Taking Pluto’s Portrait

Even the mighty Hubble Space Telescope has to strain to see this tiny, distant planet.

Images of Pluto taken with Hubble’s Faint Object Camera in June and July 1994 were enhanced and processed to make a global map of the planet at different longitudes. The tile pattern is an artifact of the processing. (Alan Stern (Southwest Research Institute), Marc Buie (Lowell Observatory), NASA and ESA)
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It wasn’t a matter of resenting the schoolkids (Buie was in fact supervising the observation for them). But it did force them to hurry up the remaining work to meet the deadline. For one thing, the images—each of which covered only part of Pluto’s surface—still had to be “unwrapped” and laid down in strips to create a flat map showing where the light and dark regions were.

On March 7, 1996, Stern and Buie stood on a stage in Washington, D.C., and unveiled images from two of the four days of Pluto observations, along with flat maps they had made from the full set of pictures, plus global maps made from those. A month later they turned in their scientific paper to the Astronomical Journal, closing out the first phase of the project.

Both scientists continue working with the images, and already they’ve improved their maps since the NASA press conference. And what do the pictures show that’s new? Not much, at least in the first analysis. Buie is pleased that his old, indirect maps turn out to be pretty accurate, except for one or two details. A bright spot near Pluto’s equator, for example, appears in the wrong place in the old maps. The Hubble pictures also reveal two bright regions just above that. And the jury’s still out on the north pole—Buie and another group had concluded it was dark, but the new Hubble pictures and another older map say it’s bright. Unfortunately, this is an area where the Hubble data is less trustworthy, due to the blurring effects.

So Pluto is still a mystery. What Stern and Buie would really like is a regular monitoring program to look for changes as the planet gets colder and more snow falls on its surface. Stern may even put in a proposal to use a new Hubble camera scheduled for installation next year. Maybe he’ll suggest taking pictures at more longitudes, or with different filters. But that’s a proposal to be written another day.


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