99942 Apophis (previoulsy known as 2004 MN4) is a Near Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a relatively large probability that it would strike the earth in 2029. A future impact on April 13, 2036, is still possible, keeping the asteroid at level 1 on the Torino impact hazard scale as of September 2005, with an estimated impact-probability of 1 in 5,560.
Apophis is expected to come close enough that on April 13, 2029 (Fri. 13th) it will become as bright as magnitude 3.3 (easily seen by the eye). This close approach will be visible from Europe, Africa, and wsestern Asia. Throughout recorded history, no other closely-approaching objects of this size have been visible to the naked eye. As a result of its close passage, it will move from the Aten (see below) to the Apollo class.
Apophis asteroid remains at level one on the Torino scale because of a very low but non-zero probability of impact in 2036. However, the approach in 2029 will substantially alter the objects orbit, making predictions uncertain without more data.
99942(asteroid number) Apophis (2004 MN4) Earth Impact Risk Summary
Torino Scale (maximum)
0
Palermo Scale (maximum)
-2.52
Palermo Scale (cumulative)
-2.52
Impact Probability (cumulative)
2.2e-05
Number of Potential Impacts
2
Vimpact
12.59 km/s
Vinfinity
5.87 km/s
H
19.7
Diameter
0.250 km
Mass
2.1e+10 kg
Energy
4.0e+02 MT
all above are mean valuesweighted by impact probability
Analysis based on 2 radar delay, 5 Doppler, and731 optical observations spanning 884.52 days(2004-Mar-15.10789 to 2006-Aug-16.626954)
Orbit diagram and elements available here. These results were computed on Oct 19, 2006
99942 Apophis (2004 MN4) Earth Impact Table
Date
Distance
Width
SigmaImpact
SigmaLOV
StretchLOV
ImpactProbability
ImpactEnergy
PalermoScale
TorinoScale
YYYY-MM-DD.DD
(rEarth)
(rEarth)
(rEarth)
(MT)
2036-04-13.37
0.53
1.19e-03
0.000
-2.43130
1.60e+03
2.2e-05
4.02e+02
-2.52
0
2037-04-13.64
0.63
1.11e-03
0.000
4.12077
1.58e+03
8.1e-08
4.01e+02
-4.97
0
rEarth = 6420 km
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Summary Table DescriptionThe Summary Table includes basic information about the hazard for this object. The maximum Torino and Palermo Scale values are listed, as well as the number of tabulated potential impacts and their corresponding cumulative Palermo Scale value and cumulative impact probability. The observation set used for the analysis is also listed. Certain parameter values depend upon the specific impact event in question, but they change little among the various table entries. For this reason we tabulate only mean values for these parameters:
Vimpact - Velocity at atmospheric entry.
Vinfinity - Relative velocity at atmospheric entry neglecting the acceleration caused by the Earth's gravity field, often called the hyperbolic excess velocity. (Vinfinity2 = Vimpact2 - Vescape2, where Vescape = ~11.2 km/s is the Earth escape velocity.)
H - Absolute Magnitude, a measure of the intrinsic brightness of the object.
Diameter - This is an estimate based on the absolute magnitude, usually assuming a uniform spherical body with visual albedo pV = 0.154 (in accordance with the Palermo Scale) but sometimes using actual measured values if these are available. Since the albedo is rarely measured, the diameter estimate should be considered only approximate, but in most cases will be accurate to within a factor of two.
Mass - This estimate assumes a uniform spherical body with the computed diameter and a mass density of 2.6 g/cm3. The mass estimate is somewhat more rough than the diameter estimate, but generally will be accurate to within a factor of three.
Energy - The kinetic energy at impact: 0.5 * Mass * Vimpact2. Measured in Megatons of TNT.
99942(asteroid number) Apophis (2004 MN4) Earth Impact Risk Summary
Torino Scale (maximum)
0
Palermo Scale (maximum)
-2.52
Palermo Scale (cumulative)
-2.52
Impact Probability (cumulative)
2.2e-05
Number of Potential Impacts
2
Vimpact
12.59 km/s
Vinfinity
5.87 km/s
H
19.7
Diameter
0.250 km
Mass
2.1e+10 kg
Energy
4.0e+02 MT
all above are mean valuesweighted by impact probability
Analysis based on 2 radar delay, 5 Doppler, and731 optical observations spanning 884.52 days(2004-Mar-15.10789 to 2006-Aug-16.626954)
Orbit diagram and elements available here. These results were computed on Oct 19, 2006
99942 Apophis (2004 MN4) Earth Impact Table
Date
Distance
Width
SigmaImpact
SigmaLOV
StretchLOV
ImpactProbability
ImpactEnergy
PalermoScale
TorinoScale
YYYY-MM-DD.DD
(rEarth)
(rEarth)
(rEarth)
(MT)
2036-04-13.37
0.53
1.19e-03
0.000
-2.43130
1.60e+03
2.2e-05
4.02e+02
-2.52
0
2037-04-13.64
0.63
1.11e-03
0.000
4.12077
1.58e+03
8.1e-08
4.01e+02
-4.97
0
rEarth = 6420 km
-->
Summary Table DescriptionThe Summary Table includes basic information about the hazard for this object. The maximum Torino and Palermo Scale values are listed, as well as the number of tabulated potential impacts and their corresponding cumulative Palermo Scale value and cumulative impact probability. The observation set used for the analysis is also listed. Certain parameter values depend upon the specific impact event in question, but they change little among the various table entries. For this reason we tabulate only mean values for these parameters:
Vimpact - Velocity at atmospheric entry.
Vinfinity - Relative velocity at atmospheric entry neglecting the acceleration caused by the Earth's gravity field, often called the hyperbolic excess velocity. (Vinfinity2 = Vimpact2 - Vescape2, where Vescape = ~11.2 km/s is the Earth escape velocity.)
H - Absolute Magnitude, a measure of the intrinsic brightness of the object.
Diameter - This is an estimate based on the absolute magnitude, usually assuming a uniform spherical body with visual albedo pV = 0.154 (in accordance with the Palermo Scale) but sometimes using actual measured values if these are available. Since the albedo is rarely measured, the diameter estimate should be considered only approximate, but in most cases will be accurate to within a factor of two.
Mass - This estimate assumes a uniform spherical body with the computed diameter and a mass density of 2.6 g/cm3. The mass estimate is somewhat more rough than the diameter estimate, but generally will be accurate to within a factor of three.
Energy - The kinetic energy at impact: 0.5 * Mass * Vimpact2. Measured in Megatons of TNT.
