This ghostly glow was also present in 2021, when scientists used data from the New Horizons spacecraft to study our solar system.
To better understand our cosmic neighborhood, astronomers studied 200,000 Hubble Space Telescope archive images and made tens of thousands of measurements as part of a project called SKYSURF. This was done to determine whether any residual glow was present in the sky. Light from stars, galaxies, planets, and zodiacal light was subtracted. In spite of this, a faint, ghostly glow persisted. A constant light equivalent to ten fireflies scattered throughout the sky. Astronomers are still unsure where this ghostly glow is coming from. We may be able to explain this phenomenon by a layer of dust that wraps around our solar system and reflects sunlight all the way to Pluto.
A Ghostly glow seen by New Horizons
Due to the random distribution of the glow, it is likely that it originates from countless dusty snowballs in the sky, called comets. They travel towards the Sun from different directions in outer space. The Sun’s heat causes the ice to sublimate, spewing dust as the objects travel. A study from 2021 supports this idea. NASA’s New Horizons spacecraft was used by astronomers to measure the bottom of the sky. Having passed Pluto in 2015 and a small Kuiper belt object in 2018, New Horizons is now headed into interstellar space. Measurements were made between 4 billion and 5 billion miles from the Sun by the probe.
A new, unquantified element of the solar system
Planets and asteroids do not orbit at this distance. Consequently, interplanetary dust is not present. Additionally, it detected something slightly fainter that may have come from a longer distance than Hubble. Likewise, New Horizons’ backlight is unexplained. Many theories have been proposed, including dark matter decay and a large population of distant galaxies. A further explanation is that since residual light levels are higher than New Horizons, scientists believe the phenomenon is local and not external to the solar system. As a result, it may represent a new, unquantified element of the solar system’s content.