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View Full Version : Change in Orbit of Asteroid 2003 DZ 15



Ross 54
2013-Jul-20, 04:16 PM
The orbit of asteroid 2003 DZ 15 has apparently changed. Yesterday the NASA Near Earth Objects Program page showed it approaching Earth to within 7.6 Lunar diameters on July 29th, at a relative velocity of 14.54 Km per sec. Today this has been revised, as follows: closest approach -- 9.1 Lunar diameters on July 30th, at 14.34 Km per second. As this object has had its orbit observed and refined for the past ten years, something has presumably happened recently to change its orbit. Perhaps a jet of volatiles from near its surface, which tend to blur the distinction between asteroids and comets, a bit, or an impact by another, small, unknown asteroid. 2003 DZ 15 is approaching Earth from outside our planet's orbit, drawing ever nearer the Sun. In the usual scheme of things, I believe this should see it increasing its speed over time, not decreasing it, as seems to be the case.

Hornblower
2013-Jul-20, 05:57 PM
The orbit of asteroid 2003 DZ 15 has apparently changed. Yesterday the NASA Near Earth Objects Program page showed it approaching Earth to within 7.6 Lunar diameters on July 29th, at a relative velocity of 14.54 Km per sec. Today this has been revised, as follows: closest approach -- 9.1 Lunar diameters on July 30th, at 14.34 Km per second. As this object has had its orbit observed and refined for the past ten years, something has presumably happened recently to change its orbit. Perhaps a jet of volatiles from near its surface, which tend to blur the distinction between asteroids and comets, a bit, or an impact by another, small, unknown asteroid. 2003 DZ 15 is approaching Earth from outside our planet's orbit, drawing ever nearer the Sun. In the usual scheme of things, I believe this should see it increasing its speed over time, not decreasing it, as seems to be the case.

My educated guess is that they just now got around to updating that item. Do you know how long the previous values had been displayed?

Ross 54
2013-Jul-20, 09:01 PM
The previous values were displayed since at least May 10th. It seemed odd that an object with over 100 observations, over a period of 10 years, should need to have its orbit revised so much that the closest approach from went from 7.6 to 9.1 Lunar diameters, a difference of about 360,000 miles, all at once.

Hornblower
2013-Jul-20, 10:53 PM
The previous values were displayed since at least May 10th. It seemed odd that an object with over 100 observations, over a period of 10 years, should need to have its orbit revised so much that the closest approach from went from 7.6 to 9.1 Lunar diameters, a difference of about 360,000 miles, all at once.

My bold. Correction, for the sake of novice readers: That is lunar distance, not diameter. It is the mean distance between Earth and Moon. Your number of miles is correct.

Yes, it seems odd, but I would want to rule out errors in the posted numbers before inferring an impact. This one will be a minimum separation of some 2 million miles which is not very close compared to the headline-making ones that have come much closer. Perhaps it was low on the attention list and a long-standing error went unnoticed for a long time.

Ross 54
2013-Jul-21, 12:10 AM
Quite right, I mistyped Lunar diameters for Lunar distances in two different posts(!) Just not my day, I guess. I consider an impact or propulsive outgassing merely interesting possibilities. If the effect is real and not an error, it increased the closest Earth approach distance by roughly 20%. I will contact the appropriate source within NASA, and see if this was an error, or not. Will report any reply received here.

Ross 54
2013-Jul-22, 05:35 PM
A Mr. Ron Baalke at JPL replies to my query. In very general terms, he remarks that all changes in distance figures for NEOs are due refinements in the orbital calculations.
He then seems to contradict himself, saying the the orbit of 2003 DZ15 is very well determined. If it is already very well determined, as one would expect of an object under observation for ten years, how explain a shift of 20% in the Earth approach figure, in one day's time?
He also seems to categorically rule out any possibility of simple transcription errors, impacts of one asteroid on another, or small thrusts due to outgassing from asteroids, which are apparently sometimes comets nearing extinction.
All very interesting, but I believe I'll still keep an eye on this object, until it begins to lengthen its distance from Earth.

korjik
2013-Jul-22, 09:13 PM
a 200m/s change is too large for anything which would not be really really obvious, if it were a real change, but a 1.5% refinement in velocity for a tiny black object against a black background is not all that suprising.