Physics

Planetary paparazzo

NASA satellite snaps historic photographs of Mercury

April 20, 2011 at 6:31 pm

Hey, Mercury, say “cheese”!

Mercury via MESSENGER — MESSENGER’s closeup pictures of Mercury give scientists new views on craters large and small. The large, bright white spot in the photo is the Kuiper crater, 39 miles in diameter. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

We earthlings can now get a better look at the planet closest to the sun. Since March 29, NASA’s MESSENGER spacecraft has been beaming back to Earth images of Mercury — the first ever taken from within the tiny planet’s orbit.

The first photographs include glimpses of Mercury’s surface never before seen by spacecraft. The images also show a lot of small craters, which look like pits in the ground. (To make a crater, drop a baseball into a sandbox, remove the baseball, and note the impression it leaves behind.) Large craters form when giant rocks, like asteroids, smash into the planet. When such collisions happen, debris from the surface is thrown skyward and then falls to the ground, forming those other, smaller craters.

In MESSENGER’s first three days as a planetary paparazzo, the pics poured in, totaling about 1,500 by March 31. More than 1,000 photographs may sound like a lot, but MESSENGER is just getting warmed up.

Mapping Mercury — This MESSENGER image of Mercury shows named craters identified during previous spacecraft missions. The triangle-like formation in the bottom center of the image shows a part of Mercury’s surface not seen by spacecraft until MESSENGER began orbiting the planet. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

“That’s the barest hint of what we’ll have on a regular basis,” said lead scientist Sean Solomon, who works at the Carnegie Institution for Science in Washington, D.C. Over 12 months, MESSENGER will take more than 75,000 pictures. (On average, the spacecraft will take more than 200 photographs per day.)

On March 17, MESSENGER became the first spacecraft to orbit Mercury. This means that, like a moon, MESSENGER is held close to Mercury by the planet’s gravity. Gravity is a force of attraction that increases with more mass. The more mass, or amount of stuff inside something, the stronger the pull. Any two objects with mass, even you and your pencil, have gravity that pulls them toward each other. In the case of you and your pencil, the masses are too small for you to feel drawn together.

Gravity holds the solar system together. The sun’s gravity keeps Earth from flying off into the Milky Way, and Earth’s gravity keeps the moon and satellites nearby. Mercury doesn’t have a lot of mass, but it has enough to keep MESSENGER in the neighborhood. In 12 months, MESSENGER will make about 700 laps around Mercury.

The spacecraft left Earth on August 3, 2004. Since then, it has flown past Mercury three times, each time sending back photographs of the planet. Now MESSENGER is settled in Mercury’s orbit for a complete scientific investigation of the planet. On April 4, all the onboard instruments began sending scientific measurements back to Earth on a regular basis. The scientific studies will last for a year, and researchers hope to learn more about the history, atmosphere, magnetic field and cratered landscape of the sun’s nearest planetary neighbor.