1. Center for Natural Sciences, College of Liberal Arts and Sciences, Kitasato University, 1-15-1 Kitazato, Sagamihara, Kanagawa 228-8555, Japan
2. Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
3. Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
4. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, Hawaii 96720, USA
5. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
6. Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
7. Present address: Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan

Correspondence to: Yoshiko Kataza Okamoto^1,2,7 okamtoys@cc.nao.ac.jp

Pictoris ( Pic) is a main-sequence star with an edge-on dust disk^{1, 2, 3} that might represent a state of the early Solar System. The dust does not seem to be a remnant from the original protoplanetary disk, but rather is thought to have been generated from large bodies like planetesimals and/or comets^{4, 5}. The history and composition of the parent bodies can therefore be revealed by determining the spatial distribution, grain size, composition and crystallinity of the dust through high-resolution mid-infrared observations. Here we report that the sub-micrometre amorphous silicate grains around Pic have peaks in their distribution around 6, 16 and 30 au (1 au is the Sun–Earth distance), whereas the crystalline and micrometre-sized amorphous silicate grains are concentrated in the disk centre. As sub-micrometre grains are blown quickly out from the system by radiation pressure from the central star, the peaks indicate the locations of ongoing dust replenishment, which originates from ring-like distributions of planetesimals or 'planetesimal belts'.

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