On Monday, two small asteroids gave Earth a “close shave” as they passed between the Earth and the Moon, but astronomers are keeping a closer eye on two large asteroids that could pose potential problems in the near future.
Space.com reported that two small asteroids passed by Earth in rapid succession on Monday, March 26th. The first asteroid, 2012 FP35, was about the size of a small bus and flew within 96,000 miles of the Earth. The second asteroid, 2012 FS35, came even closer to Earth at 36,000 miles. Both asteroids were only detected last weekend, but posed no risk of impact as they were both small enough to have not survived a trip through Earth’s atmosphere.
That may not be the case with two larger asteroids. On February 23, 2012, observers at the La Sagra Sky Survey near Granada, Spain, discovered a new asteroid that may have the potential to pose a threat as early as February 2013. Named 2012 DA14, the asteroid has an estimated diameter of about 150 feet across and was discovered in a part of the sky where asteroids typically are not seen.
Scientists calculate that 2012 DA14 will pass uncomfortably close to Earth on February 15, 2013, at about 14,000 miles from the Earth’s surface, with some calculations showing the nearest approach being as close as 12,680 miles. For comparison, 2012 DA14’s passage will be closer to Earth than many satellites in orbit, and may be as close to Earth as the International Space Station, which orbits at 240 miles above the Earth’s surface.
Astronomers emphasize that 2012 DA14 is not an impact threat, however, some believe that there may be the possibility for a collision in the “future.” Dr. Gerhard Drolshagen, of the European Space Agency’s Space Situational Awareness (SSA) Office, said that 2012 DA14 will offer a great view in the sky next February (being easily visible through a pair of binoculars), but that “In future times the possibility of a collision cannot be completely excluded. It is highly unlikely, but the chance is greater than zero.”
Although 2012 DA14 will not make a direct impact on Earth in 2013, some scientists have not ruled out the effects on Earth if the asteroid exploded in our atmosphere over an inhabited area. There could be major repercussions if such an event occurred.
The most recent event in recorded history of a large meteor or comet entering Earth’s atmosphere and exploding over land is the 1908 Tunguska Event, which had an estimated force of about 5-30 megatons. Approximately 830 square miles were affected, and the explosion knocked down trees and produced a shock wave estimated to have been a 5.0 on the Richter Scale. A similar event these days would be capable of destroying a major metropolitan area. As Dr. Drolshagen points out, “That is an area the size of Greater London.”
In addition to 2012 DA14, scientists are also keeping very close watch on another asteroid which may pose an impact threat to Earth in 2040. Asteroid 2011 AG5 is a humongous chuck of rock about 460-feet wide, and “currently has the highest chance of impacting the Earth…in 2040,” says Detlef Koschny of the European Space Agency’s Solar System Missions Division in The Netherlands. The concern is great enough that some scientists are already discussing how to deflect the asteroid, and the topic was on the agenda at the 49th Scientific and Technical Subcommittee of the United Nations’ Committee on the Peaceful Uses of Outer Space held in Vienna, Austria, earlier this month.
2011 AG5 was first discovered in January 2011 by astronomers at the Mount Lemmon Observatory near Tucson, Arizona. Astronomers acknowledge that because they have been unable to determine the full orbit of 2011 AG5, the risk of direct impact remains unknown, but current odds are 1 in 625. As Koschny points out, “We have only observed it for about one-half an orbit, thus, the confidence in these calculations is still not very high.” He added that for this asteroid to be considered a real threat, scientists would need to observe it for at least one, if not two, complete orbits. The next tracking opportunities will occur in September 2013 and November 2015.
Because 2011 AG5 will be observable from the ground in 2013 and 2015, Donald Yeomans, Head of the Near-Earth Object Observation Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, California, believes “there will be time to mount a deflection mission to alter its course before the 2023 keyhole.” A “keyhole” is a small region of space where a planet’s gravity can perturb the orbit of a passing asteroid so that the asteroid would collide with that planet on a future orbital pass. It is estimated that 2011 AG5 may pass through such a keyhole in 2023, in which Earth’s gravitational influence would have the potential to place the asteroid on an impact course for February 5, 2040.
Threats from asteroids are very real, and astronomers are continually seeking ways to locate them earlier. NASA’s Asteroid Watch Program “detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called ‘Spaceguard,’ discovers these objects…and determines their orbits to determine if any could be potentially hazardous to our planet.”
With an estimated half million near-Earth objects believed yet to be discovered, odds are that one will make its deep impact known here on Earth eventually. When, where, and how big of an impact remains to be seen. “Of the four billion life forms which have existed on this planet, three billion, nine hundred and sixty million are now extinct… Some by wanton extinction, some through natural catastrophe, some destroyed by meteorites and asteroids. In the light of these mass extinctions it really does seem unreasonable to suppose that Homo sapiens should be exempt…”
– P. D. James, The Children of Men.