It was a lazy, hazy, crazy day on the dwarf planet Pluto when New Horizons, a spacecraft from Earth, flew by at a speed of 31,000 mph (miles per hour) two years ago. The spacecraft took a bunch of photos, made some quick measurements of Pluto's atmosphere, and sent them all back here, giving planetary scientists their first up-close look of the distant dwarf planet.
One of the more bizarre things they found was that the haze in Pluto's atmosphere was much thicker than previously thought. The planet also had an atmosphere much cooler than earlier estimates, topping out at −333.4°F.
Now, a study published in Nature links those two atmospheric observations. A computer model developed by planetary scientist Xi Zhang and colleagues shows the haze of tiny droplets in the upper atmosphere is likely scattering light from the Sun, preventing heat from reaching the planet below. We see hazy skies on Earth too, from time to time, whenever solid particles get suspended in the air—from water-based fogs, to ash from fires, to the toxic droplets that make up a thick smog. But on Earth, the overall temperature of the planet is dominated by the distribution of gases in our atmosphere.
On Pluto, the authors suggest, haze might be more influential. Particles can reflect light from the Sun here on Earth: It happens after volcanoes erupt, emitting clouds of particles that reflect the Sun's rays into the atmosphere. Some people even propose imitating this phenomenon to alleviate the effects of climate change. But our planet isn't dominated by that process, or at least it hasn't been for a few billion years.
If Pluto's atmosphere is very different from ours and from that of other nearby planets, it could help scientists expand their understanding of planetary atmospheres. But right now, this is just a good guess based on data from New Horizons and a sophisticated computer model, not direct observations of the haze's composition.
There are other theories floating around to explain Pluto's cool temperatures, including blaming the cold air on gases in the atmosphere.
Luckily, the authors will get a chance to test their notions when the James Webb Space Telescope launches later. That observatory can detect different spectrums of light, which the hazy Plutonian atmosphere would be positively glowing with as it scattered sunlight. The researchers just have to wait and see if the light from the telescope validates their bright idea.