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© NASA
Photos newly released by NASA this February show the most detailed pictures of Pluto that have ever been taken. The Hubble telescope captured these images using its Advanced Camera for Surveys as recently as 2003. To put this in perspective, each picture is only a few pixels in size, and through computer analysis, the pictures were overlaid and enhanced to create a composite image of higher quality.

The significance of these pictures comes in comparisons. These new pictures were studied as part of a collection that included Hubble images from 1994, 2002 and 2003, as well as ground-based telescope images taken in 1988 and 2002. Among the changes observed over this time span are a doubling of the mass of Pluto's atmosphere, as well as a brightening of the North pole of the planet, and a darkening of the Southern hemisphere.

Pluto's surface has regions of different materials, resulting in the orange, white and black blotches of color. The atmosphere of Pluto is dynamic, resulting in this change in appearance. The increase in atmospheric mass is likely due to melting of nitrogen ice, which releases gas into the atmosphere.

Pluto's seasonal changes differ greatly from those on Earth. The eccentricity of Pluto's orbit makes it such that its seasons are not equal in length, since the planet accelerates as it gets closer to the sun. By comparison, Earth's orbit is relatively circular, resulting in seasons of equal length and intensity based on the tilt of Earth's axis.

One year on Pluto is equal to 248 Earth years, making each season on Pluto very long. Since its discovery, less than half a Pluto-year has elapsed.

Even higher quality images of Pluto will be obtained in the near future. The New Horizons mission, launched by NASA in 2006, will reach Pluto in 2015.

Within a six-month window, New Horizons will capture the highest ever quality pictures and relay them back to Earth. Despite this large window of time, it will only be able to record one hemisphere. The images from the 2003 pictures and others will be used to help calibrate and focus the 2015 images.

"These images provide a broader and more complete context from which to plan the New Horizons encounter," Marc Buie, principal investigator at the Southwest Research Institute in Boulder, Colorado, said in an e-mail to The News-Letter.

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© NASA, ESA and G. Bacon (STScI)The artist's concept above shows the Pluto system from the surface of one of the candidate moons. The other members of the Pluto system are just above the moon's surface. Pluto is the large disk at center, right. Charon, the system's only confirmed moon, is the smaller disk to the right of Pluto. The other candidate moon is the bright dot on Pluto's far left.
"It serves to confirm the albedo patterns which are important for simple things like choosing an exposure time for taking pictures with the spacecraft instruments."

Pluto has always been mysterious. Astronomers predicted the existence of Neptune and Pluto based on observations of Uranus' orbit. Recently, the question arose whether Pluto should be classified as a planet.

Many discoveries were made of large bodies that were part of the Kuiper Belt, a region beyond Neptune. In 2005, a new body beyond Pluto and larger than Pluto itself was discovered. Due to this and other evidence, the International Astronomical Union declassified Pluto from a planet to a dwarf planet in 2006 by redefining the term 'planet.'

"The noted changes begin to tell us just how dynamic a world Pluto is and certainly adds to the building excitement as we wait in anticipation of the flyby in 2015," Buie wrote.