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Pluto/Charon: Surface Features Emerging

One of the more memorable moments from yesterday’s teleconference on the New Horizons mission was Alan Stern’s comment that the latest pixelated images of Pluto/Charon constituted his ‘meet Pluto moment.’ If anyone has an interest in meeting Pluto, it’s Stern (Southwest Research Institute), who serves as principal investigator and whose unflagging efforts made it possible. As for those pixelated views, well, they’re a glimpse of what is to come, but even now, they’re telling us helpful things about the target. The animation below speaks volumes, with the first showing Charon’s rotation with the center of Pluto fixed in the frame. The images were acquired with the Long Range Reconnaissance Imager (LORRI) camera.


Image: A series of LORRI images of Pluto and Charon taken at 13 different times spanning 6.5 days, from April 12 to April 18, 2015. During that time, the spacecraft’s distance from Pluto decreased from about 111 million kilometers to 104 million kilometers. Pluto and Charon rotate around a center-of-mass (also called the “barycenter”) once every 6.4 Earth days, and these LORRI images capture one complete rotation of the system. The direction of the rotation axis is shown in the figure. In one of these movies, the center of Pluto is kept fixed in the frame, while the other movie is fixed on the center of mass (accounting for the “wobble” in the system as Charon orbits Pluto). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

The second image shows the same view with the motion around the barycenter clearly revealed, a spectacular teaching tool for those trying to explain rotation around the center of mass.


Image: The 3x-magnified view of Pluto highlights the changing brightness across the disk of Pluto as it rotates. Because Pluto is tipped on its side (like Uranus), when observing Pluto from the New Horizons spacecraft, one primarily sees one pole of Pluto, which appears to be brighter than the rest of the disk in all the images. Scientists suggest this brightening in Pluto’s polar region might be caused by a “cap” of highly reflective snow on the surface. The “snow” in this case is likely to be frozen molecular nitrogen ice. New Horizons observations in July will determine definitively whether or not this hypothesis is correct. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

The zoomed image is particularly notable because it clearly shows different brightness patterns as Pluto rotates (and notice that Charon, even though much smaller, still stays relatively the same, an indication that the surface is more uniform than Pluto, or as Stern said in the news conference, more ‘muted’). An apparent oddity here actually is not — If you look closely at the view of Pluto in the center, it seems to show an uneven surface. This is only an optical effect caused by the fact that dark areas on the dwarf planet are rotating in and out of view.

These albedo changes on the Plutonian surface are striking. Stern commented that it was unusual that we should be seeing such marked effects from such a distance. The possibility of a polar cap — probably made of highly reflective frozen molecular nitrogen ice — seems strongly enhanced by the bright area that persists in the zoomed image. JHU/APL has used a mathematical technique called deconvolution to improve the resolution of the raw LORRI images, giving us about the best resolution the camera and detector can provide at this distance.

And speaking of raw images, be aware of the raw image archive being assembled on the LORRI Images from the Pluto Encounter page. The imagery is, of course, going to keep getting better. We’ll get another sequence from an observing run scheduled for May 8 through May 14, producing another ‘movie’ in mid-May, followed by a lengthy pause to downlink the data that lasts until the 27th. The spacecraft will then begin observing Pluto/Charon daily at ever higher resolution. Fasten your seat belt.


Comments on this entry are closed.

  • Lionel Ward April 30, 2015, 8:56

    Wonderful, and every picture of Pluto from now on will be even better than this!

    I’m intrigued by the notion of planets having polar caps at such a great distance from the Sun. Mars and Earth have dramatic temperature contrasts between their equator and the poles because of the vast difference in solar radiation flux that each sq. km. of surface receives at the equators vs. at the poles. Geometry out at Pluto works the same way of course, but since solar radiation intensity out there is about a thousandth of what it is on Earth, I wouldn’t have thought being at the poles vs. being at the equator would make much difference at all… glad to be wrong, it’s much more interesting to have N2 polar caps of course!

  • Alex Tolley April 30, 2015, 11:35

    All my life, Pluto has been nothing more than a bright dot in a telescope. Even the best Hubble images were vague shadings. Yet within months Pluto will join the pantheon of well-imaged worlds with a wealth of associated data, with the bonus of Charon that was once unknown.

  • ljk April 30, 2015, 13:38

    Not to be a stickler, but we could have known about Pluto and its moons (and rings?) up close in 1986:


    Quoting some key points:

    Voyager 1 would have brought a magnetometer and a more diverse array of space plasma instruments to bear on Pluto than we will. But it’s more important that New Horizons has much more advanced mapping cameras and a far more capable radio science experiment to determine atmospheric pressure and temperature. We also carry a dust impact detector. “Voyager did not have such a device to study Pluto’s environment.”

    One key technical advantage stemming from Voyager’s larger antenna and higher power budget was the ability to send data back at much faster rates-about 10 times faster than New Horizons. Voyager also had a scan platform that allowed its remote sensing instruments to be trained on their targets even while the spacecraft was transmitting data to Earth- a high-cost technology that the New Horizons team chose to forego.

    And although Voyager would have been able to map Pluto’s entire surface in 1986, since that surface was then oriented equator-on to the Sun (unlike the high-latitude illumination to be seen in 2015, leaving much of the winter hemisphere in darkness), Voyager’s memory storage was much, much smaller, so the resulting dataset would have been correspondingly less.

  • Hop David April 30, 2015, 14:04

    I am hoping they will more precisely nail down the orbital elements of Pluto/Charon.

    From the knowledge we now have, they’re mutually tidelocked. Eccentricity is close to zero, obliquity is close to zero.

    I believe it’d be possible to have an elevator centered at the Pluto/Charon L1 that extends to Charon as well as Pluto. With the very near circular orbits and near zero obliquity, there’d be little flex on the tether.

    With such an elevator, Pluto/Charon would be like Robert Forward’s Rocheworld.

  • Lionel Ward April 30, 2015, 16:31

    ljk, sounds like New Horizons is overall a much better probe, the key being the enormous difference in memory it held. New Horizons will gather so much more data, and I quite like the fact that it will come through over the course of >1 year, spreads out the fun!

    In a curious parallel to Voyager not going to Pluto, I read in an interview with Alan Stern that his group submitted plans for a New Horizons II that would have launched about the same time as NH. It would’ve done flybys of Uranus or Neptune plus one Kuiper belt object! As it would’ve been an identical probe to New Horizons and had the same operating team he said the mission would’ve cost £400 million. Seems like such a bargain to me, what a pity it didn’t happen. Still it’s awesome what’s being achieved with New Horizons, it’s visit to Pluto is quite likely to be remembered as the highest point in planetary science this decade

  • Joy April 30, 2015, 19:16

    The choice to swing Voyager 1 past Titan in 1986 was a tradeoff. But, I still think the right decision. The Pluto option was higher risk. We also got the benefit of sending Voyager 1 out of the system at 35 degrees ecliptic latitude (in contrast to Voyager 2’s minus 34 degrees ecliptic latitude) to get a better survey of the heliosphere. I don’t think that Pluto is massive enough to be used for much of a course change.

  • Christopher Phoenix April 30, 2015, 21:32

    Exciting stuff, it is great to see our first close-up view of Pluto/Charon unfolding as New Horizons approaches its objective!! I’m definitely going to keep a close eye on the progress of this little spacecraft over the ensuing months.

  • ljk May 1, 2015, 8:53

    Lionel Ward said on April 30, 2015 at 16:31:

    “ljk, sounds like New Horizons is overall a much better probe, the key being the enormous difference in memory it held. New Horizons will gather so much more data, and I quite like the fact that it will come through over the course of >1 year, spreads out the fun!”

    Voyager 1 would have imaged the entire surface of Pluto and I am guessing Charon as well, whereas NH will not be able to see that world’s winter hemisphere, so basically we will have the same situation at Pluto as we did when Mariner 10 flew by Mercury in 1974-75, with only half of that world imaged. Will we have to wait another three decades or more for Pluto’s version of MESSENGER to complete the job?

    And let us hope NH doesn’t have any mechanical problems when it has to keep pivoting the entire probe around first to image the Pluto system then aim back at Earth to transmit all the data, which it will have to do very slowly. Shades of Mariner 4! :^) I also keep thinking of Voyager 2 during its encounter with Saturn in 1981, when its scan platform jammed due to some local debris and they missed some of the highest resolution images of several moons. Sure Cassini picked up the slack but that was decades later. Not to be rude but not all of us are going to be around 3 to 4 decades from now, or perhaps at least not in fully functioning order – though I am hoping for those mind transfers to perfect android bodies technologies will be developed by then.

    And last but not least, we could have seen what Pluto was like in 1986. This was when Pluto was approaching the closest point in its orbit to the Sun, which only happens once every 248 years. Gases frozen to that alien body’s surface for centuries were starting to heat up and release themselves. Maybe even some geysers were being activated like with Triton, which people have been saying is what Pluto is probably like ever since its closeup courtesy of Voyager 2 in 1989.

    And thank goodness for the Voyagers or our knowledge of outer Sol system would still be so painfully incomplete! Plus they have the Golden Record. ;^)

  • ljk May 1, 2015, 9:00

    And about Voyager 1 passing by Titan in 1980: It was pretty obvious even with the crude Pioneer 11 images of that moon in 1979 that Titan’s cloud cover was thick and opaque – hoping for breaks in the clouds was wishful thinking. And even when Cassini was able to penetrate that orange cloak in 2004, scientists were initially quite confused with what they saw on the surface of Titan, so even a few holes in those alien clouds would not have done much in terms of our understanding that moon.

    And yes I am aware that Voyager 1 did see Titan’s surface in different wavelengths, but that was not realized until much later:



    So yes, Voyager 1 should have been reaimed to Pluto because as our space program has shown as of late, planetary missions to the outer worlds are few and far between and even our remote sensing isn’t the same as being there.

  • ljk May 1, 2015, 14:17

    Finally someone recognizes the robot space probes as fellow explorers:


    Without them, we would know so much less about the Sol system and beyond.

  • Lionel Ward May 1, 2015, 19:46

    @Hop David

    That’s awesome. Perhaps the flexing that does arise can harnessed as an energy source

  • Ricardo Orsini C. Amarante May 3, 2015, 14:24

    The albedo discrepancies features are notable.

  • ljk May 4, 2015, 9:46

    How I Helped Get Us To Pluto

    Ron Miller

    4/11/13 11:00 am

    Back in 1991 I did a series of illustrations for a set of US commemorative postage stamps, one for each planet and the Moon. There was a spacecraft associated with each world . . . except Pluto. And there was something about that stamp that rankled a lot of scientists.

    In 1993 JPL engineer Robert Staehl explained what the problem was in a paper titled, “To Pluto from a First-Class Postage Stamp.” “During 1991,” he wrote, “with Voyager 2’s Neptune encounter two years behind us, the U.S. Postal Service issued ten stamps commemorating the success of planetary exploration.

    On a stamp for each of the first eight planets and the Moon appeared an illustration of the celestial body with one of the spacecraft which visited it. The stamp for Pluto simply announced, NOT YET EXPLORED, as if to taunt engineers and scientists at Pasadena’s Jet Propulsion Laboratory (JPL) , where the stamp were unveiled in a first-day-of-issue ceremony on October 1 . . .”

    Full article here:


  • ljk May 4, 2015, 14:43
  • ljk May 7, 2015, 15:41

    NH is on the lookout for any unexpected moons – and rings – and who knows what else:


    To quote:

    On 11 May, a telescope aboard a NASA craft will turn and stare at Pluto — like a space-robot equivalent of a sailor watching for shoals that could take out his vessel.

    As the New Horizons craft hurtles towards its 14 July rendezvous with Pluto, mission scientists are preparing to guide it through what could be a dangerous dusty realm. It will skim the orbit of the dwarf planet’s largest moon, Charon, at more than 48,000 kilometres per hour. At that speed, hitting a dust particle the size of a rice grain could be fatal.

    To minimize the risk of hitting debris from Charon or another, unknown moon, scientists will conduct seven 45-minute observation sessions between 11 May and 1 July. If they find a potential hazard, the team can change the spacecraft’s course. That would mean for­going some science observations, but it could also mean the difference between life and death for the first spacecraft ever to visit Pluto.

    Mission leaders calculate that the chance of a dust particle knocking out New Horizons is just 1 in 10,000. The only way to avoid the hazard completely would be to stay away from Pluto altogether, says Marc Buie, a mission co-investigator at the Southwest Research Institute in Boulder, Colorado.

  • ljk May 15, 2015, 10:47

    NH has now imaged all the known moons of Pluto:


    It is the unknown satellites we have to wonder about next.

  • ljk May 27, 2015, 14:30

    As the opening line says, what a difference 20 million miles makes: