By Rick Nowell

NASA’s New Horizon’s spacecraft’s closest approach to Pluto was Tuesday, July 14 at 5:50 p.m.

It zipped past at 49,600 km/h at a distance of just 12,500 km. It sent back the best photo ever. For a look at the plateaus, chasms and craters, as well as the dark north pole, see the NASA link (the July 13 photo is shown below).

(The closest photos won’t get here until late tonight – there is a signal delay of 4.5 hours at the speed of light; and the spacecraft is snapping photos and taking temperature and atmosphere samples, too busy to call back until done).

Pluto has five moons. Pluto’s biggest moon, Charon, is about 1,208 km in diameter. These other moons may sound familiar from old Greek mythology: Styx, Charon, Nix, Hydra and Kerberos.

Charon, son of Nix and Erebus, is the ferryman of Hades who carries souls of the newly dead across the river Styx. Kerberos (aka Cerberus) was the gigantic hound that guarded the gates of Hades. And Hydra was a many-headed serpent guarding an underwater entrance to the Underworld.  Who was Pluto, the principal body here? Pluto was the ruler of the underworld, who presided over the afterlife.

So, like Charon, the spacecraft carries a sample of the cremated remains of Clyde Tombaugh, discoverer of Pluto in 1930.

Pluto is thought to have a rocky core 70% of its diameter in size, covered by layers of water ice, nitrogen, methane and carbon monoxide ice. The dark pole is likely frozen solid nitrogen ice, since the average surface temperature is a nippy -229°C, and nitrogen gas turns liquid at -196°, and freezes to an ice at -210° (and the college physics lab does an interesting liquid nitrogen demo on this—we can even make drops of liquid oxygen at -183°). Although it’s not quite cold enough for simple superconductivity, rare-earth superconductor compounds like yttrium-barium-copper-oxide at -181° would work fine here.

When frozen, nitrogen forms large, transparent crystals several inches across, so the ground should sparkle in the dim sunlight. The landscape has a pinkish color caused by particles of haze that slowly fall from the thin, cloudless atmosphere. Dark gray splotches around the equator may have been impacted by comets with carbon-rich materials or gritty dirt.

Pluto (the ninth planet) has just been found to be slightly bigger than earlier estimates, having a diameter of 2,370 km. The previous estimate was 2,300 km; which was 30 km smaller than Eris, the tenth planet (ok, now like Pluto, demoted to just a dwarf planet). It settles the debate over which was bigger – Pluto or Eris?

PS: For astronomy fans the College of the Rockies in Cranbrook is offering Astronomy 100 again in September on Mondays and Thursdays 4-5:30 p.m. with a lab Tuesday evenings 6-9 p.m.; and we have some nice telescopes and cameras to use. We have eight students signed up already.

Continuing Ed also has some star constellation courses later in the fall and winter semester.

Lead image: Not to scale, Pluto (top right) remains in debate as to whether or not it is a planet in our solar system. One thing that is now irrefutable is Pluto joins the rest of the planets in the solar system as being closely photographed by humans. It took New Horizon nine years to reach.

– Rick Nowell is the Physics Lab Tech at College of the Rockies in Cranbrook.

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