Hubble Detects Ghostly Glow Surrounding Our Solar System

by Troy Oakes December 17, 2022

written by Troy Oakes December 17, 2022

A survey of the residual light in the night sky has uncovered an eerie, omnipresent glow spread throughout the Solar System, thought to be caused by sunlight reflected from cometary dust. (Image: NASA & ESA)

A survey of the residual light in the night sky has uncovered an eerie, omnipresent glow spread throughout the Solar System, thought to be caused by sunlight reflected from cometary dust.

Over its 30-plus years of operations, astronomers have become accustomed to subtracting the background light from the Solar System from Hubble’s images. They are interested in the faint, discrete objects that are other stars and galaxies. But the SKYSURF team realized that Hubble’s images would be an excellent set of survey data to measure the Solar System’s background light.

The illustration shows a simple diagram of the Solar System with white speckling representing comet dust. The Sun is represented as a fuzzy yellow sphere at the center. It is surrounded by four concentric ovals labeled ‘Planetary Orbits’, which represent the orbital paths of Jupiter, Saturn, Uranus, and Neptune, as viewed from an oblique angle to the orbital plane. (Image: A. James via NASA, ESA)

The residual glow of the Solar System

The SKYSURF program used 200,000 images from the NASA/ESA Hubble Space Telescope to look for any residual background light in the sky. This would be any leftover light after subtracting the glow from planets, stars, galaxies, and from dust in the plane of our Solar System (called zodiacal light). The excess that they found was extremely faint – equivalent to the steady glow of 10 fireflies spread across the entire sky.

Aitoff equal-area projections in Ecliptic coordinates of all ACS/WFC and WFC3/UVIS+IR images with texp ≥ 200 s that are publicly available as of September 23, 2019. The Galactic plane and bulge are represented by the light gray band, and the Celestial Equator is indicated by the pink curve (upper left). SKYSURF measures the absolute all-sky surface brightness S(λ, t, lEcl, bEcl) in 12 main broadband filters at ∼0.2–1.7 μm in wavelength from 249,861 HST Archival images in ∼1400 independent HST fields. (Image: via ‘The Astronomical Journal (2022)’)

The researchers say that one possible explanation for this 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. If real, this dust shell could be a new addition to the known architecture of the Solar System.

Magnitude vs. half-light radius plot for the F606W original and replicated images. The black points are the original objects, and the other colors are the 2×, 3×, and 4× XDF replications’ objects. Each successive color has more transparent markers, and there are more blue marks than green, more green than red, and more red than black. This figure was modeled after Figure 3 in Windhorst et al. (2008) so features could be marked and compared. The pink band represents the natural confusion limit with a range between 1/25 and 1/50 objects per beam (see, e.g., Serjeant et al. 1997; Silva et al. 2005). The cyan dashed curve represents the 174.4ks surface brightness limit of the XDF F606W data. Its shape has been changed from Windhorst et al. (2008) as the curve is only intended to draw the eye to the trend and the cutoff of the objects, demonstrating the exposure time and resolution limits to observing these objects. The dark gray dashed line represents the limit below which point sources with fainter magnitudes cannot be resolved, as they blend in with the sky distribution. All curves have been shifted in magnitude to account for the mVega to mAB conversion. This figure demonstrates that natural confusion (pink band) is an important completeness constraint for bright large objects that make up most of the IGL (mAB ≲ 28.5 mag). It also demonstrates that the three main limits on the original HUDF sample remain the same for the replicated samples, validating our methods of replication, namely the point-source detection limit (horizontal gray dashed line), the surface brightness limit (slanted cyan dashed line) and the natural confusion limit due to statistical object overlap (pink band). (Image: ‘The Astrophysical Journal Letters (2022)’)

Provided by ESA/Hubble Information Centre [Note: Materials may be edited for content and length.]

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Troy Oakes

Troy was born and raised in Australia and has always wanted to know why and how things work, which led him to his love for science. He is a professional photographer and enjoys taking pictures of Australia's beautiful landscapes. He is also a professional storm chaser where he currently lives in Hervey Bay, Australia.

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