

massive planets around nearby stars

The transit method of planet detection works best for

big planets in edge-on orbits around small stars

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 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.

Which planet can we see occasionally transit across the face of the Sun

Mercury

Which planet search technique is currently best suited to finding Earth-like planets?

gravitational lensing

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

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

A planet is detected via the Doppler technique. The repeating pattern of the stellar motion tells us

the orbital period of the planet.

A planet is detected via the Doppler technique. The shape of the periodic velocity pattern tells us

the orbital eccentricity of the planet

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

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 composition of a planet’s atmosphere be measured during a transit by analyzing

the excess absorption of starlight at specific wavelengths

What do models suggest make up the clouds on "hot Jupiters"?

rock dust

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 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.

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.

Viewed from afar, the transit of Earth would cause the Sun’s brightness to dim by approximately one part in

10,000

If every star had an Earth-like planet in an Earth-like orbit, how many could be detected by a transit?

1 in 200

Astronomers have discovered more planets around other stars than in our Solar System

true

Most of the planets discovered around other stars are more massive than Jupiter.

true

The Doppler technique for planet detection has found Earth-like planets around nearby Sun-like stars.

false

Planetary orbits that are face-on to our line of sight produce no Doppler shift in the stellar spectrum.

true

The density of a planet can be determined by combining Doppler and astrometric measurements.

false

A planet’s size can be determined by observing its transit across a star

true

Transits of multiple planet systems can be analyzed to infer planetary masses

true

Multiple-planet systems have been identified around other stars via the Doppler technique

true

Because we have not found another planetary system like our own, we can conclude that our Solar System must be quite unusual.

false

Once a planet forms in a disk-like nebula around a star, its orbit is fixed and will never change.

false

Multiple planets have been identified around other stars via the transit technique

true

The signature of a planet is largest in radial velocity measurements when the planet and star are lined up along the line of sight to the telescope

true

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.

true

The total amount of light from a star-planet system drops when the planet goes behind the star.

true

What is an extrasolar planet

a planet that orbits a star that is not our own Sun

About how many extrasolar planets have been discovered (as of 2008)?

between 100 and 1,000

As of 2008, most known extrasolar planets have been discovered by

the Doppler technique

What information does the Doppler technique give about an extrasolar planet

the planet’s minimum mass

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

Which detection techniques can find the planet’s orbital distance (assuming we know the mass of the star)?

doppler technique, transit technique, astrometric technique

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

What is the closest that extrasolar planets have been found to their stars

nearer to their stars than Mercury to our Sun

Based on available data, what kind of objects in our solar system do most of the known extrasolar planets resemble

jovian planets

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 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

How will the Kepler mission (scheduled for 2008 launch) look for planets around other stars?

It will look for slight changes in a star’s brightness that repeat at regular intervals

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

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.

Why is it so difficult to take pictures of extrasolar planets

Their light is overwhelmed by the light from their star

The astrometric technique looks for planets with careful measurements of a star’s

position in the sky

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.

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

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

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

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

Which of the following is not expected for a "hot Jupiter" that orbits 0.05 AU from its star?

intense volcanism

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

To date, we’ve 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

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

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.

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