(99942) Apophis

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( 99942 ) Apophis is a near-Earth asteroid of Aten - type of about 300 m in diameter, the Roy Tucker, David J. Tholen and Fabrizio Bernardi discovered at Kitt Peak National Observatory on 19 June 2004 as part of the University of Hawaii Asteroid Survey. Observations over a few months showed that the provisionally as 2004 MN4 designated asteroid earth will come very close to the April 13, 2029. Short term: a collision probability of 2.7 % was calculated and made ​​a rating of 4 on the Torino scale of risk with appropriate media coverage. Days later he was identified on older photographs, its orbit much less uncertain and a collision in 2029 excluded. In fact, he will fly past Earth in 2029 over the ring of geostationary satellites in the. In this millennium event he will reach an apparent magnitude of 3.3 m but remain point-like in binoculars.

This close flyby will change its orbit drastically. However, the Earth will cross the new orbit of the asteroid annually on 13 April. Already in 2036 there is a new approach. The distance is not precisely known, since small uncertainties related to the position on April 13, 2029 grow quickly after deflection. It's about inaccurate train observations in the past and to bad in estimating the perturbations.

Between 2008 and 2011, Apophis was close to the sun and was therefore unobservable. During this time there was a residual risk of a collision in 2036, which was eliminated on the basis of optical measurements in early 2012. This finding was extended in early 2013 to the entire 21st Century through more precise radar measurements during the conjunction. Apophis is thus only of scientific interest.

Its discoverers named 2004 MN4 after the Egyptian deity, at the same time an antagonist in the science fiction series Stargate: " Apophis ".

Train

Until 2029 Apophis is moving at a distance of 0.746 ( perihelion ) to 1.098 ( aphelion ) astronomical units in 323 days and 12 hours around the sun. The orbital eccentricity is thus 0.191. Its orbit is inclined at 3,331 degrees only slightly to the ecliptic crosses the Earth's orbit and at a relative speed of 5.87 km / s It rotates once in 30 hours and 37 minutes on its axis. The orientation of the axis is not precisely known, but important for the direction of the Yarkovsky effect.

Apophis will pass Earth on April 13, 2029 in more than 31,000 kilometers above the earth's surface. In this case, it flies at approximately 7.4 km / s across the ring of geostationary satellites. The proximity to Earth will significantly change its orbit and self-rotation, in particular, is its semi-major axis to increase to over 1.1 AE, so that he shall be considered as Apollo type.

Possible consequences of an impact

Apophis would in the event of an impact release an energy of about 900 megatons ( TNT equivalent ). By comparison, the largest man-made nuclear explosion ( by the Tsar - bomb) corresponded to 50 megatons of TNT. The energy release of an earthquake of magnitude 8.0 corresponds to about 1000 megatons of TNT.

The precise consequences of an impact would depend on the composition of the asteroid and the location and angle of impact. In an impact on the mainland, although regionally massive damage would occur; but could already have a distance of about 250 km from the point of impact be sufficient to survive with a very high probability. In an impact in deep water would be a large-scale threat of massive tsunamis, which are expected to reach a height of over 100 meters at the nearby coasts, to distant shores 30 meters.

For global destruction, the impact energy would be 100 times larger.

Chronicle of the forecasts and observations

The spread in the media original NASA report of 23 December 2004 called a strike probability of " about 1 in 300 ." The actual estimate of NASA at that time was 1 to 233 and led to the classification in the stage 2 of the Turin scale. Later in the day, the NASA estimate was increased ( by 64 observations ) to 1 to 62 ( corresponding to 1.6 percent). So level 4 of the Turin scale was achieved. Apophis is the first object that at all, even if only for a short time, reached a higher risk assessment than level 1. At the Palermo scale risk assessment of the impact reached the value of 1.80.

On 24 December 2004, the probability is given first with 1 to 42 ( 2.4 percent ) and later (after 101 observations ) with 1 to 45 (2.2 percent).

On 27 December 2004, the impact probability was increased ( by 176 observations) to 1 in 37 (2.7 percent). In the course of this day, the accuracy of the path data has been greatly improved by the additional presentation of past recordings. In order for a collision could be excluded, a passage within the Roche limit, however, not yet. This was followed on February 3, 2005 with the announcement of the results of a multi-day Doppler radar survey by the Arecibo Observatory.

The classification on the Torino scale was reduced for 2029 to 0, but left in place for 2036 to 1. This meant that the distribution was so extended for the possible positions on 13 April 2036 that they included the earth. The railways, which would hit the Earth were, for the encounter in 2029 apart by only a few 100 m. That this Gravitational keyhole would be taken, was not excluded. In addition, the exact location the keyholes itself was still unsure: Although recent work led to a better understanding of possible path disorders, lack of new data not yet been to more accurate predictions - a situation similar to that at 1950 DA. On 14 December 2006, the Planetary Society donated a prize worth $ 50,000 worked out proposals, such as within a decade its path must be determined as accurately by a mission to Apophis, that result from a decision on defensive measures could be made dependent.

The winners were announced on 26 February 2008. In the missions, it was all about probes should only accompany the asteroid - the interest was finally focus not an arbitrary point of impact.

Was realized none of these proposals, because a re-evaluation of previous observations was sufficient to rule out a meeting of the keyhole for sure: On 7 October 2009, NASA lowered the probability of a collision in 2036 from 1 to 45,000 to 1 in 250,000. The classification on the Torino scale was reduced to 0 and the value on the Palermo scale was negative. The latter means that the impact probability of Apophis was now smaller than that any other object of comparable size hitting the Earth.

In January 2013, the heat radiation of Apophis measured with the Herschel space telescope and estimated by comparison with the reflected light its diameter to 325 ± 15 m. The shape and rotation axis are still unknown.

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