In Deep （旧）

　米航空宇宙局（NASA）は4日、ハッブル宇宙望遠鏡（Hubble Space Telescope）で撮影した冥王星の写真を公開し、観測の結果、冥王星の輝きが数年前よりも著しく赤みを増したことが明らかになったと発表した。

　写真の冥王星には、糖みつ色のまだら模様の中に、ひときわ赤い個所が見える。日なたになった極の方で表面の氷が溶解し、次いで日陰になった反対側の極で再凍結した過程を示していると考えられる。　　

　こうした色の変化は2000〜02年に起こったとみられる。冥王星は単なる氷と岩石の球体ではなく、大気が劇的に変化する活力あふれた世界であることが立証されたと、NASAの科学者らは話している。

Since its discovery in 1930, Pluto has been a speck of light in the largest ground-based telescopes. But NASA's Hubble Space Telescope has now mapped the dwarf planet in never-before-seen detail. The new map is so good, astronomers have even been able to detect changes on the dwarf planet's surface by comparing Hubble images taken in 1994 with the newer images taken in 2002-2003. The task is as challenging as trying to see the markings on a soccer ball 40 miles away.

Hubble's view isn't sharp enough to see craters or mountains, if they exist on the surface, but Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto's surface, leaving behind a dark, molasses-colored, carbon-rich residue. Astronomers were very surprised to see that Pluto's brightness has changed ― the northern pole is brighter and the southern hemisphere is darker and redder. Summer is approaching Pluto's north pole, and this may cause surface ices to melt and refreeze in the colder shadowed portion of the planet. The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes.