Imagine walking into a room at night, turning off all the lights and curtains. Yet an eerie glow emanates from the walls, ceiling and floor. The dim light is barely enough to see your hands in front of your face, but it’s there. Sounds like a scene from Ghostbusters? No, it’s the real deal for astronomers. But looking for something close to zero is not easy. Astronomers looked at 200,000 archived Hubble Space Telescope images and took tens of thousands of measurements on those images to find any remnants of background glow in the sky.

They took away the light of stars, galaxies, planets, zodiac lights, as if turning off the lights of a room. Surprisingly, a faint ghostly glow remained. This is equivalent to the steady light of ten fireflies scattered across the sky.

Where is this from?

One possible explanation is that the dust envelope covers our solar system up to Pluto and reflects sunlight. It is not surprising to see dust falling under the sun’s rays while cleaning the house. But it must have a more exotic origin. Because the glow is so smooth, the likely source is numerous comets – free-flying dusty ice snowballs.

As the ice sublimes under the heat of the sun, they blast dust into the air and fall towards the sun from all directions. If true, it would be a newly discovered architectural element of the solar system. It remained invisible until the arrival of creative and curious astronomers and the power of Hubble.

Apart from the tapestry of twinkling stars and the glow of the growing and waning moon, the night sky appears black as ink to the casual observer. But how dark is it?

To find out, astronomers sequenced 200,000 images taken by NASA’s Hubble Space Telescope and performed tens of thousands of measurements on these images to find any remnants of background glow in the sky as part of an ambitious project called SKYSURF. This would be any light remaining after removing the glow (the so-called zodiac light) from planets, stars, galaxies, and dust in the plane of our solar system.

When the researchers completed this inventory, they found an extremely small excess of light, equivalent to the constant glow of 10 fireflies scattered across the entire sky. It’s like seeing an eerie glow coming from the walls, ceiling and floor as you turn off all the lights in a shuttered room.

A possible explanation for this residual glow, the researchers say, is that our inner solar system contains a sphere of diluted dust from comets falling into the solar system from all directions, and the glow is sunlight reflected from that dust. If this dust shell is real, it could be a new addition to the known architecture of the Solar System.

This idea is supported by the fact that in 2021 another team of astronomers used data from NASA’s New Horizons spacecraft to also measure the sky background. New Horizons passed Pluto in 2015 and a small Kuiper Belt object in 2018 and is now heading into interstellar space. New Horizons measurements were made between 4 and 5 billion miles from the Sun. This is far beyond the world of planets and asteroids, where there is no pollution from interplanetary dust.

New Horizons detected something a little dimmer, apparently from a more distant source than Hubble found. The source of the background light seen by New Horizons also remains unclear. There are many theories, from the decay of dark matter to the invisible large population of distant galaxies.

“If our analysis is correct, there is another dust component between us and the distance New Horizons is measuring. That means some kind of extra light coming from inside our solar system,” he said.

“Now that our measurements of light are higher than New Horizons, we believe this is a local phenomenon not far outside the Solar System. There may be a new element in the solar system that has been proposed but not measured. Until now,” Carlton said.

Senior Hubble astronomer Rogier Windhorst, also from ASU, first came up with the idea of ​​collecting Hubble data to look for any “ghost light.”

“More than 95% of the photons in Hubble archive images come from less than 3 billion miles from Earth. Since Hubble’s inception, most Hubble users have dismissed these sky photons because they are interested in faint discrete objects. Windhorst says, “like stars and galaxies. “In the Hubble images, however, these sky photons contain important information that can be gained thanks to Hubble’s unique ability to measure faint luminosity levels with high precision over its thirty-year lifespan.” Source