March 12, 2011

Rare View Of Mercury As NASA Craft Orbits

A small NASA spacecraft called Messenger will enter into the orbit of the planet Mercury on St. Patrick 's Day, circling as close as 125 miles from the rocky planet's surface and revealing parts of Mercury never before seen by human eyes.

Coincidentally, a few days earlier will be the best time this year for people here on Earth to see Mercury with the naked eye, the Associated Press reported.

Despite being the planet closest to the sun, some scientists believe Mercury contains tons of ice in its craters, something Messenger's scientists hope to soon confirm.

Sun scorched Mercury is in many ways the strangest planet in the solar system, with its days somehow lasting longer than its years. Just slightly bigger than the moon, Mercury also exhibits the most extreme temperature variations of all the planets in the solar system. 

Although Mercury is not easy to see without a telescope, a rare pairing with the giant planet Jupiter will make it easier to view beginning Sunday.

Geoff Chester of the U.S. Naval Observatory in Washington said people in the Northern Hemisphere should look to the west after sunset, when Jupiter will be about 10 degrees above the western horizon.  Mercury will be about slightly to the right of Jupiter, he told the Associated Press.

"Mercury has sometimes been called the forgotten planet," said planetary geologist Sean Solomon, Messenger's chief scientist.

"It is extreme in many respects. It is the smallest, closest to the sun. It is made of the densest materials," he told the AP.

Although NASA's Mariner probe approached Mercury in 1974 and 1975, and Messenger flew by it in 2008 and 2009, this is the first time a spacecraft will attempt the difficult task of entering Mercury's orbit, circling the planet for one year.

To achieve that goal, Messenger will have to overcome the vast pull of the sun. 

The heat on Mercury's sunny side will melt parts of some of Messenger's instruments, which, by design, serve as a heat buffer for more sensitive equipment. The melted parts will then refreeze when the spacecraft enters a cooler zone, said Messenger system engineering chief Eric Finnegan.

Mercury orbits around the sun once every 88 Earth-days, whizzing around at a faster pace than any other planet in the solar system.   It has an extremely elongated orbit, making its distance from the sun range from 29 million to 43 million miles.  

However, its own rotation is surprisingly slow, taking 59 Earth-days to rotate one time around its axis. This means that a solar day on Mercury, from noon to noon at the same place, is 176 Earth-days, which is two Mercury years.

Because of Mercury's bizarre attributes, Messenger's orbit will be egg-shaped, distorted by the sun's gravity.

While Venus is the hottest planet in the solar system, Mercury rates first in terms of temperature swings.  Indeed, the planet can reach temperatures of 800 degrees in parts that face the sun, while on the opposite side it can be 300 degrees below zero, said mission scientist Ralph McNutt of Johns Hopkins University.

Deep craters created by comets and asteroids exist near Mercury's poles, which "never see any sunlight and haven't for maybe a billion years," McNutt told the AP.

This has led scientists to believe the craters may have ice left behind from the comet strikes.  

Solomon said radar has suggested that ice up to several feet thick may exist.

"You're staring out in the blackness of space and it's extremely cold," he said.

Although Messenger will likely not be able to take pictures inside the craters, the spacecraft will aim devices that should be able to determine the chemical composition of what's inside, Solomon said. 

Mission scientist Jean-Luc Margot told the AP he believes there will be plenty of data to help astronomers learn more about Mercury's geology, such as its surprising magnetism and extraordinarily high density.

"This will be our first really close look at this enigmatic planet. It's going to be a blast," he said.


Image 1: The spectacular image shown here is one of the first to be returned from MESSENGER's second flyby of Mercury. The image shows the departing planet taken about 90 minutes after the spacecraft's closest approach. The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. For most of the terrain east of Kuiper, toward the limb (edge) of the planet, the departing images are the first spacecraft views of that portion of Mercury's surface. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper. This extensive ray system appears to emanate from a relatively young crater newly imaged by MESSENGER, providing a view of the planet distinctly unique from that obtained during MESSENGER's first flyby. This young, extensively rayed crater, along with the prominent rayed crater to the southeast of Kuiper, near the limb of the planet, were both seen in Earth-based radar images of Mercury, but were not previously imaged by spacecraft. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Image 2: Artist's concept of MESSENGER in orbit around Mercury. Credit: NASA


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