For most of us, space is still one massive mystery.

We have some rudimentary knowledge of what’s out there, but in reality it stretches out further than most human brains can even begin to fathom.

So that’s why it’s no surprise when new things are discovered. And NASA’s latest discovery is nothing like anything we’ve seen before.

In an article that has been published recently in the journal Proceedings of the National Academy of Sciences, researchers explained the newly-discovered type of space object, known as a ‘dark comet’.

These moving objects are unusual, since they subvert what we previously thought we knew about the objects that we share our solar system with, forming a kind of hybrid between an asteroid and a comet. And they may once have served a very important purpose, as the scientists explain in the paper:

“Dark represent a potentially widespread class of small bodies that further populate the continuum between asteroids and comets. We report detections of seven dark comets which demonstrate that there are two distinct populations based on their orbits and sizes. These objects represent a class of Solar System objects that may have delivered material to the Earth necessary for the development of life such as volatiles and organics.”

Just like how SpaceX flights deliver necessary supplies into space, the researchers suggest that these celestial objects may have delivered important material – like water – to our planet early in its formation.

And these really are new to us. Scientists only identified the first dark comet two years ago; over the past two years, we have become aware of a total of fifteen of these objects hurtling through space. The researchers’ first understanding of these objects came when they noticed anomalous behaviour in what they’d initially thought was an asteroid. However, its accelerations weren’t typical of asteroids, which led them to take a closer look – as Davide Farnocchia, from NASA’s Jet Propulsion Laboratory, explained in a statement:

“When you see that kind of perturbation on a celestial object, it usually means it’s a comet, with volatile material outgassing from its surface giving it a little thrust. But try as we might, we couldn’t find any signs of a comet’s tail. It looked like any other asteroid — just a pinpoint of light. So, for a short while, we had this one weird celestial object that we couldn’t fully figure out.”

This led them to work towards a deeper understanding of these mysterious flying objects. When space telescopes started to identify more and more of these objects – that looked like an asteroid but travelled like a comet – they were given their own celestial object category, under the name ‘dark comets’.

Once these objects had been firmly categorised by their similarities (appearance and movement), the researchers then looked into what set these objects apart.

as Darryl Seligman from Michigan State University noted in the NASA statement:

“We had a big enough number of dark comets that we could begin asking if there was anything that would differentiate them. By analyzing the reflectivity and the orbits, we found that our solar system contains two different types of dark comets.”

In those years since dark comets were first identified, scientist have found numerous ways in which dark comets are distinct from one another. Most importantly, they found that the dark comets differ in size; the biggest ones are found in the outer solar system, with smaller ones travelling on their speedy trajectories around our inner solar system.

The dark comets that are found in the outer solar system follow elliptical orbits and are over one hundred meters wide; the inner dark comets, meanwhile, are les than ten meters wide and follow a circular trajectory.

And perhaps the most fascinating new fact about dark comets is their celestial purpose, as Seligman explains:

“Dark comets are a new potential source for having delivered the materials to Earth that were necessary for the development of life. The more we can learn about them, the better we can understand their role in our planet’s origin.”

Scientists don’t have all the answers yet, but this new understanding of dark comets is the next step in growing our collective knowledge of the wider universe around us.

And when it comes to how our planet came to be, these mysterious celestial objects could give us the clearest answer yet.

If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.