Bakersfield Night Sky – December 21, 2013
By Nick Strobel
Happy solstice day! Today marks the December solstice when the Sun is at its farthest point south of the celestial equator. For us here in the northern hemisphere, it marks the beginning of the season of winter. The Sun will travel its lowest arc across the sky today, rising as far south of east and setting as far south of west as it will all year. With such a low arc across the sky, the Sun will be up above our horizon the least amount of time. During the rest of the days of winter, the Sun will slowly move northward and the amount of daylight will increase.
Last weekend, China joined the United States and former Soviet Union in the exclusive club of nations that have landed a craft on the Moon. Their craft is a lander and a solar-powered rover that China hopes will travel a few kilometers and use a suite of instruments including a ground-penetrating radar to see what natural resources are available for extraction back to Earth for manufacturing as well as future development on the Moon. There is also a telescope on board that will be used to study the interaction of solar particles with our atmosphere. The rover is expected to explore the Moon's surface for three months and the stationary lander that delivered the rover will operate for a year. China has a long-term goal of eventually building a permanently-manned station on the Moon and they are willing to spend the time and money it takes to achieve that goal.
A few days before the lunar landing, news was coming from the American Geophysical Union meeting about new discoveries by the Curiosity Mars Science Laboratory (MSL) mission. Last March the MSL scientists reported that Mars definitely once had a habitable environment with neutral pH, drinkable water, nutrients that could be used for metabolism by certain types of microbes and an energy source to drive the process of metabolism. Since then, the mission has changed from finding habitable environments to a more selective one of finding habitable environments that could preserve organic carbon. That's the next step in our search for life (present or past) on Mars.
Mars today is not habitable on the surface because of its very thin atmosphere and its lack of a magnetic field. Both of those things could provide a shield protecting the surface from harmful radiation coming from outer space. That includes high energy particles called cosmic rays and particles from the Sun such as solar wind and solar flares or coronal mass ejections. Without the protective shields of a magnetic field and thick atmosphere, the nasty radiation can break apart organic compounds at the surface. That radiation is also strong enough to penetrate into rock, so at a depth of 1 meter below the surface, the organics in a rock could be reduced to just one-thousandths their original amount over a time period of 650 million years.
The minerals that make up the sedimentary rocks where Curiosity landed have been dated using radiometric dating (the first time this has been done on another planet) to between 3.86 billion and 4.56 billion years old with a best-guess estimate of 4.2 billion years. The sedimentary rocks would have formed more recently than that (perhaps as recently as 3.5 billion years ago) from the super-fine sediment particles eroded away from the rock around the rim of Gale Crater and then were transported in streams flowing down to the lake at the floor of the crater. The sediments settled on the bottom of the lake in layers that solidified over long periods of time to make the sedimentary rocks that Curiosity has been sampling. Organic compounds (and any possible microbes) that were mixed in with the sediments would be locked up in the sedimentary rocks. However, organic compounds would need to buried down several meters below the surface to be shielded from the harsh radiation. Otherwise, the continual bombardment of the radiation from outer space will break them apart over hundreds of millions of years.
Well, if the drill on Curiosity's arm can only go down four to five centimeters, how could they expect to find any organic compounds from the time when Mars was habitable a few billion years ago? Organic compounds within only a few centimeters from the surface would have long been destroyed over the billions of years the surface rocks have been around. Here's the next crucial discovery: the sedimentary rocks Curiosity has been sampling were eroded away relatively recently, just 80 million years ago. The sedimentary rocks now exposed on the surface used to be several meters below the surface. Sandblasting by the wind wore back the cliff (scarp) that once was well in front of where Curiosity was drilling. About 80 million years ago, the sandblasting had eroded the scarp enough to expose the sediment rocks into which Curiosity was drilling. The scarp is now several tens of meters away from where Curiosity was drilling.
Two conclusions to make from this are: (1) we CAN expect to find organic compounds in the rocks Curiosity will be able to drill into in the following months; and (2) future targets for drilling should be near scarp edges that Curiosity will be passing by on its way to where it will start climbing the huge mound of sedimentary rock called Mt Sharp. The team has already identified the next drilling places.
Besides highlighting the great science coming from Curiosity, these two conclusions are also important to let NASA know that the mission is worth continued funding. Because of coming budget cuts, NASA will likely have to choose between the two major flagship planet missions underway now: the Curiosity rover and the Cassini spacecraft that has been orbiting Saturn and flying by its interesting moons like Titan, that has an atmosphere thicker than Earth's and is the only other body in our solar system to have bodies of liquid on its surface, and Enceladus, that has liquid water below its icy crust and great geysers spewing water and organics from giant cracks in the crust. My guess is that Curiosity will win out since Cassini has been exploring the Saturn system since the end of 2004 and is well past its initial four-year mission while Curiosity still has another year to go in its initial mission. Cassini is still working fine and there are still plenty of things to find out about Saturn and its two moons of greatest astrobiological significance, Titan and Enceladus.
Another planetary science discovery announced at the AGU meeting was the possible detection of geysers coming from Jupiter's moon, Europa. Europa is slightly smaller than our Moon and it has a liquid water layer below its icy crust, like Enceladus. The detection was made by astronomers using the Hubble Space Telescope that is orbiting the Earth. I said "possible detection" because the observation needs to be reproduced and other things should be seen if Europa is spewing stuff including infrared emission (heat energy) from the warmed material. Now those observations are pretty hard to make from hundreds of millions of miles away even with the Hubble Space Telescope. It is much easier to spot geysers spewing stuff if you can get your camera to the other side of Europa and look back toward the Sun and you can also spot the warmed material a heck of a lot easier from just a few hundred miles away or closer. There won't be a mission to Europa for many years, so we'll just have to push the capabilities of the Hubble Space Telescope orbiting the Earth and huge telescopes on the ground to look for signs of geysers that can be detected from the Earth.
Tonight at about 6:30 PM, you may be able to spot the two brightest planets up above the horizon at the same time. Low in the southwest will be Venus and low in the northeast will be Jupiter. Both of them are brighter than any star in the night sky. Venus sets about two hours after the Sun and it is now in a definite thin crescent as it continues to catch up to us in its faster orbit. Jupiter will rise among the stars of Gemini an hour and ten minutes after sunset but the mountains and haze near the horizon will hide Jupiter until a bit later, hence my statement of about 6:30 PM being the time that you can spot both of the planets. Jupiter is continuing its retrograde motion moving westward, so it is now just inside the line of stars that make up the twin named Pollux of Gemini as shown in the first star chart below. Jupiter will continue moving westward until the last week of February, almost reaching the Castor line of stars in Gemini.
The first star chart below also shows the brilliant winter constellations of Orion, Canis Major, Canis Minor, Auriga, and Taurus. They have the stars of the Winter Hexagon. It is formed by connecting in clockwise order: Capella in Auriga, Aldebaran at the eye of Taurus, Rigel at the knee of Orion, Sirius at the neck or nose of Canis Major, Procyon at the hindquarters of Canis Minor, and Pollux or Castor at the heads of Gemini.
The Moon was full on December 17th, so tonight it will rise as a Waning Gibbous a bit after 9 PM. The attached star chart shows that it will be next to Regulus at the end of the sickle part of Leo. By early Christmas morning the Moon will be at Third (or last) Quarter, rising after midnight among the stars of Virgo. Next to the Third Quarter Moon will be the orange-planet of Mars. Early Christmas morning, the Moon will be visible by 1:15 AM and Mars about thirty minutes later. Mars will pass under the double star Porrima in Virgo during the last week of December. Saturn becomes visible by 4:15 AM among the dim stars of Libra. The second star chart below shows the early morning view of the sky.
Although we are constantly being bombarded by messages to spend, spend, spend during this holiday season, I hope that you will consider boosting the economy in a different fashion by donating to a worthy charity in honor of someone else. I also hope you all have a blessed and joyous holiday season and safe travels!
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