Fifth Moon of Pluto Discovered by Hubble Space Telescope

These two images, taken about a week apart by NASA’s Hubble Space Telescope, show four moons orbiting the distant, icy dwarf planet Pluto. Image Credit: Nasa/ESA/M. Showalter

Nearly a year ago, the Pluto-Charon Dwarf Planet system made headlines with the announcement that a fourth moon had been detected. Today, Alan Stern (SWRI) has announced via twitter ( @alanstern ) that a fifth moon has been detected in orbit around Pluto.

What has been released so far is a mini-abstract of an upcoming scientific paper:


M. R. Showalter (SETI Institute), H. A. Weaver (Applied Physics Laboratory, Johns Hopkins University), S. A. Stern, A. J. Steffl, M. W. Buie, W. J. Merline (Southwest Research Institute), M. J. Mutchler, R. Soummer (Space Telescope Science Institute) and H. B. Throop (NASA Headquarters) report the discovery of a fifth satellite of Pluto. The object, provisionally designated S/2012 (134340) 1 and referred to as “P5″, was detected in 14 separate sets of images taken by the Hubble Space Telescope WFC3/UVIS. Each image set comprises 11-12 three-minute exposures. Upon co-adding, S/N = 5-8 in five sets and S/N = 3-5 in nine sets where the detection was somewhat degraded by P5′s close proximity of Pluto II (Nix). Times and positions are as follows:

June 26.51-26.67 UT, 3 sets, 1″.99 from Pluto at p.a. 158 deg
June 27.78-27.94 UT, 3 sets, 1″.71 from Pluto at p.a. 182 deg
June 29.64-29.80 UT, 3 sets, 1″.44 from Pluto at p.a. 219 deg
July 7.42- 7.58 UT, 3 sets, 1″.76 from Pluto at p.a. 352 deg
July 9.41- 9.51 UT, 2 sets, 1″.42 from Pluto at p.a. 31 deg

The satellite’s mean magnitude is V = 27.0 +/- 0.3, making it 4 percent as bright as Pluto II (Nix) and half as bright as S/2011 (134340) 1. The diameter depends on the assumed geometric albedo: 10 km if p_v = 0.35, or 25 km if p_v =0.04. The motion is consistent with a body traveling on a near-circular orbit coplanar with the other satellites. The inferred mean motion is 17.8 +/- 0.1 degrees per day (P = 20.2 +/- 0.1 days), and the projected radial distance from Pluto is 42000 +/- 2000 km, placing P5 interior to Pluto II (Nix) and close to the 1:3 mean motion resonance with Pluto I (Charon).

Below is an HST image showing P5:

This image, taken by NASA’s Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5, as photographed by Hubble’s Wide Field Camera 3 on July 7. Image Credit: NASA/ESA/M. Showalter

According to a Space Telescope Science Institute (STScI) press
release, “P5″ is provisionally designated as S/2012 (134340) 1, and
was detected in nine separate sets of images taken by Hubble’s Wide
Field Camera 3 during late June/early July 2012. HST is being used to
detect potential hazards to the New Horizons spacecraft. At a speed of
over 13 kilometers per second, New Horizons could easily be destroyed
if it were to collide with debris in the Pluto-Charon system.

Harold Weaver (Johns Hopkins University) mentioned, “The discovery of
so many small moons indirectly tells us that there must be lots of
small particles lurking unseen in the Pluto system.”

Data from the Hubble Space Telescope will allow scientists to better
steer NASA’s New Horizons spacecraft through the Pluto system in 2015,
when the spacecraft is scheduled to make a historic, high-speed flyby
of Pluto.

“The inventory of the Pluto system we’re taking now with Hubble will
help the New Horizons team design a safer trajectory for the
spacecraft,” added New Horizons Principal Investigator Alan Stern
(Southwest Research Institute).

The research team members are: M. Showalter (SETI), H.A. Weaver (Johns
Hopkins University), and S.A. Stern, A.J. Steffl, and M.W. Buie

Source: STSci News Release

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