Hubble Space Telescope detects fifth moon of Pluto (Update)

Jul 11, 2012 by Ray Sanders report
These two images, taken about a week apart by NASA's Hubble Space Telescope, show four moons orbiting the distant, icy dwarf planet Pluto. The green circle in both snapshots marks Pluto's fourth moon, temporarily dubbed P4, found by Hubble in June 2011. Image Credit: NASA/ESA/M.Showalter

( -- Nearly one year ago, Pluto made headlines as the discovery of a fourth moon (shown above), dubbed "P4" was announced by a team which included Alan Stern, Principal Investigator for the New Horizons mission enroute to Pluto. Today, via twitter, Alan Stern has announced the discovery of a fifth moon by the Hubble Space Telescope: "Just announced: Pluto has some company-- We've discovered a 5th moon using the Hubble Space Telescope!"

Additionally, the IAU Central Bureau for Astronomical Telegrams # 9253 reports the discovery. Below is a short abstract, including some orbital parameters:

"M. R. Showalter (), H. A. Weaver (Applied , Johns Hopkins University), S. A. Stern, Andrew Steffl, M. W. Buie, W. J. Merline (Southwest Research Institute), M. J. Mutchler, R. Soummer ( 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 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

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

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 I (Charon)."

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 (SwRI).

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More information:
Press release

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5 / 5 (4) Jul 11, 2012
I remember when the Galileo spacecraft imaged an asteroid(gaspra?); it was beautiful; suddenly, everyone wanted to image asteroids! For some strange reason these asteroids, comets and moons hold as much if not more fascination than the planets!?

A Dawn spacecraft has been in orbit around an asteroid Vesta(should be called a planetoid by now); it's an absolutely amazing world! This spacecraft will leave Vesta and go in orbit around Ceres the largest asteroid of the asteroid belt; i'd expect that to be really exciting!

Anybody who's been enjoying the asteroids can just feel that Pluto will be cool! But, lately, Pluto has been getting really cool! I shouldn't have to explain why Pluto is going to be exciting; the only disappointment is that the Pluto probe will rocket past the 'Pluto system'. The Jet propulsion laboratory is busy right now much less when the Pluto Probe gets to Pluto to figure out how to image all this stuff and take as much data as possible; we're going to see . .
4.4 / 5 (7) Jul 11, 2012
pluto has more moons that all the inner planets combined
5 / 5 (2) Jul 11, 2012
. . . we're going to see democracy at work in terms of what science to do at the 'Pluto system'!

Hopefully, we'll get to see Sedna and other Kuiper belt objects because jetting past the 'Pluto system' so quickly is going to be a little bit disappointing; it would have been nicer to just go in orbit and really study the 'Pluto system.'

Asteroids in orbit around asteroids is not new; but, this Pluto system looks to take the cake!
5 / 5 (3) Jul 11, 2012
@flashgordon: It would have been nice to put it in orbit but it would have to have been sent at a slow speed or with a lot of extra fuel for braking in order to pull that off. If I remember right there was some urgency to get there sooner rather than later. It's moving away from the sun and they wanted to study the atmosphere before it froze and fell to the surface. Sedna sadly isn't going to be in the right place. They are currently looking for other KBO targets past Pluto in roughly the same direction (fuel limitations again) for an extended mission.
5 / 5 (2) Jul 11, 2012
@flash - The pluto probe is called New Horizons, and is projected to fly by Pluto in July 2015 (Only 3 More years). I'm very excited.

While New Horizons won't be able to pick up Cassini level detailed science and observations, The science will be just as invaluable, compared to the fact that right now, pluto is just a dot with a few other dots, and a spectrograph.

I think that just by a few pictures and observations from a quick but close flyby will yield more science than you think!

I too am excited and look forward to the pluto mission. Meanwhile, recent observations show that the Ceres mission is likely to be far more interesting than Vesta. There appears to be ice on the surface and other interesting characteristics that are not common to asteroids.
4.4 / 5 (5) Jul 11, 2012
Isn't it amazing that a tiny dwarf planet has so many moons, of significant mass in comparison with it? I should think that makes the system very gravitationally complicated - can we even solve a five-body problem analytically? BTW, pick up your game, Venus.
2.7 / 5 (3) Jul 12, 2012
thanks, nuge, 'that_guy', PieRSquared for the interesting constructive thoughts.

I'm thinking the Pluto flyby will take a month to approach; meaning they can take pictures and do spectroscopy for a month and then a month as they are going away; so that's two months; that's not too bad!

On Pluto's size . . . i mean to argue some in support of the whole downgrading of Pluto as a planet and to argue in support at the same time. Those argueing against Pluto as a planet do so because it's composed of the same materials as comets. I agree to some extent. But, if we're to do so, what about the different nature of the Jovian planets versus the inner terrestrial planets? The outer Jovian planets are gas giants. The inner terrestrial planets are much smaller rocky planets(five counting the moon; and even more counting the moons of the gas giants!) So, one could say there's four or five inner rocky planets depending on whether we want to count the moon, and four outer gas giants . . .
3 / 5 (2) Jul 12, 2012
. . . and then a lot of icy smaller than even the rocky inner planets.

Pluto is still an oddball by this standard though! Pluto is much larger than your average comet(maybe five kilometers, maybe in the tens of kilometers). Pluto is in the thousand kilometer diameter range.

I'm not strictly against downgrading Pluto from planet hood; but, if we're going to go there, I've indicated above that we can go a bit further and downgrade the inner rocky planets from the Jovian gas giants; or, at least distinguish them from one another.
5 / 5 (2) Jul 12, 2012
I'm not strictly against downgrading Pluto from planet hood; but, if we're going to go there, I've indicated above that we can go a bit further and

That's no planet; that's a space station...

On reading more about the NH mission, I thought it interresting that the third stage booster is actually on its way out of the solar system too (as well as a couple other boosters from other missions). Interstellar space junk. Kinda makes me wonder how much space junk must be floating around the cosmos if we aren't the only ones. Needles in haystacks, but doesn't it tickle your imagination? Imagine finding something like Voyager, with a golden record and images on it, but not being able to figure out where it came from. Funny thing is, even if we spotted something headed into the solar system, with our current tech it would be extremely difficult to intercept unless the trajectory was favorable to intercept.
5 / 5 (2) Jul 12, 2012
@flashgordon: The definition of what is and isn't a planet isn't really objective so will probably always be a matter of religious debate. For what it's worth here's the IAU definition: http://en.wikiped...f_planet

When asteroids were first being discovered they got categorized as planets but that changed because their nature and character were different and there were getting to be too many of them for the definition to be meaningful. The recent demotion of Pluto was done for the same reasons. If you check the link there are a lot of large KBOs already identified and there are probably way more out there to be found. At least let's have mercy on the school children and not force them to memorize 463 planet names.

As for gas giants we already call them gas giants so problem solved.

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