(25143) Itokawa

(25143) Itokawa is an Apollo-type asteroid, discovered in 1998 by the LINEAR (Lincoln Near-Earth Asteroid Research) location and tracking system. Its composition is type S with an elongated shape (similar to that of a peanut), in addition to a rotation period of 12.1 hours. Its image was collected by the radar of the Goldstone Observatory.

The asteroid was named after Japanese rocket engineer Hideo Itokawa.

Discovery and naming

Asteroid Itokawa was discovered on September 26, 1998 by astronomers from the Lincoln Near-Earth Asteroid Research (LINEAR) program at the Lincoln Laboratory Experimental Test Site (ETS) near Socorro, New Mexico, in United States.

Provisionally it was assigned the name 1998 SF₃₆.

The asteroid was named in memory of the Japanese space scientist Hideo Itokawa (1912-1999), who is considered the father of Japanese rocketry.

The official name designation of the asteroid was published August 6, 2003 by the Minor Planet Center (MPC).

Orbit and classification

Itokawa belongs to the Apollo-type asteroids, which are Earth-crossing asteroids and the largest dynamic group of near-Earth objects with nearly 10,000 known members.

This asteroid orbits the Sun between 0.95 and 1.70 astronomical units, once every 18 months (557 days), with a semimajor axis of 1.32 AU. The orbit eccentricity reaches 0.28 and it has an inclination with respect to the ecliptic of almost 2°.

The minimum low Earth orbital intersection distance (Earth MOID) of (251439 Itokawa) is 1,960,000 km (0.0131 AU), which corresponds to 5.1 lunar distances.

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  Itokawa orbital chart in December 2006.

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  Itokawa (green) and Earth (blue) animated orbits

Exploration of (25143) Itokawa

In 2000, the asteroid was selected as a target for the Hayabusa mission of the Japanese Space Agency (JAXA), arriving in the vicinity of Itokawa on September 12, 2005, and locating itself on an asteroid-Sun line at 20 km, and then 7 km from the asteroid (Itokawa's weak gravity did not allow the probe to orbit it, so Hayabusa had to adjust its orbit around the Sun until it coincided with that of the asteroid). The Hayabusa space probe landed for thirty minutes on the asteroid on November 20, but was unable to operate a device designed to collect soil samples. Five days later, a landing and sampling sequence was attempted again.

The sample capsule was sent back to Earth and successfully landed in Woomera, South Australia, on June 13, 2010, at about 13:51 UTC. On November 16, 2010, JAXA reported that dust collected during Hayabusa's journey corresponded to the asteroid.

Surface characteristics

The names of the main surface features were proposed by Hayabusa scientists and accepted by the Working Group for Planetary System Nomenclature of the International Astronomical Union. In addition, the scientific team de Hayabusa is using working names for smaller surface features. The following tables list the names of the asteroid's geological features. No naming conventions have been disclosed for surface features at Itokawa.

Craters

Ten impact craters were named on the surface of the asteroid (25143) Itokawa, on February 18, 2009.

Regions

They are large areas marked by reflectivity or color distinctions from adjacent areas in planetary geology. The following regions have been named in Itokawa.

Physical characteristics

Itokawa is a stony S-type asteroid. Radar images from Goldstone in 2001 observed an ellipsoid 630±60 meters long and 250±30 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 and stuck to each other. The Hayabusa images show a surprising lack of impact craters and a very rough surface dotted with rocks, described by the mission team as a pile of rubble. Additionally, the asteroid's density is too low for it to be made of rock. solid. This would mean that Itokawa is not a monolith, but rather a pile of rubble made up of fragments that have cohered over time. Based on measurements of the Yarkovsky-O'Keefe-Radzievskii-Paddack effect, a small section of Itokawa is estimated to have a density of 2.9 g/cm³, while a largest section is estimated to have a density of 1.8g/cm³.

Rotation period and poles

Since 2001, a large number of Itokawa rotational light curves have been obtained from photometric observations. Top-ranked lightcurve analysis by Mikko Kaasalainen gave a sidereal rotation period of 12,132 hours with a high brightness variation of magnitude 0.8, indicative of the asteroid's non-spherical shape (U = 3). In addition, Kaasalainen also determined two spin axes of (355.0°, −84.0°) and (39°, −87.0°) in ecliptic coordinates (λ, β). Alternative light curve measurements were made by Lambert (12:00 p.m.), Lowry (12:1 and 12:12 p.m.), Ohba (12:15 p.m.), Warner (12:09 p.m.), Ďurech (12:1323 p.m.), and Nishihara (12:1324 p.m.).

Composition

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

Scientists used various chemistry and mineralogy techniques to analyze the Itokawa dust. Itokawa's composition was found to match the common type of meteorites known as 'ordinary low-iron, low-metal chondrites.' Another team of scientists determined that the dark color of the iron in the Itokawa's surface was the result of the abrasion of micrometeoroids and high-speed particles from the Sun that had converted the normally whitish coloration of iron oxide.

Hayabusa results in 2018

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

Hayabusa results in 2020

At the 2020 Lunar and Planetary Science Conference, a third group reported on water and organic compounds, via a third Hayabusa particle, RA-QD02-0612, or 'Amazon'. Olivine, pyroxene and albite contain water. The isotopic compositions indicate a clear extraterrestrial origin.

Hayabusa results in 2021

Another report from Daly's group was published that supported the theory that a large source of Earth's water comes from hydrogen atoms carried on particles in the solar wind that combine with oxygen on asteroids and then reach Earth in space dust. Using atomic probe tomography, the study found hydroxide and water molecules on the surface of a single grain of particles recovered from the asteroid Itokawa by the Japanese Hayabusa space probe.