Friday, January 11, 2013

Near Earth Object Alert Update: Asteroid Apophis won't hit us in 2036



Another doomsday threat dies out: Asteroid Apophis won't hit us in 2036

 

Apophis, nicknamed the "Doomsday Asteroid," was once considered a potential threat, but now scientists realize the chance of the asteroid colliding with Earth is negligible. NBC's Brian Williams reports.

Radar observations made during this week's close encounter with the asteroid Apophis have ruled out the risk of a catastrophic cosmic collision in 2036, NASA says. Experts say it'll be much farther away at that time than it is right now.

The crucial readings came on Wednesday when the space rock, which is thought to measure at least 885 feet (270 meters wide), approached within 9 million miles (14.5 million kilometers) of Earth. NASA is monitoring Apophis with its 230-foot (70-meter) Goldstone radio dish in California. Optical readings also have come in from the Magdalena Ridge Observatory in New Mexico and the Pan-STARRS observatory in Hawaii.
The bottom line? "We have effectively ruled out the possibility of an Earth impact by Apophis in 2036," Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory, said today in the all-clear news release. "The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036. Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future."
Jon Giorgini, who developed JPL's online Horizons database to keep track of solar system objects, would go even further. He says that according to calculations based on the Goldstone data, Apophis will probably pass by Earth at a distance of 36 million miles (58 million kilometers, or 0.39 AU), and absolutely no closer than 14 million miles (22 million kilometers, or 0.15 AU). "That is a very extreme minimum," he told NBC News. "Nothing else plausible can get you closer."
Apophis, a.k.a. 2004 MN4, created a huge splash when it was discovered in 2004 because the initial assessment of its orbit gave a 1-in-40 chance of Earth impact in 2029. That would be catastrophic: The space rock is big enough to wipe out a city if it struck land, or create killer tsunami waves if it splashed into the ocean.
Additional orbital data quickly eliminated the risk for 2029, but showed that it would pass within 20,000 miles (32,000 kilometers) of our planet at that time. That's so close that Earth's gravitational field will perturb Apophis' orbit. The experts worried that if the asteroid passed through a particular half-mile-wide zone in space, known as a "keyhole," its orbit would be perturbed just enough to set up a smash-up during the 2036 encounter. Fortunately, the latest observations indicate that Apophis will miss the keyhole by a long shot.
Did I just hear a cosmic sigh of relief?

There are still a few uncertainties surrounding Apophis: Astronomers don't yet have enough data to determine how the asteroid is spinning or how solar radiation is affecting its orbital path — a phenomenon known as the Yarkovsky effect. Giorgini said that even under the worst-case scenario, the effect won't push Apophis into a collision in 2036. But there could conceivably be other risky encounters in the decades or centuries ahead.
"There's a non-linear amplification that can really move it around more," Giorgini said.
Also, there are questions about Apophis' exact size. Just this week, readings from the European Space Agency's Herschel space telescope suggested that the asteroid may be nearly 20 percent bigger than previously thought. But that larger size estimate is based on the assumption that Apophis is a spheroid, and astronomers already know that it's elongated.
"We're not seeing that larger size in the radar data," Giorgini said.
By the end of next month, continued radar observations from Goldstone as well as the Arecibo Observatory in Puerto Rico should give astronomers a much better fix on Apophis' spin and its size. When those factors are fully accounted for, the Jet Propulsion Observatory will update its official risk assessment for Apophis — and could take this bad boy off the hit list for good.
Update for 6:30 p.m. ET: Clark Chapman, senior scientist at the Southwest Research Institute, weighed in on the current state of the asteroid hunt in an email:
"One thing you should be aware of, and might mention, is that the next Planetary Defense Conference, an every-two-year international meeting, will be held April 15-19 in Flagstaff, Arizona. ... Some presentations are already listed in the program, which should be finalized a week from now, which is the due date for abstracts.
"An interesting tie-in with the new observations of Apophis is that a similar thing happened with 2011 AG5 a few weeks ago, when observations with the huge Gemini telescope in Hawaii showed that it would, in 2023, miss the roughly 350-km-wide 'keyhole' and, therefore, not strike the Earth in 2040.  Prior to these critical observations, the chance of a 2040 impact was unusually high (though still low in everyday terms) at 1 in 500.
"A point to be realized is that while the chances of impact in these cases are very low by ordinary standards, they aren't zero, and the consequences of an impact could be very terrible, so it is important to plan and prepare for the possibility of impact until it is ruled out.
"It was important to get these observations of AG5 in the autumn of 2012, because if it had turned out that AG5 was actually on an impact trajectory, it would have given us an additional year to mount a deflection mission and succeed in deflecting it from the 2023 keyhole. Without making a major observational effort with a very large telescope this autumn, the next routine observational opportunity wasn't until this coming autumn."
Update for 8:30 p.m. ET: One of NASA's experts on the asteroid threat and two former NASA astronauts have weighed in on the report about Apophis. David Morrison of NASA's Ames Research Center sent these comments via email:
"One possible angle is the recent proposal from [NASA Administrator] Charlie Bolden, based on a Keck study, that we retrieve a 7-meter carbonaceous near-Earth asteroid and bring it into lunar orbit. There are many questions about this idea, but the one I have in mind is our assumed ability, without Sentinel, to find 7-meter C-type asteroids in Earthlike orbits. If you can't find them, you can’t protect against them, or do anything with them as potential resources."
Now here's an email from Ed Lu, a veteran of two space shuttle missions and an extended stay on the International Space Station. Lu now serves as chairman and CEO of the B612 Foundation, which is planning to launch the Sentinel space telescope to track half a million near-Earth asteroids:
"While it is great that Apophis is much better understood, and we know it won't hit us in 2036, the greatest danger from an asteroid strike is from the ones we haven't yet found.  Of asteroids larger than the one that struck Tunguska in 1908, we know of less than 1 percent of them.  And as David Morrison points out, we can't protect ourselves from the unknown asteroids (or make use of them either). The B612 Foundation Sentinel Space Telescope is going to work on finding and tracking these asteroids."
And here are some comments from Apollo 9 astronaut Rusty Schweickart, who has played a key role in raising awareness about the threats and opportunities presented by near-Earth objects. It was Schweickart who warned in the wake of Hurricane Katrina that asteroids like Apophis could spark a much more devastating "cosmic Katrina":  
"I'm hoping that you don’t follow the bad (surprisingly wide) precedent of stating that [the risk from] Apophis has been eliminated.  Please look on the JPL risk page  and especially the more detailed info and note that 1) The 2036 impact possibility is, while significantly reduced, still possible, and 2) that the 2068 impact possibility is now elevated ... to a level that exceeds what the 2036 impact was prior to this apparition.
"There’s certainly good news re the 2036 impact decreasing in probability ... but frankly it was 1 in 234,000 prior to the new observations ... not exactly an impact probability to worry one. (There are many NEOs with higher impact probability ... but no one pays attention to them ... they aren't the 'poster child' that Apophis is.) My personal reaction was one of surprise that the new 2036 impact was not zero!
"But/And ... there are more radar observations to integrate in ... as well as optical tracking both now and for the next several years.  Apophis isn't going away ... the impact possibilities are simply shifting around a bit with refinement of the tracking data. 2036 is now less probable; 2068 is now more probable (but still very low).
"Until JPL and the other guys get more data (enough to really define the Yarkovsky effect), we really won’t be able to get definitive data for longer time scales that we can rely on."
JPL's Giorgini said the risk assessment that Schweickart mentioned won't be full updated until after Goldstone and Arecibo finish their observational campaign in mid-February — so there may still be a non-zero risk listed until then. But Giorgini is confident that the 2036 risk will disappear when all the observations are factored in. (As of this writing, the estimated risk of collision is listed at 1 chance out of 10,989,000.) But you're right, Rusty: In order to eliminate the risk completely, astronomers will have to get more data about Apophis' physical characteristics. And then there are all those other unknown killer asteroids that might be out to get us...
More doomsday worries addressed:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.




Asteroids – Overview
Asteroids are small, airless rocky worlds revolving around the sun that are too small to be called planets. They are also known as planetoids or minor planets. In total, the mass of all the asteroids is less than that of Earth's moon. But despite their size, asteroids can be dangerous. Many have hit Earth in the past, and more will crash into our planet in the future. That's one reason scientists study asteroids and are eager to learn more about their numbers, orbits and physical characteristics. If an asteroid is headed our way, we want to know that.
Most asteroids lie in a vast ring between the orbits of Mars and Jupiter. This main belt holds more than 200 asteroids larger than 60 miles (100 kilometers) in diameter. Scientists estimate the asteroid belt also contains more than 750,000 asteroids larger than three-fifths of a mile (1 kilometer) in diameter and millions of smaller ones. Not everything in the main belt is an asteroid — for instance, comets have recently been discovered there, and Ceres, once thought of only as an asteroid, is now also considered a dwarf planet.

Many asteroids lie outside the main belt. For instance, a number of asteroids called Trojans lie along Jupiter's orbital path. Three groups — Atens, Amors, and Apollos — known as near-Earth asteroids orbit in the inner solar system and sometimes cross the path of Mars and Earth.
This enlarged view of photo of the asteroid Lutetia is one of the closest views ever of the asteroid. It was taken by Europe's comet probe Rosetta from 80,000 km away during a July 10, 2010 flyby.
This enlarged view of photo of the asteroid Lutetia is one of the closest views ever of the asteroid. It was taken by Europe's comet probe Rosetta from 80,000 km away during a July 10, 2010 flyby.
CREDIT: ESA
This enlarged view of photo of the asteroid Lutetia is one of the closest views ever of the asteroid. It was taken by Europe's comet probe Rosetta from 80,000 km away during a July 10, 2010 flyby.
CREDIT: ESA
Formation
Asteroids are leftovers from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today.
Physical Characteristics
Asteroids can reach as large as Ceres, which is 940 kilometers (about 583 miles) across and is also considered a dwarf planet. On the other hand, one of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.
Nearly all asteroids are irregularly shaped, although a few are nearly spherical, such as Ceres. They are often pitted or cratered — for instance, Vesta has a giant crater some 285 miles (460 km) in diameter.
As asteroids revolve around the Sun in elliptical orbits, they rotate, sometimes tumbling quite erratically. More than 150 asteroids are also known to have a small companion moon, with some having two moons. Binary or double asteroids also exist, in which two asteroids of roughly equal size orbit each other, and triple asteroid systems are known as well. Many asteroids seemingly have been captured by a planet's gravity and become moons — likely candidates include among Mars' moons Phobos and Deimos and most of the distant outer moons of Jupiter, Saturn, Uranus and Neptune.
The average temperature of the surface of a typical asteroid is minus 100 degrees F (minus 73 degrees C). Asteroids have stayed mostly unchanged for billions of years — as such, research into them could reveal a great deal about the early solar system.
Classification
In addition to classifications of asteroids based on their orbits, most asteroids fall into three classes based on composition. The C-type or carbonaceous are greyish in color and are the most common, including more than 75 percent of known asteroids. They probably consist of clay and stony silicate rocks, and inhabit the main belt's outer regions. The S-type or silicaceous asteroids are greenish to reddish in color, account for about 17 percent of known asteroids, and dominate the inner asteroid belt. They appear to be made of silicate materials and nickel-iron. The M-type or metallic asteroids are reddish in color, make up most of the rest of the asteroids, and dwell in the middle region of the main belt. They seem to be made up of nickle-iron. There are many other rare types based on composition as well — for instance, V-type asteroids typified by Vesta have a basaltic, volcanic crust.
Earth Impacts
Ever since Earth formed about 4.5 billion years ago, asteroids and comets have routinely slammed into the planet. The most dangerous asteroids are extremely rare, according to NASA.
An asteroid capable of global disaster would have to be more than a quarter-mile wide. Researchers have estimated that such an impact would raise enough dust into the atmosphere to effectively create a "nuclear winter," severely disrupting agriculture around the world. Asteroids that large strike Earth only once every 1,000 centuries on average, NASA officials say.
Smaller asteroids that are believed to strike Earth every 1,000 to 10,000 years could destroy a city or cause devastating tsunamis.
Dozens of asteroids have been classified as "potentially hazardous" by the scientists who track them. Some of these, whose orbits come close enough to Earth, could potentially be perturbed in the distant future and sent on a collision course with our planet. Scientists point out that if an asteroid is found to be on a collision course with Earth 30 or 40 years down the road, there is time to react. Though the technology would have to be developed, possibilities include exploding the object or diverting it.
For every known asteroid, however, there are many that have not been spotted, and shorter reaction times could prove more threatening.
When an asteroid, or a part of it, crashes into Earth, it's called a meteorite. Here are typical compositions:
Iron Meteorites:
  • Iron 91%
  • Nickel 8.5%
  • Cobalt 0.6%
Stony Meteorites:
  • Oxygen 36%
  • Iron 26%
  • Silicon 18%
  • Magnesium 14%
  • Aluminum 1.5%
  • Nickel 1.4%
  • Calcium 1.3%
Discovery
In 1801, while making a star map, Italian priest and astronomer Giuseppe Piazzi accidentally discovered the first and largest asteroid, Ceres, orbiting between Mars and Jupiter. Ceres accounts for a quarter of all the mass of all the thousands of known asteroids in or near the main asteroid belt.
Naming
Since the International Astronomical Union is less strict on how asteroids are named when compared to other bodies, there are asteroids named after Mr. Spock of "Star Trek" and rock musician Frank Zappa as well as more solemn tributes, such as the seven asteroids named for the crew of the Space Shuttle Columbia killed in 2003. Naming asteroids after pets is no longer allowed.
Asteroids are also given numbers — for example, 99942 Apophis.
Exploration
The first spacecraft to take close-up images of asteroids was NASA's Galileo in 1991, which also discovered the first moon to orbit an asteroid in 1994.
In 2001, after NASA's NEAR spacecraft intensely studied the near-earth asteroid Eros for more than a year from orbit, mission controllers decided to try and land the spacecraft. Although it wasn't designed for landing, NEAR successfully touched down, setting the record as the first to successfully land on an asteroid.
In 2006, Japan's Hayabusa became the first spacecraft to land on and take off from an asteroid. It returned to Earth in June 2010, and the samples it recovered are currently under study.
NASA's Dawn mission, launched in 2007, began exploring Vesta in 2011 and is slated to explore Ceres in 2015 and will be the first spacecraft to visit either body.
In 2012, a company called Planetary Resources, Inc. announced plans to eventually send a mission to a space rock to extract water and mine the asteroid for precious metals.
RELATED: See our overview of Solar System Facts or learn more about the Solar System Planets.
21st Century Astronomy: The Solar System (3rd Edition) by Hester, Jeff (Google Affiliate Ad)

    Wednesday, March 27, 2013

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    1. www.cnn.com/2012/12/21/us/space-asteroid.../index.html
      Dec 24, 2012 – An asteroid feared to be on a collision course with our planet no longer poses a threat, NASA said Friday.
      Dec 12, 2012
      Asteroid 2012 XE54 also passed through Earth's shadow a few hours before its closest approach, generating an eclipse on the space rock's surface, researchers said. [Video: Asteroid 2012 XE54 Flies Closer Than Moon] ...
      Dec 12, 2012
      But another smaller asteroid passed much closer today. (E. De Jong and S. Suzuki, JPL, NASA) As if 12/12/12 wasn't curious enough of a date already with the whole Mayan-doomsday-but-not-really thing, there's also the ...
      Dec 10, 2012
      Despite some panic, NASA's Johnson Space Center in Houston insisted that this was not a sign of the coming destruction of the planet, but rather, just a rogue asteroid originating from the asteroid belt between the planets ...
       
       
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