NEO 2020 JJ 5/04/20

Another Near Earth Object encounter.  This time with a unique announcement:

Figure 1.

Notice that 2020 JJ has an anomalous distance of encounter of zero AU.  It is rounded off, of course.  The managers of this source will be contacted to encourage more decimal places!  By other sources, I find the “miss” distance to be about 16,200 miles which is indeed less than 0.1 Lunar Distances.

This, again is worthy of a more detailed diagram with a better picture of the Earth (Thanks, NASA!).

The approaching asteroid did not pass across the celestial equator – where all the geosynchronous communication satellites are – but further to the South.

The JPL Small Body Database Browser, which is also the source for the “circle and arrows” diagrams you have seen on these pages, has undoubtedly given us a more accurate figure.  However, it does have some limitations, which are clearly explained in the website:

“This orbit viewer was implemented using two-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances.”

https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000%20CH59;old=0;orb=1;cov=0;log=0;cad=0#orb

The alert readers (most of you) will point out that “planetary encounter circumstances” is exactly what I am talking about.  That statement means that when asteroids get close to a planet, their mutual gravity has a significant effect that is not calculated in this utility.  So, that 16,200 miss distance is not keenly accurate and almost certainly too large.  Not only that, but it also means that the orbit after the near encounter will have been altered.  It will need to be recalculated and replaced in the database.

JPL has a utility for that, called the “Horizons system” and NASA has an organization to keep track of these things (and studies methods to avoid collisions) called the Planetary Defense Coordination Office.  That said, rocks this small (about 13 feet across) are not easily detected far in advance.  They are also less destructive should they fall to Earth.  This one was small compared to the Chelyabinsk meteor.

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