Planets: Top 10 Questions

December 2008

Thanks to Jason Barnes, Professor of Astrophysics at the University of Idaho; and Dr. Gary L. Bennett, retired scientist and program manager for NASA for the answers.

1: Why is Pluto not a planet anymore?

When we first discovered Pluto in 1930 we thought it was a planet because it was the brightest thing we found in that orbit. It turns out that in 1993 we started finding other, what seemed to be planets, about the same size as Pluto in similar orbits to Pluto. Instead of Pluto being the only planet in its part of the solar system, it turns out there are hundreds of icy planets in a big swarm. So like the asteroid belt, when the first asteroid was found, it was called a planet as well. As we found more and more planets that were in the same or similar orbits, we realized it wasn't a full planet itself, only a member of a swarm of minor planets. We find the same thing is true for Pluto; it's only the largest and brightest element of a larger swarm of what we call corporate belt objects. (From Jesse at Wapello Elementary School in Blackfoot.)

2: There are other galaxies, so are there other planets that sustain life?

What we do know right now is that there are at least 300 planets outside of our own solar system. Astronomers have detected these by various mechanisms, primarily looking at the wobble of the parent sun. Most of these planets are what have been described as super jupiters. They're much larger than our own planet Jupiter, and many of them are in weird positions, very close to their parent star. We're still looking for earth-type planets, and with the dust clouds that have been seen around some stars plus these planets that have been found, the odds are pretty good that we're going to find planets that are like the earth. As to other galaxies, those are a bit too far away for us to really tell anything, but there are at least 300 extra solar planets that have been discovered. (From Jennings in Mrs. McCamish Cameron's class at Cynthia Mann Elementary in Boise.)

3: What color are the planets?

Mercury looks a lot like the moon, based on the images that have been taken by the two spacecraft that have visited mercury. Mercury is the closest planet to the sun. Venus, at least in some of the images that came back from spacecraft, actually has a yellowish cast; that could be the result of how they processed the images because other images show it not quite looking like that. Perhaps it is because they wanted to show that it has sulfuric acid in the atmosphere. Our own planet is a beautiful blue and white. Mars has an orangish red color. Jupiter and Saturn have got bands, very colorful bands, and they're different colors. Saturn tends to be more yellow while Jupiter looks gray with a giant red spot. Uranus and Neptune are in the bluish range. Neptune is a beautiful blue, Uranus is a greenish-blue, and Pluto - we'll find out when the New Horizon spacecraft gets there (it may just be covered with ice). (From Andrew in Twin Falls, who is at home school.)

4: How is a planet formed?

Planets are thought to have been formed at the same time that stars are formed. Our sun was formed 4.5 billion years ago from the collapse of a giant cloud of gas and dust. As the gas and dust collapsed under its own gravity the planets formed out of a disk, a flat part of the formation process that's orbiting the sun and is very thin, and composed of dust and rocks. Slowly the dust and rocks grew on to bigger and bigger objects that became rocky planets like the earth and mars. (From Karl in Mrs. McCamish Cameron's class at Cynthia Mann Elementary in Boise.)

5: How hot is the sun?

It is believed that it is 6,000 degrees on the surface but at the center it's on the order of 15, perhaps 20, million degrees on the metric scale. Very hot, but at those temperatures it allows the nuclear fusion to occur, which gives us the light and the warmth that we need. (From James in Mrs. Rice's class at Millcreek Elementary School in Middleton.)

6: What is a meteor?

A meteor is an asteroid and as asteroids are flying around the inner solar system, they're on crazy, random orbits. Sometimes a asteroid crashes into earth and as it's flying through the atmosphere it burns up on the way through. When you look up and see a big flash of light, that's this little asteroid burning up in the earth's atmosphere and that's a meteor. (From Timmer in Mrs. Schweitzer's class at Riverside Elementary School in Boise.)

7: Is Planet "X" a planet or a moon?

We don't know much about Planet "X." in fact, at one point it was thought that perhaps there was another additional planet beyond Neptune. This was about 100 years ago. people looked for that planet and actually found Pluto. There is an idea that maybe there are additional planets further out in our solar system, but by looking at the orbits of the planets we do know about, if there were one out there, we'd be able to see it because the motion of the other planets would change just slightly. The planet Neptune was found and as predicted, people saw the orbit of Uranus change; they knew Neptune was there before they even saw it. Planet "X" was an idea we thought might be there, but we no longer feel that is true. (From Callan at the Northwest Children's Home Education Center in Lewiston.)

8: What is the coldest planet?

The coldest planet would be Uranus or Neptune; they are about the same temperature. They are so far out they only receive a small amount of the light we get on earth. (From Rachel in Mrs. Hunt's class at Cynthia Mann Elementary in Boise.)

9: Why does Saturn have rings around it?

We found rings around Jupiter, Saturn, Uranus and Neptune. There's even speculation that earth may have a ring early in its history. The rings appear to be a combination of things such as debris which the planets have collected and in many cases it may simply be the result of very small satellites that were in orbit around the planet, such as Saturn. They may have collided and broken apart and then the dust just got spread out and formed rings around the planet. Saturn has 19 rings around. We have a spacecraft there right now which is looking at the rings amongst other things. (From Audrey in Mrs. Woodall's class at Hayden Meadows Elementary in Hayden.)

10: How far away is the sun and the moon from Earth?

The moon is about 250,000 miles from the earth; if you were to walk around the earth that would be about 25,000 miles. So if you have to walk around the earth 10 times, the sun is farther away still. The sun is 93 million miles away. It's almost 400 times farther away than the moon is. (From Audrey at the Northwest Children's Home Education Center in Lewiston.)

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