Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Early yesterday morning, while cruising through black space, a U.S.-made probe opened one of its photomechanical eyes and captured this historic image of Mercury.
It might not register as momentous at first - it sort of looks like a garden-variety Moon shot - but this is the first time we have ever seen Mercury from orbit.
Since its launch in 2004, the MESSENGER space probe (MErcury Surface, Space ENvironment, GEo-chemistry, and Ranging) has traveled more than 4.9 billion miles toward the small, scarred planet closest to the sun. Guided by scientists in Laurel, Md., MESSENGER eased into orbit on March 17. It is the second craft to visit Mercury - Mariner 10 performed three flybys in the 1970s - and by far the most ambitious attempt to pierce the planet's shroud of mystery.
Mercury, about the size of the Moon, has the oldest surface of all the planets but remains the least explored. Its face is pocked with impact craters because it has only the thinnest of atmospheres to burn up incoming rocks. Temperatures on its surface swing from 800 degrees Fahrenheit to negative 290 degrees, and there might be ice at the poles. Mercury has a magnetic field that is just 1 percent as powerful as Earth's yet retains a strange energy. According to NASA, the sun's own field sometimes reaches out to connect with Mercury's, creating "intense magnetic tornadoes that funnel the fast, hot solar wind plasma down to the surface."
Over the course of the next year, MESSENGER will map the entire surface of Mercury in color, employing a bevy of imaging equipment that includes an energetic particle and plasma spectrometer, a magnetometer, a laser altimeter and the equivalent of X-ray specs. Scientists will carefully analyze downlinked data on the crust's composition, the large, metallic core and the violent magnetosphere. By studying the extreme planet, they hope to gain a better understanding of how all the planets in the solar system formed and evolved.
So what are you seeing in the image above? The huge crater is Debussy, 50 miles wide at its center with rays spreading outward hundreds of miles. It's one of the most identifiable features on Mercury. To the west is a smaller divot called Matabei with unusual dark rays, perhaps evidence that whatever smashed into the planet lifted up material from deep within the ground. The shadowy bottom portion shows the planet's south pole, never seen before by spacecraft.
And here is a color-enhanced image that MESSENGER made in 2008 as it journeyed toward the little planet. The central feature is the 932-mile-wide Caloris basin, one of the largest impact craters in the solar system. The orange patches around the basin's lip are thought to be volcanic vents.