(NPR) — Scientists used a spacecraft over four billion miles from Earth to measure visible light that's not connected to any known source like stars or galaxies.
“There's as much light outside of galaxies as there is inside of galaxies.”
Scientists have used a NASA probe way out in space, beyond Pluto, to measure visible light that's not connected to any known source like stars or galaxies.
Some astronomers have wondered about that all that dark space–about how dark it really is.
“Is space truly black?” says Tod Lauer, an astronomer with the National Optical Astronomy Observatory in Arizona. He says if you could look at the night sky without stars, galaxies, and everything else known to give off visible light, “does the universe itself put out a glow?”
New Horizons was originally designed to explore Pluto, but after whizzing past the dwarf planet in 2015, the intrepid spacecraft just kept going. It's now more than four billion miles from home—nearly 50 times farther away from the Sun than the Earth is.
That's important because it means the spacecraft is far from major sources of light contamination that make it impossible to detect any tiny light signal from the universe itself. Around Earth and the inner solar system, for example, space is filled with dust particles that get lit up by the Sun, creating a diffuse glow over the entire sky. But that dust isn't a problem out where New Horizons is. Plus, out there, the sunlight is much weaker.