Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: MONDAY, November 7, 1994 TAG: 9411080036
SECTION: NATIONAL/INTERNATIONAL PAGE: A-5 EDITION: METRO
SOURCE: Dallas Morning News BETHESDA, Md.
DATELINE: LENGTH: Medium
New Hubble Space Telescope images show that the planet's great dark spot has disappeared since the Voyager 2 spacecraft passed Neptune five years ago. Neptune also has grown brighter over the past two decades, though planetary scientists can't say why.
This year the Hubble Space Telescope produced the most detailed pictures of Neptune that have been taken since Voyager 2 flew past the planet in August 1989. As did Voyager, Hubble revealed a pale blue planet punctuated by wispy white clouds.
Planetary scientists' first observation after seeing the Hubble pictures was that ``Voyager went by Neptune when it was pretty dull,'' said Heidi Hammel, a planetary scientist at the Massachusetts Institute of Technology in Cambridge, Mass.
But planetary scientists are changing their tune after seeing Hubble's pictures.
``This is a very, very changeable planet,'' said David Crisp, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Along with colleagues from MIT and the Lowell Observatory in Flagstaff, Ariz., Hammel has begun analyzing images of Neptune taken last month by the Hubble Space Telescope. Another set of images, taken by Hubble in June, is being studied by Crisp and researchers from NASA's Jet Propulsion Laboratory and the University of Michigan in Ann Arbor.
Neptune is extremely difficult to study because it is 2.8 billion miles from the sun, 30 times farther from the center of the solar system than Earth. So, even though Neptune is four times as big across as Earth, to Earth-bound telescopes it appears the size of a headlight seen from two miles away.
The most surprising thing about the Hubble observations was the dark spot's absence. When they first saw it five years ago, planetary scientists likened Neptune's spot to the great red spot on Jupiter. The great red spot is a storm that has picked up a red coloring agent.
But Neptune's atmosphere must not have what it takes to sustain a spot for hundreds of years, the planetary scientists said. Either the storm broke up, or the dark material coloring the spot dissipated, Crisp said.
by CNB