Leia o texto para responder às questões [...].

Life probably exists beyond Earth. So how do we find it?

Sara Seager, 47, is an astrophysicist whose specialty is exoplanets, namely all the planets in the universe except the ones you already know about revolving around our sun.

When Seager entered graduate school in the mid-1990s, we didn’t know about planets that circle their stars in hours or others that take almost a million years. We didn’t know about planets that revolve around two stars, or rogue planets that don’t orbit any star but just wander about in space. In fact, we didn’t know for sure that any planets at all existed beyond our solar system, and a lot of the assumptions we made about planet-ness have turned out to be wrong.

Today we have confirmed about 4,000 exoplanets. The majority were discovered by the Kepler space telescope, launched in 2009. Kepler’s mission was to see how many planets it could find orbiting some 150,000 stars in one tiny patch of sky — about as much as you can cover with your hand with your arm outstretched. But its ultimate purpose was to resolve a much more freighted question: Are places where life might evolve common in the universe or vanishingly rare, leaving us effectively without hope of ever knowing whether another living world exists?

Kepler’s answer was unequivocal. There are more planets than there are stars, and at least a quarter are Earth-size planets in their star’s so-called habitable zone, where conditions are neither too hot nor too cold for life. With a minimum of 100 billion stars in the Milky Way, that means there are at least 25 billion places where life could conceivably take hold in our galaxy alone — and our galaxy is one among trillions.

It’s no wonder that Kepler, which recently ran out of fuel, is regarded almost with reverence by astronomers. It’s changed the way we approach one of the great mysteries of existence. The question is no longer, “is there life beyond Earth?” It’s a pretty sure bet there is. The question now is, how do we find it?

The Kepler telescope was retired, but new telescopes promise dramatic improvement in the hunt. Until now, the search for extraterrestrial intelligence has focused on detecting an incoming radio signal. With increasing computational power and more sensitive telescopes, researchers are expanding the search to optical and infrared emissions, targeting the “technosignatures” of advanced civilizations. These could include laser pulses, polluting gases, or megastructures built around a nearby star to harness its energy.

No quarto parágrafo, a resposta inequívoca da missão Kepler à pergunta feita no parágrafo anterior é

A

embora se conheça em torno de 100 bilhões de estrelas, há poucas possibilidades de encontrar vida em galáxias distantes.

B

se nossa galáxia não tem planetas nem muito quentes nem muito frios, não há como haver vida fora da Terra.

C

se há inúmeras possibilidades de vida em nossa própria galáxia, pode haver infinitamente mais no universo.

D

não há necessidade de buscar no resto do universo o que pode ser encontrado em nossa própria galáxia.

E

há mais planetas do que estrelas, mas as chances de haver mais de um planeta do tamanho da Terra em nossa galáxia são pequenas.