Gilmer Free Press

Stargazing - 06.21.12

The planet Mercury is peeking into view quite low in the west-northwest as the sky begins to darken.

It looks like a bright star, but it is so low that it’s tough to find. Tonight, Mercury is a little to the upper right of the crescent Moon.

Moon and Mercury

No probe has ever drilled into the core of Mercury. In fact, no probe has ever even landed on the planet. Even so, scientists have looked all the way to Mercury’s center. The view is still a bit blurry, but it’s revealed the likely layout of the solar system’s smallest planet.

Scientists have pieced together the picture of Mercury’s interior from several sources. They’ve looked at small “wobbles” in the planet’s rotation recorded by radio telescopes. And they’ve measured the planet’s gravitational and magnetic fields with two spacecraft — Mariner 10 in the 1970s, and Messenger, which is orbiting Mercury now.

These readings show that Mercury’s core accounts for about 85% of the planet’s diameter — almost twice the size of Earth’s core.

It probably consists of three layers. The outer layer is solid, and is made of iron and compounds of sulfur. The middle layer is probably molten iron and nickel. And the inner layer is probably solid iron and nickel. As the planet rotates, the layers spin at different rates, generating a weak magnetic field around the planet — and providing a peek into Mercury’s heavy heart.

And Mercury is peeking into view in the early evening. It’s quite low in the west-northwest as the sky begins to darken. It looks like a bright star, but it’s so low that it’s tough to find. Luckily, there’s a bright signpost to point the way tonight: the crescent Moon. Mercury is a little to the Moon’s upper right.