Exoplanets and Life in the Universe

1. Build a true sentence about the Kepler mission.

Answer: Kepler found planets by watching transits

Kepler discovered planets from the tiny dips as they transited their stars.

2. NASA's ____ space telescope, launched in 2009, used the transit method to discover thousands of exoplanets.

• Keplercorrect
• Hubble
• Voyager
• Cassini

The Kepler telescope stared at one patch of sky and found thousands of planets by their tiny transit dips.

3. Match each detection method to what it mainly reveals.

Answer: Transit method = Planet size; Radial velocity = Planet minimum mass; Direct imaging = An actual photo of the planet

Different methods measure different things about a planet.

4. In the transit method of finding exoplanets, what does an astronomer actually measure?

• A small, regular dip in the star's brightness
• A shift of the whole star to a red colour
• Radio pulses bouncing off the planet
• The planet's gravity bending starlight into a ring

When a planet crosses in front of its star it blocks a little light, so the star's brightness dips slightly and regularly.

5. Which statements about exoplanet detection are correct? (Choose all that apply.)

• The transit method reveals a planet's radiuscorrect
• Radial velocity reveals a planet's minimum masscorrect
• Direct imaging favors young, bright, widely separated giants
• The transit method works no matter how the orbit is tilted

Each method has its strength, but transits require the orbit to be edge-on to our line of sight.

6. The radial velocity method usually gives only a lower limit on a planet's mass, because the tilt of its orbit is unknown.

Answer: True

We measure mass times the sine of the orbit's inclination, so without the tilt we only get a minimum mass.

7. Build a true sentence about a possible ocean world.

Answer: Europa may hide a liquid ocean

Under its icy shell, Europa probably holds a global ocean of liquid water.

8. Tardigrades, tiny animals also called water bears, have survived being exposed to the vacuum of space.

Answer: True

Tardigrades can enter a dried-out state and have survived the vacuum and radiation of space in experiments.

9. Organisms that thrive in harsh places like boiling vents or acid pools are called ____.

• extremophilescorrect
• exoplanets
• meteorites
• constellations

Extremophiles are living things that do well in conditions that would kill most other life.

10. Match each extremophile to the extreme it loves.

Answer: Thermophile = Extreme heat; Halophile = Extreme salt; Psychrophile = Extreme cold

Each type is named for the harsh condition it survives.

11. Which of these are promising places to search for microbial life? (Choose all that apply.)

• Europa's subsurface oceancorrect
• The plumes of Enceladuscorrect
• Ancient wet environments on Marscorrect
• The blazing surface of the Sun

Water-rich moons and old Martian lakebeds could host microbes; the Sun's surface cannot.

12. In what year did the Cassini spacecraft discover the water plumes of Enceladus?

Answer: 2005 year

Cassini spotted the icy plumes of Enceladus in 2005, revealing an ocean world.

13. Which of these are genuine factors inside the Drake equation? (Choose all that apply.)

• The rate of star formationcorrect
• The fraction of stars with planetscorrect
• The lifetime of a communicating civilizationcorrect
• The temperature of the cosmic microwave background

Star formation, planets and civilization lifetime are Drake factors; the microwave background belongs to cosmology, not the equation.

14. The Drake equation gives one exact, certain number that all scientists agree on.

Answer: False

Several of its factors are very uncertain, so the equation gives a wide range of guesses, not one agreed answer.

15. In the Drake equation, the letter ____ stands for how long a civilization keeps sending detectable signals.

• Lcorrect
• N
• R
• fp

L is the average lifetime of a communicating civilization, one of the hardest values to guess.

16. How many separate factors are multiplied together in the Drake equation?

Answer: 7 factors

The Drake equation multiplies seven factors, from star formation rate to civilization lifetime.

17. In the Drake equation, the factor fp stands for the fraction of stars that...

• have planetscorrect
• are older than the Sun
• will explode as supernovae
• give off radio waves

fp is the fraction of stars that have their own planets, a value we now know is high.

18. Three of these are factors in the Drake equation. Which is the odd one out?

• The mass of the black hole at the galaxy's centercorrect
• The fraction of stars with planets
• The fraction of life-bearing worlds with intelligence
• The lifetime of a communicating civilization

The central black hole is not part of the Drake equation; the other three are real factors in it.

19. Build a true sentence about the Fermi paradox.

Answer: Fermi asked where the aliens are

The Fermi paradox is the puzzle of why we see no aliens even though they seem likely.

20. Which of these could count as evidence in the search for life beyond Earth? (Choose all that apply.)

• A biosignature gas like oxygen in a planet aircorrect
• An artificial narrow radio signal (a technosignature)correct
• A planet simply being very large
• A star simply being very bright

Biosignatures and technosignatures are real clues; size and brightness alone tell us nothing about life.

21. A technosignature is a possible sign of alien technology, such as an artificial radio signal.

Answer: True

Technosignatures are clues of technology, like radio broadcasts or giant structures, rather than signs of life itself.

22. A ____ is a sign of life, such as oxygen made by living things in a planet air.

• biosignaturecorrect
• technosignature
• constellation
• meteor shower

Biosignatures are chemical or other clues that living things are present, unlike technosignatures which point to technology.

23. Match each term to its meaning.

Answer: Biosignature = Sign of life; Technosignature = Sign of technology; Fermi paradox = Where is everybody?

These are the key ideas in the search for alien life.

24. In what year was the famous unexplained 'Wow!' radio signal detected?

Answer: 1977 year

In 1977 a SETI-style survey recorded a strong, brief signal so striking an astronomer wrote 'Wow!' beside it.

25. Build a true sentence about the habitable zone.

Answer: The habitable zone allows liquid water

In the habitable zone temperatures let water stay liquid.

26. Which statements about the habitable zone are correct? (Choose all that apply.)

• It is where surface liquid water is possiblecorrect
• Its location depends on the star's brightnesscorrect
• It is the same distance for every star
• It exists only around black holes

The zone is set by liquid-water temperatures and shifts with how bright the star is.

27. Around a small red dwarf, a habitable-zone planet is often tidally ____, keeping one face always toward the star.

• lockedcorrect
• spun
• melted
• flared

Close-in planets around red dwarfs tend to become tidally locked, so one side is always in daylight and the other in darkness.

28. Match each part of the habitable zone to what happens there.

Answer: Inner edge = Too hot, water boils away; Outer edge = Too cold, water freezes; Middle = Just right for liquid water

The zone runs from a hot inner edge to a cold outer edge.

29. Compared with the Sun, a hotter and more luminous star has a habitable zone that lies...

• farther out from the starcorrect
• closer to the star
• at exactly the same distance
• inside the star itself

A brighter star pours out more heat, so the zone where water stays liquid is pushed farther out.

30. The habitable zone of a hotter, brighter star lies closer to the star than the Sun's habitable zone does.

Answer: False

A brighter star heats space more strongly, so its habitable zone actually lies farther out, not closer.