For decades, Pluto has been the most famous object lurking on the outer edge of our solar system. Now, scientists may have found another distant world that could eventually join it in a very exclusive club.
Astronomers using the NSF–DOE Vera C. Rubin Observatory in Chile have identified a distant object known as 2026 ED138, and it could become the sixth officially recognized dwarf planet in our solar system. The discovery was announced this week, although scientists still need more observations before they can confirm its status.
So, Are There Planets Beyond Neptune?
Neptune is the eighth and most distant officially recognized planet in our solar system. Beyond its orbit are numerous smaller objects known as trans-Neptunian objects, or TNOs. Some are large enough that scientists consider them dwarf-planet candidates.
ED138 is one of those objects. It is currently about 46 times farther from the Sun than Earth is, putting it beyond Pluto’s average distance of about 40 astronomical units. Scientists estimate that ED138 could be between about 600 and 1,500 kilometers wide.
That size range is significant because an object’s own gravity can potentially pull it into a roughly spherical shape, which is one of the requirements for dwarf-planet status.
But ED138 isn’t officially a dwarf planet yet.
Researchers need additional observations to determine its exact size and physical characteristics. Infrared observations could help scientists get a better measurement, and the object’s final classification will depend on what those observations reveal.
What Happened to Pluto?
Pluto’s status is one reason this discovery is particularly interesting.
Pluto was discovered in 1930 and was considered the ninth planet in our solar system for decades. (Being able to claim that you remember when Pluto was a planet is turning into a right of passage). That changed in 2006, when the International Astronomical Union adopted a formal definition of what qualifies as a planet (poor Pluto).
Under that definition, a planet must orbit the Sun, be massive enough for its gravity to make it nearly round and have cleared the neighborhood around its orbit. Pluto met the first two requirements but not the third. It shares its region of the solar system with other objects, so the IAU reclassified it as a dwarf planet.
That decision left the solar system with eight official planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Pluto remained a dwarf planet, alongside Ceres, Eris, Haumea, and Makemake.
Astronomers Might Have Discovered a New Dwarf Planet
If scientists confirm that the object they recently discovered is large enough and meets the necessary criteria, it could become the sixth officially recognized dwarf planet.
What’s especially interesting is that ED138 wasn’t necessarily invisible all these years. Rubin Observatory found it in observations taken earlier this year, but researchers were also able to locate the object in archival images dating back to 2016. In total, Rubin observed it 30 times across 20 nights between March and July.
The object was difficult to spot because it sits in a particularly crowded section of the sky near the plane of the Milky Way, where countless background stars can make distant objects difficult to identify.
The discovery could also be just the beginning. The Rubin Observatory is designed to repeatedly survey the southern sky, giving astronomers a much better opportunity to find distant objects that previous surveys missed.
So while there may not be a ninth planet waiting to be added to the solar system’s official lineup (our very educated mother is still serving us nachos), there could be more worlds hiding far beyond Neptune, and scientists are finally getting better tools for finding them.
