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| 1620 Geographos | |
|---|---|
| Name | Geographos |
| Designation | (1620) |
| Discoverer | Benjamin Jekhowsky |
| Discovery date | 1933-09-14 |
| Discovery site | Algiers Observatory |
| Mp category | Near-Earth object (Apollo asteroid) |
| Epoch | 2024-01-01 |
| Aphelion | 1.606 AU |
| Perihelion | 0.649 AU |
| Semimajor | 1.127 AU |
| Eccentricity | 0.424 |
| Period | 1.20 yr |
| Inclination | 13.3° |
| Dimensions | 2.6 × 2.0 × 1.5 km |
| Albedo | 0.22 |
| Spectral type | S-type |
| Absolute magnitude | 15.9 |
1620 Geographos is a well-studied near-Earth asteroid belonging to the Apollo asteroid group. It was discovered in 1933 and later became notable for its highly elongated shape, rapid rotation, and role as a target for radar imaging and photometric studies. Geographos has been used as a reference object in research by organizations and observatories investigating planetary science, asteroid dynamics, and impact risk assessment.
Geographos was discovered by Benjamin Jekhowsky at the Algiers Observatory on 14 September 1933, during a period of increased minor planet surveys that also produced objects observed by Karl Reinmuth, Cuno Hoffmeister, Gustav Stracke, and Sylvain Arend. It was independently rediscovered and tracked in the 1970s by teams from Palomar Observatory, Jet Propulsion Laboratory, and Lowell Observatory during dedicated near-Earth object searches led by researchers like E. F. Helin, E. Bowell, and Tom Gehrels. The name honors the geographic discipline and cartographic practice exemplified by publications such as the work of Waldo R. Tobler, the atlases of Rand McNally, and the maps associated with National Geographic Society; the naming followed conventions overseen by the International Astronomical Union.
Geographos follows an eccentric orbit that crosses the paths of Venus and Earth, with semimajor axis near 1.127 AU and eccentricity around 0.424, producing perihelion close to 0.65 AU and aphelion near 1.61 AU. Its orbital inclination of ~13.3° places it relative to the ecliptic plane and yields interactions with resonances influenced by Jupiter and Mars. The object completes an orbit in about 1.20 years and exhibits perturbed motion due to close approaches influenced by the gravitational fields of Earth, Venus, and Mars, as modeled by teams at NASA and the European Space Agency. Long-term integrations have included perturbations from Saturn and relativistic corrections associated with General Relativity in high-precision ephemerides maintained by JPL Horizons.
Geographos is an elongated, irregular body with principal axes roughly 2.6 × 2.0 × 1.5 km as constrained by radar and lightcurve inversion studies. Photometric measurements give an absolute magnitude around 15.9 and a relatively high geometric albedo near 0.22, consistent with silicate-rich surfaces observed in bodies studied by missions such as OSIRIS-REx, Hayabusa, and NEAR Shoemaker. Bulk density estimates, informed by shape, rotation, and assumed composition, suggest a coherent or fractured monolithic structure rather than a loosely bound rubble pile; comparisons have been drawn with 243 Ida and 433 Eros based on density and spectral analogs. Surface roughness, thermal inertia, and regolith properties have been inferred from thermal models using data similar to analyses performed for WISE and Spitzer Space Telescope observations.
Geographos exhibits a rapid rotation period near 5.22 hours determined from extensive lightcurve campaigns by observers at Palomar Observatory, Lowell Observatory, and amateur networks coordinated with professionals such as Brian Warner and Raoul Behrend. Its extreme elongation was first revealed by delay-Doppler radar images from Arecibo Observatory and later imaged by Goldstone Solar System Radar, allowing the construction of detailed shape models via computational techniques pioneered by groups at MIT and the University of Arizona. Inversion methods and dynamical studies examined non-principal axis rotation and the influence of the Yarkovsky–O'Keefe–Radzievskii–Paddack effect on spin-state evolution, connecting to theoretical work by David Rubincam and David Vokrouhlický.
Spectroscopy places Geographos in the S-type taxonomic class, with reflectance features similar to ordinary chondrite meteorites recovered near fall sites cataloged by The Meteoritical Society and curated at institutions like the Smithsonian Institution and Natural History Museum, London. Visible and near-infrared spectra obtained at facilities such as Mauna Kea Observatories, Cerro Tololo Inter-American Observatory, and Kitt Peak National Observatory show olivine and pyroxene absorption bands analogous to samples studied by NASA Johnson Space Center laboratories. Comparisons have been made to composition models used for mission planning by ESA, JAXA, and Roscosmos teams.
Geographos is classified as a potentially hazardous asteroid in monitoring catalogs maintained by NASA's Center for Near Earth Object Studies and the European Space Agency's NEO Coordination Centre. Its Earth minimum orbit intersection distance is small enough to warrant long-term trajectory analyses, with close approaches historically computed by researchers at Jet Propulsion Laboratory using Monte Carlo methods similar to those applied in risk assessments for (99942) Apophis and (29075) 1950 DA. Impact probability remains negligible on human timescales, but continued tracking by networks including Pan-STARRS, Catalina Sky Survey, and the Sloan Digital Sky Survey ensures updated hazard evaluations.
Geographos has been a prime radar and photometric target for facilities such as Arecibo Observatory, Goldstone Solar System Radar, and optical programs at Palomar Observatory and Mauna Kea, contributing to techniques later used in missions like NEOWISE and DART. It has been included in mission concept studies by NASA and ESA as an illustrative near-Earth target for rendezvous, sample return, and deflection demonstration scenarios, informing planning frameworks similar to those applied to Hayabusa2 and OSIRIS-REx. Ongoing ground-based campaigns and archived datasets continue to refine its orbit, physical model, and suitability for future spacecraft investigations.
Category:Near-Earth asteroids Category:Apollo asteroids