What’s Hot about Mercury?

Posted October 13th, 2008 by SkyGuy

The MESSENGER probe is circling Mercury right now. Why is it there? What’s so interesting about Mercury?

Special thanks to Amy Gahran for editing a great script and making it fun!

Planets are pretty cool.In fact, you’re on a planet right now! And so am I!

The Earth is one of eight major planets that make up our solar system. But all of the planets are really cool. So I’m going to start telling you more about them one by one.

Let’s start with the planet that’s closest to the Sun: Mercury.

David, age 10 from Los Angeles, wrote in to ask me: “I heard that right now we have a spacecraft flying around Mercury. What’s it doing there? What’s so hot about Mercury?”

It’s funny you say that, David, because Mercury is a really hot place! At least, half of it is, half of the time. It’s a pretty unusual planet, and it appears to do some weird stuff we don’t quite understand yet.

NASA’s Messenger mission to Mercury is a probe that was launched in August 2004 — more than four years ago. This is only the second time human beings have sent a probe to Mercury. The first was Mariner 10, which completed its mission in March 1975 — 33 years ago! I was just a little kid then!

Also, Mariner didn’t even get into orbit around Mercury. It just did a “fly-by” on its way to visit the outer planets. That’s kind of like driving by and waving instead of walking up to someone’s porch

So you could say that our neighbor Mercury was long overdue for a real visit. That’s why we sent Messenger on such a long trip.

But we’re not going to so much trouble and expense JUST to be neighborly.

Here’s one of the weirdest things about Mercury that scientists hope to learn more about: It shrunk!

By looking at features on Mercury’s surface, it’s pretty obvious that at some point this planet once was bigger than it is today. Scientists are very curious about this, since they didn’t think rocky planets COULD shrink! And since Earth is a rocky planet too, we’d kind of like to know how this can happen.

Over many years, astronomers have figured out that under Mercury’s rocky surface lies a thick layer or “mantle” of some kind of hot liquid material, maybe molten rock. But for a long time, scientists were pretty sure that since Mercury is SO small (in fact, it’s the smallest planet in our solar system), it should have cooled down WAY too quickly for it to have a molten mantle.

And under that mantle, in the middle of Mercury, is a spinning iron ball (called a “core”) which gives Mercury a weak magnetic field. Scientists didn’t think Mercury could have a magnetic field. I’ll talk more about magnetic fields around planets in another episode of SkyGuy.

And of course, Messenger is taking lots and lots of pictures of Mercury. It’s also making very detailed maps of the entire planet. Remember, technology has improved a LOT since the 1970s, when the Mariner mission flew by Mercury. So Messenger’s pictures will be much, much better than what we had before! Also, Mariner was only able to get pictures of less than half of Mercury. This time, we’re going to see what the entire planet looks like.

One more weird thing about Mercury: Even though this planet is so close to the sun that some places on its surface can get as hot as 800 degrees F, some scientists think there might actually be ice there, too! Can you imagine that? How could that happen? Well, there are craters on Mercury that are in permanent shade. It’s possible that ice formed there. We’ll see…

What do you think is interesting about Mercury? Just go to SkyGuy.com for October 13, 2008 and post a comment.

In the next SkyGuy video, I will talk about Venus. Before you see that video, however, think about this question: what is the hottest planet in the solar system?

Offical MESSENGER site

5 Responses to “What’s Hot about Mercury?”

  1. Dave

    Hey Skyguy, here’s a Mercury question for you. Which came first, the naming of the planet, the element or the god?

    Thanks for another great episode!

  2. SkyGuy

    Hey, that’s a good question, Dave. I think the name would come first, since the names come from Greek/Roman mythology. However, it’s definitely something I’ll have to investigate.

  3. Amy Gahran

    Honey, I shrunk the planet!


  4. Michelle @Everyday Celebrating

    How cool is this?????
    Heard about it on HARO.
    I’ve got a 2 year old that points out the moon every night and talks about space. We’re definitely going to be following! Thanks!

  5. Tom

    Another HARO member. Very nice site. I’ll be sure to spread the word. Keep it up SkyGuy!

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