NASA New Horizons mission helps scientists figure out how dark space is

One key answer for helping scientists figure out how many galaxies there are in the universe is how dark space is. Astronomers have been able to estimate the total number of galaxies in the universe by counting everything visible in a Hubble deep field. Then they multiply that by the total area of the sky. The problem with that process is that there are some galaxies that are too faint and far away to be directly detected.

While those galaxies are too far away and faint to be detected, their light still makes the blackness of space glow. To measure the amount of glow in the universe, satellites have to be outside the inner solar system, and the light pollution created when sunlight reflects off dust. The New Horizons mission to Pluto and the Kuiper Belt is being used to help figure out exactly how dark space is.

We look up the nighttime sky, it looks very dark, but NASA says space isn't absolutely black. New measurements of the weak background glow show that the unseen galaxies are less plentiful than some theories suggested. According to the new study, unseen galaxies number "only" in the hundreds of billions rather than the 2 trillion previously theorized.

The larger previous estimate was extrapolated from very deep sky observations made by Hubble. It used mathematical models to estimate how many galaxies were too small and faint for Hubble to see. In that study, researchers concluded 90 percent of galaxies in the universe were unviewable by Hubble. The new and much more modest number relied on measurements taken from the New Horizons mission.

One researcher on the project says if we take all the galaxies Hubble can see and double that number, that's what the New Horizons team believes is out there. The team sought to measure the weak afterglow of the Big Bang itself before stars existed. Currently, the New Horizon spacecraft is more than 4 billion miles away from Earth and experiences an ambient sky ten times darker than the darkest sky accessible to Hubble.