Zodiacal Light Beyond Earth Orbit Observed with Pioneer 10

TL;DR

This study reanalyzed Pioneer 10 data to examine zodiacal light beyond Earth orbit, confirming the model's validity for the main dust cloud and identifying a local dust cloud at 2.94 au, with implications for extragalactic background light detection.

Contribution

It introduces an improved method for subtracting foreground light and provides new insights into zodiacal dust distribution beyond Earth orbit, including evidence of a local dust cloud.

Findings

Good correlation between model zodiacal light and residual brightness at r<2 au.

Reflectances of interplanetary dust are consistent with previous studies.

Zodiacal light is not significantly detectable beyond 3 au.

Abstract

We reanalyze the Imaging Photopolarimeter data from Pioneer 10 to study the zodiacal light in the B and R bands beyond Earth orbit, applying an improved method to subtract integrated star light (ISL) and diffuse Galactic light (DGL). We found that there exists a significant instrumental offset, making it difficult to examine the absolute sky brightness. Instead, we analyzed the differential brightness, i.e., the difference in sky brightness from the average at high ecliptic latitude, and compared with that expected from the model zodiacal light. At a heliocentric distance of r<2 au, we found a fairly good correlation between the J-band model zodiacal light and the residual sky brightness after subtracting the ISL and DGL. The reflectances of the interplanetary dust derived from the correlation study are marginally consistent with previous works. The zodiacal light is not significantly detectable at r>3 au, as previously reported. However, a clear discrepancy from the model is found at r=2.94 au which indicates the existence of a local dust cloud produced by the collision of asteroids or dust trail from active asteroids (or main-belt comets). Our result confirms that the main component of the zodiacal light (smooth cloud) is consistent with the model even beyond the earth orbit, which justifies the detection of the extragalactic background light after subtracting the zodiacal light based on the model.