Bernie Badger: Passing space rocks are not a hazard
Today is a lucky day for near-Earth asteroids. According to spaceweather.com, there are three recently discovered asteroids flying past Earth today. They all have similar provisional designations (2015 EF, 2015 EK, and 2015 EP). These designations indicate that they were discovered in the first half of March, 2015. Their diameters range from 62 to 95 feet, which is longer than a semi-trailer. As is usual with such small asteroids, they are only discovered days before their encounter with Earth.
The asteroids will all pass safely by at greater distances than the moon, from 2.5 to 7 LD (lunar distance). They are also not listed as potentially hazardous asteroids (PHAs), because of their relatively small size. PHAs are space rocks larger than approximately 100 meters that can come closer to Earth than 0.05 au. They are certainly close enough: 0.05 au is 19.4 times larger than 1 mean moon-Earth distance, but they are not considered hazardous enough to make the list.
There are plenty of larger objects that do qualify as PHAs. On March 12,there were 1557 potentially hazardous asteroids. Although none of the known PHAs is on a collision course with our planet, astronomers are finding new ones all the time.
Since these asteroids are not listed as PHAs, just how hazardous could they be? The famous Chelyabinsk super-bolide exploded in the Earth's atmosphere over Russia on Feb. 15, 2013. This was about the size of the smallest of the three asteroids passing today. It exploded high in the Earth's atmosphere, partly because of its high speed.
The largest of today's trio of near-Earth objects has a diameter of about 29 meters. Its volume is therefore about 3.4 times larger. It certainly has some hazardous potential.
The "mother of all asteroids" is 1 Ceres. It was discovered on Jan. 1, 1801. Ceres is quite large, having a radius of over 450 miles, giving it a surface area about equal to that of India. Ceres has an extremely stable orbit out between Mars and Jupiter, so it is not "hazardous."
NASA's Dawn probe has just this week started orbiting Ceres, so we can look forward to a new flood of scientific data about this largest of all asteroids.
Bernie Badger is project coordinator at the Eastern Florida State CollegePlanetarium in Cocoa. Send questions, suggestions, or comments to mailto:badgerb@easternflorida.edu
At the planetarium
The EFSC Planetarium in Cocoa open to the public Friday and Saturday evenings and Wednesday afternoons. The astronomy shows are up first followed by an IMAX movie. Friday and Saturday schedules also include an exciting laser music show and the observatory. There are new paintings in the art gallery featuring classic cars and motorcycles.
Friday
7 p.m. Amazing Universe
8:15 p.m. Whales (IMAX)
9 p.m. Pink Floyd "Dark Side of the Moon"
Saturday
7 p.m. The Planets
8:15 p.m. The Living Sea (IMAX)
9 p.m. Led Zeppelin
Wednesday
2 p.m. The Planets
3:15 p.m. Solar Max (IMAX)
You may access the schedule and descriptions using the online calendar at http://www.calendarwiz.com/planetarium. You may call the box office at (321) 433-7373 to hear the prices and schedule for the planetarium shows.