Astronomers have spotted two mysterious objects in the outer solar system

Now two new research papers using data from the Atacama Large Millimeter/Submillimeter Array (ALMA) have resurfaced the possibility of a Planet X lurking at the edge of the solar system.

The papers were published on a server called arXiv where some scientists publish rough versions of papers before they're peer-reviewed and accepted for publication in a journal. The scientists use this "pre-publishing" to engage other experts in their field and get feedback.

The papers have launched a heated debate among astronomers about whether a "Planet X" may really exist or not.

The first paper is about an object detected in the same part of the sky as our neighboring binary star Alpha Centauri. The researchers detected a moving object near the star system. It's labeled as U in the image below:

arXiv/Liseau et al

They have three guesses for what it might be: a small icy chunk about 9 billion miles away from Earth, a "super Earth" (that would fit the bill of "Planet X") orbiting somewhere around 28 billion miles away from Earth, or it could be a brown dwarf (an object too large to be called a planet but too small to be called a star) much farther away — about 20,000 Astronomical Units (AU) from Earth. (One AU is about 93 million miles.)

The second paper describes evidence of another moving object in the same part of the sky as the star W Aquilae. The researchers have nicknamed it "Gna," and they say it could be a small body only a few hundred miles wide (they classify it as a "centaur" object which is a type of minor planet) orbiting on the outskirts of our solar system somewhere between 12 and 25 AU away (between the orbits of Saturn and Neptune). Alternatively, it could be a very distant planet-sized object 4,000 AU away.

However, other researchers have pointed out two big problems with these claims.

The ALMA telescope has a very small field of view and the astronomers only made a few observations of either object. They weren't able to track them for very long. So it's possible that it's just a data glitch.

Astronomer Mike Brown pointed out on Twitter why it's unlikely that ALMA could have spotted something planet-sized with its tiny field of view:

—Mike Brown (@plutokiller) December 10, 2015

—Mike Brown (@plutokiller) December 10, 2015

—Mike Brown (@plutokiller) December 10, 2015

And as astronomer Phil Plait pointed out in a Slate blog post, if either object does exist, it seems much more likely that they're one of the thousands of trans-Neptunian objects (TNOs) in our solar system — small icy bodies that are floating out beyond Neptune. Pluto and Eris are examples of TNOs. TNOs are much smaller than actual planets.

Wouter Vlemmings, an astronomer that worked on both papers, told Tech Insider in an email that the research is not conclusive and that's why both papers were published on arXiv. (They've both been submitted to the journal of Astronomy & Astrophysics.)

Here's what Vlemmings described as the most likely explanation for the observations:

The chance that [the objects], or at least one of them, is, as noted in my paper, a relatively nearby icy-body of a few 100 km in size has I think the largest probability of the options that have so far been suggested. Hopefully further feedback or a referee will be able to give further insights. My second option would be after all, despite careful checks, a data reduction artifact. None of my fellow experts at ALMA has so far come up with how this could be generated (which was one of the reasons to engage the larger community).

Vlemmings and the other researchers hope to examine the objects more closely in the future.

While we have a lot of reason to be skeptical about these new papers, it seems there's more evidence that there's something going on in the outer solar system that we can't totally explain yet.

Whether or not it's an elusive Planet X remains to be seen.