Question 1

In the searches so far, only about 1 in 10 stars show evidence for planets around them.

Accepted Answer

According to the current searches, only around 1 in 10 stars have been found to have planets around them.

Question 2

Describe the impact the discovery of extrasolar planets has had for understanding the origin of our own Solar System.

Accepted Answer

The answer of Describe the impact the discovery of extrasolar...

Question 3

Why is it so difficult to make a direct image of a planet around another star?

Accepted Answer

The answer of Why is it so difficult to make...

Question 4

Briefly describe the three most commonly used methods of indirect planet detection.

Accepted Answer

The answer of Briefly describe the three most commonly used...

Question 5

Astronomers have discovered more extrasolar planets around other stars than the number of planets in our own Solar System.

Accepted Answer

As of October 2021, over 4,000 confirmed exoplanets have been discovered, while there are only 8 planets in our Solar System (not including Pluto).

Question 6

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

Accepted Answer

When a planet passes between its star and an observer, it blocks out a portion of the star's light. The amount of light blocked can be measured and used to determine the planet's size, among other characteristics. This method is known as the transit method.

Question 7

You have observed the wobble in the velocity curves of two otherwise identical stars. Star A has a period of 6 months and Star B has a period of 1 year. What can you say about these stars?

Accepted Answer

The period of the wobble in the velocity curve is related to the distance between the star and its orbiting planet. Since Star A has a shorter period than Star B, its planet must be closer to it. Therefore, we can say that Star A's planet must be closer than Star B's planet. We cannot determine the mass of the planets or whether Star B has a planet like Earth based on this information alone.

Question 8

A star is seen to have two transiting planets. Planet 1 transits every 3 months, and Planet 2 transits every 15 months. What can we infer about their orbits?

Accepted Answer

The orbital period of a planet (the time it takes to complete one orbit around its star) is directly related to the size of its orbit, as described by Kepler's third law of planetary motion. A longer orbital period, such as that of Planet 2 (15 months), indicates that it has a larger semimajor axis compared to Planet 1, which has a shorter orbital period of 3 months. This means Planet 2 is further from the star than Planet 1.

Question 9

The star Rho Cancri B has about the same mass as our Sun, and the planet discovered around it orbits somewhat closer than Mercury orbits our Sun. The mass of the planet is estimated to be 1.1 times the mass of Jupiter. Why, according to our theory of solar system formation, is it surprising to find a planet the size of Rho Cancri B's planet orbiting at this distance?

Accepted Answer

The answer of The star Rho Cancri B has about...

Question 10

Planetary masses measured using the Doppler technique are lower limits to the possible planetary mass.

Accepted Answer

This is because the Doppler technique measures the reflex motion of the star caused by the gravitational pull of the orbiting planet. The measured velocity amplitude is related to the planet's mass, but only if we know the inclination of the planet's orbit relative to our line of sight. If the orbit is close to face-on, the true mass of the planet will be larger than the measured mass, while if the orbit is close to edge-on, the true mass will be close to the measured mass. Therefore, the measured mass represents a lower limit to the true mass.

Question 11

Indirect detection of an extrasolar planet means .

Accepted Answer

Indirect detection methods, such as radial velocity or transit observations, involve observing the planet's effect on its host star. This can reveal information about the planet's mass, orbit, and even atmospheric composition without directly imaging the planet itself. Sending a space probe to the planet (A) would be a direct detection method, while seeing the planet with the naked eye (C) or acquiring images or spectra of the planet (D) would also be direct detection methods that are currently beyond our technological capabilities for most extrasolar planets.

Question 12

Which new idea has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?

Accepted Answer

The discovery of extrasolar planets has shown that some planets can migrate from their birthplace orbits to new ones, which has led to the addition of this idea to our theory of solar system formation.

Question 13

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

Accepted Answer

A planet's orbit can change due to gravitational interactions with other planets or objects, tidal forces from the star, or other factors.

Question 14

What would happen to the planets in a solar system where the central star did not have a strong wind?

Accepted Answer

A strong wind from the central star helps to remove any excess gas and dust from the solar nebula, allowing planets to continue to grow through accretion without migrating inwards. Without this wind, the planets would experience drag from the gas in the nebula, causing their orbits to migrate inward over time.

Question 15

The astrometric technique of planet detection works best for

Accepted Answer

The astrometric technique involves measuring the small changes in a star's position due to the gravitational pull of an orbiting planet. This method works best for massive planets (Jupiter-like) around nearby stars because their gravitational influence on the star is stronger and easier to detect. Large planets (those with a large radius but low mass) do not necessarily have a strong enough gravitational pull to produce a measurable effect on the star's position. Also, detecting planets around distant stars is more challenging because their positions are harder to measure accurately.

Question 16

The Doppler technique can be used to measure the orbital period of a planet by

Accepted Answer

The Doppler technique, also known as the radial velocity method, measures the star's line-of-sight velocity by analyzing the star's spectrum. As a planet orbits a star, it causes the star to move slightly towards and away from the observer, causing a periodic Doppler shift in the star's spectrum. By measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, we can determine the orbital period of the planet.

Question 17

The majority of planets are estimated to be gas giants.

Accepted Answer

The majority of planets, especially in our galaxy, are believed to be terrestrial or rocky planets, as gas giants are less common.

Question 18

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

Accepted Answer

The Doppler technique, while effective in detecting exoplanets, is more sensitive to large, Jupiter-sized planets close to their stars and has difficulty detecting small, Earth-like planets due to their lesser gravitational effect on their host stars.

Question 19

You are observing the wobble of a star caused by the orbit of a planet around that star. Which property of this system listed below most significantly affects the period of that wobble?

Accepted Answer

The period of the wobble is directly proportional to the square root of the planet's orbital radius. This means that as the planet's orbital radius increases, the period of the wobble also increases. The planet's mass, on the other hand, has a much smaller effect on the period of the wobble.

Question 20

Extrasolar planets have been discovered with average densities similar to

Accepted Answer

Extrasolar planets, also known as exoplanets, exhibit a wide range of average densities, reflecting their diverse compositions and structures. Some have densities similar to water, indicating they may be largely composed of ices or fluids. Others have densities comparable to iron, suggesting a predominantly metallic composition. There are also exoplanets with very low densities, akin to that of styrofoam, which implies they are gas giants with large atmospheres and possibly small cores. This diversity in exoplanet characteristics underscores the variety of planetary systems in our universe.

Quiz 10: Other Planetary Systems: the New Science of Distant Worlds