"The chance that there's a planet like Earth out there with life on it is very high," Massachusetts Institute of Technology planetary science and physics Professor Sara Seager told the House Science Committee.
"The question is: Is there life near here, in our neighborhood of stars? We think the chances are good," she said, answering a question from Rep. Ralph Hall, R-Texas, who asked: "Do you think there's life out there, and are they studying us? And what do they think about New York City?"
Seager was one of three Ph.D.-credentialed witnesses prominent in a scientific field once considered speculative who testified at a hearing called "Astrobiology: The Search for Biosignatures in Our Solar System and Beyond."
A biosignature is a substance -- such as an element, molecule or even a phenomenon -- that provides scientific evidence of past or present life.
Seager studies gases on distant planets that might indicate life.
The others testifying were NASA astrobiologist Mary Voytek and science historian and astrobiologist Steven J. Dick of the Library of Congress.
Voytek and Dick also answered Hall's question.
"Whether they're looking at New York or some small town in Indiana, the diversity of life here and the way that we live our lives is phenomenal, and I think it goes all the way down from humans to microbes," Voytek said.
Dick said, "I think the guiding principle holds that what's happened here has happened elsewhere in our huge universe," the Washington Post reported.
The 90-minute hearing, called by committee Chairman Lamar Smith, R-Texas, brought praise and respect from Democrats in the room but partisan mockery from a Democratic campaign committee outside.
The Democratic Congressional Campaign Committee, which works to elect Democrats to the House, said GOP lawmakers were holding a hearing on "space aliens" rather than tackling issues such as immigration reform or a minimum-wage increase.
"No wonder the American people think this Republican Congress is from another planet -- they're more interested in life in space than Americans' lives," committee spokeswoman Emily Bittner said in a statement.
"Saying this Republican Congress has misplaced priorities is an understatement of galactic proportions," she said.
Seager, whose scientific research has earned her a MacArthur Foundation "genius grant," told lawmakers scientists now had the capacity to make a breakthrough.
"This is the first time in human history we have the technological reach to cross the threshold," she said in remarks quoted by Britain's Guardian newspaper.
The next-generation James Webb Space Telescope, scheduled for launch in 2018, and other advances are changing the search for alien life forms, she told lawmakers.
"If life really is everywhere, we actually have a shot at it," she said.
The Hubble Space Telescope, carried into orbit by a U.S. space shuttle in 1990, recently detected water in the atmospheres of five planets outside the solar system, two published studies reported by NBC News Tuesday indicated.
The testifying scientists appealed to lawmakers for funding, including investment in space telescopes designed to detect biosignatures.
The latest White House budget calls for $17.7 billion for NASA, a slight decrease from 2012.
"I know that funding is tough, but it's the best thing that you can do," said Voytek in remarks quoted by the Guardian.
"You've pretty much indicated [the discovery of] life on other planets is inevitable," Rep. Bill Posey, R-Fla., told the panelists. "It's just a matter of time and funding."