Blue Haze of Pluto

Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Smog getting you down? Consider this: even Pluto has got that!

Scientists stitched together images from the Long Range Reconnaissance Imager (LORRI) from NASA’s New Horizons spacecraft when it was about 120,000 miles (200,000 kilometers) away from Pluto. The resulting image of Pluto’s receding crescent shows a spectacular blue “haze” in the dwarf planet’s atmosphere:

Scientists believe the haze…

It’s time to redefine what qualifies as a planet

PLANET OR NOT? A group of planetary scientists label Pluto and many other orbs in the solar system as planets, despite the definition set down by the International Astronomical Union in 2006.

Pluto is a planet. It always has been, and it always will be, says Will Grundy of Lowell Observatory in Flagstaff, Arizona. Now he just has to convince the world of that.

For centuries, the word planet meant “wanderer” and included the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. Eventually the moon and sun were dropped from the definition, but Pluto was included, after its discovery in 1930. That idea of a planet as a rocky or gaseous body that orbited the sun stuck, all the way up until 2006.

Then, the International Astronomical Union narrowed the definition, describing a planet as any round object that orbits the sun and has moved any pesky neighbors out of its way, either by consuming them or flinging them off into space. Pluto failed to meet the last criterion (SN: 9/2/06, p. 149), so it was demoted to a dwarf planet.

Almost overnight, the solar system was down to eight planets. “The public took notice,” Grundy says. It latched onto the IAU’s definition — perhaps a bit prematurely. The definition has flaws, he and other planetary scientists argue. First, it discounts the thousands of…