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Friday, February 11, 2011


99942 Apophis, This is Not the Killer Asteroid You Are Looking For

Asteroid 99942 Apophis visualised in Celestia.

The asteroid 99942 Apophis (2004 MN4) is in the news again. The Bad Astronomer has already railed about the media mangling of the research on this asteroid, absurdly over-hyping the minuscule probability that the asteroid will hit us in 2036. Since the BA has already dealt with these issues, and there is no way I can improve on his excellent writing, I'm giving you an updated Celestia file for 99942 Apophis instead.

The elements are taken from the latest MPEC data, BUT .... it doesn't come close to Earth on 13 April 2029, as it should. I suspect something is wrong with the Mean Anomaly, as JPL Horizons, Wikipedia and MPEC all give different Mean Anomalies, by huge amounts (using the Wikipedia MA values give the closest approach of the bunch, around 0.113 AU).

There's probably something highly obvious I'm missing, but have a play with it anyway.

As allways, cut and paste the data below into a new file 2004MN4.ssc and copy the file 2004MN4.ssc into the Celestia extras folder.
# This file contains the orbital elements for the asteroid 99942 Apophis (2004 MN4)
# Ian Musgrave February 10, 2011. Using orbital elements from MPEC from MPO 164109.

"2004 MN4:99942 Apophis " "Sol"
Class "asteroid"
Mesh "ky26.cmod"
Texture "asteroid.jpg"
Radius 0.248233 # maximum semi-axis
MeshCenter [ -0.000718 -0.000099 0.000556 ]

InfoURL "http://en.wikipedia.org/wiki/99942_Apophis"

Epoch 2455542.05876
Period 0.885711
SemiMajorAxis 0.9222941
Eccentricity 0.1911154
Inclination 3.33190
AscendingNode 204.4313
ArgOfPericenter 126.42496
MeanAnomaly 294.96917 #339.94 -wiki , 11.34117 - JPL
#MeanMotion 1.11275587
AphelionDistance 1.0987
Albedo 0.3
RotationPeriod 1.2667

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I get a bit more than 2 LD on April 14th 2029. I expcet that it will be clearer in time to come. Might add I still used 137 as mean anomaly.
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