Strange patterns in the orbits of small objects in the outer solar system could be explained by gaps in our understanding of gravity rather than an as-yet-unseen new world
A theory developed to replace dark matter may mean bad news for Planet Nine, a hypothetical as-yet-unseen world in the outer solar system. The odd orbital alignments of icy objects in this region that were initially considered a smoking-gun signature for the putative planet’s gravitational influence could instead be caused by gravity itself behaving against expectations, some researchers say.
“We thought we would probably disrupt Planet Nine’s predictions a little bit through MOND,” Mathur says. “It took us completely by surprise when we found that, in fact, we could explain the whole alignment that is seen by MOND, and so it becomes an alternative to Planet Nine.” But critics of MOND are plentiful, and they maintain that it falls short of standard dark-matter-based approaches in accounting for a host of well-known cosmic phenomena. “It doesn’t explain all the data,” says Kathryn Zurek, a cosmologist at the California Institute of Technology. “All of these cosmological datasets, combined, give us a consistent picture only works in the presence of dark matter.
Batygin, who is intrigued by the recent results, isn’t completely convinced about the alignment. “You could reasonably make the argument that the alignment is suggestive,” he says. “It might be a coincidence.”