WHAT'S OUT THERE? JUST DO THE MATH
Astronomers have recently found planets orbiting stars other than our sun (exoplanets) that could be similar to Earth. Studying these planets will provide clues to how Earth itself formed and evolved. Are there natural environments like the Earth's? How many might there be? Ben R. Oppenheimer, chairman of the Department of Astrophysics, American Museum of Natural History, provides estimates from the latest science. Just fill in the blanks.
1. Our sun is one of about 200 billion stars in the Milky Way, but it is not typical. In fact, only about 5 percent of stars are similar in mass and luminosity to the sun. There are ____ stars in the galaxy similar to our sun.
2. Recent results from NASA's Kepler space observatory indicate that 23 percent of sunlike stars have Earth-size planets in orbit around them. The maximum number of Earth-size planets orbiting sunlike stars in the galaxy is ____.
3. If 10 percent of those planets are at a similar distance from their suns as Earth is from its sun (so that the temperature range is right for liquid water to exist on the surface), there could be ____ Earth-like planets in the galaxy.
4. There are 150 stars similar to the sun within 70 light-years of our solar system. Using the galaxy-wide percentages, we could expect ____ of them to host an Earth-like planet.
LIFE IN THE BALANCE: OUR WORLD AND OTHERS
It makes sense that NASA, the people behind the Kepler mission to find other potentially habitable planets, would pay attention to Earth Day (April 22). This year, scientists at NASA's Jet Propulsion Lab at the California Institute of Technology put together questions on planets beyond our solar system. To learn more, visit NASA's PlanetQuest Web site.
1. Man isn't the only threat to the planet. Which circumstance could end life on Earth?
a. The aging sun continues to heat up. In a billion years, Earth gets too hot, oceans evaporate, carbon dioxide disappears, plant life dies out.
b. A huge asteroid smashes into Earth, vaporizing vast swaths of the surface and permanently changing the atmosphere.
c. All of the above.
d. None of the above.
2. Mars once had running water that carved canyons and other features into its surface. What happened to the water?
a. Mars is just too far from the sun and too cold to sustain water.
b. Marsquakes caused all the water to seep into cracks in the crust.
c. An asteroid clobbered Mars and vaporized the water.
d. Most of Mars's atmosphere, and water, evaporated.
3. Earth isn't the only body in the solar system with rivers and lakes. Which other world has similar features?
a. Mercury (liquid lead)
b. Saturn's moon Titan (liquid methane)
c. Saturn (liquid oxygen)
d. Neptune's moon Triton (liquid ammonia)
4. Earth and Venus are rocky planets of about the same size, but Earth's average surface temperature is about 59° F (15° C), while Venus's is 1350° F (732° C), hot enough to melt lead or aluminum. Why the difference?
a. Venus has a stronger greenhouse effect than Earth has.
b. Venus is made of denser rock than Earth.
c. Earth is more geologically active than Venus.
d. Ice caps and oceans on Earth absorb energy from the atmosphere.
5. Earth is called a "Goldilocks planet" because:
a. The amount of land surface is not too big, not too small.
b. Its distance from the sun is "just right" for life.
c. It has bears on it.
d. Scientists don't refer to Earth this way.
6. Earth's magnetic field shields us from harmful solar wind and also helps Earth hold onto its atmosphere and water. To what do we owe this invisible protector?
a. The aurora borealis
b. Plate tectonics
c. Earth's circulating liquid metal core
d. Iron in Earth's crust
True or False
7. Earth is the only body in the solar system thought to have oceans of liquid water.
8. Earth is smack in the middle of the "habitable zone" around the sun, where temperatures are right for liquid water to exist.
9. Exoplanets that have lots of volcanic activity and exist in systems with lots of asteroids are considered bad prospects for looking for extraterrestrial life.
10. Small, Earth-size planets are a rarity in the galaxy.
GO TO ANSWERS.
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