Eerie "ghost light" detected emanating from within the solar system
Astronomers have detected an eerie glow of “ghost light” that could represent a previously unknown component of the solar system. Comparing data from two distinct viewpoints – Hubble and New Horizons – the researchers subtracted light from known objects and discovered a dim, unexplained glow still remained.
If you were to step out into your backyard and stare up at the night sky, you’d see countless stars and other points of light, but if you left your porch light on you’d miss out on many more faint objects. The same kind of thing applies to telescopes – the solar system has its own glow that can wash out fainter galaxies.
A project called SKYSURF is aiming to catalog the light seen from Earth to figure out how much is coming from local light sources, how much from more distant stars and galaxies, and how it’s all spread out. To do so, the scientists analyzed 200,000 images snapped by the Hubble Space Telescope, subtracting the glow from known objects including the planets, moons, asteroids and comets in our own solar system, as well as the stars and galaxies beyond it. Another major source is what’s called the zodiacal light, which is sunlight reflecting off the dust in the inner solar system.
After accounting for all of these, the team discovered that a tiny, ghostly glow remained. This light was equivalent to about 10 fireflies spread across the whole sky, and couldn’t be attributed to any known source.
More intriguingly, the scientists were able to begin zeroing in on how far this light was from Earth. That’s thanks to data from New Horizons, a NASA probe that’s on its way out of the solar system entirely. From this distant perspective, the spacecraft detected far less unexplained light than Hubble, indicating the majority of it lay somewhere inside the 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,” said Tim Carleton, an author of the new studies. “It may be a new element to the contents of the solar system that has been hypothesized but not quantitatively measured until now.”
The researchers hypothesize that this newly identified “ghost light” could be caused by a cloud of dust around the solar system. If this exists, it would most likely have been left behind from the tails of comets as they enter the inner solar system, where they heat up and material begins vaporizing off them.
But what of the extra light that New Horizons detected? The researchers suggest this could be coming from the dim, unknown galaxies that we can’t see from Earth, or perhaps something more exotic like the decay of dark matter.