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Title: (25143) Itokawa: The Power of Radiometric Techniques for the Interpretation of Remote Thermal Observations in the Light of the Hayabusa Rendezvous Results
Author: T. G. Müller, S. Hasegawa, F. Usui

The near-Earth asteroid (25143) Itokawa was characterised in great detail by the Japanese Hayabusa mission. We revisited the available thermal observations in the light of the true asteroid properties with the goal to evaluate the possibilities and limitations of thermal model techniques. In total, we used 25 published ground-based mid-infrared photometric observations and 5 so far unpublished measurements from the Japanese infrared astronomical satellite AKARI in combination with improved H-G values. Our thermophysical model (TPM) approach allowed us to determine correctly the sense of rotation, to estimate the thermal inertia and to derive robust effective size and albedo values by only using a simple spherical shape model. A more complex shape model, derived from light-curve inversion techniques, improved the quality of the predictions considerably and made the interpretation of thermal light-curve possible. The radiometrically derived effective diameter value agrees within 2% of the true Itokawa size value. The combination of our TPM and the final Itokawa in-situ shape model was then used as a benchmark for deriving and testing radiometric solutions. The consolidated value for the surface-averaged thermal inertia is 700 ± 200 Jm^-2s^-0.5K^-1. We found that even the high resolution shape models still require additional small-scale roughness in order to explain the disk-integrated infrared measurements. Our description of the thermal effects as a function of wavelengths, phase angle, and rotational phase facilitates the planning of crucial thermal observations for sophisticated characterisation of small bodies, including other potentially hazardous asteroids. Our analysis shows the power of radiometric techniques to derive the size, albedo, thermal inertia, and also spin-axis orientation from small sets of measurements at thermal infrared wavelengths.

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The Anatomy of an Asteroid

ESO's New Technology Telescope (NTT) has been used to find the first evidence that asteroids can have a highly varied internal structure. By making exquisitely precise measurements astronomers have found that different parts of the asteroid Itokawa have different densities. As well as revealing secrets about the asteroid's formation, finding out what lies below the surface of asteroids may also shed light on what happens when bodies collide in the Solar System, and provide clues about how planets form.
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Asteroid 25143 Itokawa makes its closest approach to the Earth (0.645 AU) on the 16th Deceber, 2012.



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Asteroid fragments could hint at the origin of the solar system

University of Manchester scientists are among the few in the world selected to analyse minute asteroid fragments which could shed light on the origin and evolution of the solar system.
The tiny pieces of rock - at 50-100 micrometers smaller than a human hair - have been captured from asteroid Itokawa by the Japanese mission Hayabusa. They were carefully unpacked by experts at the Universitys School of Earth, Atmospheric and Environmental Sciences.

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Japanese asteroid age and status to be examined by Curtin

Curtin University planetary scientists will analyse grains of rock from the first asteroid ever to be sampled in the hope of uncovering new knowledge about the history of the solar system.
The scientists will analyse the largest and most precious grains from the Itokawa asteroid retrieved in the Japanese Space Agency's 2005 mission to determine the asteroid's age, how long it has been exposed to space and the composition of solar wind exposure.

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Scientists have established that the surface materials on Itokawa have at some stage experienced long-term heating up at 800 degrees, something unlikely to have happened on a body so small (the asteroid currently is only some 500m across).
The implication therefore is that Itokawa is actually the remnants of a much larger asteroid (bigger than 20km across) that was broken up. It is the classic rubble pile that has been swept up and reassembled into a small jumbled heap by gravity.

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Samples from 25143 Itokawa show it has similar make-up to most meteorites on Earth.

Dust grains scooped from a 500-metre-long asteroid have been linked to the most common type of meteorites found on Earth, report a team of Japanese scientists in a suite of papers in Science today.
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Asteroid Itokawa Formed Soon After Birth Of Solar System

The asteroid Itokawa was created through collisions of asteroids and other bodies soon after the solar system formed roughly 4.5 billion years ago, according to Japanese universities studying particles taken from the asteroid.
In analysing the particles brought back by Japan's Hayabusa space probe, researchers at Osaka University, Tohoku University and others discovered characteristics similar to those found in ordinary chondrite meteors, which formed around 4.5 billion years ago.

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Japan probe collected particles from Itokawa asteroid

Japanese scientists have confirmed that particles found inside the Hayabusa probe after its seven-year space trip are from the asteroid Itokawa.
A statement from the country's space agency said microscopic analysis of 1,500 grains retrieved from the craft's sample canister proved they were of extraterrestrial origin.

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Asteroid 25143 Itokawa makes its closest approach to the Earth (0.568 AU) on the 6th August, 2010.

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