AKARI's observations of asteroid Itokawa

Aug 23, 2007

The space-borne infrared observatory AKARI, observed asteroid Itokawa last month with its Infrared Camera. The data will be used to refine estimates of sizes of potentially hazardous asteroids in the future.

The data collected by AKARI, a JAXA mission with ESA participation, complements that from JAXA’s asteroid explorer Hayabusa in late April this year.

As AKARI observed Itokawa on 26 July it was in the constellation of Scorpius, and was about 19 magnitudes bright in visible light. The asteroid and Earth were closest to each other, at a distance of about 42 million km (for comparison, Earth is 150 million km from the Sun). Given how close it was, Itokawa moved a significant distance on the sky over the short observing time.

Using observational data of asteroids such as Itokawa in combination with data from the explorer, models that estimate asteroid sizes can be made more accurate. This is especially useful for estimating the size of potentially hazardous asteroids which may be discovered in the future.

Before Hayabusa arrived at Itokawa, many observations to determine the asteroid's approximate size had already been attempted. Among the many different methods of measurement, the most accurate estimate was achieved by mid-infrared observations.

Motion of Itokawa

With AKARI, it was possible to observe Itokawa at several different wavelengths in the mid-infrared range, obtaining a much more comprehensive set of data. This data is very important, not only for the study of the asteroid’s infrared properties, but also for use as a template and source of comparison with other asteroids, to improve the estimates of their sizes.

Most sunlight falling on Itokawa is absorbed, heating the asteroid up. It then re-emits this energy as bright infrared light, which was in turn observed by AKARI. Only a small fraction of the incident sunlight is reflected from Itokawa, making it a very faint object when observed in visible light. It is very hard to observe using telescopes of sizes similar to that of AKARI from ground.

Positions of Itokawa and Earth

Asteroid size is one of the most sought-after pieces of information. For asteroids that are not explored directly, their sizes can be estimated based on various observations from Earth. The temperature of asteroids is determined by the balance between the energy input from incident sunlight, and the output, emitted as infrared radiation.

Existing computer models estimate the temperature distribution in asteroids by considering their shape, rotational motion, and surface conditions.

Observational data in the mid-infrared gives information on the infrared light emitted by the asteroid. Asteroid size can be derived by comparing observational data in the mid-infrared, with that expected from the calculations of the model. The models can further be improved by using the infrared observational data of well-studied asteroids, such as Itokawa.

AKARI has also made observations of possible candidates for future asteroid exploration. It is expected that this detailed information will help greatly further our knowledge of these interesting relics of our Solar System.

Source: European Space Agency

Explore further: Astronomers release most detailed catalogue ever made of the visible Milky Way

add to favorites email to friend print save as pdf

Related Stories

The dual personality of comet 67P/C-G

Jul 18, 2014

(Phys.org) —This week's images of comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape. We had hints of that in last week's images and in the unscheduled previews that were seen a few ...

The anatomy of an asteroid

Feb 05, 2014

ESO's New Technology Telescope has been used to find the first evidence that asteroids can have a highly varied internal structure. By making measurements astronomers have found that different parts of the ...

Hayabusa 2 Mission approved by Japanese government

Feb 01, 2012

In 2010, the Japanese spacecraft Hayabusa completed an exciting although nail-biting mission to the asteroid Itokawa, successfully returning samples to Earth after first reaching the asteroid in 2005; the ...

Recommended for you

Mystery of rare five-hour space explosion explained

53 minutes ago

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray ...

Glowing galaxies in telescopic timelapse

57 minutes ago

We often speak of the discoveries and data flowing from astronomical observatories, which makes it easy to forget the cool factor. Think of it—huge telescopes are probing the universe under crystal-clear ...

Violent origins of disc galaxies probed by ALMA

7 hours ago

For decades scientists have believed that galaxy mergers usually result in the formation of elliptical galaxies. Now, for the the first time, researchers using the Atacama Large Millimeter/sub-millimeter ...

User comments : 0