by Kim Malville

Overhead in the August evenings is the super-constellation known as the Summer Triangle. It consists of three of the brightest stars of the northern skies: Vega, which is directly overhead at 9pm in early September; Altair, below it to the south; and Deneb to the northeast. Each one of these stars is the brightest of its own constellation: Lyra (Vega), Aquilla (Altair) and Cygnus (Deneb). The Milky Way flows past these constellations. Deneb is in the tail feathers of Cygnus the Swan, which is flying to the south along the Milky Way.

September 22: Autumnal equinox at 8:29pm MDT.

September 27: At dusk, in the southwestern skies, Mars passes close to Antares, the red heart of Scorpius. The two have about the same ruddy color, but Mars will be a little brighter. Also in the same area of the sky look for the crescent moon and Saturn. It should be a nice show. 

September 28 and 29: Get outside again on these two nights and look to the southwest. The crescent moon passes Mars and Antares.

 Rosetta and its comet

Last month I wrote about Rosetta approaching its “holy grail” in the darkness of interplanetary space. It was an amazing piece of navigation and celestial mechanics when, after ten years of flight, the Rosetta space craft met up with a distant comet on August 6. The orbit of the comet and path of the space craft were calculated with extraordinary precision. Why is it so wonderful to rendezvous with a tiny comet?  On its pitch-black flanks and icy interior, this comet contains memories of the ancient days in our solar system. Planets have changed and evolved, continents have drifted, mountains have eroded, but comets remain frozen in time, unchanged for 4.5 billion years. They are as black as coal because they are covered by dark tar-like carbon compounds.  Only where there is a gap in the coating does gas evaporate to become gigantic plumes forming tails millions of miles long. The oceans of Earth, as well as those that once covered Venus, may have been formed by comets. We don’t know how much of our water on Earth came from comets, but it is certain is that they brought complex organic molecules such as amino acids to the earth. Comets could have been the triggers for life on Earth. 

This particular comet was discovered in 1967 by two astronomers at the Kiev Astronomical Observatory, Klim Churyumav and Svetlana Gerasimenko, for whom it is now named: 67P/Churyumov–Gerasimenko.  67P means it’s number 67 on a list of short period comets. The comet orbits the sun every 6.45 years and spins on its axis every 12.7 hours. Kudos to Ukraine!   

Rosetta has not yet been captured by the gravity of the comet and is firing its thrusters to execute a series of triangular paths bringing it closer and closer to the comet. On October 7, it will be within 18 miles of the comet, at which time it is hoped that the gravity of the comet will kick in, and its orbit will become circular. Thrusters will be used to lower it to 12 miles, where it should orbit the comet at the same rate it is spinning, like a geosynchronous satellite, keeping Rosetta always above its sunlit side. These new photographs are stunning. Dust has apparently settled into the valley between the two blobs and there apparently has been an avalanche, which carried large rocks into that valley. 

The oceans & sand dunes of Titan

Another space craft, Cassini, has been trolling the space around Saturn for seven years. Among other spectacular discoveries, it has found seven new moons, bringing Saturn’s family to 62 named moons. Titan is the largest and the second largest moon in the solar system, after Jupiter’s moon Ganymede. Titan is the only other world in the entire solar system with liquid lakes and oceans. Interestingly, these are not oceans of water, but liquid nitrogen. Titan is bitter cold. Receiving only 1% of the sunlight that Earth receives, its temperature is -292°F. Its nitrogen-based weather creates surface features similar to those of Earth: sand dunes, eroded river beds and river deltas. 

Titan is one of the few other spots in our solar system that could host some form of life. The chances of any form of life ever existed on this brutally cold world seem low. However, Cassini has recently detected polycyclic aromatic hydrocarbons (PAH) in its atmosphere. These complex molecules could have been the foundation for more complex biological molecules. Both good and bad, they come in many forms: one PAH is a carcinogen in cigarette smoke 

Titan has sand dunes, great sand dunes, in fact. They are up to 300 ft high and hundreds of miles long. Powerful winds that produced dunes are the result of tidal forces from Saturn on Titan’s atmosphere. These tides are 400 times stronger than the tidal forces of the Moon on Earth. As the atmospheric tides raise the atmosphere, low pressure areas are created, pulling winds toward the equator. This wind pattern causes sand dunes to build up in long parallel lines aligned, as you might expect,  west-to-east. The sand on Titan is not made up of small grains of silicates like the sand on Earth, but instead is formed when liquid methane rains pour down on water ice bedrock, eroding small away tiny pellets of ice covered with soil.  

Just recently hints of waves sloshing on Titan’s oceans have been found by Cassini. Titan has oceans at its poles and scattered lakes at the equator, of which Shangri-La is one of the largest. It is one-third the size of Great Salt Lake and is filled with liquid methane, some three to five feet deep. Liquid methane is thick and viscous, like molasses, and doesn’t easily budge. Strong winds are necessary to move the thick black liquid around.  Possible reflections of radar signals off of waves on one of its oceans were recently detected by the Cassini spacecraft. However, don’t see your travel agent quite yet:  it’s not a surfer’s paradise.  The waves reach terrifying heights of three-quarters of an inch.