August 2015

Saturn is the only bright planet visible after twilight this month and dominates the skies in the south-southwest after sunset. The ringed planet lies in eastern Libra (the Scales, which used to be the pinchers of Scorpio) about 10° west of Antares. On these warm August evenings you might enjoy looking upward to locate the Summer Triangle, which will be overhead in the evening. It consists of the brightest stars of three different constellations: Deneb (Cygnus, the Swan), Altair (Aquila the Eagle), and Vega (Lyra, the Lyre).

August 2: Saturn stops moving retrograde

August 12, 11, and 12: This year will be a banner year for observing the Perseid meteor shower. The sky will be dark because the moon will be new on August 14. The early morning before dawn will be best, especially the morning of August 12/13.

August 22: Quarter moon is near Antares and Saturn

August 24: Moon is above the stinger of Scorpio

August 28: Full moon. The first of three super-moons this fall. The full moon occurs at perigee, when it is closest to the earth.

On August 14 NASA’s New Horizons spacecraft made its swift passage of Pluto, moving at a speed of 30,000 miles per hour. The photos and discoveries from this event are, to use the words of the scientists involved, “truly jaw-dropping.” This is a remarkable experience for all humankind, to share in exploring and discovering this cold, distant, dark world, once considered to be the ninth planet of the solar system. In the past when new lands were being discovered, such as searching for the source of the Nile or exploring Antarctica, there was a long wait before the results could be shared. Now it is only the four hours it takes radio signals to travel from New Horizons to Earth and the time needed to process the data.

There have been two major media briefings by the New Horizons team, July 17 and July 24. The first briefing revealed images of revealed 11,000-foot-high mountains of water ice and a huge craterless plain that appears to be no more than 100 million years old. The mountains, which also had no craters, were named after Tenzin Norgay, the companion of Edmund Hillary during the first ascent of Mt. Everest and the ice plain after the Russian spacecraft Sputnik.

The second briefing showed extraordinary details of the Texas-sized plain, named Sputnik Planum, which evidence moving glaciers composed of methane, nitrogen, and carbon monoxide ice and an entirely new mountain range which has been named after Tenzin’s companion on Mt. Everest, Sir Edmund Hillary. Even at Pluto’s temperatures of minus 390°F, these ices can flow when the weight of the overburden of ice causes melting and lubricates underside of the glaciers. The latest briefing also showed a stunning photo of a total eclipse of the sun by Pluto as viewed by the spacecraft. It revealed a layer of dust some 100 miles high.

Pluto has five moons of which the largest, Charon, the mythological boatman who ferried unfortunate souls across the river Styx to Hades. Charon is about half the size of Pluto, and they deserved to be called double planets. They are 12,000 miles apart, and are gravitationally locked, each one always facing the other. The earth’s moon is 240,000 miles from us, and, as you known, always keeps the same face to the earth. Charon orbits Pluto every 6.4 days; its rotation period is 6.4 days and Pluto’s rotation period is 6.4 days. Perhaps this intense gravitational locking has produced heating of the interiors of these two objects. Like Pluto, there are regions of Charon that show no craters, meaning that it too has been an alive and active planet, coating it surface with water ice, perhaps spewed out by water geysers. It has a strange dark area in its north which has been named Mordor of Middle Earth fame.

The mountains of Pluto are apparently composed of water ice because ice made of methane, carbon monoxide, or nitrogen would not have the internal strength to support such high peaks. Frozen nitrogen and methane would crumble under their own weight at those elevations. The large area containing the ice plain and the two mountains is named Tombaugh Regio after Clyde Tombaugh who discovered Pluto in 1930.

Sputnik Planum is unlike anything else in the solar system. It has a broken surface of irregularly-shaped segments, roughly 12 miles across, bordered by shallow troughs. Some of these troughs have darker material within them, while others contain hills that rise above the surrounding terrain. Elsewhere, the surface appears to be etched by small pits that may have formed by sublimation, in which ice turns directly from solid to gas. Pluto has a rocky core covered with a layer of ice and also, perhaps, an ocean of water. These ice mounds may be a product of convection, similar to bubble in boiling water. On Pluto, convection would occur within a surface layer of frozen carbon monoxide, methane and nitrogen, driven by the warmth of Pluto’s warmer interior.

An atmosphere as high as 1,000 miles was another surprise. It appears to consist largely of nitrogen. The atmospheric nitrogen is being plucked away from the planet by the solar wind flowing past the planet, carrying it more than 10,000 miles into space.

Jupiter has 67 moons. Saturn has 62 moons. Uranus has 27 moons. Neptune has at least 14 moons. Pluto has 5 moons, maybe more. How is it that our Earth has only one? There are two kinds of planets in the solar system: the Terrestrial planets (Mercury, Venus, Earth, Mars), and the Jovian planets (Jupiter, Saturn, Uranus, Neptune). While the Jovian planets have a total observed number of moons of close to 90, the Terrestrial planets have only 3 (the Moon, and two small moons around Mars). This huge difference is linked to the formation of the solar system. The two small moons of Mars are probably captured asteroids. In the case of our moon, it appears to have been produced by the collision of a large wandering proto-planet with the Earth, perhaps the size of Mars. Most of the proto-planets near the earth had been evaporated by the intensity of sunlight. This collision would have ejected a lot of material into Earth’s orbit that contracted to form our satellite. The Jovian planets were surrounded by such wandering small condensed rock and ice and easily captured their moons. The story of Pluto’s moons is still a mystery.

Note: At the time of writing this was “breaking news”. Because the last briefing on July 24 was days and days after Kizzen’s deadline for submission, I am grateful to the editor for her understanding.   😉