It’s really hot, really cold and maybe even a bit icy.
It is the planet Mercury, and this month it is ready for its extended close-up. On Wednesday, NASA showed off the first pictures taken by its Mercury Messenger spacecraft since entering the planet’s orbit on March 17. The Messenger is to spend at least a year photographing, measuring and studying Mercury.
The visit to Mercury is the last frontier of planetary exploration that NASA will reach for quite some time.
“This is the last of the classical planets, the planets known to the astronomers of Egypt and Greece and Rome and the Far East,” said Sean C. Solomon of the Carnegie Institution of Washington, the mission’s principal investigator. “It’s an object that has captivated the imagination and the attention of astronomers for millennia.”
But never before has science had such a good front-row seat. “We’re there now,” Dr. Solomon said.
The space agency has sent orbiters to five planets — Mercury, Venus, Mars, Jupiter and Saturn — but it will most likely be another decade or two before a spacecraft enters orbit around Uranus or Neptune. (A study on future planetary missions put a Uranus orbiter on the wish list.) NASA does have a spacecraft, New Horizons, that will zoom past Pluto in 2015, but, alas, Pluto is no longer counted as a planet.
Mercury has been seen close up, albeit briefly, in half a dozen flybys by NASA probes: three by the Mariner 10 in the 1970s and three by the Messenger in the last three years. But now that the Messenger has pulled into an orbit of Mercury, planetary scientists will be able to get their first long look at the smallest of the eight planets. The day side of Mercury can broil at 800 degrees Fahrenheit; the night side drops to minus 300 degrees.
Particularly intriguing, scientists say, are the shadows in craters near Mercury’s poles. There, the Sun never shines, and in the frigidity, some scientists expect that the Messenger will find frozen water.
The Messenger arrived at its final destination after a 6.5-year loop the loop through the inner solar system. A 15-minute engine burn slowed the spacecraft sufficiently for it to be captured by Mercury’s gravity.
By design, the Messenger loops around the planet on a highly elliptical orbit, dipping down as close to 160 miles to Mercury’s surface and rising as far up as 9,300 miles.
Since its arrival, engineers have been checking out the orbiter’s systems and gear. Finding everything in working order, they turned on the instruments, including the camera. The first picture, showing a bright crater called Debussy, was taken early Tuesday. By the end of Thursday, 1,500 photographs will have been taken. More than 75,000 are planned over the next year.
The spacecraft’s seven instruments have also begun measuring emissions of neutrons, X-rays and gamma rays, which will allow scientists to deduce many of the minerals of the surface. The extended observation will help them understand how Mercury, which is half the mass of Mars, still has a magnetic field — presumably generated by a molten outer core — while Mars does not.
James W. Head III, a geology professor at Brown University and an investigator on the Messenger mission, said Mercury could even give clues about how plate tectonics — the motion of pieces of crust — started on Earth. On other bodies, like Mars and the Earth’s moon, there is no sign of plate tectonics, with the crust remaining in one piece. On Mercury, however, there are long tectonic ridges extending thousands of miles, which could have represented the first stage of the crust breaking up into plates, although the pieces never started moving as on Earth.
“It’s kind of embryonic, halted,” Dr. Head said. “It didn’t quite get going, but it could give us clues.”
The spacecraft will officially begin its scientific measurements on Monday.
Link to slide show, First Close-Ups of Mercury (opens in new page)
Personal comment, learned something new.... Mars does not have a magnetic field.
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