25143 Itokawa

Discovery and naming

Itokawa was discovered on 26 September 1998 by astronomers with the Lincoln Near-Earth Asteroid Research (LINEAR) 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 (1912–1999), who is regarded as the father of Japanese rocketry. The official was published by the Minor Planet Center on 6 August 2003 (M.P.C. 49281).

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 (557 days; semi-major axis of 1.32 AU). 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 0.0131 AU, which corresponds to 5.1 lunar distances.

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, and later 7 km, from the asteroid (Itokawa 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. |access-date=11 August 2008 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20090226224419/http://www.isas.jaxa.jp/e/snews/2006/image/0602/b/08.jpg |archive-date=26 February 2009

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Craters

Ten impact craters on the surface of Itokawa were named on 18 February 2009.

Regiones

Regiones (singular: regio) are large area marked by reflectivity or color distinctions from adjacent areas in planetary geology. The following regiones have been named on Itokawa.

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. |access-date=11 August 2008 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20080512042313/http://www.planetary.org/news/2005/0916_Hayabusa_Itokawa_Beckons_as_Japans.html |archive-date=12 May 2008

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 (355.0°, −84.0°) and (39°, −87.0°) in ecliptic coordinates (λ, β). Alternative lightcurve measurements were made by Lambert ( h), Lowry ( and h), Ohba ( h), Warner ( h), Ďurech ( h), and Nishihara ( h).

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.

2018 Hayabusa results

Two separate groups report water in different Itokawa particles. Jin et al. report water in low-calcium pyroxene grains. The water's isotope level corresponds with inner Solar System and carbonaceous chondrite water isotope levels. Daly et al. report "OH and " apparently formed by implantation of solar wind hydrogen. The rims of an olivine particle "show an enrichment of up to ~1.2 at % in OH and H2O". 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".

2020 Hayabusa results

At the 2020 Lunar 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.

2021 Hayabusa results

A further report by Daly's group was published which supported the theory that a large source of Earth's water has come from hydrogen atoms carried on particles in the solar 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.

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. 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.

Notes

References

References

1. S. M. Lederer, et al., "Physical characteristics of Hayabusa target Asteroid 25143 Itokawa", ''Icarus'', v. 173, pp. 153–165 (2005)
2. Atkinson, Nancy. (16 November 2010). "Confirmed: Hayabusa Nabbed Asteroid Particles". [[Universe Today]].
3. "The Anatomy of an Asteroid". ESO Press Release.
4. (25 August 2011). "Asteroid Dust Confirms Meteorite Origins". The New York Times.
5. (26 August 2011). "Most Earth meteorites linked to single asteroid". Los Angeles Times.
6. (2018). "The origin of hydrogen in space weathered rims of Itokawa regolith particles". 2018 Hayabusa Symposium.
7. (2018). "Establishing Itokawa's water contribution to Earth". 2018 Hayabusa Symposium.
8. (2020). "First Identification of Indigenous Organic Matter Alongside Water In Itokawa Particle Returned By The Hayabusa Mission".
9. (December 2021). "Solar wind contributions to Earth's oceans". Nature Astronomy.
10. (November 30, 2021). "Up to half of Earth's water may come from solar wind and space dust".
11. "Eros's puzzling surface".