Pluto Returns to Public Popularity

UA Flandrau Science Center
July 13, 2015

On Tuesday, NASA's New Horizons mission spacecraft is set to reach Pluto and will send back the first-ever close-up photos of the famous dwarf planet. 

To celebrate this astronomy milestone, the University of Arizona's Flandrau Science Center and Planetarium, in collaboration with the Lunar and Planetary Laboratory, is hosting "Pluto Week," which will include a live video feed of NASA's New Horizons "Phone Home" event, talks, laser light shows and film screenings.

Bill Plant, UA Flandrau Science Center exhibits director, and Michael Magee, senior technical director at Flandrau Science Center, share some of the most interesting tidbits about the once-classified planet.

"Pluto: Another Global View," an artist's concept of Pluto. (Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

What is Pluto?

For many years, Pluto was known as the ninth planet and the most distant one in the solar system. 

But in 2006, astronomers reclassified Pluto as a dwarf planet because they realized that there were several other similar-size objects in deep orbit around our sun. 

How long does it take to get to Pluto?

The time it will take the New Horizons spacecraft to reach Pluto is around nine years.

Its speed of over 36,000 mph makes it the fastest spacecraft to leave Earth's orbit. That's more thaan 100 times faster than your average jet airliner.

Pluto is not a particularly hospitable place, with temperatures hovering around minus-375 degrees Fahrenheit.

"New Horizons" (Photo courtesy of the Flandrau Science Center)

Could there be life on Pluto?

Alan Stern, NASA New Horizons principal investigator, explains that the surface of Pluto is extremely cold.

"But inside the planet, as you go deeper and deeper and the pressure increases from the ice and rock that's above you, the material does reach a temperature, where, if there's water-ice, it can liquefy and become an ocean on the inside of Pluto, much like Europa and other worlds that we’ve discovered," Stern says.

"And if there's an ocean, then there’s a possibility of biology."

Size comparisons (Image courtesy of Flandrau Science Center)

Say cheese!

Pictures sent back from the New Horizons spacecraft will take about 4.5 hours to reach Earth, traveling at the speed of light.

The closest star beyond our solar system is more than four light-years away. 

How large is Pluto?

Pluto is much smaller than Earth, and even smaller than the moon.

Pluto is about two-thirds the size of Earth’s moon, but it is the largest object in the Kuiper Belt, a band of rocky objects that orbits the sun at the edge of the solar system and is named after Gerard Kuiper, the astronomer who founded the Lunar and Planetary Lab at the UA. Also, Pluto has less than 1 percent of the mass of the Earth.

So, if you weigh 180 pounds on Earth, you would weigh only 11 pounds on Pluto.

Pluto and Charon (Image: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute)

Pluto's moons

We know that Pluto has five moons, but it could have even more. In fact, three of Pluto's moons were discovered only in recent years.

Pluto's moon Charon is more than half the size of Pluto itself, which led astronomers to originally classify the Pluto-Charon system as a "double planet."

Scientists also considered them "binary planets" because the smaller Charon does not actually orbit around Pluto; rather, Pluto and Charon orbit a common gravitational center.

Contact: Michael Magee at; for more information about Flandrau Science Center and Planetarium, visit or call 520-621-4516.


Resources for the media