Ida (asteroid)

Ida (asteroid)
243_ida.jpg: NASA/JPL derivative work:  Chzz  ► · Public domain · source
Name	243 Ida
Caption	Galileo image of Ida and Dactyl
Discovered	29 September 1884
Discoverer	Johann Palisa
Discovery site	Austrian Naval Observatory
Mpc name	(243) Ida
Alt names	A884 SA, 1931 UN
Named after	Ida (mythology)
Epoch	4 September 2017 (JD 2458000.5)
Aphelion	3.164 AU
Perihelion	2.211 AU
Semimajor	2.688 AU
Eccentricity	0.177
Period	4.41 yr
Inclination	3.85°
Dimensions	56.4 × 24.2 × 18.5 km
Mass	~4.2×10^16 kg
Density	~2.6 g/cm^3
Spectral type	S-type

Ida (asteroid) is a main-belt S-type asteroid notable for being the first asteroid discovered to have a natural satellite. It was imaged by the Galileo probe during its flyby en route to Jupiter and named after the mythological figure Ida. Ida's discovery and satellite detection influenced studies by organizations such as the International Astronomical Union and informed missions including NEAR Shoemaker and concepts for Hayabusa.

Discovery and Naming

Ida was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at the Austrian Naval Observatory; contemporaries included observers at the Royal Observatory, Greenwich, Paris Observatory, Lick Observatory, Pulkovo Observatory, and Vienna Observatory. The provisional designation A884 SA reflected practices described by the Minor Planet Center and catalogs maintained by the Harvard College Observatory and Yerkes Observatory. Ida received the number 243 in lists compiled by MPC and was named after the nymph associated with Mount Ida (Crete) and Mount Ida (Turkey), following naming conventions promulgated by bodies such as the Astronomische Gesellschaft and later overseen by the International Astronomical Union. Early astrometric observations were published in circulars by the Astronomische Nachrichten, and Ida's orbital elements were refined over decades by teams at the Royal Greenwich Observatory and the US Naval Observatory.

Physical Characteristics

Ida is an irregular, elongated object with principal axes approximately 56.4, 24.2, and 18.5 kilometers, as measured from high-resolution imaging by the Galileo mission; shape modeling was refined using techniques developed by researchers at the Jet Propulsion Laboratory, Max Planck Institute for Solar System Research, Smithsonian Astrophysical Observatory, Cornell University, and California Institute of Technology. Spectroscopy classifies Ida as an S-type asteroid in taxonomies developed at the Tholen classification and by the Bus–DeMeo taxonomy, showing silicate and metal signatures similar to ordinary L-chondrite meteorites studied by teams at the Smithsonian Institution and Natural History Museum, London. Photometric lightcurve analysis from observatories including Mauna Kea Observatory, Kitt Peak National Observatory, Palomar Observatory, and the European Southern Observatory yielded Ida's rotation period near 4.63 hours and revealed albedo variations studied by researchers at the Max Planck Institute for Solar System Research and the University of Arizona. Density estimates, informed by mass constraints from the satellite's orbit measured by investigators at JPL and NASA, suggest a bulk composition consistent with fractured rock and moderate porosity; mineralogical comparisons were made with collections at the Field Museum and American Museum of Natural History.

Dactyl: The Moon of Ida

Ida's small satellite, Dactyl, was the first moon discovered orbiting an asteroid and was identified in images returned by Galileo by scientists at JPL, University of Arizona, Cornell University, Smithsonian Astrophysical Observatory, and NASA Ames Research Center. Dactyl's diameter is roughly 1.4 kilometers and its orbit provided the first direct means to estimate Ida's mass; teams from Jet Propulsion Laboratory and the Space Telescope Science Institute used those data to calculate gravitational parameters and density. The discovery prompted comparative studies involving binary systems cataloged by the International Astronomical Union Working Group on Small Body Nomenclature, with follow-up observations cross-referenced against surveys by the Sloan Digital Sky Survey, NEOWISE, and ground programs at European Southern Observatory and Kitt Peak National Observatory. Dactyl's existence influenced theoretical work at institutions such as MIT, Caltech, University of Colorado Boulder, and Brown University on satellite formation mechanisms including subcatastrophic impact models and rotational fission.

Orbit and Classification

Ida orbits within the main asteroid belt between the orbits of Mars and Jupiter, with a semimajor axis near 2.69 AU, eccentricity ~0.177, and inclination ~3.85°. Its orbital parameters place it outside major resonances with Jupiter but within family identification analyses using methods from the Hierarchical Clustering Method applied by researchers at the Observatoire de Paris and Kazan Federal University. Ida has been associated with the Koronis family in studies by the Minor Planet Center and the Planetary Science Institute, with compositional links to other S-type members surveyed by teams at Tokyo Institute of Technology and University of Helsinki. Long-term orbital integrations performed at JPL and the University of Nice considered perturbations from Saturn, Uranus, the Yarkovsky effect parameterized by groups at Cornell University and University of Pisa, and collisional lifetime models from the Southwest Research Institute.

Exploration and Observations

Ida was imaged during the Galileo spacecraft's flyby on 28 August 1993, an encounter planned by mission teams at NASA, Jet Propulsion Laboratory, Caltech, European Space Agency, and NASA Ames Research Center. Data sets were processed and distributed by the Planetary Data System and analyzed by researchers at Brown University, University of Arizona, Max Planck Institute for Solar System Research, Smithsonian Astrophysical Observatory, and Cornell University. Subsequent spectral and photometric observations were carried out by facilities including Keck Observatory, Very Large Telescope, Subaru Telescope, Arecibo Observatory, and Goldstone Deep Space Communications Complex. Ida and Dactyl were included in comparative analyses with targets from missions such as NEAR Shoemaker, Hayabusa, Dawn, and OSIRIS-REx, informing instrument planning at institutions like JPL, Johns Hopkins University Applied Physics Laboratory, and NASA Goddard.

Scientific Significance and Studies

The discovery of Dactyl around Ida revolutionized understanding of small-body binaries and influenced theoretical frameworks developed at MIT, Caltech, University of Arizona, Southwest Research Institute, and Brown University. Ida's composition and morphology provided empirical links to ordinary chondrite meteorites curated at the Smithsonian Institution and Natural History Museum, London, impacting meteoritics research at Observatoire de la Côte d'Azur and collision modeling at the University of Bern. Studies leveraging Ida's imagery informed regolith mechanics, cratering processes, and internal structure models produced by teams at Max Planck Institute for Solar System Research, University of Colorado Boulder, Planetary Science Institute, Lunar and Planetary Institute, and NASA Johnson Space Center. Ida remains a benchmark object in catalogs maintained by the Minor Planet Center, a reference in taxonomic schemes from the Small Bodies Node of the Planetary Data System, and a touchstone in planetary science curricula at universities such as Harvard University and Massachusetts Institute of Technology.

Category:Main-belt asteroids Category:Discoveries by Johann Palisa