Our solar system glows on the inside. Get yourself somewhere truly dark in spring in the northern hemisphere and about an hour after sunset—just above where the sun has recently set—and you’ll see a triangular glow. Known as a “false dusk,” this so-called zodiacal light is sunlight reflecting off cosmic dust left in the solar system.
That dust orbits the sun in the same plane as all of the planets. Some think it’s “Mars Light,” with the red planet shedding dust into interplanetary space. Either way, it’s the biggest thing in the solar system and it may have been there long as the solar system has existed. Some of it may be from passing asteroids and comets, but it could also be the leftovers of the formation of the planets themselves.
Scientists now think there’s a similar glow around the solar system.
Astronomers working on the SKYSURF project processed 200,000 images from Hubble Space Telescope’s archive to discover a residual background glow in the sky. They did it by removing all light from stars, galaxies, planets—as well as zodiacal light. Unlike zodiacal light, this glow insult in the same plane as the planets, but in a spherical shape all over the solar system.
The Hubble Space Telescope is uniquely able to precisely measure faint brightness levels—something it’s been doing for over 30 years.
So what is this glow from? Distant galaxies that are yet to be seen by telescopes? Decaying dark matter? The shell of dust around our solar system—as far out as ex-ninth planet Pluto—is most likely may be pollution from comets, claim the scientists.
Comets orbit the Sun, but only occasionally enter the solar system. As they get close to the Sun they begin to melt, spewing dust and ice as they do.
A spacecraft that flew by Pluto in 2015, New Horizons, has measured the sky background before, but this new discovery is something separate. “If our analysis is correct there’s another dust component between us and the distance where New Horizons made measurements. That means this is some kind of extra light coming from inside our solar system,” said Tim Carleton, of Arizona State University (ASU). “It may be a new element to the contents of the solar system that has been hypothesized but not quantitatively measured until now.”
Wishing you clear skies and wide eyes.