 Image of Itokawa from the Hayabusa spacecraft | |
| Discovery[1] | |
|---|---|
| Discovered by | LINEAR |
| Discovery site | Lincoln Lab's ETS |
| Discovery date | 26 September 1998 |
| Designations | |
| (25143) Itokawa | |
| Pronunciation | /ˌiːtoʊˈkɑːwə/ Japanese:[itoꜜkawa] |
Named after | Hideo Itokawa[2] |
| 1998 SF36 | |
| Orbital characteristics[3] | |
| Epoch 27 April 2019 (JD 2458600.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 20.38yr (7,443 d) |
| Aphelion | 1.6951AU |
| Perihelion | 0.9532 AU |
| 1.3241 AU | |
| Eccentricity | 0.2801 |
| 1.52 yr (557 d) | |
| 288.88° | |
| 0° 38m 48.48s / day | |
| Inclination | 1.6214° |
| 69.081° | |
| 162.82° | |
| Earth MOID | 0.0131 AU (5.10LD) |
| Physical characteristics | |
| Dimensions | 535 m × 294 m × 209 m[4] |
| 313 m[5] 330 m[3] 350 m[6][7] | |
| Mass | (3.51±0.105)×1010 kg[4] (3.58±0.18)×1010 kg[8] |
Meandensity | 1.9±0.13 g/cm3[4] 1.95±0.14 g/cm3[8] |
| 12.132 h[6][9] | |
| 0.23[7] 0.283±0.116[5] 0.36±0.22[10] 0.53[11] | |
| 18.61[14] · 18.95(R)[15] 19.00[13] · 19.2[1][3] 19.48[6][7] · 19.51±0.09[5] | |
25143 Itokawa (provisional designation1998 SF36) is a sub-kilometernear-Earth object of theApollo group and also apotentially hazardous asteroid. It was discovered by theLINEAR program in 1998 and later named after Japanese rocket engineerHideo Itokawa.[1] The peanut-shapedS-type asteroid has arotation period of 12.1 hours and measures approximately 330 meters (1,100 feet) in diameter. Due to its low density and high porosity, Itokawa is considered to be arubble 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 asample-return mission, of the Japanese space probeHayabusa, which collected more than 1500regolith dust particles from the asteroid's surface in 2005. Since its return to Earth in 2010, themineralogy,petrography, chemistry, andisotope ratios of these particles have been studied in detail, providing insights into theevolution of the Solar System. Itokawa was the smallest asteroid to be photographed andvisited by a spacecraft prior to theDART mission toDimorphos in 2022.
Itokawa was discovered on 26 September 1998 by astronomers with theLincoln Near-Earth Asteroid Research (LINEAR) program atLincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. It was given theprovisional designation1998 SF36. The body'sobservation arc begins with its first observation by theSloan Digital Sky Survey just one week prior to its official discovery observation.[1] Theminor planet was named in memory of Japanese rocket scientistHideo Itokawa (1912–1999), who is regarded as the father of Japanese rocketry.[1][16] The officialnaming citation was published by theMinor Planet Center on 6 August 2003 (M.P.C. 49281).[17]
Itokawa belongs to theApollo asteroids. They areEarth-crossing asteroids and the largest dynamical group ofnear-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 (557 days;semi-major axis of 1.32 AU). Its orbit has aneccentricity of 0.28 and aninclination of 2° with respect to theecliptic.[3] It has a lowEarthminimum orbital intersection distance of 0.0131 AU (1,960,000 km), which corresponds to 5.1lunar distances.[3]
In 2000, it was selected as the target of Japan'sHayabusa 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 atWoomera, South Australia on 13 June 2010, around 13:51 UTC (23:21 local). On 16 November 2010, theJapan Aerospace Exploration Agency reported that dust collected during Hayabusa's voyage was indeed from the asteroid.[18]
Names of majorsurface features were proposed byHayabusa scientists and accepted by the Working Group for Planetary System Nomenclature of theInternational Astronomical Union.[16] Also, the Hayabusa science team is using working names for smaller surface features.[19][20] The following tables list the names of geological features on the asteroid.[16] No naming conventions have been disclosed for surface features on Itokawa.
Tenimpact craters on the surface of Itokawa were named on 18 February 2009.[21]
| Crater | Coordinates | Diameter (km) | Approval Date | Named After | Ref |
|---|---|---|---|---|---|
| Catalina | 17°S14°E / 17°S 14°E /-17; 14 (Catalina) | 0.02 | 2009 | Catalina Station (astronomical observatory) in Arizona, United States | WGPSN |
| Fuchinobe | 34°N91°W / 34°N 91°W /34; -91 (Fuchinobe) | 0.04 | 2009 | Fuchinobe inSagamihara, Japan | WGPSN |
| Gando | 76°S155°W / 76°S 155°W /-76; -155 (Gando) | n.a. | 2009 | Gando,Canary Islands; Spanish launch facility | WGPSN |
| Hammaguira | 18°S155°W / 18°S 155°W /-18; -155 (Hammaguira) | 0.03 | 2009 | Hammaguir, Algeria; abandoned Frenchlaunch site and missile testing range in the Sahara desert | WGPSN |
| Kamisunagawa | 28°S45°E / 28°S 45°E /-28; 45 (Kamisunagawa) | 0.01 | 2009 | Kamisunagawa, town in Hokkaido Japan, where a microgravity test facility is located | WGPSN |
| Kamoi | 6°N116°W / 6°N 116°W /6; -116 (Kamoi) | 0.01 | 2009 | Japanese town of Kamoi inYokohama, location of the NEC Toshiba Space Systems Ltd. factory | WGPSN |
| Komaba | 10°S102°E / 10°S 102°E /-10; 102 (Komaba) | 0.03 | 2009 | Komaba inMeguro, Japan, where the Institute of Space and Astronautical Science is located | WGPSN |
| Laurel | 1°N162°E / 1°N 162°E /1; 162 (Laurel) | 0.02 | 2009 | U.S. city ofLaurel in Maryland, whereAPL/JHU is located | WGPSN |
| Miyabaru | 40°S116°W / 40°S 116°W /-40; -116 (Miyabaru) | 0.09 | 2009 | Radar site of theUchinoura Space Center in Japan | WGPSN |
| San Marco | 28°S41°W / 28°S 41°W /-28; -41 (San Marco) | n.a. | 2009 | San Marco platform, an old oil platform near Kenya that served as a launch pad for Italian spacecraft | WGPSN |
Regiones (singular: regio) are large area marked by reflectivity or color distinctions from adjacent areas inplanetary geology. The following regiones have been named on Itokawa.[16][21]
| Regio | Coordinates | Diameter (km) | Approval Date | Named After | Ref |
|---|---|---|---|---|---|
| Arcoona Regio | 28°N202°E / 28°N 202°E /28; 202 (Arcoona) | 0.16 | Feb. 18, 2009 | Arcoona, Australia | WGPSN |
| LINEAR Regio | 40°S232°E / 40°S 232°E /-40; 232 (LINEAR) | 0.12 | Feb. 18, 2009 | Lincoln Near-Earth Asteroid Research | WGPSN |
| MUSES-C Regio | 70°S60°E / 70°S 60°E /-70; 60 (MUSES-C) | 0.3 | 2006 | MUSES-C, name of theHayabusa probe prior to launch | WGPSN |
| Ohsumi Regio | 33°N207°E / 33°N 207°E /33; 207 (Ohsumi) | 0.14 | Feb. 18, 2009 | Ōsumi Peninsula | WGPSN |
| Sagamihara Regio | 80°N15°E / 80°N 15°E /80; 15 (Sagamihara) | 0.23 | 2006 | Sagamihara, a town in Japan whereInstitute of Space and Astronautical Science is located | WGPSN |
| Uchinoura Regio | 40°N90°E / 40°N 90°E /40; 90 (Uchinoura) | 0.07 | 2006 | Uchinoura, a town in Japan (now part ofKimotsuki), the location ofUchinoura Space Center, Hayabusa launch site | WGPSN |
| Yoshinobu Regio | 39°S117°E / 39°S 117°E /-39; 117 (Yoshinobu) | 0.16 | Feb. 18, 2009 | Launch site in the Tanegashima Space Center, Japan | WGPSN |
_Itokawa.jpg)
Itokawa is a stonyS-type asteroid.Radar imaging byGoldstone in 2001 observed an ellipsoid630±60 meters long and250±30 meters wide.[23]
TheHayabusa mission confirmed these findings and also suggested that Itokawa may be acontact binary formed by two or more smaller asteroids that have gravitated toward each other and stuck together. TheHayabusa images show a surprising lack ofimpact craters and a very rough surface studded with boulders, described by the mission team as arubble pile.[4][24] Furthermore, the density of the asteroid is too low for it to be made from solid rock. This would mean that Itokawa is not amonolith but rather a rubble pile formed from fragments that have cohered over time. Based onYarkovsky–O'Keefe–Radzievskii–Paddack effect measurements, a small section of Itokawa is estimated to have a density of2.9 g/cm3, whereas a larger section is estimated to have a density of 1.8 g/cm3.[4][25]
Since 2001, a large number of rotationallightcurves of Itokawa have been obtained fromphotometric observations. Analysis of the best-rated lightcurve byMikko Kaasalainen gave a siderealrotation period of12.132 hours with a high brightness variation of 0.8magnitude, indicative of the asteroid's non-spherical shape (U=3). In addition, Kaasalainen also determined twospin axes of (355.0°, −84.0°) and (39°, −87.0°) inecliptic coordinates (λ, β).[6][9] Alternative lightcurve measurements were made byLambert (12 h),[26]Lowry (12.1 and12.12 h),[27][28] Ohba (12.15 h),[29]Warner (12.09 h),[30][a]Ďurech (12.1323 h),[31] and Nishihara (12.1324 h).[15]
The 26 August 2011 issue ofScience devoted six articles to findings based on dust thatHayabusa had collected from Itokawa.[32] Scientists' analysis suggested that Itokawa was probably made up from interior fragments of a larger asteroid that broke apart.[33] Dust collected from the asteroid surface is thought to have been exposed there for about eight million years.[32]
Scientists used varied techniques ofchemistry andmineralogy to analyze the dust from Itokawa.[33] Itokawa's composition was found to match the common type ofmeteorites known as "low-total-iron, low metal ordinarychondrites".[34] Another team of scientists determined that the dark iron color on the surface of Itokawa was the result of abrasion bymicrometeoroids and high-speed particles from the Sun which had converted the normally whitish iron oxide coloring.[34]
Twoseparate groups reportwater indifferent Itokawa particles. Jin et al. report water in low-calciumpyroxene grains. The water's isotope level corresponds withinner Solar System and carbonaceous chondrite water isotope levels.[35] Daly et al. report "OH andH2O" apparently formed by implantation ofsolar wind hydrogen. The rims of anolivine particle "show an enrichment of up to ~1.2 at % in OH and H2O".[36] The water concentrations of the Itokawa grains would indicate an estimated BSI (Bulk Silicate Itokawa) water content in line with Earth's bulk water, and that Itokawa had been a "water-rich asteroid".[37]
At the 2020Lunar and Planetary Science Conference, a third group reported water and organics, via a third Hayabusa particle- RA-QD02-0612, or "Amazon." Olivine, pyroxene, and albite contain water. Isotopic compositions indicate a clear extraterrestrial origin.[38]
A further report by Daly's group was published which supported the theory that a largesource of Earth's water has come from hydrogen atoms carried on particles in thesolar wind which combine with oxygen on asteroids and then arrive on Earth in space dust. Using atom probe tomography the study found hydroxide and water molecules on the surface of a single grain from particles retrieved from the asteroid Itokawa by the Japanese space probe Hayabusa.[39][40]
Dust ponds are identified in the asteroid. They are a phenomenon where pockets of dust are seen in Celestial bodies without a significant atmosphere. Smooth deposits of dust accumulate in depressions on the surface of the body (like craters), contrasting from the Rocky terrain around them.[41] In the Sagamihara and Muses-Sea regions of the asteroid dust ponds were identified. Dust particles had a size varying from millimeters to less than a centimeter.
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