Friday, February 1, 2013

Will Comet C/2013 A1 (Siding Spring) Hit Mars?

Image of the JPL Orbit widget which shows Mars and comet C/2013 A1 on top of each other on October 19, 2014, but note the caveat in the applet that says "The applet was implemented using 2-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstance"

A reader pointed out that the JPL Orbit Diagram for comet C/2013 A1 (Siding Spring) shows the Comet and Mars on top of each other on October 19, 2014 (see the diagram here). Does this indicate an impact between the comet and Mars?

No, if you go to the bottom of the orbit diagram and click on the [show close approach] link, you will see that the nominal close approach is 0.006 AU (compare this to the 0.00023 AU close approach of 2012 DA14, which misses us by two Earth diameters).

Simulation of the close approach of C/2013 A1 to Mars in Celestia using the latest MPC elements (click to embiggen)

The error associated with this estimate includes an impact though (and a maximum miss of 0.24 AU), so an impact can't be ruled out at this stage.

However, as further observations are added and the orbit is refined, we will have a better idea of whether it will impact. The latest Minor Planet Ephemeris data suggests that an impact is unlikely, with a nominal pass of 0.015 AU (2,277,700 Km from Mars's surface).

Simulation of the telescopic view of Mars and C/2012 A1 on October 19 as seen from Adelaide near closest approach..

Importing the latest elements into SkyMap or Stellarium suggests that from Earth we will see the comet and Mars less than 2 minutes of arc from each other, which will look quite nice in telescope eye pieces (but hard to image as the comet will be a dim magnitude 8.5 and Mars bright).

I've also made a Celestia file for you. As usual, copy the code below and save as it as a text file 2013A1.ssc in the Celestia extras folder.
"Siding-Spring:C2013 A1" "Sol"
#Close approach of this comet to Mars
Class "comet" # Just copying the data for Halley
Mesh "halley.cmod"
Texture "asteroid.jpg"
Radius 3 # best guess at maximum semi-axis
MeshCenter [ -0.338 1.303 0.230 ]

Epoch 2456955.47179 # 2014 25 Oct
Period 217204.51919319 # (q/(1-e))^1.5 hyperbolic orbit
SemiMajorAxis -3613.3711384783 #Hyperbolic orbit
PericenterDistance   1.396000248531628       
Eccentricity 1.000467
Inclination 128.9984
AscendingNode 300.9204
ArgOfPericenter 2.4695
#MeanAnomaly 359.9970184682824    #MA messes up hyperbolic orbits

# Again, this data is copied straight from the ssc files for Halleys’ Comet
# chaotic rotation, imperfectly defined:
# this version from "The New Solar System", 4th Edition; Eds.
# JK Beatty, CC Petersen, A Chaikin
Period 170 # 7.1 day axial rotation period
Inclination 66
PrecessionPeriod 3457004.12 # 3.7 day precession period

Albedo 0.8


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