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Ask Dr. Universe planets
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How do scientists know the mass and size of planets? – Lucy, 10, Illinois

Dear Lucy,

When I go to the veterinarian, they measure how big I am. They use a scale to check my weight. They find my length and height with a measuring tape.

But nobody can put a planet on a scale. Or wrap a measuring tape around it.

I asked my friend Katie Cooper about it. She’s a geologist at Washington State University. She studies our planet and other planets, too.

She told me we send satellites to orbit our solar system. When a satellite swoops around a planet, it snaps pics and takes measurements. Those images and measurements help scientists estimate the … » More …

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Besides telescopes and spaceships, how do we really know that there are other planets? – Ia, 12, Montana

Dear Ia,

I looked through a high-power telescope for the first time in college. I couldn’t believe how many stars I saw. It’s hard to imagine all the planets orbiting all those stars.

I talked about how we know those planets are out there with my friend Jose Vazquez. He’s an astronomer at Washington State University.

He told me that scientists look for planets outside our solar system using a number of instruments—like a photometer. That's a tool that attaches to a telescope and measures light.

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Dr. Universe: How were Saturn’s rings made? -Amelia, 9, Washington State

We still don’t know exactly how the rings around Saturn formed, but scientists who study Saturn’s rings have come up with a couple of ideas. One common theory many scientists agree upon is that Saturn’s rings are made from the little leftover pieces of what used to be a moon. My friend David Atkinson is really curious about the solar system and told me more about it. He is a graduate of Washington State University and now works at the NASA Jet Propulsion Laboratory. He also worked on the Cassini-Huygens space research mission which helped us learn more about Saturn, Saturn’s large moon Titan, and the entire Saturn system. Read More ...