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With only days to go before NASA’s New Horizons spacecraft makes its closest pass of Pluto on July 14, Lowell Observatory astronomers have confirmed some good news: the icy planet still has an atmosphere for the mission to study.

A team of astronomers, including five from Lowell, made the confirmation last week by observing Pluto pass between Earth and a distant star — an event called an occultation.

By watching how the star’s light dims, blinks out and then reappears, astronomers can make conclusions about Pluto’s atmosphere.

While the scientists were fairly confident from past observations that the dwarf planet still has an atmosphere, it was worth checking because some models say it likely won’t be around in the next decade or two, said Amanda Bosh, an astronomer at Lowell and the Massachusetts Institute of Technology and one of the leads on the occultation observation project.

Due to Pluto’s elliptical orbit, it is now moving away from the sun, causing temperatures to drop. That means the atmosphere is cooling as well and some scientists say it will likely freeze sometime in the near future, forming a dusting of frost over Pluto’s surface as the gas transforms into a solid, Bosh said.

Last week’s observation confirmed that Pluto’s atmosphere — already about one million times thinner than the Earth’s — is still there and also hinted that something is changing in the lower atmosphere, Bosh said. She's still working on exactly what that change is. 

The close-up images taken by New Horizons promise to add a new layer of information to what has been collected by astronomers over years of occultation observations. Data from the flyby will provide a one-time chance for astronomers like Bosh to compare their on-the-ground observations with those taken a relative hair's width from Pluto.

"Those data give us the truth of what's happening on Pluto so we won't have to theorize about what the surface potentially looks like," Bosh said.

Having solid information about the quantity and distribution of ices on Pluto's surface gives astronomers clues about what its atmosphere may be like because the two are closely linked, Bosh said.

Probing atmospheres in our solar system allows astronomers to begin hypothesizing about what sort of atmospheres may be found on planets rotating around other stars, said Stephen Levine, Bosh's husband and another Lowell astronomer who observed the Pluto occultation.

Scientists have discovered there are many different types of atmospheres that exist even in our solar system, Levine said.

Years of prep

Observing the occultation wasn’t as simple as firing up one of Lowell’s telescopes. The phenomenon was only visible from the southern hemisphere, so the team that included Lowell scientists manned about a dozen telescopes across Australia and New Zealand on the night of June 29 in hopes of catching a glimpse of the process. They also put astronomers on SOFIA, NASA’s airborne observatory, that flew south of New Zealand to capture the best view of the action.  

The team spent two weeks making observations from telescopes at Lowell, the U.S. Naval Observatory in Flagstaff and the Southeastern Association for Research in Astronomy in Chile to figure out exactly where to best position SOFIA to be in line with the center of the occultation.

In all, it was two years of preparation for an event that lasted two minutes, Levine said.

But occultations are the most precise way to get clues about planetary atmospheres from Earth. Astronomers first observed an occultation event involving Pluto in 1988 and now have observations spanning 27 years, Levine said.

Last week's event was the brightest star ever occulted by Pluto, Bosh said. 

“By studying these different types of atmospheres, you gain a deeper understanding of what atmospheres are like and how they evolve,” she said.

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Emery Cowan can be reached at (928) 556-2250 or


Environment, Health and Science Reporter

Emery Cowan writes about science, health and the environment for the Arizona Daily Sun, covering everything from forest restoration to endangered species recovery efforts.

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