Hubble Spots Ghostly Glow Around Our Solar System – Zoo House News
- December 10, 2022
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Imagine walking into a room at night, turning off all the lights and closing the blinds. But 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 persists. Sounds like a scene from Ghost Hunters? No, for astronomers this is the real deal. But looking for something that is almost nothing is not easy.
One possible explanation is that a dust shell envelops our solar system all the way to Pluto, reflecting sunlight. The sight of dust in the air caught by the sun’s rays is not a surprise when you are cleaning the house. But this must have a more exotic origin. Because the glow is so evenly distributed, the likely source is myriad comets — free-flying balls of dusty ice. They fall toward the Sun from all directions, spewing out dust as the ice sublimates due to the Sun’s heat. If this were really the case, this would be a newly discovered architectural element of the solar system. It remained invisible until the very imaginative and curious astronomers and the power of Hubble emerged.
Aside from a carpet of glittering stars and the glow of the waxing and waning moon, the night sky looks inky black to the casual observer. But how dark is dark?
To find out, astronomers in an ambitious project called SKYSURF decided to sort through 200,000 images from NASA’s Hubble Space Telescope and make tens of thousands of measurements on those images, looking for remnants of the background glow in the sky. This would be all the light left after subtracting the glow from planets, stars, galaxies and dust in the plane of our solar system (called zodiacal light).
When the researchers completed this inventory, they found an extremely tiny excess of light, equivalent to the even glow of 10 fireflies scattered across the sky. It’s like turning off all the lights in a room with shuttered windows and still finding an eerie glow emanating from the walls, ceiling, and floor.
The researchers say one possible explanation for this residual glow is that our inner solar system contains a thin ball of dust from comets falling into the solar system from all directions, and that the glow is sunlight reflected off that dust. If real, this dust shell could be a new addition to the known solar system architecture.
Supporting this idea is 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 flew past Pluto in 2015 and a small Kuiper Belt object in 2018 and is now making its way into interstellar space. The New Horizons measurements were taken at a distance of 4 to 5 billion miles from the Sun. This is well outside the realm of planets and asteroids where there is no contamination from interplanetary dust.
New Horizons has detected something fainter that appears to be from a more distant source than Hubble detected. The source of the background light seen by New Horizons also remains unexplained. There are numerous theories ranging from dark matter decay to a vast, invisible population of distant galaxies.
“If our analysis is correct, there is another dust component between us and the distance at which New Horizons took measurements. That means this is some kind of extra light coming from inside our solar system,” said Tim Carleton of Arizona State University (ASU).
“Because our measurement of the residual light is higher than that of New Horizons, we believe it is a local phenomenon, not far outside the solar system. It could be a new element in the solar system’s content that has been assumed but not measured quantitatively until now,” Carleton said.
Veteran Hubble astronomer Rogier Windhorst, also from ASU, first came up with the idea of collecting Hubble data to search for a “ghost light.” “More than 95% of the photons in Hubble’s archival images come from distances less than 3 billion miles from Earth. Since Hubble’s inception, most Hubble users have discarded these celestial photons because they are interested in the faint discrete objects in Hubble’s images, such as stars and galaxies,” said Windhorst. “But these celestial photons contain important information that, thanks to Hubble’s unique ability to to measure faint levels of brightness with high precision over its three-decade lifetime.”
A number of graduate and undergraduate students contributed to the SKYSURF project, including Rosalia O’Brien, Delondrae Carter and Darby Kramer from ASU, Scott Tompkins from the University of Western Australia, Sarah Caddy from Macquarie University in Australia and many others.