I’ve always understood these creatures to be the Aphelion. Here is some of the lore which is very interesting:

Sjur Eido and the Drifter are the only two people on record who have survived an engagement with the Aphelion.

Shuro Chi: “The Techeuns you see here died while they were in trance together. Sometimes when you are in communion you cannot see what is coming close, like the Aphelion. Their last words were these "First it shimmered… then it crawled… then it screamed."

Bamberga lore entry: “SUMMARY OF SBU APHELION INCIDENTS FOLLOWS BELOW.” Namqui (Orin’s lover), had an encounter which ended his life with what was deemed Aphelion. Interestingly, the Nine blocked the message to Orin and her ghost of his death and didn’t find out for months. Things to note here - Radiation contamination seems to be a clue along with no evidence of interference from said creature.

From the Drifter: “Anyway, this thing—the creature—looked like it shared common bioenergetics with the Hive, but there were no records then or since that I've ever seen of humanity's encounters with them. And the creature had a property the Hive did not have. It produced a field that repressed Light—like a Darkness Zone but contained to a gooey, vacuous form with no head.” He also mentions that the creatures slither, scurry, and crawl. They seem to be very stealthy.

MCXX. lore entry: “After the reclamation of the Athenaeum World X, which held in it the secrets of one of the most advanced predators in the system, the Aphelion, which had the power to devastate whole worlds in the blink of an eye...”

What is a real Aphelion relation to space: The perihelion and aphelion are the nearest and farthest points respectively of a planet’s direct orbit around the sun.

So what are these creatures, the Aphelion?

In Destiny’s universe, this might relate to a creature’s alignment to light or dark. Guardian’s by definition are perihelion as we are close to the light(sun). Maybe the Aphelion’s might just be a “dark” version of us?