25143 Itokawa

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25143 Itokawa
Hayabausa Image of the asteroid Itokawa.jpg
Greyscale (black & white) image of 25143 Itokawa as observed by Hayabusa, provided by JAXA.
Discovery
Discovered by LINEAR
Discovery date 26 September 1998
Designations
Named after
 Hideo Itokawa
1998 SF36
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)
1.324 AU (198.044 Gm)
Eccentricity 0.280
1.52 a (556.355 d)
25.37 km/s
294.502°
Inclination 1.622°
69.095°
162.760°
Physical characteristics
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]
~0.1 mm/s²
~0.2 m/s
0.5055 d (12.132 h)[3]
Albedo 0.53
Temperature ~206 K
Spectral type
 S
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, 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,[4] 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.[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. 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.[8]

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.[9]

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.[10][11] The following tables list the names of geological features on the asteroid.[12] 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[13]

The 26 August 2011, issue of Science devoted six articles to findings based on dust that Hayabusa had collected from Itokawa.[14] Scientists' analysis suggested that Itokawa was probably made up from interior fragments of a larger asteroid that broke apart.[15] Dust collected from the asteroid surface was believed to have been exposed there for about eight million years.[14]

Scientists used varied techniques of chemistry and mineralogy to analyze the dust from Itokawa.[15] Itokawa's composition was found to match the common type of meteorites known as "low-total-iron, low metal ordinary chondrites".[16] 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.[16]

See also

References

  1. ↑ 1.0 1.1 1.2 Akira Fujiwara, et al., The Rubble-Pile Asteroid Itokawa as Observed by Hayabusa, Science, Vol. 312. no. 5778, pp. 1330 – 1334, 2 June 2006
  2. ↑ 2.0 2.1 Shinsuke Abe, et al., Mass and Local Topography Measurements of Itokawa by Hayabusa, Science, Vol. 312. no. 5778, pp. 1344 – 1347, 2 June 2006
  3. ↑ M. Kaasalainen, et al., CCD photometry and model of MUSES-C target (25143) 1998 SF36, Astronomy and Astrophysics, v.405, p.L29-L32 (2003)
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found. mirror
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found. mirror
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found. mirror
  12. ↑ USGS: Itokawa nomenclature
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ 14.0 14.1 Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ 15.0 15.1 Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ 16.0 16.1 Lua error in package.lua at line 80: module 'strict' not found.

Further reading

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External links

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