A likely detection of a local interplanetary dust cloud passing near the Earth in the AKARI mid-infrared all-sky map

¹ Graduate School of Science, Nagoya University, Chikusa-ku, 464-8602 Nagoya, Japan
e-mail: ishihara@u.phys.nagoya-u.ac.jp
² Institute for Space-Earth Environmental Research, Nagoya University, Chikusa-ku, 464-8601 Nagoya, Japan
³ Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, 153-8902 Tokyo, Japan
⁴ Korea Astronomy and Space Science Institute, 34055 Daejeon, Republic of Korea
⁵ Graduate School of Science, The University of Tokyo, Bunkyo-ku, 113-0033 Tokyo, Japan
⁶ Institute of Space Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan

Received: 18 May 2016
Accepted: 4 April 2017

Abstract

Context. We are creating the AKARI mid-infrared all-sky diffuse maps. Through a foreground removal of the zodiacal emission, we serendipitously detected a bright residual component whose angular size is about 50° × 20° at a wavelength of 9 μm.

Aims. We investigate the origin and the physical properties of the residual component.

Methods. We measured the surface brightness of the residual component in the AKARI mid-infrared all-sky maps.

Results. The residual component was significantly detected only in 2007 January, even though the same region was observed in 2006 July and 2007 July, which shows that it is not due to the Galactic emission. We suggest that this may be a small cloud passing near the Earth. By comparing the observed intensity ratio of I_{9 μm}/I_{18 μm} with the expected intensity ratio assuming thermal equilibrium of dust grains at 1 AU for various dust compositions and sizes, we find that dust grains in the moving cloud are likely to be much smaller than typical grains that produce the bulk of the zodiacal light.

Conclusions. Considering the observed date and position, it is likely that it originates in the solar coronal mass ejection (CME) which took place on 2007 January 25.