The Numbers Behind the Search: teacher key

Aliens and UFOs, grade 10 edition, written for 10th grade. The search for life beyond Earth runs on numbers: dips of 80 parts per million, wobbles of 9 centimeters per second, and an equation whose answer swings from one to a million. The figures show what can and cannot be known.

Read the book. Print this page for the key.

Questions and answers

1. About how much does an Earth-size planet dim a Sun-like star in a transit?
   • 1.7 percent
   • 80 parts per million (answer)
   • 13 percent
2. Why are small planets harder to find with the wobble method?
   • Earth moves the Sun only about 9 centimeters per second, which is very hard to measure (answer)
   • Small planets have no gravity
   • Small planets are too hot
3. What does the habitable zone tell scientists?
   • That a planet has life
   • The age of a star
   • Where liquid water could exist on a planet's surface (answer)
4. Why does the Drake equation give such a wide answer?
   • Many of its factors are poorly known and the uncertainty grows with each (answer)
   • It uses only one number
   • It was never written down
5. What was the Wow! signal?
   • A strong, narrow radio signal from 1977 that was never heard again (answer)
   • A flash seen by Kepler
   • A message that was decoded
6. What does declassified mean?
   • Destroyed
   • No longer secret (answer)
   • Lost

Words

• exoplanets: far-off planets
• spectrum: color bands
• habitable: livable
• atmosphere: a planet's air
• declassified: no longer secret