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Greyscale (black & white) image of Asteroid 25143 Itokawa as observed by Hayabusa, provided by JAXA.
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Discovery
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| Discovered by | LINEAR |
| Discovery date | September 26, 1998 |
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Designations
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| Named after | Hideo Itokawa |
| Alternate name(s) | 1998 SF36 |
| Minor planet category |
Apollo asteroid, Mars-crosser asteroid |
| Epoch August 18, 2005 (JD 2453600.5) | |
| Aphelion | 1.695 AU (253.520 Gm) |
| Perihelion | 0.953 AU (142.568 Gm) |
| Semi-major axis | 1.324 AU (198.044 Gm) |
| Eccentricity | 0.280 |
| Orbital period | 1.52 a (556.355 d) |
| Average orbital speed | 25.37 km/s |
| Mean anomaly | 294.502° |
| Inclination | 1.622° |
| Longitude of ascending node | 69.095° |
| Argument of perihelion | 162.760° |
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Physical characteristics
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| Dimensions | 535 × 294 × 209 m [1] |
| Mass | (3.51±0.105)×1010 kg,[1] (3.58±0.18)×1010 kg [2] |
| Mean density | 1.9 ±0.13 g/cm³,[1] 1.95 ± 0.14 g/cm³ [2] |
| Equatorial surface gravity | ~0.0001 m/s² |
| Escape velocity | ~0.0002 km/s |
| Rotation period | 0.5055 d (12.132 h) [3] |
| Albedo | 0.53 |
| Temperature | ~206 K |
| Spectral type | S |
| Absolute magnitude (H) | 19.2 |
25143 Itokawa ( /ˌiːtoʊˈkɑːwə/; Japanese: イトカワ [itokawa]) is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.
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The asteroid was discovered in 1998 by the LINEAR project and was given the provisional designation 1998 SF36. In August 2003,[4] it was officially named after Hideo Itokawa, a Japanese rocket scientist.
Itokawa is an S-type asteroid. Radar imaging by Goldstone in 2001 observed an ellipsoid 630 ± 60 m long and 250 ± 30 m wide.[5][6]
The Hayabusa mission confirmed these findings and also suggested that Itokawa may be a contact binary formed by two or more smaller asteroids that have gravitated toward each other and stuck together. The Hayabusa images show a surprising lack of impact craters and a very rough surface studded with boulders, described by the mission team as a 'rubble pile'.[7] Furthermore, the density of the asteroid is too low for it to be made from solid rock. This would mean that Itokawa is not a monolith but rather a ‘rubble pile’ formed from fragments that have cohered over time.
Shape from Goldstone and Arecibo Radars (Itokawa).
In 2000, it was selected as the target of Japan's Hayabusa mission. The probe arrived in the vicinity of Itokawa on September 12, 2005 and initially "parked" in an asteroid–sun line at 20 km (12 mi), and later 7 km (4.3 mi), from the asteroid (Itokawa's gravity was too weak to provide an orbit, so the spacecraft adjusted its orbit around the sun until it matched the asteroid). Hayabusa landed on November 20 for thirty minutes, but failed to operate a device designed to collect soil samples. On November 25, a second landing and sampling sequence was attempted. The sample capsule was returned to Earth and landed at Woomera, South Australia on June 13, 2010, around 13:51 UTC. On November 16, 2010, the Japan Aerospace Exploration Agency reported that dust collected during Hayabusa's voyage was indeed from the asteroid.[8]
Names of major surface features were proposed by Hayabusa scientists and accepted by the Working Group for Planetary System Nomenclature of the International Astronomical Union. Also, the Hayabusa science team is using working names for smaller surface features.[9][10] The following tables list the names of geological features on the asteroid.[11] No naming conventions have been disclosed for surface features on Itokawa.
| Crater | Named after |
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| Catalina | Catalina Observatory which performs Catalina Sky Survey |
| Fuchinobe | Fuchinobe in Sagamihara, Japan |
| Gando | Gando, Canary Islands |
| Hammaguira | Hammaguira French Special Weapons Test Centre, Hammaguir |
| Kamisunagawa | Kamisunagawa, Hokkaidō |
| Kamoi | Kamoi, Yokohama |
| Komaba | Komaba in Meguro, Tokyo |
| Laurel | Laurel, Maryland |
| Miyabaru | Radar site of the Uchinoura Space Center in Japan. |
| San Marco | San Marco platform, an old oil platform near Kenya that served as a launch pad for Italian spacecraft. |
Regiones (geologically distinct areas) on Itokawa.
| Regio | Named after |
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| Arcoona Regio | Arcoona, Australia |
| LINEAR Regio | Lincoln Near-Earth Asteroid Research |
| MUSES-C Regio | MUSES-C, name of the Hayabusa probe prior to launch. |
| Ohsumi Regio | Ōsumi Peninsula |
| Sagamihara Regio | Sagamihara, a town in Japan where Institute of Space and Astronautical Science is located. |
| Uchinoura Regio | Uchinoura, a town in Japan (now part of Kimotsuki), the location of Uchinoura Space Center, Hayabusa launch site. |
| Yoshinobu Regio | Launch site in the Tanegashima Space Center, Japan. |
The August 26, 2011, issue of Science devoted six articles to findings based on dust that Hayabusa had collected from Itokawa.[12] Scientists' analysis suggested that Itokawa was probably made up from interior fragments of a larger asteroid that broke apart.[13] Dust collected from the asteroid surface was believed to have been exposed there for about eight million years.[12]
Scientists used varied techniques of chemistry and mineralogy to analyze the dust from Itokawa.[13] Itokawa's composition was found to match the common type of meteorites known as "low-total-iron, low metal ordinary chondrites".[14] Another team of scientists determined that the dark iron color on the surface of Itokawa was the result of abrasion by micrometeoroids and high-speed particles from the sun which had converted the normally whitish iron oxide coloring.[14]
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