Astronomers with the SKYSURF project have searched through 200,000 archival images from the NASA/ESA Hubble Space Telescope and made tens of thousands of measurements on these images to look for any residual background glow in the sky. Like turning out the lights in a room, they subtracted the light from stars, galaxies, planets and the zodiacal light. Surprisingly, a ghostly, feeble glow was left over. It’s equivalent to the steady light of ten fireflies spread across the entire sky.
This artist’s illustration shows the location and size of a hypothetical cloud of dust surrounding our Solar System. Image credit: NASA / ESA / Andi James, STScI.
“One possible explanation for the residual glow is that our inner Solar System contains a tenuous sphere of dust from comets that are falling into the Solar System from all directions, and that the glow is sunlight reflecting off this dust,” said Arizona State University astronomer Tim Carleton and colleagues.
“If real, this dust shell could be a new addition to the known architecture of the Solar System.”
This idea is bolstered 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 flew by Pluto in 2015, and a small Kuiper belt object in 2018, and is now heading into interstellar space.
The New Horizons measurements were done at a distance of 6-8 billion km (4-5 billion miles) from the Sun.
This is well outside the realm of the planets and asteroids where there is no contamination from interplanetary dust.
New Horizons detected something a bit fainter that is apparently 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 the decay of dark matter to a huge unseen population of remote galaxies.
“If our analysis is correct there’s another dust component between us and the distance where New Horizons made measurements,” Dr. Carleton said.
“That means this is some kind of extra light coming from inside our Solar System.”
“Because our measurement of residual light is higher than New Horizons we think it is a local phenomenon that is not from far outside the Solar System.”
“It may be a new element to the contents of the Solar System that has been hypothesized but not quantitatively measured until now.”
Arizona State University astronomer Rogier Windhorst first got the idea to assemble Hubble data to go looking for any residual light.
“More than 95% of the photons in the images from Hubble’s archive come from distances less than 5 billion km (3 billion miles) from Earth,” Dr. Windhorst said.
“Since Hubble’s very early days, most Hubble users have discarded these sky-photons, as they are interested in the faint discrete objects in Hubble’s images such as stars and galaxies.”
“But these sky-photons contain important information which can be extracted thanks to Hubble’s unique ability to measure faint brightness levels to high precision over its three decades of lifetime.”
The findings appear in four papers in the Astronomical Journal and the Astrophysical Journal Letters.
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Timothy Carleton et al. 2022. SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements: II. First Limits on Diffuse Light at 1.25, 1.4, and 1.6 μm. AJ 164, 170; doi: 10.3847/1538-3881/ac8d02
Rogier A. Windhorst et al. 2022. SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements. I. Survey Overview and Methods. AJ 164, 141; doi: 10.3847/1538-3881/ac82af
Darby M. Kramer et al. 2022. SKYSURF-3: Testing Crowded Object Catalogs in the Hubble eXtreme Deep Field Mosaics to Study Sample Incompleteness from an Extragalactic Background Light Perspective. ApJL 940, L15; doi: 10.3847/2041-8213/ac9cca
Rosalia O’Brien et al. 2022. SKYSURF-4: Panchromatic Full Sky Surface Brightness Measurement Methods and Results. AJ, in press; arXiv: 2210.08010
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