The world's largest single-dish radio telescope is nestled deep in the lush green hills of Puerto Rico, where it performs tasks like searching for gravitational waves, listening for extraterrestrial signals and tracking asteroids that might be on a collision course with Earth.

But the outlook is increasingly faint for the Arecibo Observatory, which features a 1,000-foot-wide (305-meter-wide) dish used in research involving stars that led to a Nobel Prize.

Dwindling funds from the U.S. government and construction of bigger, more powerful telescopes in places like China and Chile are threatening the existence of the telescope even as a group of scientists campaigns to keep it open, saying it can still be used for important research.

"It's the most sensitive telescope on Earth, and that's a very good reason why we should keep funding it," said Robert Kerr, a former director at the observatory. "With that kind of power, I can hear an ant walking on the surface of Mars."

Each year the telescope draws about 90,000 visitors and some 200 scientists who come to do research. Cinema-goers have seen it in the Jodie Foster film "Contact" and the James Bond movie "GoldenEye."

Scientists use the facility, which resembles a giant satellite dish rather than a typical elongated, lens-based telescope, to detect radio emissions emitted by objects such as stars and galaxies — essentially, humanity's ear turned toward the cosmos.

The first hint the 53-year-old observatory was in peril came a decade ago, when a group of experts recommended it be shut down unless other institutions could help the U.S. National Science Foundation.

NASA now helps, but the Arlington, Virginia-based science foundation still pays two-thirds of the observatory's $12 million annual budget and has warned it cannot afford to keep operating the facility at a time when its overall budget is being squeezed.

"We don't have the funding to continue to support everything that people would like us to support," Jim Ulvestad, director of the foundation's astronomical sciences division, said by telephone.

The foundation is preparing an environmental impact statement, which Ulvestad said is done "whenever the federal government is considering a significant change to one of its facilities." Proposals include shutting down the observatory, suspending operations or transitioning to an education-based operation, which would lower the cost of running the telescope.

A decision is expected by mid-2017.

Government officials also have questioned the relevance of the observatory at a time when new telescopes are being built. One recently completed in southwestern China will take over the title of the world's largest single-dish radio telescope when it begins operations in September. And a cluster of radio telescopes was recently installed in northern Chile, where crews are building yet another telescope that will feature the world's largest digital camera.

During a U.S. congressional hearing this month, Ulvestad said the new telescope in Chile would do a better job than the Arecibo Observatory in identifying asteroids that might threaten Earth. He dismissed concerns that suspending or ending operations in Arecibo would put the planet in danger, noting that other telescopes also track asteroids.

However, Republican Rep. Dana Rohrabacher of California urged Ulvestad and other scientists to keep Arecibo open at least until the new telescopes actually start operating.

"What's really important is making sure our Earth isn't destroyed by some space object and all of us die," he said.

Scientists fighting to keep Arecibo open say it is still involved in key research.

The telescope searches for pulsars, which are the remains of stars that can be used to detect gravitational waves, a phenomenon Albert Einstein predicted in his theory of general relativity. It also searches for neutral hydrogen, which can reveal how other cosmic structures are formed.

"Arecibo is by far the most sensitive, detailed instrument that we have anywhere on the planet, existing or planned," said Anthony van Eyken, the observatory's interim director.

Scientists say that despite the new telescopes coming online, Arecibo would remain the world's largest radio telescope with planetary radar and the most sensitive one as well.

"Many secrets of the universe are very subtle and very dim and hard to pick out," Kerr said, "and the sensitivity is necessary to unfold the secrets of nature."