The proliferation of space objects is a rapidly increasing source of artificial night sky brightness

M Kocifaj,S Bará,F Kundracik,J C Barentine

doi:10.1093/mnrasl/slab030

Abstract

ABSTRACT The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite ‘mega-constellations’ in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 $\mu$cd m−2, which amounts to an approximately 10 per cent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.

Highlights

Artificial satellites orbiting the Earth have been a concern of astronomers since the launch of the first such object, Sputnik 1, in 1957
As of 1 January 2021, some 3,372 satellites are in orbit (UCS 2021) along with many tens of thousands of pieces of space debris; we refer to both satellites and space debris here as “space objects.”
Space objects remain directly illuminated by sunlight as seen from the night side of the Earth; they appear in images obtained with ground-based telescopes as streaks of various lengths and apparent brightness depending on the orbital parameters of the objects

Summary

INTRODUCTION

Artificial satellites orbiting the Earth have been a concern of astronomers since the launch of the first such object, Sputnik 1, in 1957. The orbital altitudes of space objects range from a few hundred kilometres in the case of objects in Low-Earth Orbit (LEO) to beyond the 35,786-km height defining geosynchronous orbits At such altitudes, space objects remain directly illuminated by sunlight as seen from the night side of the Earth; they appear in images obtained with ground-based telescopes as streaks of various lengths and apparent brightness depending on the orbital parameters of the objects. The number of space objects orbiting Earth is expected to increase by more than an order of magnitude in the decade due to the launches of fleets of new, large ’constellations’ of communications satellites.

SKY BRIGHTNESS DUE TO SPACE OBJECTS

Spectral radiance

Zenith sky luminance

Findings

DISCUSSION

PROSPECTS AND CONCLUSIONS