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Small objects
Discovery & follow-up for 28 June–4 July
With the full Moon and short nights in the northern hemisphere, seven observatories (six northern and one Australian) still managed to track five small asteroids this past week, although not 2004 ME6, the only one with impact solutions (“small” is defined at right).
Since last Monday, only eight minor object discoveries have been announced. Six were distant, and discovered back in February-March. Another, an NEO announced June 29th but not seen since June 20th, was found to have impact solutions, as did the the remaining discovery, a smallish asteroid (H=21.7) announced June 29th (see June 30th). No H>22.0 asteroids were announced.
For close approaches by small asteroids, the Minor Planet Center has 2004 MC as having been at 3.66 lunar distances (LD) of Earth at 2004 June 29.51. JPL is showing that 2004 LK, which hasn't been reported since June 17th, will be at 29.9 LD on July 7th, 2004 MO4 will be at 10.4 LD on July 8th, and co-orbital candidate 2003 YN107 will be at 23.3 LD on July 10th.
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What’s so big about “small objects”? If an asteroid’s orbit brings it to within 0.05 astronomical units (AU) of Earth's orbit, it is categorized as “potentially hazardous” unless it has an absolute magnitude H greater than 22.0, which corresponds to a diameter on the order of 135 meters/yards. Larger H means less bright, thus smaller size. And 0.05 AU is about 19.5 times the distance between Earth and Moon (0.00256 AU). To be discovered and tracked, such objects usually must come close (a few are Earth’s nearest neighbors, coming closer than the Moon). They are exposed samplings of distant asteroid populations, they have within their own population tomorrow’s meteors, and their discovery and follow-up represents today’s best amateur and professional asteroid observing work.
Diameter & Earth MOID: In the following observation summary table, the stated diameters are rough best estimates from a standard but very inexact H-to-size
formula using H (absolute magnitude, or brightness) from the JPL NEO Orbital Elements page, source also for Earth MOID (minimum orbital intersection distance). Current Minor Planet Center H is also given, along with the original H from each object's discovery MPEC.
Other sources: Planetary MOIDs are from Lowell Observatory. Priorities and visibilities are from the European Spaceguard Central Node ( SCN). And flyby distances and times are from the JPL Close Approach Table except as noted. See also the Sormano Observatory SAEL list of asteroids with H>22.0 and Earth MOID<0.015 AU.
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