Pluto: a Dwarf Planet With Rings?

Hubble image of Pluto and its four known moons. NASA, ESA, and M. Showalter (SETI Institute)


NASA’s New Horizons spacecraft is currently speeding through the outer solar system toward its July 2015 date with Pluto, when it will take a good close look at the dwarf planet’s mysterious surface, atmosphere, moons, and… rings?

Less than three-quarters the size of our moon, Pluto nevertheless has no shortage of fascinating features. It has a curiously mottled coloration that seems to change with its seasons, an atmosphere that expands and falls back onto its surface, a system of four moons in orbit around it — the most recent of which, currently called “P4”, was announced just last summer — and, according to Planetary Science Institute senior scientist Henry Throop, possibly even a system of rings.

Astronomers have suggested before that Pluto could have rings… probably not an elaborate system like Saturn’s, of course, but rather a thin ring made up of small bits of rock, dust, gas and ice. These could be the remains of a small moon or even ejected material from one of the existing ones.

In fact, concerns over the existence of such rings have recently arisen, as running into unseen debris at 14 kilometers a second — the velocity at which New Horizons will pass by Pluto — would pose a serious risk to the spacecraft and its sensitive suite of instruments.

Artist's concept of the New Horizons spacecraft during its planned encounter with Pluto. (JHUAPL/SwRI)

“Even particles less than a milligram can penetrate our micrometeoroid blankets and do a lot of damage to electronics, fuel lines and sensors,” said New Horizons Principal Investigator Alan Stern.

While it’s not known if Pluto has such rings, or perhaps even more moons in tow, Throop’s team is using occultation data gathered with the four-meter Anglo-Australian Telescope in Australia to search for any hints of hidden ring structures.

“As Pluto passes in front of a star, the star’s light blinks out, like a moth blocking out the beam from a flashlight,” Throop said at the Division for Planetary Sciences meeting in Nantes, France. “We searched through the observations to try to find any hint that the star light was being blocked by rings of Pluto.”

Although no conclusive evidence for rings has yet been found, Throop’s research is still valuable to the New Horizons mission. After all, knowing where rings aren’t is just as important as knowing where they are when planning a safe path for the spacecraft.

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Changing Planet

I'm a graphic designer and space blogger, currently writing for National Geographic News, Discovery News, Universe Today and on my own blog, Lights in the Dark. The Universe is an amazing place and I'm going to tell you about it, one discovery at a time.