James Green leads NASA's solar system exploration and astrobiology research. By clicking through these slides, you''ll see him explain which moons and planets in our solar system could have alien life and what leads NASA to believe that.

(Photo: Ted)

Mars

"We thought initially that is was moon-like and full of craters in a dead world. So about 15 years ago we started a series of mission to go to Mars and see if water existed on Mars in its past that changed its geology,” Green said. “We [have] to be able to notice that. And indeed, we started to be surprised right away. Our higher resolution images showed deltas and river valleys and gullies that were there in the past.”

Overall, NASA discovered an ancient ocean where water flowed rapidly for perhaps hundreds of millions of years. Grey material was found, and it was organics with carbon, hydrogen, oxygen and sulfur.

“So Mars in its past with a lot of water and perhaps plenty of time, could've had life, had that spark and could've grown. Is that life still there? We don't know that,” he said.

A few months ago, the fairytale came true. NASA announced to the world that they found liquid water in the craters.

(Photo: Ted)

Enceladus (Saturn's moon

"This object should be ice," Green said, explaining that it's outside of the traditional habitable zone.

But surprisingly, it's blasting sheets of water out into the solar system. Silicon particles have also been found.

"Where does the Silica come from? It must come from the ocean floor,” he said. “The tidal energy created by Saturn is pulling and squeezing this moon, melting that ice and creating an ocean. But it’s also doing that to the core. The only thing we can think of that does that here on Earth as an analogy are hydrothermal vents."

On earth, these hydrothermal vents are teeming with life.

"We believe because it has water and has had it for a significant period of time and because it has hydrothermal vents with the right organic material, it could be a place where life exists—and not just microbiol—because it has had time to evolve,” Green said.

(Photo: Ted)

Europa (Jupiter's moon)

Europa has an under the ice crust ocean and plumes of water spraying from the cracks of the southern hemisphere, just like Enceladus. But again, this moon is not in the traditional habitable part of the solar system.

“This is a fabulous set of discoveries because these moons have been in this environment like that for billions of years,” Green said. “Life started here on earth after about the first 500 million, and look where we are.”

(Photo: Ted)

Titan (Saturn's moon)

Lakes almost the size of the Black Sea have been found in some places. Methane has been found as well.

"If there's any place in the solar system where life is not like us, where the substitute of water is another solvent and it could be methane, it could be Titan,” Green said.

(Photo: Ted)

Observer

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Is there life beyond Earth in the solar system? NASA director of planetary science James Green says we don’t know yet, but that we’re “hot on the pursuit” and will answer that question in 10 years.

“The data that we’re receiving is really exciting in telling us, forcing us to think about this in new and exciting ways. I believe we’re on the right track…If we answer it, and it’s positive, then life is everywhere in the solar system. Just think about that—we might not be alone,” he said.

This prediction was said in a Ted Talk—given at TedTalks Live last November and just uploaded to Ted.com—where he details why NASA thinks they’re on the brink of of answering this question and where in the solar system alien life is most likely to live. You can find these planets and moons listed in the slideshow above along with his explanation as to why NASA believes they may have life.

It’s all about the ingredients needed for life: liquid water, energy and organic material.

“I have to tell you that early in my career when we looked at these three elements, I didn’t believe that they were beyond Earth for any length of time and in any real quantity,” he said during the talk. “Venus is way too hot—it’s got no water. Mars is dry and arid—it’s got no water. And beyond Mars, the water in the solar system is all frozen.”

He continued:

“But recent observations have changed all of that. It’s now turning our attention to the right places for us to take a deeper look and start to answer our life question. So when look out into the solar system, where are the possibilities?”

NASA Director Reveals the 4 Places Most Likely to Have Alien Life in Our Solar System

Mars

Enceladus (Saturn's moon

Europa (Jupiter's moon)

Titan (Saturn's moon)

Lakes almost the size of the Black Sea have been found in some places. Methane has been found as well.

"If there's any place in the solar system where life is not like us, where the substitute of water is another solvent and it could be methane, it could be Titan,” Green said.

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Mars

Enceladus (Saturn's moon

Europa (Jupiter's moon)

Titan (Saturn's moon)

Lakes almost the size of the Black Sea have been found in some places. Methane has been found as well. "If there's any place in the solar system where life is not like us, where the substitute of water is another solvent and it could be methane, it could be Titan,” Green said.

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Lakes almost the size of the Black Sea have been found in some places. Methane has been found as well.

"If there's any place in the solar system where life is not like us, where the substitute of water is another solvent and it could be methane, it could be Titan,” Green said.