(5587) 1990 SB

Lore & Background

1990 SB was discovered on 16 September 1990 by Henry E. Holt and J. A. Brown, who noted its fast motion. Its discovery was announced in an International Astronomical Union Circular on 22 September. The asteroid was also observed by the Crimean Astrophysical Observatory on 23 October 1990, but was initially reported as a new asteroid with the provisional designation 1990 UV12. The Minor Planet Center linked these observations on 4 June 1993, assigning the minor planet number 5587. As of 2025, it remains unnamed.

Orbitally, 1990 SB is an Amor asteroid with a semi-major axis of 2.40 AU, taking 3.72 years to orbit the Sun. Its distance from the Sun varies from 1.09 AU at perihelion to 3.71 AU at aphelion, with an orbital eccentricity of 0.54 and an inclination of 18° to the ecliptic.

Physically, 1990 SB is about 3.57 km in size, based on thermal-infrared observations from the Keck telescope. Photometric observations indicate a highly elongated shape with axes ratios a/b = 2.0 and b/c = 1.2, and a regular, symmetrical form with no deep concavities. It is classified as a stony Sq-type asteroid under the Bus classification scheme, though it was previously suggested to be intermediate between Q- and R-types after spectroscopic observation in 2001. Its lightcurve shows a rotation period of 5.05 hours, with its spin pole pointing toward the ecliptic south, indicating retrograde rotation.

Reader's Guide

1990 SB is significant as a representative of the Amor class of near-Earth asteroids, which have orbits that approach but do not cross Earth's path. Its highly elongated shape and retrograde rotation provide insights into the physical diversity of small Solar System bodies. The asteroid's stony Sq-type composition links it to the broader population of S-complex asteroids, which are common among near-Earth objects. The discovery and subsequent linking of observations from different observatories highlight the collaborative nature of asteroid tracking and the importance of the Minor Planet Center in resolving duplicate designations. As an unnamed object, 1990 SB remains a subject for future naming, reflecting the ongoing cataloging of minor planets. Its study contributes to understanding the dynamics and physical properties of asteroids that may pose impact risks or offer resources for future exploration.

Did You Know?

• 1990 SB was discovered on 16 September 1990 by Henry E. Holt and J. A. Brown using the 48-in Schmidt telescope at Palomar Observatory.
• It has a highly elongated shape with axes ratios a/b = 2.0 and b/c = 1.2.
• The asteroid rotates in a retrograde direction, with a rotation period of 5.05 hours.
• It was observed by the Crimean Astrophysical Observatory on 23 October 1990 and initially given the provisional designation 1990 UV12.