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

## TL;DR

The paper reports the serendipitous detection of a small interplanetary dust cloud passing near Earth, likely originating from a solar coronal mass ejection, based on mid-infrared all-sky maps from AKARI.

## Contribution

It presents the first evidence of a local interplanetary dust cloud passing near Earth, identified through mid-infrared observations and analysis of dust grain properties.

## Key findings

- Detected a bright residual component in 2007 January only
- The dust grains are likely smaller than typical zodiacal dust
- The cloud probably originated from a solar CME on 2007 January 25

## 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 x 20 deg. at a wavelength of 9 micron. 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_9um/I_18um 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.