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Planetary paparazzo

NASA satellite snaps historic photographs of Mercury

Hey, Mercury, say “cheese”!

Flying circles around Mercury MESSENGER, shown in an artist’s drawing, will spend 12 months in orbit around Mercury. . Credit: NASA

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.

Mercury via MESSENGER

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.

“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.

Mapping Mercury

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.

POWER WORDS (adapted from the New Oxford American Dictionary)

orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

gravity The force that attracts a body toward the center of the earth, or toward any other physical body having mass.

mass The amount of matter in an object.

crater A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon, typically caused by an explosion or the impact of a meteorite or other celestial body.

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