Pluto is King of the Kuiper Belt!

A portrait from the final approach. Pluto and Charon display striking color and brightness contrast in this composite image from July 11, showing high-resolution black-and-white LORRI images colorized with Ralph data collected from the last rotation of Pluto. Color data being returned by the spacecraft now will update these images, bringing color contrast into sharper focus. (Credits: NASA-JHUAPL-SWRI)
A portrait from the final approach. Pluto and Charon display striking color and brightness contrast in this composite image from July 11, showing high-resolution black-and-white LORRI images colorized with Ralph data collected from the last rotation of Pluto. Color data being returned by the spacecraft now will update these images, bringing color contrast into sharper focus. (Credits: NASA-JHUAPL-SWRI)

LAUREL, Md. (NASA PR) — NASA’s New Horizons mission has answered one of the most basic questions about Pluto—its size.

Mission scientists have found Pluto to be 1,473 miles (2,370 kilometers) in diameter, somewhat larger than many prior estimates. Images acquired with the Long Range Reconnaissance Imager (LORRI) were used to make this determination. This result confirms what was already suspected: Pluto is larger than all other known solar system objects beyond the orbit of Neptune.

“The size of Pluto has been debated since its discovery in 1930. We are excited to finally lay this question to rest,” said mission scientist Bill McKinnon, Washington University, St. Louis.

Pluto’s newly estimated size means that its density is slightly lower than previously thought, and the fraction of ice in its interior is slightly higher. Also, the lowest layer of Pluto’s atmosphere, called the troposphere, is shallower than previously believed.

This graphic presents a view of Pluto and Charon as they would appear if placed slightly above Earth's surface and viewed from a great distance. Recent measurements obtained by New Horizons indicate that Pluto has a diameter of 2370 km, 18.5% that of Earth's, while Charon has a diameter of 1208 km, 9.5% that of Earth's. (Credits: NASA-JHUAPL-SWRI)
This graphic presents a view of Pluto and Charon as they would appear if placed slightly above Earth’s surface and viewed from a great distance. Recent measurements obtained by New Horizons indicate that Pluto has a diameter of 2370 km, 18.5% that of Earth’s, while Charon has a diameter of 1208 km, 9.5% that of Earth’s. (Credits: NASA-JHUAPL-SWRI)

Measuring Pluto’s size has been a decades-long challenge due to complicating factors from its atmosphere. Its largest moon Charon lacks a substantial atmosphere, and its diameter was easier to determine using ground-based telescopes. New Horizons observations of Charon confirm previous estimates of 751 miles (1208 km) kilometers) across

LORRI has also zoomed in on two of Pluto’s smaller moons, Nix and Hydra.

“We knew from the time we designed our flyby that we would only be able to study the small moons in detail for just a few days before closest approach,” said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado. “Now, deep inside Pluto’s sphere of influence, that time has come.”

Nix and Hydra were discovered using the Hubble Space Telescope in 2005. Even to Hubble, they appeared as points of light, and that’s how they looked to New Horizons until the final week of its approach to Pluto. Now, the latest LORRI images show the two diminutive satellites not as pinpoints, but as moons seen well enough to measure their sizes. Nix is estimated to be about 20 miles (about 35 kilometers) across, while Hydra is roughly 30 miles (roughly 45 kilometers) across. These sizes lead mission scientists to conclude that their surfaces are quite bright, possibly due to the presence of ice.

The approximate sizes of Pluto’s moons Nix and Hydra compared to Denver, Colorado. While Nix and Hydra are illustrated as circles in this diagram, mission scientists anticipate that future observations by New Horizons will show that they are irregular in shape. (Credits: JHUAPL/Google)
The approximate sizes of Pluto’s moons Nix and Hydra compared to Denver, Colorado. While Nix and Hydra are illustrated as circles in this diagram, mission scientists anticipate that future observations by New Horizons will show that they are irregular in shape. (Credits: JHUAPL/Google)

What about Pluto’s two smallest moons, Kerberos and Styx? Smaller and fainter than Nix and Hydra, they are harder to measure. Mission scientists should be able to determine their sizes with observations New Horizons will make during the flyby and will transmit to Earth at a later date.

  • therealdmt

    Man, Pluto is a gnarly one.

  • Snofru Chufu

    Yes, I like the mission, but the NASA’s media circus is quite exaggerated. I do not like to hear this style of NASA’ propaganda machine all the time. “All, all … is great. “. Oh man, even the diameter is some smaller, oh man the density is someone lower. Oh no, man, how is this possible? Come on, Alan Stern do not exaggerate in this way.

  • Kapitalist

    I think that one must consider the general public which catches only a few news items about this. I think NASA does a great job with outreach to the public, compared to ESA or JAXA or Roscosmos or private space companies (although announcements of the Roscosmos-boss are sometimes more entertaining.)

  • Snofru Chufu

    This kind of selling scientific missions is quite dangerous, because next time even more most exaggerated and great spoken to interest the public. Where is the limit?

  • Aerospike

    Yeah like getting the general public excited about space exploration would be such a bad thing!!!
    *shakes head in disbelief*

    Really Snofru? What on earth are you talking about?

  • Paul_Scutts

    And is punching like an all growed up planet should.

  • Snofru Chufu

    It is about right dose and method.

  • Kapitalist

    “Selling” science is different than conducting science. I basically agree with you and I didn’t even watch the next to last press conference about NH because I was fatigued by the old same same talk. But we are surrounded by billions of people who don’t know and haven’t cared. I think that the general media message, fed by NASA, about what is happening now is fairly appropriate for the world audience.

    This is not only a historical scientific event, it is a top world news event too. Stupid media after all does know something about how to reach out to people. Maybe (unintentionally) inspiring thousands of new astronomers and rocket scientists. In the history books the year 2015 will be remembered for reaching Pluto. Stuff like Crimea and Greece will soon be forgotten. I mean, who knows anything about the politics of Spain or Portugal around the year 1500? Because then something else happened which overshadowed all of that temporary in-house quarrel. Outreach has to be a bit stupid, that’s the only way it works, unfortunately. Stimulating interest is the name of the game. Knowledge and understanding is then up to each one to find out, to the degree they have become interested. One can only throw the dice and count the eyes. The result is up to everyone.

  • Kapitalist

    Actually, exploration is all about being stupid, isn’t it? One has to start out stupid in order to learn something. Why send humans to Mars or a probe to Pluto? We don’t know. That’s why we should do it! Exploration is to find out what we don’t know. This is the cliff between engineers and astronomers, as I imagine it. One works on what is possible, the other on what is impossible, that which is to be discovered.

  • Snofru Chufu

    Thank you for detailed reflections. You may know that I am also a very great space exploration and utilization advocate. My problems may arise at first from the “aggressive” US-style of presentation and selling. I personally like more the old Soviet/Russian style (in respect to space and S/F), which has a philosophical and romantic touch and it is no so noisy. However, you are right, today; we observed an important step in exploration of outer solar system. Let us celebrate the day.

  • Hug Doug

    Don’t freak out just because someone is passionate about something and you are not. After all, this is their life’s work, of course they are excited about their findings!

  • Vladislaw

    An you honestly believe that all this “hype” is going to actually pull most of humanity away from their cell phones long enough to actually watch and listen to Alan Stern talk about pluto?

  • DavidR2015

    I guess the question is, is Alan Stern simply trying to share his excitement and experiences with the world, or is it a case of media hype and exaggeration? I believe its the former, but I can see how someone could draw similarities between the reporting of a remarkable event and the promotion of something less remarkable.

  • DavidR2015

    Although it looks rough round the middle and smooth on the sun facing pole. I don’t know if this is a trick of the light or if the geology really has been more active around the equator of Pluto than elsewhere.

  • Kapitalist

    I’ve recently tried to start learning something about biology, which is a very mysterious world. It has given me some new mental perspectives on human civilization. We are going to space, we are spreading life to other planets/moons/everything, this is unstoppable. It is happening one way or another. Falcon 9 maybe is better than SLS and NASA is better than Roscosmos. But even a Soviet SLS would send humans to Mars, it is just a matter of time, very very short time in the history of cosmos.

    First stone tools date back to only 0.0033 billion years ago. As soon as an ape slams two stones together, it builds settlements on Mars. No delay, no hesitation, just going directly to space instinctively. One can speculate about why it is happening and how it will happen, but it is happening.

  • Snofru Chufu

    I am sorry, but I do not share this linear, progressive, leftist/liberals (to the better or “end of history” ) view of history. History has no goals and is not guided by a
    world-spirit (as well as evolution is blind and not guided actively) as philosopher Hegel proposed.

    Civilizations arise, mature, decline and die. In the moment we are witness the decline of Western civilization (dominated at present by its anglo-american variant) despite this temporary space events. What about fall of US-empire, which seems also not unlikely if you consider what review present situation of US military overstretch, huge debt and internal conflicts in USA? Means of man have increased considerable, but also hazards, which originate from it.

  • Snofru Chufu

    Not really!

  • Kapitalist

    Oh “the mind” (whatever it is as long as it is biological) will quickly reappear if its genes are around. It might take millions of years, but that is nothing in cosmic or biological time scales. And there might be more interesting things than minds around.

    I think you confuse civilization with government. Governments fall because government means using violence to destroy the productive activities in society. It is the productive part of society which has anything of value for the violence using elite to loot, that’s why government always attacks and destroy the most productive parts of society first. Government is a small group of greedy individuals who use violence to steal other people’s money. If you imagine that your violent ruler wants and can do anything good for society, then you are simply fooled! And please skip ridiculous labels like “liberal” or “right/left”. Instead see things for what they actually are, without any dreams.

  • DTARS

    Reading this on my cell. 🙂