25143 Itokawa (provisional designation ) is a sub-kilometer
near-Earth object
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...
of the
Apollo group
Apollo Education Group, Inc. is an American corporation based in the South Phoenix area of Phoenix, Arizona, with an additional corporate office in Chicago, Illinois.
The company owns and operates several higher-learning institutions, including ...
and a
potentially hazardous asteroid
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...
. It was discovered by the
LINEAR
Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
program in 1998 and later named after Japanese rocket engineer
Hideo Itokawa.
The peanut-shaped
S-type asteroid
S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the secon ...
has a
rotation period
The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...
of 12.1 hours and measures approximately in diameter. Due to its low density and high porosity, Itokawa is considered to be a
rubble pile
In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the ...
, consisting of numerous boulders of different sizes rather than of a single solid body.
It was the first asteroid to be the target of a
sample return mission
A sample-return mission is a spacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as lo ...
, the Japanese space probe ''
Hayabusa
was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis.
''Hayabusa'', formerly known as MUSES-C fo ...
'', which collected more than 1500
regolith
Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...
dust particles from the asteroid's surface in 2005. After its return to Earth in 2010, the
mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
,
petrography
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The class ...
, chemistry, and
isotope ratios of these particles have been studied in detail, providing insights into the
evolution of the Solar System
The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into ...
. Itokawa was the smallest asteroid to be photographed and
visited by a spacecraft prior to the DART mission to Dimorphos in 2022.
Discovery and naming
Itokawa was discovered on 26 September 1998 by astronomers with the
Lincoln Near-Earth Asteroid Research
The Lincoln Near-Earth Asteroid Research (LINEAR) project is a collaboration of the United States Air Force, NASA, and the Massachusetts Institute of Technology's Lincoln Laboratory for the systematic detection and tracking of near-Earth objects ...
(LINEAR) program at
Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. It was given the
provisional designation
Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been cal ...
. The body's
observation arc
In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...
begins with its first observation by the
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...
just one week prior to its official discovery observation.
The
minor planet
According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...
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
The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory.
Function
...
on 6 August 2003 ().
Orbit and classification
Itokawa belongs to the
Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...
s. They are
Earth-crossing asteroids and the largest dynamical group of
near-Earth objects
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...
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
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
of 1.32 AU). Its orbit has an
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
of 0.28 and an
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
of 2
° with respect to the
ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
.
It has a low ''Earth
minimum orbital intersection distance
Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits o ...
'' of , which corresponds to 5.1
lunar distances.
Exploration
In 2000, it was selected as the target of Japan's ''
Hayabusa
was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis.
''Hayabusa'', formerly known as MUSES-C fo ...
'' mission. The probe arrived in the vicinity of Itokawa on 12 September 2005 and initially "parked" in an asteroid–Sun line at , and later , 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
Woomera, unofficially Woomera village, refers to the domestic area of RAAF Base Woomera. Woomera village has always been a Defence-owned and operated facility. The village is located on the traditional lands of the Kokatha people in the Far ...
on 13 June 2010, around 13:51 UTC (23:21 local). On 16 November 2010, the
Japan Aerospace Exploration Agency
The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into orb ...
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
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
.
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
Ten
impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
s on the surface of Itokawa were named on 18 February 2009.
Regiones
Regio or regiones are large area marked by reflectivity or color distinctions from adjacent areas in
planetary geology
Planetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites. Although the ...
. The following regiones have been named on Itokawa.
Physical characteristics
![Schematic view of asteroid (25143) Itokawa](https://upload.wikimedia.org/wikipedia/commons/4/41/Schematic_view_of_asteroid_%2825143%29_Itokawa.jpg)
Itokawa is a stony
S-type asteroid
S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the secon ...
.
Radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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
In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overconta ...
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 crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
s and a very rough surface studded with boulders, described by the mission team as a
rubble pile
In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the ...
.
[
] 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
A monolith is a geological feature consisting of a single massive stone or rock, such as some mountains. For instance, Savandurga mountain is a monolith mountain in India. Erosion usually exposes the geological formations, which are often ma ...
but rather a rubble pile formed from fragments that have cohered over time. Based on
Yarkovsky–O'Keefe–Radzievskii–Paddack effect
The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect for short, changes the rotation state of a small astronomical body – that is, the body's spin rate and the obliquity of its pole(s) – due to the scattering of solar rad ...
measurements, a small section of Itokawa is estimated to have a density of , whereas a larger section is estimated to have a density of 1.8 g/cm
3.
Rotation period and poles
Since 2001, a large number of rotational
lightcurve
In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
s of Itokawa have been obtained from
photometric observations. Analysis of the best-rated lightcurve by
Mikko Kaasalainen gave a sidereal
rotation period
The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...
of hours with a high brightness variation of 0.8
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
, 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
The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodi ...
(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
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
and mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
to analyze the dust from Itokawa. Itokawa composition was found to match the common type of meteorites
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...
known as "low-total-iron, low metal ordinary chondrite
A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primi ...
s". Another team of scientists determined that the dark iron color on the surface of Itokawa was the result of abrasion by micrometeoroid
A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface.
The term "micrometeoroid ...
s and high-speed particles from the Sun which had converted the normally whitish iron oxide coloring.[
]
2018 Hayabusa results
Two separate groups report water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
in different Itokawa particles. Jin et al. report water in low-calcium pyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
grains. The water's isotope level corresponds with inner Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
and carbonaceous chondrite water isotope levels. Daly et al. report " OH and " apparently formed by implantation of solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
hydrogen. The rims of an olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
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
The Lunar and Planetary Science Conference (LPSC), jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA Johnson Space Center (JSC), brings together international specialists in petrology, geochemistry, geophysics, geology, and astr ...
, 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
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
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.
See also
* 162173 Ryugu
162173 Ryugu, provisional designation , is a near-Earth object and a potentially hazardous asteroid of the Apollo group. It measures approximately in diameter and is a dark object of the rare spectral type Cb, with qualities of both a C-type ...
, target of sample-return mission Hayabusa2, the successor to Hayabusa
* 101955 Bennu
101955 Bennu (provisional designation ) is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on 11 September 1999. It is a potentially hazardous object that is listed on the Sentry Risk Table and has the highest cumula ...
, target of NASA sample-return mission OSIRIS-REx
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is a NASA asteroid-study and sample-return mission. The mission's primary goal is to obtain a sample of at least from 101955 Bennu, a carbonac ...
* , target of cancelled NASA sample-return mission Asteroid Redirect Mission
The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013; the mission was later cancelled. The Asteroid Retrieval Robotic ...
Notes
References
Further reading
*
External links
Hayabusa's Scientific and Engineering Achievements during Proximity Operations around Itokawa
(JAXA press release)
Gazetteer of Planetary Nomenclature
(MIT press release)
Earth impact probability of the Asteroid (25143) Itokawa to be sampled by the spacecraft Hayabusa
(paper abstract)
* Astronomy Picture of the Day
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)
''Minor Planet Center''
''Minor Planet Center''
''Minor Planet Center''
*
*
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