Don't look so blue, Neptune: Now astronomers know this planet's true color

A MARTÍNEZ, HOST:

In pictures of the farthest planets from the sun, Uranus looks like a pale-green orb, while Neptune usually looks much bluer. A new analysis revealed their true colors. Here's NPR's Nell Greenfieldboyce.

NELL GREENFIELDBOYCE, BYLINE: The only spacecraft ever to visit Uranus and Neptune was Voyager 2. It flew by both ice giants in the 1980s, sending back historic snapshots. Patrick Irwin is an astronomer with the University of Oxford. He says the images captured by this spacecraft were taken with different color filters.

PATRICK IRWIN: It's got a green filter. It's got a blue filter. It's got an orange filter.

GREENFIELDBOYCE: Those separate images then had to be recombined.

IRWIN: That's a surprisingly subtle process.

GREENFIELDBOYCE: He says, back then, choices were made when processing the images. The colors got tweaked to highlight Neptune's interesting features, like bands of clouds and a dark spot. The Voyager team was open about this. But Irwin says in the decades since then, the subtleties of how the images were made have been forgotten. These depictions of Neptune and Uranus have become entrenched.

IRWIN: People now just think, well, that's how they look.

GREENFIELDBOYCE: He and some colleagues were recently trying to better understand the clouds on these two planets using data from instruments on the Hubble Space Telescope, as well as the European Southern Observatory's Very Large Telescope. The scientists realized they could use this data to rebalance the images taken by Voyager 2.

IRWIN: And produce color images that you would actually see were you there with the spacecraft looking at the planet.

GREENFIELDBOYCE: What they found is that Uranus and Neptune actually look almost the same. They are both pale bluish green. Neptune might be slightly more blue, but the difference is nothing like what you'd see if you just Google for images of these two planets. A report on all this is published in the Monthly Notices of the Royal Astronomical Society.

A mission to orbit Uranus recently topped a wish list compiled by an expert panel that advises NASA on scientific priorities. The earliest a mission like that could launch is sometime in the 2030s.

Nell Greenfieldboyce, NPR News.

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