Planet X-Ray

In Solar System by Brian Koberlein4 Comments

Pluto is emitting x-rays, and we don’t know why. 

X-rays aren’t something we’d expect from Pluto, since the planet has no clear way of generating them. It’s a small, cold world with little magnetic field. Some solar x-rays might scatter off Pluto in our direction, but the level of x-rays is higher than what could be produced by scattering. So what gives?

The most likely explanation is that the x-rays are produced through an interaction between the solar wind and Pluto’s atmosphere.  As the New Horizon’s flyby found, Pluto’s atmosphere is actually quite stable, so interactions with the solar wind could produce x-rays. Similar interactions between the solar wind and the comas of comets have been seen to produce x-rays. But the level of x-rays from Pluto is even higher than we’d expect from such an interaction, so that isn’t the whole story.

While these x-rays are a mystery, it’s important to keep in mind that the amount of data is actually quite small. There’s enough data from the Chandra spacecraft to know that it’s not a random fluke, but it’s difficult to get much detail from such a small sample. What this study does show is that Pluto does produce x-rays, and perhaps we should give it a closer look.

Paper: C.M. Lisse, et al. The puzzling detection of x-rays from Pluto by Chandra. Icarus. (2016) DOI: 10.1016/j.icarus.2016.07.008


  1. I know nothing about astro photography. But i just could not imagine “they” were able to create a image in x-ray of Pluto (blue dot in above image) using only 7 photons. After some Googling around i noticed all pages talk about “7 photons in total collecting during almost 50 hours observation time”.

    To get an idea “A high-quality digital camera based on a multi-megapixel array will typically record an image by collecting of order 10^5 photons per pixel”. Although we can’t compare this 1 on 1…it means that if you make a photo with your 5Megapixel camera, 1 million x 5 million photons are being used (with a shutter time of a fraction of a second)….thats alot of photons.

    If i read the paper and google on, its still not clear to me. But they use a term “cts/s” which is some sort of unit for photon-count. So i guess they mean 7 photons per second, and not in total. Could anyone clear this up? Thanks in advance

    Quote from the paper;
    Added to the 2014 results, we find a total Pluto x-ray signal of 6.55 ± 1.28 cts, a total count rate of 3.7 x 10-5cps, and a 5.4σ detection of Pluto in an 11×11 pixel (5.5”x5.5”) box centered on its ephemeris position.

    1. Grrrrr… turns out to be 7 or 8 photons in total, collected during almost 50 hours of observation time

      Found this article with some more comments from Chandra team members. And the original x-ray image showing Pluto slightly bigger as a dot. So the image we see everywhere (and top of this page) is a highly blown-up image of Pluto in x-ray

      The “real” x-ray image of Pluto;

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