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  Night Sky
 

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

April 2015 night sky

—Charlie Christmann

Dawn on Ceres

NASA’s Dawn spacecraft has arrived at its second destination, the dwarf planet Ceres. After launch on September 26, 2007, the Dawn spacecraft used its ion thrusters to make its way away from Earth’s orbit, destined for the asteroid belt. A year and a half later, Dawn rounded Mars for a gravity assist and direction change to put it on an intercept course with Vesta. From July, 2011, until September, Vesta was photographed and probed by Dawn’s instruments.

It took two and a half years for Dawn to travel from Vesta to Ceres, finally entering orbit in March of 2015. About half the size of our moon, Ceres, discovered by Giuseppe Piazzi in 1801, is the largest object in the asteroid belt. Like Pluto, it was once considered a planet, but with the discovery of several other objects in a similar orbit around the sun, Ceres was demoted to asteroid status. Ceres’ promotion to dwarf planet occurred, along with Pluto’s demotion, in 2006. Of all the mass in the asteroid belt, Ceres contains about one third of it.

On approach, still millions of miles out, the Dawn spacecraft photographed a mysterious white spot on the surface of the dwarf planet. Looking back at old Hubble images, the white spot can be seen. As the spacecraft got closer, and photographic resolution increased, the white spot split into two, a brighter and a dimmer spot. Interestingly, the brightest spot was almost centered inside a large crater.

With the surface quickly coming into better focus as Dawn’s cameras get closer and can see smaller objects, maps are being made and some features are already being named. The International Astronomical Union adopted two naming themes for Ceres in October: craters will be named after agriculture deities, while other features will be named for world agricultural festivals.

Higher resolution images show the bright spot is located in the floor of a crater about fifty miles in diameter and may lie in a depression on the crater floor. As the dwarf planet turns away from the camera, the spot could be seen rising above the rim of the crater, indicating it was most likely a plume of something being spewed into space.

One other anomaly has been observed from color images of Ceres. The dwarf planet has two distinct halves, one is redder and the other more blue in color. This is a mystery that waits for answers as Dawn spirals in for a closer look and more instruments are used to analyze the surface.

Lunar Eclipse

April 4th presents us with a Lunar Eclipse. Unfortunately, the finish of the eclipse will happen after moonset, but we will experience the short totality phase beginning just before 6:00AM.

Water, water everywhere—but does it foster life?

If the plume seen on Ceres is water, as some suspect, this dwarf planet will join a host of other bodies in our solar system containing water: Europa, (Jupiter moon), Ganymede (Jupiter moon), Enceladus (Saturn moon), Triton (Neptune moon), and now Ceres.

We have known about Europa’s oceans since the Voyager missions passed by and photographed plumes rising from its surface. It is thought that Europa’s ocean is salt water under about sixty miles of ice.

Ganymede’s oceans were inferred using auras, just like our northern and southern lights on Earth. If Ganymede had no liquid oceans, it could not produce its own internal magnetic field and the auras would sway wildly over its polar regions. With an ocean, the auras would be almost pinned in place. Observations show the auras move only a small amount around the poles, indicating a liquid salt subsurface ocean.

In late March, an international team of scientists reported evidence of hydrothermal vents on the Saturnian moon Enceladus. Those reports also postulate that the rocky core of the moon reaches 190 degrees Fahrenheit! This could drive chemical reactions favorable for life in a warm pocket around the vents similar to our deep ocean thermal vents.

Orbiting counter to Neptune’s rotation, Triton is already unusual. It is thought this moon was a visitor from the Kuiper belt captured by Neptune’s gravity. If that is so, it is believed that most Kuiper belt residents are icy bodies left over after the formation of our solar system. We know there were strong tidal forces acting on the moon in the past, but over the eons, the orbit has changed from an elliptical one to a more circular one, decreasing the tidal action. There could also be radiogenic heating helping to heat the moon. In the 4.5 billion years since its formation, is the heat from tides, radioactive decay and residual heat of formation enough to keep the water liquid below the surface? That question remains to be answered by some future space probe.

Science believes that where there is liquid water and some energy source to serve as food, life could have evolved. While there are no little green men in our solar neighborhood (except for the UFOs I wrote about a couple of months ago), there could be lower life forms leisurely swimming in oceans capped with thick ice in the far reaches of our home planetary system.

 
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