2015 BP519, nicknamed "Caju", is another extreme trans-Neptunian object that points to the existence of Planet Nine. Discovered with data from the Dark Energy Survey, Caju has a relatively large diameter, estimated at around 400-700 km, meaning the object could be a gravitationally rounded dwarf planet. It also has a highly inclined orbit of 54°, which a team of scientists says can be explained by the presence of the hypothetical Planet Nine:
After discovering it, the team tried to investigate 2015 BP519's origins using computer simulations of the Solar System. However, these tests were not able to adequately explain how the object had ended with such an orbit.
But when the team added a ninth planet with properties exactly matching those predicted by the Caltech scientists in 2016, the orbit of 2015 BP519 suddenly made sense. "The second you put Planet Nine in the simulations, not only can you form objects like this object, but you absolutely do," Juliette Becker, a Michigan graduate student and lead author of the study told Quanta.
Some researchers, however, caution that Planet Nine may not be the only explanation for 2015 BP519's strange orbit. Michele Bannister, a planetary astronomer from Queen's University Belfast, in Ireland, who was not involved in the study, told Newsweek that while the latest findings were "a great discovery," other scenarios could account for its tilt. "This object is unusual because it's on a high inclination," she said. "This can be used to maybe tell us some things about its formation process. There are a number of models that suggest you can probably put objects like this into the shape of orbit and the tilt of orbit that we see today."
Also at Quanta Magazine.
Discovery and Dynamical Analysis of an Extreme Trans-Neptunian Object with a High Orbital Inclination (arXiv:1805.05355)
Related: Medieval Records Could Point the Way to Planet Nine
(Score: 2) by All Your Lawn Are Belong To Us on Thursday May 17 2018, @08:02PM
Because it could be far dimmer in either actual or observed magnitude without much difficulty?
Albedo depends on many factors, but if it were much brighter than 1/600th Pluto the odds favor it would have already been discovered by other surveys. So you have an "at least as faint as" without knowing how faint it actually could be. (It would be an interesting problem to work out - what's the maximum faintness it could be if it were a chunk asphalt or other dull nonreflecting carbon...)
This sig for rent.