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Japan Aerospace Exploration Agency

Research Introduction

Discovering Unknown Asteroids with Moving-Object-Detection Software

Japan to reclaim its preeminence in the universe of asteroid discovery

Advanced Space Technology Research Group

(From left)
Atsushi Nakajima, Hirohisa Kurosaki

Asteroid discovery today

Change in the number of asteroids discovered

Fig.1 Change in the number of asteroids discovered

Japan is full of amateur astronomers working fervently to discover comets, asteroids, supernovas, and other celestial phenomena. About half of the minor planets discovered by the world's astronomers in 1990 were discovered by Japanese. But in the second half of the 1990s, the U.S. gained dominance in the field by commissioning its LINEAR(The Lincoln Near Earth Asteroid Research) telescope (aperture: 1 m). Large-scale survey observations*1 by the LINEAR expanded the observation limits far beyond the limits of amateur machines. The rate of discovery by Japanese astronomers declined as a result. According to the Minor Planet Circular (MPC) published on November 16, 2005, Japanese astronomers registered 6,076 of the 120,437 asteroids discovered in the past, or only about 5 percent of the total registered worldwide. Fig. 1 shows the number of asteroids discovered annually in the world and in Japan. In the last few years, the number of Japanese discoveries has dwindled to only a single digit.

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Optical observation facility

JAXA Nyukasa-yama optical observation facility

Fig.2 JAXA Nyukasa-yama optical observation facility

The Advanced Space Technology Research Group is researching a technique for observing orbiting debris from old satellites and rockets after decommissioning, explosion in orbit, and so on. (See a page of "intermission break" for details on space debris). To achieve one of our important research objectives, the detection of small debris so far undiscovered, our group devised an image-processing technique based on a special method to stack multiple images. Using this technique, we have since developed and commercialized software to detect asteroids automatically (June 2004). With this software running, a telescope with an aperture as small as 35 cm (Fig. 2) has a detection power comparable to that of a large 1-meter telescope.

Expanded detection limits have led to the discovery of many asteroids by image processing

Our group analyzed data collected through the 35 cm telescope at the JAXA Nyukasa-yama optical observation facility from December 2005 through March 2006. In only four months, we discovered 70 unknown asteroids with magnitudes ranging from 19 to 22 and were given a designation as a discoverer. At this writing, this telescope is thought to have a higher detection sensitivity than all of the other small-aperture telescopes in the world-a sensitivity exceeding that of the LINEAR and approaching the Kitt Peak-Spacewatch (aperture: 0.9 m) and Mt. Lemmon Survey (aperture: 1.5 m). Fig. 3 shows an example of asteroid detection by image analysis software. The software stacks multiple images (about 40 images, each exposed for 3 minutes) to detect an asteroid automatically and then applies the blink*2 method to confirm it. Fig. 3a shows a relatively bright asteroid with a magnitude of 18.6, an asteroid confirmable even when the software checks the images one by one during the blink phase. An asteroid with a magnitude of 21.1 is more difficult to confirm. The image stack provides sufficient evidence to infer the presence of an asteroid, but the overwhelming noise prevents a definitive identification from the observation of individual images (Fig. 3 b). To overcome this challenge, we confirmed the existence of the asteroid using a method to stack the images during the blink (stacking blink) (Fig. 3 c). This and the other new methods described above have led to the discovery of a great many asteroids.
Based on the patents owned by JAXA, technology transfer to the private sector has culminated in the development of practical software for the detection of asteroids. This software has already been used to discover minor dark planets outside the range of the normal detection limit. The software runs on Windows and is easy to use. Even an astronomer peering through a small-aperture telescope has the chance to discover an asteroid. So go for it.

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Confirmation by stacking images and blink (images photographed on March 3, 2006)

Fig.3 Confirmation by stacking images and blink (images photographed on March 3, 2006)