Bakersfield Night Sky – February 16, 2013
By Nick Strobel
There were two asteroid events yesterday. The first was a surprise over the skies of Chelyabinsk in Russia, where a stony meteor/asteroid exploded in the air producing a shock wave that shattered windows for miles around. Videos from various sites near Chelyabinsk are gathered together at http://say26.com/meteorite-in-russia-all-videos-in-one-place . The airburst explosion was equivalent to about 300 kilotons of TNT, though it may have been as large as 500 kilotons of TNT. The other was the close flyby of the 150-foot diameter asteroid 2012 DA14 that passed to within just 17,150 miles of the Earth yesterday without harming anything. Although it passed closer than the ring of geosynchronous satellites that orbit the Earth, DA14's trajectory was such that it passed through the ring going from south to north. The Russia asteroid was not related to DA14. The Russia asteroid was probably about one-third the size of DA14 and it was definitely traveling in a different direction and speed than DA14. The Russia asteroid originated in the asteroid belt between Mars and Jupiter while DA14 is a "Near Earth Object" with an orbit around the Sun that is similar to the Earth's.
Something like DA14 passes near the Earth every 40 years on average and an impact happens roughly once every 1200 years. DA14 has no chance of hitting Earth for at least the next century. Something like DA14 hit the plains of northern Arizona about 50,000 years ago to make the kilometer-wide crater now called "Meteor Crater". However, the Meteor Crater asteroid was made of iron, so it packed even more of a punch than would a typical asteroid like DA14 that is made primarily of stone. More recently, something the size of DA14 is thought to have created the airburst over Tunguska, Sibera that leveled hundreds of square miles of forest in 1908. An impact of something as small as DA14 would be equivalent to 2.4 megatons of TNT---enough to wipe out a city the size of Bakersfield but not have a global effect. Something a kilometer or more in size hitting the Earth would have a global effect, threatening the survival of our civilization.
The Tunguska Event has inspired all sorts of "creative" explanations about what could have caused the airburst from the boring (but very likely) asteroid impact or comet impact to fantastical stories like mini-black holes or wayward spaceships. I am teaching an astrobiology class this semester (as I have done in previous semesters) and one of the topics that comes up is UFOs as space aliens in space ships. Well, Hollywood and science FICTION TV just love that stuff, of course, but even supposedly factual-based networks like Discovery and the History Channel have run stories on present-day space aliens or "ancient astronauts". When I found out the energy requirements it would take to travel among the stars, I became even more skeptical of the claims by space alien enthusiasts and the near-parity of humans vs. aliens battles depicted in popular shows. To travel at even a tenth of the speed of light from the nearest star system (Alpha Centauri) to here would require about 40% of the entire world's annual energy usage for a crew of 10. The world's annual energy usage is approximately equivalent to 10,000 megatons of TNT. Faster speeds or larger crew numbers would require even greater energy (the energy required increases as the square of the speed). Space aliens that can harness that much energy in craft the size of a large house are not going to be too worried about our weaponry. If the space aliens are warping space to travel through hyperspace, they would be working with energies on the order of what our Sun will generate in its entire 10-billion year lifetime. Now, in just one second, our Sun generates a million times the entire ANNUAL world's energy production and there are about 30 million seconds in a year. Multiplying these already huge numbers by 10 billion (for the Sun's lifetime), you come up with energies about a trillion times more than what it would take to pulverize the entire Earth to powder. Even if I'm off in my calculations by a factor of ten (heck, even a hundred---maybe they have a Prius warp drive), I doubt that warp-travel space aliens would be using laser blasters to hurt us, they could just wipe out the Earth, blip! Well, how depressing and that wouldn't make a good ending to a movie. Sigh! This column probably dooms my dream of being a science consultant for the Syfy channel. However, I, like most astronomers don't watch science fiction movies or TV shows for the science but for the stories, so I promise I won't critique a movie's science (or lack thereof) while I watch it with you.
In tonight's sky Mercury reaches its greatest distance from the Sun on our sky ("greatest elongation" in astronomy-talk). Look for it as a bright star low in the west shortly after sunset (see the first star chart below). Over the next week Mercury will sink back toward the Sun and it will be lost in the sunlight glare by the end of the month. Half a fist-width at arm's length below Mercury will be the dimmer orange-red Mars. The two planets might just barely fit within the same field of your binoculars. The Curiosity rover on Mars has made its first drillings into a rock and we should have preliminary results back from the two main science instruments SAM and CheMin from the analysis of the rock powder. The results may be simply that the aspirin-mass sample of powder was deposited successfully into the two instruments because the Curiosity team are being very careful in testing out every step of the process to make sure everything on the rover is working as expected. Some of the powder was used to clean the drill hardware of trace organic compounds that may have been deposited while the rover was still on Earth despite a very thorough cleaning before launch. Because the SAM instrument can detect very, very low quantities of organic materials, the cleanliness requirement for the hardware was 40 parts per billion. This is far, far better than the cleanest hospital surgery room in the world. The rock powder is transferred to a collection area called CHIMRA where it is sifted so that only particles smaller than 150 micros across are transferred to the SAM and CheMin instruments. They don't want larger particles getting stuck in the instruments because there's no one there to clean out the instruments if they get clogged up! All of this processing of the sample can take several days before it even gets to the SAM and CheMin instruments. As I said the Curiosity team is being very careful and meticulous in making sure everything is working correctly.
As shown in the first star chart below, a very fat Waxing Crescent Moon will be mid-way up in the southwestern sky at the western edge of Taurus. Tomorrow night it will be at First Quarter phase and half a fist-width below-right of very bright Jupiter. Jupiter continues to crawl eastward getting closer to Taurus' head. By the end of next month it will reached the area between the two horns. Orion is due south at about 7:45 PM. The pre-dawn sky belongs to Saturn now that Venus has disappeared into the sunlight glare and Jupiter has set by 1 AM. Saturn is a fairly bright star midway between the stars of Virgo and Libra in the east before sunrise. See the second chart below for the view at 5 AM. In my next column I'll talk about Comet PanSTARRS (C/2011 L4) that should put on quite a show for us in early March. Right now it is above our horizon only during the day.
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
last updated: February 16, 2013
Webpage contact: Nick Strobel