But the reason it may not yet have been found is due to that same distance. At that distance, the equivalent, of 600 astronomical units (1 AU is defined as the distance between the Earth and the Sun, or approximately 93 million miles), it would be 160,000 times dimmer than Neptune is. Kevin Luhman, an astronomer at Pennsylvania State University, told Quanta Magazine by way of the Washington Post that at 1,000 AU, it’s a “brick wall, basically,” making any potential planet next to impossible to see using current technology.
However, scientists believe the possibility of another planet, one which may have “10 times the mass of Earth,” does indeed exist.
“Every time we take a picture, there is this possibility that Planet Nine exists in the shot,” Surhud More, associate professor in Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo, told Quanta Magazine.
In the Oct. 2017 statement, Caltech planetary astrophysicist Konstantin Batygin, who worked with Brown, said that there “five different lines of observational evidence” that point to the existence of the planet.