by Kim Malville
December 7 – Conjunction of the Moon and Venus. In the morning of December 7 the crescent moon will come within 2° of bright planet Venus.
December 13/14 and 14/15 – Geminids Meteor Shower. The Geminids is the Queen of the meteor showers, the best shower in the heavens. This year the prediction is for 120 meteors per hour at its peak. You will note that this is a greater shower than the Perseids in August. It is less well known because it occurs in chilly December. The crescent moon will set early in the evening leaving dark skies for what could be a spectacular night, with a meteor every 30 seconds. It’s hard to beat that. Meteors will radiate from the constellation Gemini, but they can appear anywhere in the sky.
December 22 – December Solstice. The longest and darkest night of the year in the northern hemisphere. If you want to celebrate solstice, pop the cork at exactly 9:48pm.
December 25 – Full Moon.
December 29 – Mercury at Greatest Eastern Elongation. The planet Mercury reaches greatest eastern elongation of 19.7° from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.
The lost atmosphere of Mars
Mars is leaking like a punctured bike tire. The air on Mars is leaking away at the rate of a half-pound per second (that’s a double McDonald QuarterPounder at 750 calories and lots of unsaturated fat per second). This rate of is a recent result reported by the team of the MAVEN space craft (Mars Atmosphere and Volatile Evolution mission), a mission organized (I’m pleased to note) by the University of Colorado. But there is a problem. In its youth Mars had an atmosphere as thick as or perhaps even thicker than that of our planet today. But, this rate of leaking is not enough even over 4.5 billion years to decrease its atmosphere to its current state of thinness. Today, it is thin, very thin, believe me, in spite of that dust storm you have perhaps seen in the Martian movie.
Recent measurements by MAVEN have shown what happens when a gust of the solar wind hits Mars. It is very dramatic! That bombardment strips away its upper atmosphere, fast enough indeed to produce today’s cold and practically airless planet.
During its youth the sun had many more eruptions than today. Those eruptions produce a cloud of charged particles (electrons and protons) and a mass of tangled magnetic fields that flow outward from the sun into interplanetary space. Sometimes they hit the Earth, sometimes they hit Mars, or Jupiter or even Pluto—with diminishing effect, of course. In the case of Earth they reach us approximately 24 hours after we see an explosion on the sun. We have a magnetic field that protects us from these blasts. The effects are brilliant aurora and electrical currents that may short out transmission lines, but our atmosphere is not significantly stripped away.
Unlike Earth, Mars does not have a global magnetic field to deflect the solar wind. During a recent, relatively modest, solar storm experienced by MAVEN, the rate of gas loss was increased to 10 pounds a second. Over the lifetime of the solar system that rate could explain the missing atmosphere of Mars. Every time you use a compass on a hike, you might consider whispering a little expression of gratitude to our protective magnetic field.
Ice volcanoes on Pluto
A possible ice volcano on Pluto (visible at center of photograph) is seen in this NASA image, captured by the New Horizons spacecraft, released on Nov. 9, 2015. The feature, called Wright Mons, is a strange feature 100 miles wide and 13,000 feet high with a summit depression at its center. The depression is almost as deep as the volcano is high. What a view it would be from the rim!
Before the New Horizons flyby, most astronomers thought Pluto would prove to be too small to maintain the internal heat needed to power geological processes such as glacier flows and volcanism. But that fast-moving spacecraft revealed a far younger surface than expected. Something must be keeping things warm beneath the surface: another mystery of Pluto
Two enormous mountains, spanning hundreds of miles across, sit at the southern edge of the heart-shaped region on the surface of Pluto. The mountains have been informally named Wright Mons and Picard Mons, and at their crests, each peak hosts a central crater, looking like shield volcanoes on Earth.
Elsewhere in the solar system eruptions of liquid have been seen on Saturn’s frozen moon Enceladus, known for spewing material from its southern pole, but, as we shall see, the source comes from fissures in the ground rather than mountainous features. Similar eruptions have been suspected on Titan, another Saturn moon. Those volcanoes were identified by radar, but Pluto’s volcanoes are clearly visible. It will be a long time, however, before we return and can actually witness an eruption
Diving to Enceladus
On October 28, in a death-defying dive, the space craft Cassini came to within just 30 miles of the surface of Enceladus and passed through a plume of material that erupts from its icy crust. The new image shows the rough and wrinkled surface of Enceladus. The plumes that erupt from the fissures are probably emerging from a liquid water ocean that lies deep under the icy surface. Cassini will now be able to provide some information about the composition of the sprays, and potentially shed light on whether the underground environment is fit to host life.
Cassini will return and make its final flyby of Enceladus on December 19. The spacecraft has been studying Saturn and its moons for a decade, but its mission is scheduled to end in 2017. Some time that year Cassini will move closer to Saturn and make a suicide dive into the swirling atmosphere of that gas giant.