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Editor’s Report: More From Pluto

The New Horizons spacecraft continues to deliver.


After swinging within one Earth diameter of Pluto and gathering hundreds of images of the remote icy world, NASA’s New Horizons spacecraft is heading another billion kilometres outward toward a 45-kilometre-diameter Kuiper belt object known as MU69. It will reach its destination for an image-gathering flyby on January 1, 2019.

In the meantime, for the next six to eight months at least, the 80 percent of the New Horizons’ library of images and data still in the spacecraft’s memory storage will be transmitted back to NASA’s Deep Space Network antennas.

Why is it taking so long?

New Horizons is outfitted with cameras, spectrographs and particle detectors and has the latest (at the time of its launch) data storage and transmission equipment. You might expect that all we would have to do is transmit the data back to Earth at the speed of light. It takes sunlight more than eight minutes to reach Earth, and data from Mars can take as much as 20 minutes, but New Horizons is so distant that it takes more than five hours for data to be transmitted to Earth.


FASCINATING SPUTNIK PLANUM One of the most interesting features observed on Pluto by New Horizons is this craterless icy plain, informally named Sputnik Planum. Its lack of craters indicates that it is less than 100 million years old and possibly much younger. The colour of the image is enhanced to aid in feature analysis. Photo courtesy NASA

While it’s true that data are sent to us from the spacecraft at light-speed, the signal spreads out over distance, and it requires a Deep Space Network 70-metre-diameter antenna to capture the faint, diffuse signal arriving on Earth from New Horizons, which is five billion kilometres away. And even an antenna that large can collect only 125 bytes of data per second from such a remote source of relatively low power.

For a single image from the onboard camera instrument — roughly a 2.5-megabit image when compressed — it takes 20 to 40 minutes for the 70-metre dish to collect the data. Some high-resolution images take much longer than that. For this reason and because the Deep Space Network antennas have other tasks to handle, the entire library of images stored on New Horizons will not be safely on Earth until late this year.

Editor Terence Dickinson invites your comments and astronomy-related observations and photos, which can be directed to him at [email protected].

Check out the January/February issue of SkyNews (on newsstands now) for an expanded version of Terence Dickinson’s Editor’s Report.

Categories: Editor's Report
2 comments on “Editor’s Report: More From Pluto
  1. B Fenerty says:

    re light distance to Pluto correct or incorrect?

    Hi there

    In the latest/recent issues of Skynews (not in front of me as I type) I recall that Pluto is stated or titled as over five light hours from us. (I maybe misread – but that number did stick in my mind)

    Are my sky apps and some online web sources wrong in contradicting that, suggesting we are under 5 light hours from Pluto itself – about 4.7 hrs or so currently. Or is maybe the figure being confused with the distance to New Horizons rather than to Pluto?

    If current distance from us to Pluto indeed IS over 5 light hours then some apps and recent online pages have faulty info.

    Curious. Meanwhile a good holiday season to all there.
    B Fenerty
    member RASC Calgary Centre.
    monthly BC astronomy column writer.

    • Gary says:

      You’re quite correct — the headline should have read “4.5 light-hours from Earth.” Pluto just *seems* farther away.

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