Two far-off planets are likely made of water,according to NASA's research.They're "unlike any planets found in our solar system".
The system they studied is called Kepler-138 because it's located within the field of vision of NASA's Kepler spacecraft.Researchers have known about the existence of three outer planets within the Kepler-138 system,but have only just discovered two of them are likely made out of water.
They also discovered evidence for a fourth planet that hadn't been described before.But the finding isn't as clear as it might seem.The scientists didn't directly discover water at planets Kepler-138 c and Kepler-138 d.Instead,they compared the sizes and masses of the planets to models for comparison.When doing so,they found that "up to half of their volume (体积) should be made of materials that are lighter than rock,but heavier than hydrogen or helium(氦)"
"We previously thought that planets that were a bit larger than Earth were big balls of metal and rock," said Bjorn Benneke,the study's co-author. "However,we have now shown that these two planets,Kepler-138 c and d,are quite different in nature and that a big part of their entire volume is likely made up of water."
The high temperatures on these planets mean they might be enveloped in an atmosphere of steam,according to NASA."The temperature in Kepler-138 d's atmosphere is likely above the boiling point of water,and we expect a thick atmosphere made of steam on this planet," Bjorn said. "Only,under that steam atmosphere there could possibly be liquid water at high pressure."
The "water worlds" are outside their star's habitable place—the area in which temperatures allow liquid water on the surface of a rocky planet,possibly supporting life.But the new planet described by the researchers,Kepler 138-e,does fall into that just-right area,according to the research.
(1)What does the author intend to do in Paragraph 2?
A
A
A.Add some background information.
B.Summarize the previous paragraphs.
C.Provide some advice for the readers.
D.Introduce a new topic for discussion.
(2)What do we know about Kepler-138 d from the text?
D
D
A.It is a little smaller than Earth.
B.It is heavier than a rock.
C.It is like a planet in the solar system.
D.It likely has high-pressure liquid water.
(3)Which of the following may exist life according to the text?
C
C
A.Kepler-138 c.
B.Kepler-138 d.
C.Kepler-138 e.
D.A fourth planet.
(4)How does the author support the theme of the text?
B
B
A.By using examples.
B.By stating study results.
C.By describing processes.
D.By making comparisons.