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Asteroid 1997 XF11 (Earth Close-Approach)


* Summary

On October 26, 2028, the near-Earth asteroid 1997 XF11 will make a close approach to Earth. Although initial reports indicated an extremely close passage, the current analyses predict an approach distance of 0.00636 AU (951,000 km, 591,000 mi) or about 2.5 times farther than the moon. The probability that the asteroid will impact the Earth is effectively zero. (See JPL's press release.)

1997 XF11, an Apollo type asteroid, was discovered by Jim Scotti of the Spacewatch group at the University of Arizona's Lunar and Planetary Laboratory. The asteroid's orbit was derived from about 100 observations taken since that time as well as 4 pre-discovery observations taken in 1990 by Eleanor Helin, Ken Lawrence, and Brian Roman as a part of the Palomar Planet Crossing Asteroid Survey.

Key points:

  • probability of Earth impact is zero with and without the 1990 pre-discovery observations
  • effect of the 1990 pre-discovery observations moved the 2028 close-approach distance farther away and reduced the approach distance uncertainties
  • the same uncertainty analysis used here for 1997 XF11 was used for the Galileo spacecraft flybys of asteroids 951 Gaspra and 243 Ida --- at encounter, both asteroids were found to lie well within their error ellipsoids.

* Orbit Plot

The orbit of 1997 XF11 and the inner planets is shown below (all bodies are orbiting counter-clockwise in this ecliptic projection). >From the time of the plot (March 12, 1998), the Earth and 1997 XF11 will orbit the sun approximately 31 and 18 times, respectively, prior to their close-approach on October 26, 2028.

The line of nodes is the intersection of 1997 XF11's orbit plane with the orbit plane of the Earth. Notice that the asteroid passes across the line of nodes (descending through the Earth's orbital plane) at a point very near the Earth's orbit track.

Orbit Plot
Figure 0. This plot shows orbits of 1997 XF11, Mars, Earth, Venus, and Mercury projected on the ecliptic plane on March 12, 1998. The original full-size plot (created by Paul Chodas, 1998-May-20) is also available as a PostScript file.


* Earth Target-Plane Position Plots

This section illustrates the uncertainties in the close approach predictions and how they are affected by the inclusion of the pre-discovery observations. These uncertainties are depicted in the "Earth target-plane" which is the plane perpendicular to the geocentric velocity vector of the asteroid at the time of closest approach on October 26, 2028. The error ellipse (show on the following plots) encloses all the points though which the asteroid is likely (i.e. with 99% probability) to pass. The view in these plots is from the approaching asteroid and about 5 degrees below Earth's equatorial plane with North up. The asteroid passes at right angles through these plots. Note that the error ellipses (shown in red) are so narrow that they appear as lines.

It is important to understand that the position uncertainties associated with any of the orbit solutions used in this analysis constrain the asteroid to pass within the position error ellipses shown below (i.e. 99% probability of being within the error ellipse). In other words, even though we can not say exactly where 1997 XF11 will be on 2028-Oct-26, we can say that it will be somewhere within the position error ellipse. This is what allows us to say that the probability of Earth impact is zero.

* Solution using 1990 pre-discovery observations

  • Based on the current solution for 1997 XF11.
  • Most likely miss distance is 951,000 km (591,000 mi).
  • Minimum miss distance is 865,000 km (537,000 mi).
  • Probability of Earth impact is zero.

Position Error Ellipse
Figure 1. This plot shows the position error ellipse based on an orbit solution which includes the 1990 pre-discovery observations. Note that the error ellipse shown above is contained within the error ellipse associated with the solution excluding the pre-discovery observations (see Fig. 2). The original full-size plot (created by Paul Chodas, 1998-May-20) is also available as a PostScript file.

1997 XF11 orbit solution used in the above analysis
(includes 1990 pre-discovery observations)

 Solution Reference: JPL#10

 102 Observations spanning 1990-Mar-22 to 1998-Mar-04
 RMS residual = 0.644 arcsec

 Epoch = 1998 Mar 30.0 TDB
     e = 0.48374055
     q = 0.74443182 AU
    Tp = 1997-Jul-01.191519  TDB
  Node = 214.12725759 deg  (J2000)
     w = 102.47227749 deg  (J2000)
     i =   4.09477290 deg  (J2000)
     a =   1.441752196 AU
     M = 154.75017350 deg

* Solution excluding pre-discovery observations

  • Error ellipse is much longer because the observational time span is much shorter (3 months versus 8 years).
  • Most likely miss distance is 86,000 km (54,000 mi).
  • Minimum miss distance is 28,000 km (17,000 mi).
  • Probability of Earth impact is zero.

Position Error Ellipse
Figure 2. This plot shows the position error ellipse based on the original orbit solution not including the pre-discovery observations. The original full-size plot (created by Paul Chodas, 1998-May-20) is also available as a PostScript file. A closeup of this plot is shown below in Figure 3.

Position Error Ellipse
Figure 3. This plot shows a zoomed view of the previous plot (Fig. 2) near the Earth. The Earth is shown to scale. The original full-size plot (created by Paul Chodas, 1998-May-20) is also available as a PostScript file.

1997 XF11 orbit solution used in the above analysis
(excludes 1990 pre-discovery observations)

 Solution Reference: JPL#08

  98 Observations spanning 1997-Dec-06 to 1998-Mar-04
 RMS residual = 0.608 arcsec

 Epoch = 1998 Mar 30.0 TDB
     e = 0.48377234
     q = 0.74429096 AU
    Tp = 1997-Jul-01.196199  TDB
  Node = 214.12415280 deg  (J2000)
     w = 102.47682505 deg  (J2000)
     i =   4.09477745 deg  (J2000)
     a =   1.441788212 AU
     M = 154.74171751 deg

* Table of Earth Close-Approaches by 1997 XF11

The following table shows the closest Earth approach distances for the near-Earth asteroid 1997 XF11 from 1990-Mar to 2029-Feb. Tables of past and future Earth close-approaches by other small-bodies are available.
 Date of Close     Approach Distance
 Earth Approach     (AU)     (km)
-----------------  -----------------
1990-Jul-05 19:16  0.244  36,480,000
1997-May-08 21:59  0.156  23,270,000
2002-Oct-31 00:33  0.064   9,510,000
2009-Aug-27 14:21  0.262  39,170,000
2016-Jun-10 15:30  0.180  26,910,000
2021-Nov-18 23:24  0.443  66,340,000
2023-May-05 07:26  0.242  36,190,000
2028-Oct-26 06:26  0.006     954,000

* Geocentric Ephemerides for 1997 XF11

Geocentric ephemerides are available for 1997 XF11 during the following time periods (1 hour output intervals): These ephemerides were computed using the HORIZONS system. If you need information at times not covered by these ephemerides, the HORIZONS ephemeris generator can be used to generate custom ephemerides for 1997 XF11 (and other solar system bodies).

A table of osculating orbital elements is also available for 1997 XF11 during the period 1998-Mar-11 to 2029-Jan-01 at 90 day intervals.


This page written by Alan B. Chamberlin and Paul W. Chodas
Solar System Dynamics, JPL

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