At Pluto at last

This is what Pluto looks like.


The New Horizons spacecraft, launched 2006 Jan. 19, will around noon today hurtle past Pluto at a distance of about 12,500 kilometers (7,800 miles) and a speed of 45,000 km per hour (28,000 mph).

On the way, the spacecraft passed an asteroid called 132524 APL, then on 2007 Feb. 28 got a gravitational boost toward Pluto by whipping around Jupiter. Getting nearer to Pluto, it revealed that the dwarf planet has cliffs and canyons larger than the Grand Canyon, and an icy northern cap, and a diameter of 2,370 kilometers (1,473 miles), rather wider than some previous estimates, so that it must be less dense and have more ice (the Moon is 3,474 km wide); and on Sunday (July 12) at a distance of a million miles New Horizons took this photo. Fuller data will come tomorrow afternoon when the craft reports back after its passage. If it survives – collision with a near-Pluto particle the size of a rice grain could destroy it.

When Pioneer 10 and 11 and Voyager 1 and 2 were launched in the 1970s for their “Grand Tour” of the outer planets in the 1980s, this was made possible by the grand curve that had happened to come about: Neptune ahead of Uranus ahead of Saturn ahead of Jupiter, each allowing a gravitational slingshot onward to the next. Pluto, then considered an outer planet too, was left out because it was far behind this curve. (One day I will try to get the several diagrams I have made of this, in the Astronomical Calendar and Companion, printed as a poster.) So now we have the first visit to Pluto.

I remind you of the idiot story of why Pluto, now classified as a dwarf planet like the largest asteroid 1 Ceres, has an unrememberable official number. The late Brian Marsden, a magisterial scientist and a wise and courteous gentleman, keeper of the records for the International Astronomical Union, foresaw that Pluto would have to be downgraded from the status of major planet; the numbering of minor planets (asteroids) was growing toward 10000, so he suggested that this number should be reserved for Pluto. This would have kept it at the head of the list of trans-Neptunians, the others like Eris not yet having been numbered. His suggestion didn’t necessarily imply downgrading Pluto yet, but because of opposition to that possibility it was rejected by the IAU. Result, when Pluto was downgraded some years later, it became minor body number 134340.

9 thoughts on “At Pluto at last”

  1. YES! A time of interplanetary exploration is here. Alastair, I remember my parents dragging me out of bed in the middle of the nite to see the first satellite sent up by humans. And now we’re seeing pictures of Plute from something sent out NINE years ago and now signals from it take only 4 mintes. INCREDIBLE.
    And as of coincidence or planned, I believe the planets do the tango as Guy put it in a later blog, to some grand “danse ensemble”. The music of the spheres and ellipses.

  2. Well, the probe has survived its encounter at least – and hopefully there’ll be a flood of new data to follow soon.

    Incredible to think that just between my grandmother’s lifetime and mine the world has gone from having no atmospheric manned aircraft except hot-air balloons to visiting all major points to the outer edge of the Solar System (and beyond – Voyagers 1 and 2, which were both launched still within her lifetime!).

    Pluto orbiter next, please!

  3. I haven’t seen any mention within the astronomy sphere of an interesting coincidence, remarkable to those who are astrologically inclined: on the day New Horizons flies by Pluto, as seen from Earth, Pluto is at opposition to the new Moon (1810 UT 14 July), Mars (0008 UT 15 July), and Mercury (0938 UT 15 July — all times by ecliptic longitude). Pluto was at opposition to the Sun on 6 July.

    I imagine it makes practical sense to plan the flyby around the time Pluto is opposed to the Sun, for the minimum distance between Earth and New Horizons, and the least interference of solar radiation with New Horizon’s radio signal. Perhaps it makes sense to plan the flyby for a new Moon, so the Moon is out of the way. The opposition of Mercury and Mars to Pluto, I’m sure, is purely coincidental, unless you believe that the music of the spheres (or ellipses) is in perfect harmony.

    1. In the last paragraph, I wish I could change the word “coincidental” to “unintentional”.

      1. Or rather, change the phrase “purely coincidental” to the word “unintentional”.

  4. This morning will be the only time in my life that I will actually be able to say I had breakfast with Pluto. Bravo to the New Horizons’ team! As always, thanks for the great one of a kind follow-up story on Pluto, Guy.

  5. Congratulations to all who made this mission to Pluto (and beyond) possible! It is good seeing smart people do smart things.

  6. Ooooh, what an exciting time to be alive for space exploration and sight seeing. Besides what you can actually see in the sky now with your own eyes, cable TV’s NatGeo’s channel is having a special on tonite, Tues, July,14 featureing New Horizon’s mission at Pluto @9PM EDT, followed by another special about Hubble telescope. Maybe it with bolster some enthusiasm for my cause to rescue it rather than allow it to crash back into earth as a piece of space junk (see my comment under Triple Act; Part One),
    Another interesting diversion is the lack of Pluto’s symbol missing from the arc on the back or Atlas supporting the sphere of Earth on his statue in Rockefeller Plaza in NYC. I guess it hadn’t been discovered by the time the statue was made.

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