This is planetary radio. Hello again everyone. I'm Matt Kaplan. If ET phoned home, could we eavesdrop on the conversation?

It's just possible that we already have.

Of course, we're talking about the search for extraterrestrial intelligence.

This week, Dan Werthheimer of SETI at home. for extraterrestrial intelligence.

This week Dan Werthheimer of SETI at home will have the unprecedented opportunity

to revisit some of the most promising possible sources of radio signals from beyond our solar system.

He talked with us just before beginning his trip to Puerto Rico and the great Iresibo

dish.

Emily Lautwala will answer a listener's question about just how far out into the universe

we can hear and how far we can be heard.

And later Bruce Betts will dish up another installment of What's Up, including, yes, another trivia contest.

By the way, don't forget our special guest on next week's show, Sir Arthur C. Clark.

Now, from somewhat less than a light year away, here's Emily's message.

Hi, I'm Emily Loch Duwala with questions and answers.

A listener asked, would a civilization 2 million light years away be able to detect us?

After all, they would see Earth as it was 2 million years ago before we were here.

And isn't it also possible that by scanning too far, we could detect a civilization

that is no longer there?

We gave this question to the Planetary Society's study coordinator, Tom McDonough.

It's quite true that a civilization 2 million light years away would not be able to detect our civilization.

2 million years ago was before the pyramids, before agriculture, even before Homo sapiens.

In fact, human-produced signals can only be detected within a distance of around 100 light years

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