Exploring asteroids

Image sensors on the asteroid explorer Hayabusa
Measuring the surface of Itokawa and tracing the memories of the birth of the asteroid

The asteroid explorer Hayabusa gained global attention in 2010 as it made a miraculous return. Two devices for studying the composition of the surface of the asteroid Itokawa used image sensors developed by Hamamatsu Photonics.


From Hamamatsu to the World: and then to space.
Hamamatsu Photonics' optical technology shows unlimited expansion.

InGaAs image sensor used for Hayabusa's NIR spectrometer

CCD image sensor used for Hayabusa's fluorescent X-ray spectrometer

The asteroid explorer Hayabusa


Hayabusa returns

The asteroid explorer Hayabusa was launched May 9, 2003, to bring back samples of matter from the surface of the asteroid Itokawa. It succeeded in collecting fine particles from the surface of Itokawa, and it returned safely to Earth on Jun. 13, 2010. The capsule in the probe fell to Australia and completed its use. An asteroid is like a fossil; it is an astronomical object which preserves relatively well a record the time of the birth of planets. Therefore, it is said that studying the samples may give clues as to what materials formed the planets and what the solar nebula was like as the planets were forming.

Distance traveled by Hayabusa: 6,000,000,000 (6 billion) km

Hayabusa, launched in 2003, reached the asteroid Itokawa in 2005. Overcoming many problems that arose, it returned to Earth in Jun. 2010. The distance traveled with the ion engine totaled about 6 billion km. Our CCD and InGaAs image sensors used on Hayabusa operated normally despite the harsh conditions of space to measure data.


Size of the asteroid Itokawa: L 535 m × H 294 m × W 209 m

Itokawa is an asteroid discovered by the Lincoln Laboratory in the US in Sep. 1998. From Hayabusa's measurements, Itokawa's density has been estimated as being a little lower than ordinary Earth rocks. This suggests that its interior may be more porous (have larger gaps) than previously thought. It is thought that Itokawa is a fragment of a larger object that was destroyed and has on its surface fine pieces that were created at that time and fell.

Observation time of Hayabusa's fluorescent X-ray spectrometer: 700 hours

The fluorescent X-ray spectrometer was a device to study the matter on the ground of the asteroid from the space above.

Elements in matter on the ground emit fluorescent X-rays of a certain wavelength in response to energy from X-rays from the sun. The wavelengths of the fluorescent X-rays are defined for each element, so, by measuring the fluorescent X-rays emitted from the surface of an asteroid, it is possible to determine about how much of what elements are there.

The fluorescent X-ray spectrometer succeeded in measuring the material composition of Itokawa's surface, which included magnesium, aluminum, and silicon, etc. This owed to our CCDs' features of large photosensitive area and high energy resolution.


Locations on Itokawa's surface measured by Hayabusa's NIR spectrometer: 75,000

The near-infrared spectrometer (NIRS) on Hayabusa was a device to disperse and detect infrared rays from the sunlight reflected off the surface of the asteroid, in order to analyze the minerals on the ground and the form of the terrain. Our InGaAs image sensor was used for the NIRS, as the NIRS required high sensitivity in the NIR range and high reliability and durability.

Olivine and pyroxene

These were the minerals measured on Itokawa's surface by the near-infrared spectrometer using our InGaAs image sensor. When 0.8 to 2.1 μm light reflected from Itokawa was spectroscopically measured, it was found that reflectance dropped at the regions of 1 μm and 2 μm. Thus, it was concluded that the minerals on the surface include olivine and pyroxene.