Zodiacal Light Beyond Earth Orbit Observed with Pioneer 10

Abstract

We reanalyze the Imaging Photopolarimeter (IPP) 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 (IPD) 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 (EBL) after subtracting the zodiacal light based on the model.

New Horizons Observations of the Cosmic Optical Background

“…This work is of particular interest, however, as the photometry was obtained when the spacecraft were 3.2 to 5.2 au from the Sun, allowing the authors to claim that the effects of ZL were negligible. More recently, however, Matsumoto et al (2018) re-reduced the Pioneer 10 data and claimed that instrumental artifacts prevent accurate measurement of the absolute sky level. Matsuura et al (2017) obtained low-resolution 0.8 μmλ1.8 μm NIR spectra of the sky using the Cosmic Infrared Background Experiment (CIBER) rocket instrument.…”

Is the infrared background excess explained by the isotropic zodiacal light from the outer solar system?

“…Such isotropic zodiacal light component, if it exists, is made by IPD around the Earth or around the outer Solar system, because it does not show time variation by the observations from the Earth. Matsumoto et al (2018) compared the zodiacal light model (Kelsall et al 1998) with the observational data of the zodiacal light during the cruising to Jupiter by Pioneer 10, and no evidence was found that the isotropic zodiacal light component exists around the Earth. In this reason, the other possibility of the existence of IPD around the outer Solar system is investigated in this paper.…”

On the origin of the optical and near-infrared extragalactic background light

“…(2018) 4) reanalyzed the ZL data of Pioneer 10 during the cruising phase to Jupiter and discovered that the spatial distribution of the interplanetary dust is consistent with Kelsall et al's model. The spectrum of ZL has been extensively observed, which shows the solar spectrum with a slight enhancement at wavelengths longer than 1 µm.…”

“…They claimed that the sky brightness near Jovian orbit was consistent with ILG. However, a recent reanalysis confirmed the existence of instrumental offsets, which renders the observation of absolute sky brightness impossible 4 ) ; hence, we did not plot Matsuoka et al ’s results 54 ) in Fig. 1 .…”