Astronomers have defended a system intended to spot impending asteroid impacts after it mistook the European Space Agency鈥檚 Rosetta spacecraft for an incoming rock and issued an alert that a near miss was imminent.
The is on its way to rendezvous with comet in 2014. During the journey, the spacecraft must swing past Earth three times to give it the momentum needed for the final slingshot away from the Sun.
The spacecraft is due to fly past Earth at a distance of only 5300 kilometres, flying high above the Pacific Ocean at 2100 (GMT) on Tuesday, 13 November.
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During the close approach, Rosetta will look for shooting stars in the upper atmosphere and observe the magnetosphere. It will also image urban regions in Asia, Africa and Europe, and measure the light reflected from the Moon.
Alert issued
Last Thursday, however, three observatories in the US spotted an unidentified object, designated 2007 VN84, heading Earth鈥檚 way. This prompted the at the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US, which co-ordinates the search of near-Earth objects, to issue a potential near-miss warning.
The warning was later retracted after Moscow-based astronomer noticed that the object鈥檚 trajectory closely matched Rosetta鈥檚.
The mix-up generated a few red faces, but also points to some important lessons. 鈥淭he system is there to try to accurately assess an object,鈥� says Mark Bailey, director of the Armagh Observatory in Northern Ireland.
It is designed to spot objects moving towards Earth, determine their trajectory, and to disseminate necessary information as quickly as possible so that others can make measurements. 鈥淚f it鈥檚 going to hit, you need to work out when and where as quickly as possible. You don鈥檛 want them sitting on the data wondering whether it鈥檚 an asteroid or not,鈥� Bailey told 快猫短视频.
Lack of information
But the incident raises questions about how well the warning system works. The Minor Planet Center complains that, 鈥渢his incident highlights the deplorable state of availability of positional information on distant artificial objects鈥�. This lack of a centralised database makes checking incoming objects against known space probes difficult.
Bailey says that, while a good idea, it is unclear who should compile, maintain, and pay for such a database. 鈥淭hat鈥檚 a very tricky question,鈥� he adds.
Others argue that the Rosetta approach has proven the robustness of the system. 鈥淚t shows that the telescopes are picking these objects up,鈥� says Robert Massey, a spokesperson for the Royal Astronomical Society in the UK. 鈥淔or them it鈥檚 just a moving point of light that is not easy to identify as a spacecraft.鈥�
He concedes that a lack of coordination may have contributed to the error, but believes the fly-by has been a good test of the alerting system. 鈥淭he alert was not particularly alarmist, the spacecraft was identified, and no major announcement was made,鈥� he says.
Bailey agrees. 鈥淲e can live with red faces once in a while,鈥� he says.
Comets and Asteroids 鈥� Learn more about the threat to human civilisation in our .
