7187 Isobe
Likely binary Hungaria asteroid discovered by Eleanor Helin in 1992.
7187 Isobe (temporary designation 1992 BW) is a Hungaria asteroid located in the inner main belt, likely a binary system, with a diameter of about 5 kilometers. It was discovered on January 30, 1992, by American astronomer Eleanor Helin at Palomar Observatory in California. The asteroid is named for Japanese astronomer Syuzo Isobe.
This asteroid is thought to be an E-type and belongs to the Hungaria family, the innermost dense cluster of asteroids in the Solar System. Isobe orbits the Sun at a distance of 1.8 to 2.1 AU, completing one orbit every 985 days (about 2 years and 8 months). Its orbit has an eccentricity of 0.09 and an inclination of 22° relative to the ecliptic. The object was first observed as 1985 QC3 at the same observatory in 1985, extending its observation arc by seven years before its official discovery.
Measurements from NASA's WISE and NEOWISE surveys give Isobe a diameter between 4.85 and 6.05 kilometers, with an albedo ranging from 0.12 to 0.167. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.30—a compromise between 0.4 and 0.2 typical for Hungaria asteroids—and calculates a diameter of 3.85 kilometers based on an absolute magnitude of 14.0.
Since August 2004, American astronomer Brian Warner obtained several rotational lightcurves of Isobe at the Palmer Divide Observatory in Colorado. These gave a well-defined rotation period of 4.2432 hours with a brightness variation of 0.22 magnitude, after initial data suggested a shorter period of 2.4 hours. In 2012, Warner's observations indicated that Isobe is very likely a synchronous binary asteroid, with a moon orbiting every 33 hours. The satellite's size and diameter ratio remain unknown, and further observations are needed to confirm its binary nature. In September 2015, American astronomer Robert Stephens observed Isobe at the Center for Solar System Studies, reporting a period of 4.241 hours and an amplitude of 0.22 magnitude, but no mutual occultation events were detected during the two-night study.
The asteroid was named for Syuzo Isobe (born 1942), a Japanese scientist at NAOJ, an individual member of the IAU, and president of the Japan Spaceguard Association. He played a key role in establishing the Bisei Spaceguard Center, an observatory dedicated to tracking near-Earth objects and orbital debris.
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discovered
- 30 January 1992
- Discoverer
- E. F. Helin
- Discovery Site
- Palomar Obs.
- Mpc Name
- (7187) Isobe
- Named After
- Syuzo Isobe / (Japanese astronomer)
- Mp Category
- main-belt(inner) / Hungaria
- Epoch
- 4 September 2017 (JD 2458000.5)
- Uncertainty
- 0
- Observation Arc
- 30.61 yr (11,182 days)
- Aphelion
- 2.1048 AU
Facts from the source article.
Lore & Background
7187 Isobe is a presumed E-type asteroid and a member of the Hungaria family, which forms the innermost dense concentration of asteroids in the Solar System. It orbits the Sun in the inner main-belt at a distance of 1.8–2.1 AU once every 2 years and 8 months (985 days), with an eccentricity of 0.09 and an inclination of 22° with respect to the ecliptic. It was first identified as 1985 QC3 at the discovery observatory in 1985, extending the body's observation arc by 7 years prior to its official discovery observation.
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Isobe measures between 4.85 and 6.05 kilometers in diameter, and its surface has an albedo between 0.12 and 0.167. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.30 and calculates a diameter of 3.85 kilometers with an absolute magnitude of 14.0.
Since August 2004, American astronomer Brian Warner obtained several rotational lightcurves of Isobe at his Palmer Divide Observatory in Colorado, giving a well-defined rotation period of 4.2432 hours with a brightness amplitude of 0.22 magnitude. In 2012, observations by Warner also indicated that Isobe is very likely a synchronous binary asteroid, orbited by a minor-planet moon every 33 hours; the size of this satellite remains unknown. Isobe was also observed by American astronomer Robert Stephens in September 2015, giving a period of 4.241 hours with an amplitude of 0.22 magnitude, but no mutual occultation events were found.
Reader's Guide
7187 Isobe is notable as a likely binary Hungaria asteroid, a classification that places it among the innermost dense concentration of asteroids in the Solar System. Its discovery by Eleanor Helin at Palomar Observatory in 1992, and its naming after Japanese astronomer Syuzo Isobe—who contributed to establishing the Bisei Spaceguard Center for observing near-Earth objects and space debris—highlight its connection to both asteroid science and planetary defense. The asteroid's binary nature, suggested by lightcurve observations in 2012, remains unconfirmed and requires further study, underscoring the ongoing need for detailed photometric and occultation observations. The range of diameter estimates from different surveys (4.85–6.05 km from NEOWISE versus 3.85 km from the Collaborative Asteroid Lightcurve Link) reflects typical uncertainties in asteroid physical characterization. Its well-defined rotation period of about 4.24 hours and the presence of a potential moon make it a target for future research into binary asteroid formation and dynamics within the Hungaria family.
Did You Know?
- 7187 Isobe was discovered on 30 January 1992 by American astronomer Eleanor Helin at Palomar Observatory.
- It is named after Japanese astronomer Syuzo Isobe, who helped establish the Bisei Spaceguard Center.
- Its diameter is estimated between 4.85 and 6.05 kilometers by the NEOWISE mission.
More in Notable Asteroids, Part 3 1-24
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