21 (4)

Question 1

If we can determine the …….. of the star, the transit method tells us the ……… of the planet.

Answer 1

size

Question 2

The amount of light the planet blocks, called the ………. ………

Answer 2

transit depth

Question 3

transit depth is given by:

Answer 3

The area of a circle is πR²

Question 4

Answer 4

R 2

Question 5

The Doppler method allows us to estimate the …….. of a planet. If the same object can be studied by both the Doppler and transit techniques, we can measure both the ……… and the ……….. of the exoplanet.

Answer 5

mass / mass / size

Question 6

knowing the mass and the size is a powerful combination that can be used to derive the average ……… (mass/volume) of the planet.

Answer 6

density

Question 7

Transiting planets reveal such a wealth of information that the French Space Agency (CNES) and the European Space Agency (ESA) launched the …………. space telescope in 2007 to detect transiting exoplanets.

Answer 7

CoRoT

Question 8

CoRoT discovered 32 transiting exoplanets, including the first transiting planet with a size and density similar to Earth. In 2012, the spacecraft suffered an onboard computer failure, ending the mission. Meanwhile, NASA built a much more powerful transit observatory called ………….

Answer 8

Kepler

Question 9

(after kepler failure in 2013) A new NASA mission called …………………… is now carrying out a transit survey of the nearer (and therefore brighter) stars all over the sky.

Answer 9

TESS (Transiting Exoplanet Survey Satellite)

Question 10

What do we mean, exactly, by “discovery” of transiting exoplanets? A single transit shows up as a very slight drop in the brightness of the star, lasting several hours. However, astronomers must be on guard against other factors that might produce a false transit, especially when working at the limit of precision of the telescope. We must wait for a second transit of similar depth. But when another transit is observed, we don’t initially know whether it might be due to another planet in a different orbit. The “discovery” occurs only when a ………… transit is found with similar depth and the same spacing in time as the first pair.

Answer 10

third

Question 11

the Kepler mission also has a program in which non-astronomers—……….. ……….—can examine the data.

Answer 11

citizen scientists

Question 12

One of the most convincing ways to verify that a dip in brightness is due to a planet is to find more planets orbiting the same star—a planetary system. Multi-planet systems also provide alternative ways to estimate the …………. of the planets,

Answer 12

masses

Question 13

………. …….. works best for young gas giant planets that emit infrared light and reside at large separations from their host stars.

Answer 13

Direct imaging

Question 14

Since 2008 (first three found stars), a number of planets around other stars have been found using direct imaging.

However, one challenge is to tell whether the objects we are seeing are indeed planets or if they are ……….. ………… in orbit around a star.

Answer 14

brown dwarfs (failed stars)

Question 15

Direct imaging is an important technique for characterizing an exoplanet.

1. The brightness of the planet can be measured at different wavelengths. These observations provide an estimate for the …………. of the planet’s atmosphere;
2. ……….. can also be obtained from the faint light to analyze the atmospheric constituents, such as hydrogen-rich atmosphere or with evidence of methane

Answer 15

1. temperature
2. Spectra

Question 16

the “discovery space” for Kepler was limited to planets with orbital periods less than ……… days and sizes larger than ……….

Answer 16

400 / Mars

Question 17

The most common planets have radii between 1.4 and 2.8 that of Earth, sizes for which we have no examples in the solar system. These have been nicknamed ……………., while the other large group with sizes between 2.8 and 4 that of Earth are often called ……………

Answer 17

super-Earths / mini-Neptunes.

Question 18

recall that really small planets were difficult for the Kepler instruments to find. So, to estimate the frequency of Earth-size exoplanets, we need to correct for this sampling bias.

Answer 18

We see that the most common planet sizes of are those with radii from 1 to 3 times that of Earth—what we have called “Earths” and “super-Earths.”

Question 19

Comparing the average density of exoplanets to the density of planets in our solar system helps us understand whether they are ………… or ………… in nature.

Answer 19

rocky / gaseous

Question 20

A key observation so far is that planets that are more than 10 times the mass of Earth have ……….. ………. envelopes (like Uranus and Neptune) whereas lower-mass planets are predominately ………… in nature (like the terrestrial planets).

Answer 20

substantial gaseous / rocky

Question 21

for the highest mass planets (M > 1000 M_Earth) in Figure 21.25, notice that the radius stops increasing and the planets with greater mass are actually smaller. This occurs because increasing the mass also increases the …………. of the planet, so that compressible materials (even rock is compressible) will become more tightly packed, shrinking the size of the more massive planet.

Answer 21

gravity

Question 22

Often, the first step in understanding something new is to ………. …………. the range of possibilities. This sets the stage for refining and deepening our knowledge.

Answer 22

narrow down

Astronomers who work on the complex modeling of the interiors of rocky planets make the simplifying assumption that the planet consists of two or three layers. This is not perfect, but it is a reasonable approximation and another good example of how science works.

Question 23

Why do some gas giant planets have inflated radii that are larger than the fictitious pure hydrogen planet?

Answer 23

Many of these planets reside in short-period orbits close to the host star where they intercept a significant amount of radiated energy. If this energy is trapped deep in the planet atmosphere, it can cause the planet to expand.

Question 24

The first planetary system was found around the star ……….. …………. in ……… using the Doppler method,

Answer 24

Upsilon Andromedae / 1999