Bakersfield Night Sky – March 21, 2015
By Nick Strobel
Two weeks ago on March 6th at 4:39 AM Pacific Time, the Dawn spacecraft became the first spacecraft to not only visit a dwarf planet but also to go in orbit around it. That dwarf planet is Ceres, the largest of the objects in the asteroid belt between Mars and Jupiter. Another first for this mission is that the Dawn spacecraft is the first spacecraft to orbit two different objects outside the Earth-Moon system.
Dawn will spiral inward to a much closer orbit over the next several months taking thousands of pictures and spectrometer measurements while doing so. Ceres contains about a third of the mass of the asteroid belt but its density is fairly low, so beneath its dusty surface, it probably has a lot of water ice. In fact this dwarf planet probably has more fresh water than exists on Earth, though Ceres's water is frozen. Ceres is the innermost of the icy worlds in our solar system. Other icy worlds are found further out in the solar system such as several of the large Galilean moons orbiting Jupiter and those orbiting Saturn.
Another surprising thing about Ceres is that it has carbonates which were formed in the presence of water. The only other place we have found carbonates is Earth and Mars, both of which are habitable.
Some of the impact craters are quite bright which may mean those craters were formed recently, so the exposed subsurface water ice hasn't had time to sublimate away after being exposed. Two very reflective spots right next to each other in an impact basin have drawn a lot of interest. They may be the result of recent volcanism but the lava here would be water. Of course, the pseudoscience folks on the net are saying the bright spots are artificial structures. Oh brother! It's amazing what leaps of logic are required to go from bright spots on a dust-covered ice world to structures built by extra-terrestrial advanced beings.
Back to reality: Over the next several months Dawn will operate in progressively smaller orbits around Ceres. The first will be 8400 miles above Ceres to get global views and thoroughly characterize its shape. The second orbit will be 2700 miles above Ceres creating global maps of the topography with the camera and composition with its spectrometers. The third orbit will be 970 miles above Ceres for more detailed mapping. The final orbit will be just 230 miles above Ceres for its neutron spectrometer, high-resolution mapping of the surface, and mapping of its gravity field to probe its interior structure.
Although its mission might be extended if funding permits, Dawn will end its life in orbit around Ceres. The loss of two of its four reaction wheels used for precisely orienting the spacecraft will mean that Dawn cannot be sent off to another asteroid but that's okay. The first dwarf planet discovered will have plenty of secrets to uncover!
The same day that Dawn went into orbit around Ceres, a team of astronomers led by Patrick Kelly at UC Berkeley reported in Science of their Hubble Space Telescope observations of a gravitationally lensed supernova. The supernova's light has been traveling for about 9.4 billion years and on its way to us, its light was bent by the warped spacetime around a galaxy much closer to us. This is the first supernova imaged this way because it requires the supernova to be correctly aligned with the foreground galaxy and a powerful telescope looking in that direction at the right time. Now that we know where to look, we may be able to see this particular supernova's light re-appear in about 5 years as the light gets bent toward us by other galaxies in the foreground galaxy cluster.
What a perfect year for this long predicted event to finally happen! This year marks the centennial of Albert Einstein's presentation of the Theory of General Relavity to the world. His radical idea of spacetime being stretched around objects with mass is now so well-established that we use it for mapping the distribution of dark matter, hunting for exoplanets, studying galaxies that are much too distant and faint to be seen without the use of the gravitational lenses that nature has set up for us, and playing the central role in Hollywood movies. Oh, by the way, recalling the once-a-century perfect Pi day that was on last week Saturday, the number Pi appears in the General Relativity field equation.
While you ponder gravitational lenses, take a look in the evening sky at the two brightest planets, Venus and Jupiter, shining on opposite sides of the sky. The attached star chart shows the evening sky at 9 PM centered on Orion in the southwest direction. Venus will be low in the west next to Aries. Higher up in the southeast next to the dim stars of Cancer will be Jupiter. You'll probably need binoculars in our light-polluted sky to spot the Beehive Cluster (M44) to the right of Jupiter. Those lucky to be under darker skies will be able to spot the cluster without any optical aid. The gravitational lensed supernova is just off the upper left corner of the attached chart.
Earlier in the evening see if you can spot a very thin Waxing Crescent Moon close to the western horizon. Mars will be right next to the Moon. The following night a slightly less thin crescent Moon will be next to Venus. A fatter crescent Moon will be in the Hyades at the nose of Taurus on the 24th and be a First Quarter on March 26th. When the Moon passes below the Beehive Cluster and Jupiter on the 29th, it will be a bright Waxing Gibbous phase.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com