25143 Itokawa

25143 Itokawa

File:Hayabausa Image of the asteroid Itokawa.jpg Greyscale (black & white) image of 25143 Itokawa as observed by JAXA's Hayabusa
Discovery
Discovered by	LINEAR
Discovery date	26 September 1998
Designations
Named after	Hideo Itokawa
Alternative names	1998 SF36
Minor planet category	Apollo asteroid, Mars-crosser asteroid
Orbital characteristics
Epoch 18 August 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 (sidereal)	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°
Physical characteristics
Dimensions	535 × 294 × 209 m
Mass	(3.51±0.105)×1010 kg, (3.58±0.18)×1010 kg
Mean density	1.9 ±0.13 g/cm³, 1.95 ± 0.14 g/cm³
Surface gravity	~0.1 mm/s²
Escape velocity	~0.2 m/s
Synodic rotation period	0.5055 d (12.132 h)
Albedo	0.53
Temperature	~206 K
Spectral type	S
Absolute magnitude (H)	19.2

25143 Itokawa (/ˌiːtoʊˈkɑːwə/; Template:Lang-ja [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, and the smallest asteroid photographed by a spacecraft.

Discovery and naming

The asteroid was discovered in 1998 by the LINEAR project and was given the provisional designation 1998 SF₃₆. In August 2003, it was officially named after Hideo Itokawa, a Japanese rocket scientist.

Description

Itokawa is an S-type asteroid. Radar imaging by Goldstone in 2001 observed an ellipsoid 630 ± 60 m long and 250 ± 30 m 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 2.9 g/cm³, whereas a larger section is estimated to have a density of 1.8 g/cm³.

Itokawa's orbit

This artist’s impression, based on detailed spacecraft observations, shows the strange peanut-shaped asteroid Itokawa.

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 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's). 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 (23:21 local). 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

Crater	Named after
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

Regiones (geologically distinct areas) 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 (now part of Kimotsuki), the location of Uchinoura Space Center, Hayabusa launch site.
Yoshinobu Regio	Launch site in the Tanegashima Space Center, Japan.

Analysis of particles reported in August 2011

Schematic view of 25143 Itokawa

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's 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.

See also

• (341843) 2008 EV5

Further reading

• Durech, J.; Vokrouhlický, D.; Kaasalainen, M.; Weissman, P.; Lowry, S. C.; Beshore, E.; Higgins, D.; Krugly, Y. N.; et al. (September 2008). "New photometric observations of asteroids (1862) Apollo and (25143) Itokawa – an analysis of YORP effect" (PDF). Astronomy and Astrophysics. 488 (1): 345–350. Bibcode:2008A&A...488..345D. doi:10.1051/0004-6361:200809663.
• Normile, D (30 April 2010). "Spunky Hayabusa Heads Home With Possible Payload". Science. 328 (5978): 565. Bibcode:2010Sci...328..565N. doi:10.1126/science.328.5978.565. PMID 20430991.

External links

• Hayabusa's Scientific and Engineering Achievements during Proximity Operations around Itokawa (JAXA press release)
• Gazetteer of Planetary Nomenclature
• MIT's LINEAR asteroid named for Japan's 'Dr. Rocket' (MIT press release)
• JAXA Hayabusa official page
• Earth impact probability of the Asteroid (25143) Itokawa to be sampled by the spacecraft Hayabusa (paper abstract)
• Astronomy Picture Of The Day: Approaching Asteroid Itokawa, A Robot's Shadow on Asteroid Itokawa, The Missing Craters of Asteroid Itokawa, Smooth Sections on Asteroid Itokawa
• Special issue: Hayabusa at Itokawa, Science, Vol. 312, no. 5778, 2 June 2006
• Initial Scientific Results of Hayabusa’s Investigation on Itokawa ~Summary of the Special Issue of "Science"Magazine~ (ISAS/JAXA press release)
• Hot Topic: Hayabusa—Dust from Itokawa, Science, Vol. 333, no. 6046, 26 August 2011
• Animated model of Itokawa rotating (in anaglyph form for use with red-blue glasses)
• Itokawa in enhanced color (From this presentation)
• 25143 Itokawa at the JPL Small-Body Database