No truth to claims that 13-year-old found NASA error
- 00:05 17 April 2008
- NewScientist.com news service
- David Shiga
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The asteroid Apophis still has only a 1 in 45,000 chance of hitting Earth in 2036, NASA says, despite recent news reports suggesting a 13-year-old German boy had discovered a mistake in the space agency's analysis. The reports suggested the risk of an impact was actually 100 times as great as NASA's estimate.
The 250-metre-wide Apophis is on a trajectory that will take it near Earth in 2029. If Apophis passes through a "keyhole" in space just 600 metres or so across at that time, it will return to hit Earth in 2036.
NASA estimates the risk of this to be small – just 1 in 45,000. But a report on Tuesday by the Agence France Presse news agency, citing a report in a German newspaper called Bild, said a 13-year-old German boy had found that the real risk was higher.
According to the AFP story, the boy calculated the risk to be 1 in 450, based on the supposed possibility that the asteroid's path could be altered by a collision with a satellite when Apophis passes within about 38,000 kilometres of Earth in 2029.
But Steven Chesley, a scientist at NASA's Near-Earth Object Program in Pasadena, California, US, says Apophis will not pass near any satellites.
High latitudes
There are geosynchronous satellites orbiting Earth at a distance of 42,000 kilometres, but these orbit in a ring around Earth's equator, he says. Apophis's closest approach to Earth will occur at higher latitudes, however, far from the equator.
Apophis will pass over the equator about 90 minutes before its closest approach, at a distance of 52,000 kilometres, which is much too far to hit any geosynchronous satellites, he adds. The uncertainty in its path in 2029 is 1650 km - too small to allow for a satellite impact.
"The idea that we've somehow been corrected is absolutely untrue," Chesley told New Scientist. "We stand by our calculations."
A statement on NASA's website by Donald Yeomans, who heads NASA's Near-Earth Object Program Office, confirms that NASA has not changed its estimate of 1 in 45,000 for Apophis's impact risk.
Independent confirmation
The AFP story claimed NASA had told the European Space Agency that the boy's calculations were correct. But Yeomans's statement on the NASA website says this is not true.
"Contrary to recent press reports, NASA offices involved in near-Earth object research were not contacted and have had no correspondence with a young German student, who claims the Apophis impact probability is far higher than the current estimate," it says.
Chesley points out that NASA's calculations have been independently confirmed by a group of scientists at the University of Pisa, who report their results on a website called NeoDys. The NeoDys entry on Apophis puts its impact risk at 0.00207%, or about 1 in 48,000.
No chance
"We're constantly cross-checking each other's independently arrived at results," he says. "In the case of Apophis, we have good agreement."
Aldo Vitagliano of Italy's Universita di Napoli Federico II, who does his own independent calculations of asteroid trajectories and impact risks, agrees that the purported correction is wrong.
"The news is definitely a canard," he told New Scientist. "My results agree with those reported by JPL and NeoDys."
The asteroid currently appears too close to the Sun in the sky to observe, but new observations should be possible for a period of several years starting in about 2011, Chesley says. Those observations will help scientists to reduce the uncertainty in the asteroid's trajectory: "There's a 95 plus percent chance that we'll be sounding the all-clear by 2014."
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