When the first planets outside our Solar System were discovered recently, it was an epochal event. But last month, a team of astronomers was able to identify and analyze the atmosphere encircling a planet trillions of kilometers from Earth. The planet is a giant, about one third larger than Jupiter.

To find out more, VOAs Adam Phillips interviewed Robert Naeye, the editor of "Mercury Magazine," at the Astronomical Society of the Pacific and the author of two books "Signals from Space" and "Through the Eyes of Hubble." Mr. Naeye began by explaining why this latest development has stargazers so excited.

Robert Naeye: Over the last six or seven years, astronomers have discovered nearly eighty planets orbiting other stars. But in terms of the chemical composition and physical nature of the planets, we really know very little about them.

So what this recent discovery was was, using the Hubble telescope a team of American and Canadian astronomers discovered sodium gas in the atmosphere of this planet, which orbits a star very similar to the Sun. The sodium is just a very very small part of the planet's atmosphere. This particular planet, every few days, passes in front of the star. It's an event astronomer call 'transits.' In other words, from our line of sight, we see the planet moving across the disk of the star blocking some of the light from the star.

What happens is that some of the starlight passes through the atmosphere of this planet. And, as it does so, some of this light is absorbed by atoms of sodium in the planet's atmosphere. So by using the Hubble Space Telescope, they were able to detect a characteristic wavelength of sodium kind of like a fingerprint for the element sodium.

Adam Phillips:Can you tell me in kilometers how far away this planet and its sun are?

Naeye: Yeah. The planet is about six or seven million kilometers from the star. And that might seem very far away. But you have to remember that the Earth is about 150 million kilometers from the Sun.

The planet and star, from Earth, are about one hundred and fifty light years away. So we are detecting this incredibly faint event where this little planet is passing in front of a big star blocking maybe one and a half percent of the star's light every few days. And it really is a pretty amazing technical accomplishment.

Phillips:Is the excitement that this discovery has generated a celebration of our technical prowess, or is there something actually useful about this that it is so far away and we've been able to see it?

Naeye: I would say that the real significance of this discovery isn't so much that sodium was detected. You know, the planet itself is not hospitable to life. It's too hot. It's too big; in the wrong place [and] in the wrong orbit.

But eventually, astronomers are going to be finding planets much more like Earth, planets the same size as Earth at about the same distance from their stars that Earth is from the Sun. And there still is this great question: how common is life in the universe? and whether Earth is one of maybe billions of planets in our galaxy alone that harbor life, or whether Earth is very precious and unique. It is a very profound question that gets at the very heart of our origins and who we are. And I think it's possible, using techniques similar to the one used to find sodium in this planet's atmosphere, that within a reasonable time frame, maybe twenty years from now, we'll start to be answering this very profound question.