Scientists say they have discovered hints of alien life on the Saturn's
moon. The discovery of a sort of life was announced after researchers at the U.
S. space agency, NASA, analyzed data from spacecraft Cassini, which pointed to
the existence of methane-based form of life on Saturn's biggest moon.
Scientists have reportedly discovered clues showing primitive alien
beings are "breathing" in Titan's dense atmosphere filled with
hydrogen. They argue that hydrogen gets absorbed before hitting
Titan's planet-like surface covered with methane lakes and rivers. This, they
say, points to the existence of some "bugs" consuming the hydrogen at the
surface of the moon less than half the size of the Earth. "We
suggested hydrogen consumption because it's the obvious gas for life to consume
on Titan, similar to the way we consume oxygen on Earth," says NASA scientist
Chris McKay. "If these signs do turn out to be a sign of life, it would be
doubly exciting because it would represent a second form of life independent
from water-based life on Earth. " To date, scientists have not
yet detected this form of life anywhere, though there are liquid-water- based
microorganisms on Earth that grow well on methane or produce it as a waste
product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees
Farenheit), a methanebased organism would have to use a substance that is liquid
as its medium for living processes, but not water itself. Water is frozen solid
on Titan's surface and much too cold to support life as we know it.
Scientists had expected the Sun's interactions with chemicals in the
atmosphere to produce a coating of acetylene on Titan's surface. But Cassini
detected no acetylene on the surface. The absence of detectable
acetylene on the Titan's surface can very well have a non-biological
explanation, said Mark Allen, a principal investigator of the NASA Titan
team. "Scientific conservatism suggests that a biological
explanation should be the last choice after all non-biological explanations are
addressed," Allen said. "We have a lot of work to do to rule out possible
non-biological explanations. It is more likely that a chemical process, without
biology, can explain these results."
单选题
What do scientists claim to have found about Saturn?
A. Water-based life on it.
B. Methane-based life on its biggest moon.
C. A new moon moving around it.
D. Earthlike life on its biggest moon.
【正确答案】
B
【答案解析】[解析] 根据第一段最后一句话“pointed to the existence of methane-based form of life on Saturn's biggest moon.”可知，正确答案为B。
单选题
Which of the following statements about Titan is true?
A. It is as large as the Earth.
B. There is acetylene on its surface.
C. Water on it acts as a life supporting medium.
D. Hydrogen consumption is reported to be on it.
【正确答案】
D
【答案解析】[解析] 根据第三段第一句话“They argue that hydrogen gets absorbed before hitting Titan's planet-like surface covered with methane lakes and rivers.”可知，正确答案为D。
单选题
The expression "this form of life" in paragraph 5 refer to?
A. Water-based life.
B. oxygen-based life.
C. Methane-based life.
D. Liquid-based microorganisms.
【正确答案】
D
【答案解析】[解析] 根据第五段第一句话“To date, scientists have not yet detected this form of life anywhere, though there are liquid-water-based microorganisms on Earth”可知，此处的生命形式指代的是地球上的liquid-water-based microorganism．所以正确答案为D。
单选题
It can be inferred from Mark Allen's address that ______.
A. Scientists are trying to confirm these is life on Titan
B. Scientists agree that a chemical process is a convincing
explanation
C. Scientists share the opinion that a biological explanation is
reasonable
D. Scientists are arguing over whether there is life on Titan