Hubble Discovers a Fifth Moon Orbiting Pluto

P5, S/2012 (134340) 1

Credit:NASA,ESA, and M. Showalter (SETI Institute)

A team of astronomers using NASA's Hubble Space Telescope is reporting the discovery of another moon orbiting the icy dwarf planet Pluto.

The moon is estimated to be irregular in shape and 6 to 15 miles across. It is in a 58,000-mile-diameter circular orbit around Pluto that is assumed to be co-planar with the other satellites in the system.

"The moons form a series of neatly nested orbits, a bit like Russian dolls," said team lead Mark Showalter of the SETI Institute in Mountain View, Calif.

The discovery increases the number of known moons orbiting Pluto to five.

The Pluto team is intrigued that such a small planet can have such a complex collection of satellites. The new discovery provides additional clues for unraveling how the Pluto system formed and evolved. The favored theory is that all the moons are relics of a collision between Pluto and another large Kuiper belt object billions of years ago.

The new detection will help scientists navigate NASA's New Horizons spacecraft through the Pluto system in 2015, when it makes an historic and long-awaited high-speed flyby of the distant world.

The team is using Hubble's powerful vision to scour the Pluto system to uncover potential hazards to the New Horizons spacecraft. Moving past the dwarf planet at a speed of 30,000 miles per hour, New Horizons could be destroyed in a collision with even a BB-shot-size piece of orbital debris.

"The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system," said Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

"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 Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission's principal investigator.

Pluto's largest moon, Charon, was discovered in 1978 in observations made at the United States Naval Observatory in Washington, D.C. Hubble observations in 2006 uncovered two additional small moons, Nix and Hydra. In 2011 another moon, P4, was found in Hubble data.

Provisionally designated S/2012 (134340) 1, the latest moon was detected in nine separate sets of images taken by Hubble's Wide Field Camera 3 on June 26, 27, and 29, 2012 and July 7 and 9, 2012.

In the years following the New Horizons Pluto flyby, astronomers plan to use the infrared vision of Hubble's planned successor, NASA's James Webb Space Telescope, for follow-up observations. The Webb telescope will be able to measure the surface chemistry of Pluto, its moons, and many other bodies that lie in the distant Kuiper Belt along with Pluto.

The Pluto team members are M. Showalter (SETI Institute), H.A. Weaver (Applied Physics Laboratory, Johns Hopkins University), and S.A. Stern, A.J. Steffl, and M.W. Buie (Southwest Research Institute).

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Karen Randall
SETI Institute, Mountain View, Calif.
650-960-4537
krandall@seti.org

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The PI’s Perspective: Visiting Four Moons, in Just Four Years, for All Mankind

In June and July, members of the New Horizons science team, using the Hubble Space Telescope, discovered and confirmed that Pluto has a fourth moon! The new satellite, provisionally called P4, is fainter and therefore likely much smaller, than either Nix or Hydra or Charon – Pluto’s other three known moons. For comparison, while Charon is about as wide as the U.S. state of Colorado, Nix and Hydra are closer to the width of Vermont, and P4 is likely to be no wider across than Boulder County, Colorado.

New Horizons remains healthy and on course, now approximately 21 times as far from the Sun as the Earth is – well on its way, between the orbits of Uranus and Neptune.



On July 1, we completed our 2011 checkout of the spacecraft and its payload, which went very well. During that checkout, which spanned May and June, we conducted the first of two tests of our REX radio occultation experiment, using the moon to cut off a radio signal transmitted to New Horizons from Deep Space Network (DSN) antennas on Earth. This test involved many organizations, including the REX team, our mission operations team at the Johns Hopkins Applied Physics Laboratory, and the DSN itself. And it worked perfectly!



In June, we also accomplished some cruise science for our space plasma instruments – SWAP and PEPPSI – studying the charged-particle populations of the solar system. And over May and June we completed some much-needed spacecraft tracking; from every indication, we’re so close to a perfect course toward Pluto that will not need to conduct a course correction maneuver until at least 2013.



With this checkout behind us, we’ve returned our attention to planning the Pluto encounter. More specifically, the project team is working on the four-day command loads just before and just after the core nine-day load for Pluto closest approach. These “bookend” loads are the most critical portions of our Approach Phase 3 (AP3) and Departure Phase 1 (DP1) observations. Work is also well under way on the farther-out portions of AP3 and DP1. In addition, we’re analyzing and prioritizing responses to some 280 potential contingency scenarios for the 2015 encounter – just in case.

Pluto’s newest found moon (P4) orbits between Nix and Hydra, both of which orbit well beyond Charon. Could Pluto have additional moons? Perhaps, and the New Horizons team has proposed to the Hubble Space Telescope to look even harder – so that we can best plan our encounter observations, and ensure we don’t run into something we could have avoided.

New Horizons PI Alan Stern presented a mission overview talk last month at the U.S. Space and Rocket Center’s auditorium in Huntsville, Alabama.

And if all that isn’t keeping our little mission team busy enough, we’re also planning our first encounter rehearsal on New Horizons for summer 2012.



Designed as a stress test for the spacecraft, the “24-hour rehearsal” will include an intense one-day portion of the encounter near closest approach. We’ve rehearsed this portion of the timeline (and more) on our New Horizons ground simulator at APL in Maryland, and passed with flying colors. But there is no substitute for actually going through these paces on our spacecraft, verbatim. That kind of real-world test will prove the spacecraft is up to the task, and it’ll also let us check out some aspects of the timeline that we can only do in space. A good example: New Horizons will actually perform all the timelined attitude maneuvers and turns, which our ground simulator can only pretend to do.



The 24-hour rehearsal in 2012 is a precursor to the full, nine-day-long core encounter rehearsal that we will run on New Horizons during summer 2013.



What else is coming for New Horizons? We have our usual pair of “precession wakeups” from hibernation this November and in January 2012. In these annual activities we re-point our spacecraft and its communications antenna to account for Earth’s motion around the sun, and perform some spacecraft maintenance. Also in January, we will perform our second (and final) REX radio science lunar occultation test.



On tap in the coming months will be preparations for the new fault protection/autonomy and command and data handling software we’ll send up to the spacecraft next summer, as well as the planning for a jam-packed active checkout for 2012. The “C & DH” software change will feature a key bug fix, tracked down by project engineer Steve Williams of APL, which should reduce the probability of any computer resets during the 2015 encounter.



And also in the coming months, we’ll be kicking off our extensive space plasma hibernation cruise science observations with a test in October, and if all goes well, operational data collects beginning in early 2012.



While our spacecraft and operations teams are performing all those activities, our science team is leading a search for Kuiper Belt flyby targets, conducting studies of Pluto and its moons using ground-based telescopes, and planning a major scientific conference on the Pluto system for the summer of 2013.



That conference will allow the world’s astronomers and planetary scientists to review the state of knowledge about the Pluto system before our encounter and to begin detailed planning of ground-based and space-based campaigns to observe the planet and its moons in conjunction with the New Horizons flyby. The conference will also give researchers a chance to develop educated predictions about what New Horizons may find. We are discussing a similar kind of meeting for educators in 2014.

The New Horizons project expects to propose a stamp to the U.S. Postal Service to commemorate the historic flyby of Pluto and its moons that we will accomplish in 2015. But at least one country has already issued New Horizons stamps! Can you tell which country?

Finally, I’ll close by giving a big shout out of congratulations to NASA’s Dawn mission, which is now making the first reconnaissance of Vesta – the fourth-largest asteroid – which is about 500 kilometers across. Dawn’s exploration of Vesta is just beginning, but is already yielding spectacular results and showing us a much more complex world than many scientists imagined Vesta to be. You can read more about Dawn’s exploration of Vesta here.



From those of us looking forward to exploring a world almost 2,500 kilometers in diameter to those exploring fascinating Vesta, New Horizons salutes you. First-time exploration of new worlds simply rocks!



Well, that’s my update for now. Thanks again for following our journey across the deep ocean of space to a truly new frontier. I hope you’ll keep on exploring – just as we do!



Alan Stern

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NASA's Hubble Discovers Another Moon Around Pluto

Pluto's Moon System
Credit: NASA, ESA, and M. Showalter (SETI Institute)
View this image

Hubble Space Telescope's keen vision has found yet another moon orbiting the distant, icy dwarf planet Pluto. This discovery expands the size of Pluto's known satellite system to four moons. The tiny, new satellite — temporarily designated P4 — was uncovered in a Hubble survey searching for rings around the frigid dwarf planet.

The new moon is the smallest moon yet 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).

"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion km)," said Mark Showalter of the SETI Institute in Mountain View, Calif., who led this observing program with Hubble.

The finding is a result of ongoing work to support NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our solar system. Hubble's mapping of Pluto's surface and discovery of its satellites have been invaluable to planning for New Horizons' close encounter.

"This is a fantastic discovery," said New Horizons' principal investigator Alan Stern of the Southwest Research Institute in Boulder, Colo. "Now that we know there's another moon in the Pluto system, we can plan close-up observations of it during our flyby." Space Telescope Science Institute director's discretionary time was allocated to make the Hubble observations.

The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the U.S. Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.

The dwarf planet's entire moon system is believed to have formed by a collision between Pluto and another planet-sized body early in the history of the solar system. The smashup flung material into orbit around Pluto, which then coalesced into the family of satellites now seen.

Lunar rocks returned to Earth from the Apollo missions led to the theory that our Moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago. Scientists believe material blasted off Pluto's moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.

"This surprising observation is a powerful reminder of Hubble's ability as a general purpose astronomical observatory to make astounding, unintended discoveries," said Jon Morse, astrophysics division director at NASA Headquarters in Washington.

P4 was first seen in a photo taken with Hubble's Wide Field Camera 3 on June 28, 2011. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. The moon was not seen in earlier Hubble images because the exposure times were shorter. There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was largely obscured by an imaging artifact, called a diffraction spike.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
villard@stsci.edu
410-338-4514

Karen Randall
SETI Institute, Mountain View, Calif.
krandall@seti.org
650-960-4537

More about → NASA's Hubble Discovers Another Moon Around Pluto