While Neptune is the furthest planet in the solar system (remember that Pluto is a dwarf planet), that doesn’t mean there’s nothing else in those parts of the solar system. Approximately 3,000 trans-Neptunian objects (TNO) are known to move even further, from small asteroids and comets to dwarf planets like Pluto. There is even the possibility that larger yet undiscovered worlds may be hiding in these distant shadows (such as Planet Nine and other undiscovered planets).
Now, a team of American astrophysicists has discovered, using data from the Dark Energy Survey (DES), 300 TNOs, smaller planets located in the confines of the solar system. Of these, 100 were unknown.
The goal of DES, after six years of data collection, is to understand the nature of dark energy by collecting high-precision images of the southern sky by searching for supernovae in distant galaxies. Although it was not specifically designed to identify TNOs, its breadth and depth of coverage (500 square degrees) made it an expert at finding objects beyond Neptune. "The amount of TNOs you can find depends on the amount of sky you look at and what is the weakest you can find," says Gary Bernstein, co-author of The Astrophysical Journal Supplement Series.
To find supernovae, the DES compares images of the same galaxies taken at different times to see which ones have changed their brightness. Then you should rule out the possibility that the light in the image comes from something much closer.
Projects designed to look for TNOs, or smaller but closer asteroids, take pictures only a few hours apart, so if you find something moving, you can set your orbit.
"Dedicated TNO surveys have a way of looking at the movement of the object, and it’s easy to track them," the authors say. "One of the key things we did in this document was to find a way to recover those movements".
From seven billion initial points detected by the software in the first four years, they were reduced to a list of about 400 candidates (ignoring points that were in the same place for several nights, which were probably stars, galaxies, supernovae and other objects) that were seen for at least six nights of observation." We have this list of candidates, but then we have to make sure that our candidates are really real,” stated Pedro Bernardinelli, also co-author of the study.
After adjusting the analysis methods several times, the team was able to identify a total of 316 TNOs in the data. Of these, 139 items had never been seen before. These objects were at a distance of approximately 30 astronomical units (AU), which places them near the orbit of Neptune, up to more than 150 AU.
Some of the most well-known objects on the edges of our solar system beyond Neptune include the dwarf planet Makemake (pronounced mah-kay mah-kay), and the farthest world we have explored, Arrokoth.
The researchers say that in the future they plan to apply the method to the entire set of DES data from these six years, while looking for fainter objects that might have been lost in the first search. They estimate that this could reveal up to 500 new TNOs and possibly, if any, the elusive Planet Nine.
Reference: Pedro H. Bernardinelli, Gary M. Bernstein, Masao Sako, Tongtian Liu, William R. Saunders, Tali Khain, Hsing Wen Lin, David W. Gerdes, Dillon Brout, Fred C. Adams, Matthew Belyakov, Aditya Inada Somasundaram, Lakshay Sharma, Jennifer Locke, Kyle Franson, Juliette C. Becker, Kevin Napier, Larissa Markwardt, James Annis, T. M. C. Abbott, S. Avila, D. Brooks, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, F. J. Castander, L. N. da Costa, J. De Vicente, S. Desai, H. T. Diehl, P. Doel, S. Everett, B. Flaugher, J. García-Bellido, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, D. L. Hollowood, D. J. James, M. W. G. Johnson, M. D. Johnson, E. Krause, N. Kuropatkin, M. A. G. Maia, M. March, R. Miquel, F. Paz-Chinchón, A. A. Plazas, A. K. Romer, E. S. Rykoff, C. Sánchez, E. Sanchez, V. Scarpine, S. Serrano, I. Sevilla-Noarbe, M. Smith, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, A. R. Walker, W. Wester, Y. Zhang. Trans-Neptunian Objects Found in the First Four Years of the Dark Energy Survey. The Astrophysical Journal Supplement Series, 2020; 247 (1): 32 DOI: 10.3847/1538-4365/ab6bd8