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Montag, 12. Oktober 2009 um 00:00 Uhr |
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Ever since its interesting orbit was discovered almost five years ago (see Update #284), the 250-meter Near Earth Asteroid first known as 2004 MN4 and then (99942) Apophis has been the poster child for certain space activists who call for radical and expensive countermeasures to the (unquestionably real but not imminent) threat such bodies present: E.g. calls were voiced to launch a spacecraft to put a radio transponder onto Apophis so that its future orbit could be refined.
While it had been clear within days after initial confusion that an impact in 2029 was impossible, there remained the vague possibility that the close approach to Earth then would deflect its orbit in such a way that an impact in 2036 could not be ruled out - though the likelihood for that had hovered near 1:45,000 for a long time now.
Orbital experts had stated time and again that we would know the orbit much better before long (and in time to, should things turn dire), based on ground-based optical and radar tracking alone - and exactly this has happened now: Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about 1:250,000. Interestingly this finding is based largely on systematic optical observations alone. In the course of the calculation another similarly remote impact possibility in 2068 arose, but "it is expected that the 2068 encounter will diminish in probability as more information about Apophis is acquired," a NASA statement says. Thus the case of Apophis can be considered closed - and we can happily expect a harmless NEO in the skies in 20 years, visible to the naked eye even.
You can find Daniel Fischers Cosmic Mirror here. |
