Large Potentially Hazardous Asteroid Safely Passing Earth November 22, 2020

7753 (1988 XB) passes closest to Earth on 2020-Nov-22 16:55 UT at 25.76 Lunar Distances (LD) or 0.06619 au. This is a safe distance.

The orbit diagram (below) shows that this object approaches Earth from inside of Earth’s ellipse, orbiting between the orbits of Venus and Jupiter.

7753 (1988 XB) is large. Based on its measured absolute magnitude H of 18.6, and assumed limiting albedos of 0.25 to 0.05, its diameter may be between 510 meters and 1100 meters. This is over 25 to 50 times the size of the Chelyabinsk object.
JPL close approach tables show many close approaches with Venus and Earth in the interval 1900 to 2100.

Its relative velocity at closest approach of 9.75 km/s is about half the speed of the the Chelyabinsk object. Thus it would have much lower kinetic energy.

On 2020-Nov- 20, Catalina Sky Survey observed this asteroid approaching Earth near mag 16.2 G. Gaia G magnitudes are broadband optical.

On 2020-Nov-22, an observer at G40 – Slooh.com Canary Islands Observatory reported the object near 15.4 G.

Sky motion is over 14 arcsec/min.

The object’s phase angle today 105 degrees and decreasing over the next few weeks.
This results in continued brightening, peaking at mag 14.2 on 2020-Dec-02 when sky motion will be much lower. Minimum phase of 4.2 degrees is reach on 2020-Dec-23.
This general decreasing phase period offers the opportunity to measure this object’s phase curve, rotational period from light curve, and spectral phase variation. Solar elongation remains excellent for observability. Goldstone radar has observations scheduled 2020 Nov 18-Dec 1.

7753 (1988 XB) has an SMASSII spectral type of B which is an optically dark B-class object.

A paper by C. A. Wood et al. 1995 indicates that 7753 (1988 XB) may be a parent body of the “howardite-eucrite-diogenite” HED meteorites.

Y. Oshima discovered 7753 (1988 XB) as a fast-moving asteroidal object on 1988-Dec-05 at magnitude 16.0 at Gekko Observatory, Shizuoka in Japan .

Arecibo Observatory Planetary Radar studied this object in November 2004 when it approached Earth at 0.073 au. They found that it was an irregularly-shaped object with a relatively slow rotation period (19.9 ± 0.1) hours with an apparent diameter that varied between 1.3 and 2.0 km, indicating that 7753 (1988 XB) has an elongated shape.  Using Hudson’s (1993) “Shape” software, the radar team determined that a large outcropping of rock was possibly causing its irregular radar echo.

semimajor axis a = 1.4677761 au
perihelion distance q = 0.7607254
absolute magnitude H = 18.6
Estimated diameter 510 to 1100 meters (limiting albedo range 0.25 to 0.05)
Earth MOID Earth = 0.00665
NEO orbit type: Apollo

Notes:
Near-Earth Asteroid (NEA): q < 1.3 au

Apollo orbits types are Near-Earth asteroid orbits which cross the Earth’s orbit similar to that of 1862 Apollo (a > 1.0 au; q < 1.017 au).
semimajor axis of Earth a_earth = 1.00
aphelion distance of Earth Q_earth 1.017 au

Potentially Hazardous Asteroid (PHA) are NEAs whose Minimum Orbit Intersection Distance (MOID) with the Earth is 0.05 AU or less and whose absolute magnitude (H) is 22.0 or brighter. MOID <= 0.05 au, H <= 22.0

0.05 AU = 7479893.53455 km = 19.45 LD or ~ 5 Earth Hill sphere radii

1 Lunar Distance (LD) = 3.844 × 10^5 km = 384400 km = 0.00257 AU = 238900 miles = the mean distance from the Earth to the Moon


References:
Marsden, B. G., Circular No. 4688, 1988 December 7
Marsden, B. G., Circular No. 4693, 1988 December 20
Marsden, B. G., Circular No. 4709, 1989 January 9
MPEC 2020-Q225 : DAILY ORBIT UPDATE (2020 August 29)

Dreier, C.; Magri, C.; Howell, E.; Nolan, M.; A Physical Model of the NEA 1988 XB (7753) using Arecibo Radar Data, American Astronomical Society, DPS meeting #37, id.15.06; Bulletin of the American Astronomical Society, Vol. 37, p.639 (August 2005) Bibcode: 2005DPS….37.1506D

Wood, C. A.; Fevig, R.; Willman, A.; Wormer, W.; Are Hermes and 1988 XB Parent Bodies of HED Meteorites? Comparisons of Dates of Meteorite Falls and NEA Orbit Close Approaches, Abstracts of the Lunar and Planetary Science Conference, volume 26, page 1515, (March 1995) Bibcode: 1995LPI….26.1515W

Righter, K.; Garber, J.; The HED Compendium, (May 2011)
https://curator.jsc.nasa.gov/antmet/hed/index.cfm

MPC database: https://minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=7753

JPL Small Body database: https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=7753

Neese, C., Ed., Asteroid Taxonomy V6.0. EAR-A-5-DDR-TAXONOMY-V6.0. NASA Planetary Data System, 2010. PDS Small Bodies Node, Asteroid/Dust Subnode, https://sbn.psi.edu/pds/resource/taxonomy.html

Published by Charles Bell

The observer at MPC Observatory H47 near Vicksburg, Mississippi, USA

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