Hubble Views the Pluto System

Pluto System

12:45 PM (EST), October 31, 2005
Release No.: STScI-2005-19

Hubble Views the Pluto System:

These Hubble Space Telescope images, taken by the Advanced Camera for Surveys (ACS), reveal Pluto, its large moon Charon, and the planet's two new putative satellites.

In the short-exposure image [left], taken June 11, 2002, the candidate moons cannot be seen.
They do, however, appear in the middle and right-hand images. Longer exposure times were used to take these images. Pluto and Charon are overexposed in these images, causing the bright streaks or "blooms" that emerge vertically from them. The candidate moons are not overexposed because they are thousands of times less bright than Pluto and Charon.

In these unprocessed images, various optical artifacts of the Advanced Camera for Surveys system are visible, such as the radial spokes of light caused by the telescope's optics.
The enhanced-color images of Pluto and Charon were constructed by combining images taken in filters near 475 nanometers (blue) and 555 nanometers (green-yellow). The images of the new satellites were taken in a single filter centered near 606 nanometers (yellow), so no color information is available for them.

NASA's Hubble Space Telescope has spotted two possible new moons orbiting Pluto, the ninth planet in our Solar System. If confirmed, the candidate moons could provide new insight into the nature and evolution of the Pluto system and the early Kuiper Belt. The Kuiper Belt is a vast region of icy, rocky bodies beyond Neptune's orbit.

These Hubble Space Telescope images reveal Pluto, its large moon Charon, and the planet's two new candidate satellites. Between May 15 and May 18, 2005, Charon, and the putative moons all appear to rotate counterclockwise around Pluto.

Using NASA's Hubble Space Telescope to probe the ninth planet in our Solar System, astronomers discovered that Pluto may have not one, but three moons.

"If, as our new Hubble images indicate, Pluto has not one, but two or three moons, it will become the first body in the Kuiper Belt known to have more than one satellite", said Hal Weaver of the Johns Hopkins Applied Physics Laboratory, Laurel, Maryland. He is co-leader of the team that made the discovery.

Pluto was discovered in 1930. Charon, Pluto's only confirmed moon, was discovered by ground-based observers in 1978. The planet resides 3 billion miles from the Sun in the heart of the Kuiper Belt.

"Our result suggests that other bodies in the Kuiper Belt may have more than one moon. It also means that planetary scientists will have to take these new moons into account when modeling the formation of the Pluto system", said Alan Stern of the Southwest Research Institute in Boulder, Colorado. Stern is co-leader of the research team.

The candidate moons, provisionally designated S/2005 P1 and S/2005 P2, were observed to be approximately 27,000 miles (44,000 kilometers) away from Pluto. The objects are roughly two to three times as far from Pluto as Charon.

The team plans to make follow-up Hubble observations in February to confirm that the newly discovered objects are truly Pluto's moons. Only after confirmation will the International Astronomical Union consider names for S/2005 P1 and S/2005 P2.

The Hubble telescope's Advanced Camera for Surveys observed the two new candidate moons on May 15, 2005. "The new satellite candidates are roughly 5,000 times fainter than Pluto, but they really stood out in these Hubble images", said Max Mutchler of the Space Telescope Science Institute and the first team member to identify the satellites. Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.

"A re-examination of Hubble images taken on June 14, 2002 has essentially confirmed the presence of both P1 and P2 near the predicted locations based on the 2005 Hubble observations", said Marc Buie of Lowell Observatory, Flagstaff, Ariz., another member of the research team.

The team looked long and hard for other potential moons around Pluto. "These Hubble images represent the most sensitive search yet for objects around Pluto", said team member Andrew Steffl of the Southwest Research Institute, "and it is unlikely that there are any other moons larger than about 10 miles across in the Pluto system".

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington, under contract with Goddard.

The other team members for this observation are: William J. Merline, John R. Spencer, Eliot Y. Young, and Leslie A. Young, Southwest Research Institute.

Dolores Beasley / Erica Hupp
Headquarters, Washington.

Donna Weaver
Space Telescope Science Institute, Baltimore.

Other images, captions and press-release texts are available in the HubbleSite News Center.

Also see Pluto Adds Two New Moons (Sky and Telescope, October 31, 2005)

Pluto's two new moons would be named Hydra (S/2005 P1) and Nix (S/2005 P2).
Hydra's orbital period is 38.206 days. Nix's orbital period is 24.856 days.

July 20, 2011:
Astronomers using the Hubble Space Telescope have discovered a fourth moon orbiting the icy dwarf planet Pluto. The tiny, new satellite - temporarily designated P4 -- popped up in a Hubble survey searching for rings around the dwarf planet.

The new moon is the smallest discovered around Pluto. It has an estimated diameter of 8 to 21 miles (13 to 34 km). By comparison, Charon, Pluto's largest moon, is 648 miles (1,043 km) across, and the other moons, Nix and Hydra, are in the range of 20 to 70 miles in diameter (32 to 113 km).

See Hubble Discovers a New Moon Around Pluto (Science@NASA, July 20, 2011).

Other images, captions and press-release texts are available in the HubbleSite News Center.

July 13, 2012:
A team of astronomers using NASA's Hubble Space Telescope has discovered another moon orbiting the dwarf planet Pluto.

They say the new moon, Pluto's 5th, is likely irregular in shape and 6 to 15 miles across. Provisionally designated S/2012 (134340) 1, it was detected in nine separate sets of images taken by Hubble's Wide Field Camera 3 on June 26, 27, 29, and July 7 and 9. The moon circles Pluto in a 58,000 mile-diameter orbit.

See Fifth Moon Discovered Around Pluto (NASA Science, July 13, 2012).

Other images, captions and press-release texts are available in the HubbleSite News Center.


Pluto is now a "dwarf planet" by the IAU definition of "planet" and "dwarf planets".
See IAU 2006 General Assembly: Result of the IAU Resolution votes (IAU Press Releases, 24 August 2006, Prague).
See Observatorio ARVAL: Solar System Data.

On 13 September '06 the IAU Minor Planet Center assigned to Pluto the asteroid number 134340.
See IAU Minor Planet Center Circular 8747 (.pdf).

See Clyde Tombaugh, 1906 - 1997 (Discoverer of dwarf planet Pluto on February 18, 1930). [in ARVAL]

New Horizons Mission to Pluto and Charon - Kuiper Belt Objects. The first reconnaissance of Pluto and Charon - a "double planet" and the last planet in our solar system to be visited by spacecraft. Later, as part of an extended mission to 2020, New Horizons will visit one or more objects in the Kuiper Belt region beyond Neptune. Launched on January 19, 2006.
Jupiter Encounter: Closest approach occurred on February 28, 2007. New Horizons flew about 3 to 4 times closer to Jupiter than the Cassini spacecraft. New Horizons has also crossed the orbits of Saturn, on June 8, 2008, Uranus on March 18, 2011, and Neptune on August 2014. It transitioned from hibernation to active mode on Dec. 6, 2014, in preparation for the Pluto-System Encounter close approach on July 14, 2015 (11:49:59 UTC), about 12,500 kilometers (7,750 miles) from Pluto.
See New Horizons - The Flyby.

Updated: September 15 '06, April 16 '10, July 29 '11, July 14 '12, July 11 '15

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