(CNN) -- NASA scientists revealed Friday a first-of-its-kind image from space showing reflecting sunlight from a lake on Saturn's largest moon, Titan.
It's the first visual "smoking gun" evidence of liquid on the northern hemisphere of the moon, scientists said, and the first-ever photo from another world showing a "specular reflection" -- which is reflection of light from an extremely smooth surface and in this case, a liquid one.
"This is the first time outside Earth we've seen specular reflection from another liquid from another body," said Ralf Jaumann, a scientist analyzing data from the Cassini unmanned space probe.
Jaumann said he was surprised when he first saw the photos transmitting from Cassini, orbiting Saturn about a billion miles from Earth.
"It was great because if you look at photos of planets, you mostly see nothing is happening. But in two hours we saw a glint of light getting brighter."
Titan's similarities to Earth have attracted NASA's attention for decades. It's the only body besides our own in the solar system that is believed to have liquid on its surface. Like Earth, Titan has an atmosphere which is mostly nitrogen.
Experts believe the presence of liquid on a planet or moon improves the chances that some kind of life could develop there.
The photo comes from the spacecraft Cassini, which has been searching for this kind of reflection since it began circling Saturn in 2004.
Scientists with the University of Arizona were able to use previous data from Cassini to learn details about the reflection's location on Titan.
The glint appears to be coming from the southern edge of a lake called Kraken Mare -- a massive body of methane that covers about 150,000 square miles (400,000 square kilometers). That's larger than the Caspian Sea, which is the largest lake on Earth.
The hunt for the specular reflection took five years, NASA said, because the moon's northern half had been shrouded in winter darkness.
"Next, we want to find out more about Titan's liquid," said Jaumann. "Do we have some kind of weather there? Do we have changes with seasons? Does it rain? How does the liquid methane run across the surface?"
But Jaumann sounded a note of caution regarding the prospect of life in this case.
"The temperature on Titan's surface is something like minus-180 degrees Celsius," he said. "That means it's very cold. But you never know."
The project is based out of NASA's Jet Propulsion Laboratory in Pasadena, California.
This is not the first evidence of liquid on Titan. In 2008, project members used infrared technology to discover a large lake in the moon's southern hemisphere.
But this recent discovery is a sure sign that liquid exists on the moon's northern half. That region is believed to include larger basins that could hold more liquid.
The historic image shows a telltale bright reflection

NASA have revealed that a flyby of its probe Cassini past Titan, a moon of Saturn, has produced a historic image: the first photograph showing liquid on a world other than our own.

The picture shows a "specular reflection" from an extremely smooth surface, in this case a liquid. Cassini has been trying to spot one since arriving in 2004, and in 2008 used infrared data to prove that there were liquid methane lakes down there. The northern hemisphere has only been visible since August 2009, as before then it was covered by winter weather. Most of Titan's lakes are in the north.

"This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness. It’s an unsettling combination of strangeness yet similarity to Earth," said Bob Pappalardo, a Cassini scientist with NASA's Jet Propulsion Laboratory. Titan's atmosphere is, like Earth's, mainly nitrogen, but temperatures on the icy world are around -180°C. This reduces the prospect of life, although the presence of liquid does increase the likelihood.

The lake seen in the photograph is called Kraken Mare, and at 150,000 square miles (400,000 square kilometers), it isn't the largest basin on north Titan, but it is bigger than the Earth's biggest lake, the Caspian Sea.

Ralf Jaumann, another Cassini scientist, spoke of the team's hopes for the future. "Next, we want to find out more about Titan's liquid. Do we have some kind of weather there? Do we have changes with seasons? Does it rain? How does the liquid methane run across the surface?"

A team of scientists are due to propose to NASA that the agency drop a boat into a Titan lake, with Kraken Mare and the similarly sized Ligeia Mare being hot candidates. The Titan Mare Explorer (TiME) is projected to be relatively low-cost at US$400 million and would investigate the composition, density and shape of a Titan lake. If launched in 2016 it could arrive in 2023 and spend several years floating on the moon. However, several other projects are also keen to get themselves the next opportunity NASA is offering for the launch of a new project other than its own.