This is planetary radio. Hi everyone, Matt Kaplan here with the latest edition of our show. The excitement is

rising as surely is a very bright Mars is rising in

the night sky. Five spacecraft on their way there and just a week till that

mysterious planet passes closer to us than it has in 50,000 years.

A fitting time to talk with someone who can provide a good sense of the 40-year history of Mars missions.

That's why former JPL director Dr. Bruce Murray will be our guest.

We'll find out from Bruce Betts why opera singers have nothing to do with asteroid impacts and Emily explains why we're lucky

enough to have an atmosphere circling Earth.

Let's take to the air. Hi, I'm Emily Lockwala with questions and answers. A listener asked, I've heard that the sun was smaller and hotter when it was young.

If this was true, wouldn't the Earth's oceans have evaporated?

It is true that the sun's luminosity has changed over the four and a half billion years of its life.

Current stellar formation models suggest that since the Sun was born, its luminosity has increased.

This increase in luminosity probably did have an effect on the early

atmospheres of all of the planets, but the terrestrial planets, which include Mercury,

Venus, Earth, and Mars, do not have their original atmospheres intact.

The first atmospheres on all of these planets were probably destroyed by a young and active

sun.

Scientists believe that just after a star forms from a cloud of gas and dust,

there is a phase called the T-Tory stage.

During the T-Tory stage, violent winds from the sun blew away the fragile atmospheres of light elements that formed around the

young planets, leaving balls of naked rock.

So where did our atmosphere and oceans come from?

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