Possible Pluto Polar Cap Appears In Latest New Horizons Photos

This image of Pluto and it largest moon, Charon, was taken by the Long Range Reconnaissance Imager (LORRI) on NASA’s New Horizons spacecraft on April 15, 2015. The image is part of several taken between April 12-18, as the spacecraft’s distance from Pluto decreased from about 69 million miles (93 million kilometers) to 64 million miles (104 million kilometers). Credits: NASA/JHU-APL/SwRI
This series of images of Pluto and it largest moon, Charon, was taken by NASA’s New Horizons spacecraft between April 12-18, 2015. The spacecraft’s distance from Pluto decreased from about 69 million miles (93 million km) to 64 million miles (104 million km) during that time. The blue cross is the system’s center of gravity. Credits: NASA/JHU-APL/SwRI

For the first time, images from NASA’s New Horizons spacecraft are revealing bright and dark regions on the surface of the dwarf planet Pluto. The latest photos were taken from 64-70 million miles away in mid-April using the telescopic Long-Range Reconnaissance Imager (LORRI) camera on the probe. 70 million may sound far until you realize that Pluto’s currently more than 3 billion miles from Earth today.

Pluto and Charon with Pluto's rotation axis shown. The bright spot at the right is a possible polar cap. Credit:
Pluto and Charon with Pluto’s rotation axis shown. The bright spot at the right is a possible polar cap. Pluto’s axis is tilted 122°, much more than Earth’s 23.5°. Besides bright areas, there appears to be dark, band-like feature across Pluto’s middle. Credit: NASA/JHU-APL/SwRI

Besides those dark and bright regions, there’s a bright area at one of Pluto’s poles. A polar cap? Maybe. We also see Pluto’s largest and brightest moon, Charon, rotating in its 6.4-day long orbit in the photos. Since the exposures were brief – 1/10 of a second – none of the dwarf planet’s tiny, fainter moons are seen.

NASA's New Horizons mission
NASA’s New Horizons mission launched in Jan. 2006 and will arrive at Pluto on July 14. After the flyby, NASA hopes to send it on to explore additional asteroids in the outer asteroid belt called the Kuipter Belt. Credit: NASA

“After traveling more than nine years through space, it’s stunning to see Pluto, literally a dot of light as seen from Earth, becoming a real place right before our eyes,” said Alan Stern, New Horizons principal investigator. “These incredible images are the first in which we can begin to see detail on Pluto, and they are already showing us that Pluto has a complex surface.”

Still frame from the animations above. Credit: NASA/JHU-APL/SwRI
Still frame from the animations above. Credit:

Although just a blobby dot, these are the best images of Pluto EVER, even better than those taken with the Hubble Space Telescope. And the good news is, we’re hardly even close. During its mid-July flyby, New Horizons will swoop only 7,800 miles (12,500 kilometers) above Pluto’s surface. Polar bears anyone?

16 Responses

    1. astrobob

      Hi David,
      Yes, that shows well in the photos. This we did know in advance. Pluto’s albedo is ~0.6 (reflects 60% of the light it receives from the Sun) while Charon’s is ~.37, nearly twice as dark.

  1. Thank You Bob for this, the most comprehensive recap of today’s briefing that I have read so far (and that includes the one on UT and BA).
    We are living at a privileged moment when 3 probes sent by humanity are examining up close 3 types of celestial bodies never observed before at the same time. Whether you think of Rosetta-67P, DAWN- 1Ceres or New Horizons- Pluto, the upcoming years of data analysis will make us awe with each new discovery. 🙂

    1. astrobob

      You’re too kind BC – thank you. It is amazing that there are so many probes out there simultaneously. Plus there are 2 sending daily pix from Mars and Cassini at Saturn. Messenger looks to take its final shots of Mercury tomorrow. Eyes are everywhere!

  2. allison

    Aren’t polar caps formed when the poles are colder than the equatorial regions? I would think Pluto would be so unfathomably cold that there would be little temperature difference between the poles and the equator. Maybe the sun still puts out enough heat at 30 AU to make a difference.

    1. astrobob

      Of course it’s still early on, but at this point it appears like a polar cap. Whether it really is one is another matter. Still, it’s possible. When nearest the Sun, nitrogen and methane vaporize to form a temporary atmosphere. Some of that might migrate to the poles and coat the surface similar to the way seasonal ice forms at Mars’ poles. Just a hunch.

  3. caralex

    Bob, why is Pluto’s axial tilt stated as 122 degrees, rather than 32? What determined whether it had tilted more than 90 degrees to reach 122, rather than just tiling a comparatively short distance to 32, not a lot more than Earth? Is it something to do with North being ‘up’? If so, how do we know which is the north, and which the south, pole?

    1. astrobob

      Fabulous question! Astronomers apply the “right hand rule”. Hold you right hand out with your thumb up. That represents 0 degrees. Now turn your fist counterclockwise – with thumb still up – to represent Earth’s axial tilt from the plane of its orbit. Keep turning your fist in that direction and you’ll arrive at 90 degree and then past 90 to 122 (for Pluto). If you keep going till your thumb points nearly straight down, you’re at 177 degrees, Venus’ axial tilt. Once a planet’s axis is past 90 degrees, it’s considered to be rotating in retrograde compared to “normal” rotation.

        1. astrobob

          Yes, but in conjunction with the right hand rule which makes the Earth spin counterclockwise as seen from the above the north pole.

          1. this might be a sad observation but the reference to “clockwise” could be lost to most readers under the age of 30. now if we could come up with a term that would associate rotation of an object to the video buffering symbol on today’s operating systems, we’d be “in” again 😉

  4. Hi Bob,

    After watching this new video of Pluto, I’m thinking that its actually less than completely round…maybe shaped kind of like two or three huge spheres that have crashed into each other. An off shaped snow-ball.

    This video has completely surprised me…I thought Pluto was going to be just another impact crater covered orb like the Moon or Mercury, or the many other moons around the giant planets. I dont know how that can be with this new video.

    Cant wait till New Horizons sends some clearer images…this is truly exciting stuff!


    1. astrobob

      That’s certainly possible – we’ll have to wait just a little while longer to see. At 1,471 miles, Pluto is large enough to crush itself into a sphere, but who knows what impacts it may have suffered that could affect its shape.

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