Close Approach Calculation Sensitive to Changes in Parameters Used

The calculation of the point of closest approach appears to be sensitive to small changes in the parameters used. This result used a step size of 0.0005 days and averaged the acceleration over the interval. A close approach point near the South Pole makes the positions difficult to determine precisely.

2012 DA14 on NASA JPL Live

src: nasajpl2

2012 DA14 Close Approach Details

I just got through recalculating today's close approach details for 2012 DA14. I used the fitted position and velocity of the asteroid on Feb 9.0 and subtracted the values for the motion of the Earth's center relative to the Earth-Moon barycenter to get the position and velocity relative to the Earth's center at that time. The gravitational attraction of the Sun, Earth and Moon were used to compute 2013 DA14's trajectory. Since the Earth and Moon are also accelerating due to the Sun's attraction the difference between the asteroid's acceleration and the Earth's was used to get the acceleration relative to the Earth. My computed time for close approach is Feb 15, 2013 23:46 UT (15:46 PST) at a distance from the Earth's center of 6.477 Earth radii. The JPL ephemeris gave a time of 19:20 UT and a radial distance of 5.492 Earth radii.

Supplemental (Feb 15): 2012 DA14 may not be visible at the time of close approach since it is likely to be passing through the Earth's shadow during the middle of the night.

2012 DA14 Track Anaglyph

To get a better picture of what 2012 DA14 is doing in 3D I used the previous set of observations and the corresponding fit to make an anaglyph. The horizontal axis is the RA in degrees and the vertical axis is the Decl in degrees so that both scales have the same unit of measurement. The separation of our "eyes" is the diameter of the Earth and our "vista point" is the Earth-Moon barycenter. The time span ranges from Feb 6.388 to Feb 11.496 and points further away occur earlier in time.

red-cyan 3D glasses required for viewing

Cubic Fit to the 2012 DA14 Observations

There was enough data to get a cubic fit to the 2012 DA14 observations. The results are shown in the image below. The positions are again given relative to the Earth-Moon barycenter.

The extrapolated close approach is Feb 15, 2013 19:54 UT.  There was little change in the minimum distance.

The Earth's gravitational attraction should change the results some.

2012 DA14 Tracking Update

 

  The MPC 2012 DA14 obsersvations for Feb 2013 are now showing signs of acceleration.

 

 

  The latest least squares fit for position, velocity and acceleration has an rms angular deviation of about 3 asec. I used MPC's longitude and parallax constants for the observatories for the first time.

 

 

  The fit now indicates a close approach at Feb 15, 2013 11:30 UT with a radial distance from the center of the Earth of 7.3 Earth radii. There may be more signs of acceleration as the asteroid approaches. The formula for the fitted position is X=X₀+V₀Δt+A₀Δt² with Δt=t-t₀ and t₀=6.388. Distance was measured relative to the Earth-Moon barycenter.

 

 

Tracking Results For 2012 DA14

 

  Some observations are now coming in at the Minor Planet Center for 2012 DA14. There is some deviation from where the 2012 predictions say 2012 DA14 will be. I used the observations from Feb 6 through Feb 8 to get an estimated position and velocity for the asteroid. A simple projection along the direction of the velocity indicates that the close approach will occur in early March.

 

 

  I merged the gravitational attraction of the Earth and Moon into a single body to get a better estimate of the close approach.

 

 

  This is also a rough estimate but it doesn't appear that 2012 DA14 will approach as closely as predicted a year ago. My fit wasn't particularly good with the asteroid at about 600 Earth radii away. The uncertainty in angular direction is magnified by this distance to increase the uncertainty in the asteroid's position. The uncertainty in the velocity also contributes to the uncertainty in the distance of close approach. One needs to take the Earth's motion and the Sun's gravitational field into account to get a better path for the asteroid's motion. The estimated position and velocity above are given relative to the Earth's center.