25143 Itokawa
25143 Itokawa is a sub-kilometer near-Earth object of the Apollo group and a potentially hazardous asteroid. It was discovered by the LINEAR program in 1998 and later named after Japanese rocket engineer Hideo Itokawa. The peanut-shaped S-type asteroid has a rotation period of 12.1 hours and measures approximately in diameter. Due to its low density and high porosity, Itokawa is considered to be a rubble pile, consisting of numerous boulders of different sizes rather than of a single solid body.
It was the first asteroid to be the target of a sample return mission, the Japanese Hayabusa space probe, which collected more than 1500 regolith dust particles from the asteroid's surface in 2005. After its return to Earth in 2010, the mineralogy, petrography, chemistry, and isotope ratios of these particles have been studied in detail, providing insights into the evolution of the Solar System. Itokawa is the smallest asteroid ever photographed and visited by a spacecraft.
Discovery and naming
Itokawa was discovered on 26 September 1998 by astronomers with the Lincoln Near-Earth Asteroid Research program at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. It was given the provisional designation. The body's observation arc begins with its first observation by the Sloan Digital Sky Survey just one week prior to its official discovery observation. The minor planet was named in memory of Japanese rocket scientist Hideo Itokawa, who is regarded as the father of Japanese rocketry. The official was published by the Minor Planet Center on 6 August 2003.Orbit and classification
Itokawa belongs to the Apollo asteroids. They are Earth-crossing asteroids and the largest dynamical group of near-Earth objects with nearly 10,000 known members. Itokawa orbits the Sun at a distance of 0.95–1.70 AU once every 18 months. Its orbit has an eccentricity of 0.28 and an inclination of 2° with respect to the ecliptic. It has a low Earth minimum orbital intersection distance of, which corresponds to 5.1 lunar distances.''Hayabusa'' exploration
In 2000, it was selected as the target of Japan's Hayabusa mission. The probe arrived in the vicinity of Itokawa on 12 September 2005 and initially "parked" in an asteroid–Sun line at, and later, from the asteroid. Hayabusa landed on 20 November for thirty minutes, but it failed to operate a device designed to collect soil samples. On 25 November, a second landing and sampling sequence was attempted. The sample capsule was returned to Earth and landed at Woomera, South Australia on 13 June 2010, around 13:51 UTC. On 16 November 2010, the Japan Aerospace Exploration Agency reported that dust collected during Hayabusa's voyage was indeed from the asteroid.Surface features
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. The following tables list the names of geological features on the asteroid. No naming conventions have been disclosed for surface features on Itokawa.Craters
Ten impact craters on the surface of Itokawa were named on 18 February 2009.| Crater | Coordinates | Diameter | Approval Year | Eponym | Ref |
| Catalina | 0.02 | 2009 | Catalina Station in Arizona, United States | ||
| Fuchinobe | 0.04 | 2009 | Fuchinobe in Sagamihara, Japan | ||
| Gando | n.a. | 2009 | Gando, Canary Islands; Spanish launch facility | ||
| Hammaguira | 0.03 | 2009 | Hammaguir, Algeria; abandoned French launch site and missile testing range in the Sahara desert | ||
| Kamisunagawa | 0.01 | 2009 | Kamisunagawa, town in Hokkaido Japan, where a microgravity test facility is located | ||
| Kamoi | 0.01 | 2009 | Japanese town of Kamoi in Yokohama, location of the NEC TOSHIBA Space Systems Ltd. factory | ||
| Komaba | 0.03 | 2009 | Komaba in Meguro, Japan, where the Institute of Space and Astronautical Science is located | ||
| Laurel | 0.02 | 2009 | U.S. city of Laurel in Maryland, where APL/JHU is located | ||
| Miyabaru | 0.09 | 2009 | Radar site of the Uchinoura Space Center in Japan | ||
| San Marco | n.a. | 2009 | San Marco platform, an old oil platform near Kenya that served as a launch pad for Italian spacecraft |
Regiones
Regio or regiones are large area marked by reflectivity or color distinctions from adjacent areas in planetary geology. The following regiones have been named on Itokawa.| Regio | Named after |
| 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, the location of Uchinoura Space Center, Hayabusa launch site |
| Yoshinobu Regio | Launch site in the Tanegashima Space Center, Japan |
Physical characteristics
Itokawa is a stony S-type asteroid. Radar imaging by Goldstone in 2001 observed an ellipsoid meters long and meters wide.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. 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. Based on Yarkovsky–O'Keefe–Radzievskii–Paddack effect measurements, a small section of Itokawa is estimated to have a density of, whereas a larger section is estimated to have a density of 1.8 g/cm³.
Rotation period and poles
Since 2001, a large number of rotational lightcurves of Itokawa have been obtained from photometric observations. Analysis of the best-rated lightcurve by Mikko Kaasalainen gave a sidereal rotation period of hours with a high brightness variation of 0.8 magnitude, indicative of the asteroid's non-spherical shape. In addition, Kaasalainen also determined two spin axes of and in ecliptic coordinates. Alternative lightcurve measurements were made by Lambert, Lowry, Ohba, Warner, Ďurech, and Nishihara.Composition
The 26 August 2011 issue of Science devoted six articles to findings based on dust that Hayabusa had collected from Itokawa. Scientists' analysis suggested that Itokawa was probably made up from interior fragments of a larger asteroid that broke apart. Dust collected from the asteroid surface is thought to have been exposed there for about eight million years.Scientists used varied techniques of chemistry and mineralogy to analyze the dust from Itokawa. Itokawa composition was found to match the common type of meteorites known as "low-total-iron, low metal ordinary chondrites". 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.