Are we alone in the universe? Top NASA scientists say the answer is almost certainly no.

"I believe we are going to have strong indications of life beyond Earth in the next decade and definitive evidencein the next 10 to 20 years," EllenStofan,chiefscientist for NASA, said at a public panel Tuesday in Washington.

"We know where to look, we know how to look, and in most cases we have the technology," she said.

Jeffery Newmark, interim director of heliophysics at the agency put it this way: "It's definitely not an if, it's a when."

However, if visions of alien invasions are dancing in your head, you can let those go.

"We are not talking about little green men," Stofan said. "We are talking about little microbes."

Over the course of an hourlong presentation, NASA leaders described a flurry of recent discoveries that suggest we are closer than ever to figuring out where we might find life in the solar system and beyond.

For example, Jim Green, director of planetary science at NASA, cited a studythat analyzed the atmosphere aboveMars' polar ice caps and suggests that 50% of the planet's northern hemisphere once had oceans up to a mile deep, and that it had that water for a long period of time -- up to 1.2 billion years.

"We think that long period of time is necessary for life to get more complex," Stofan said.

She added that getting human field geologists and astrobiologists on Mars would greatly improve the chances of finding fossils of past life on our nearest planetary neighbor.

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NASA: We'll find alien life in 10 to 20 years