School textbooks could soon be in need of an update. After Pluto was dethroned as not being a planet, the Solar System, from the Earth's point of view has only eight planets. Astronomers now think that there has to be another planet-sized body out there.
While scientists are yet to directly observe this planet orbiting the Sun, what astronomers do have is enough circumstantial evidence pointing toward its existence. No telescope has been able to spot it yet, reports the Washington Post.
However, astronomer Michael Brown of the California Institute of Technology, points out that he is "eternally optimistic" about its discovery. While adding that the planet by itself, might just be invisible to existing Earth-based observatories to actually spot.
Planet Nine, or the evidence for its existence reportedly first surfaced in 2014. Astronomers found a "planetoid" as well as a handful of small ice-worlds out in the Solar System. These bodies, notes the report, were discovered to have similar paths around the sun.
As a rule of thumb, "If things are in the same orbit, then something's pushing them," said Scott Sheppard, from the Carnegie Institution for Science in Washington and one of the astronomers who found the planetoid.
In a talk at the University of Tokyo, Surhud More said that "Every time we take a picture, there is this possibility that Planet Nine exists in the shot."
As to why Planet Nine has not been spotted yet, that is because it is far away and sunlight at those distances gets really dim. The report explains that relative to the distance between the Sun and Earth –one astronomical unit (AU)—planets that are twice as far, appear 16 times dimmer. Planets do not produce their own light, so they have to reflect the Sun's. Sunlight weakens by a factor of four going out to those distances. It has to be reflected and come back, that distance travelled alone is enough to dim by another factor of four.
That means Planet Nine would be about 160,000 times dimmer than Neptune, which is at 30 AU. If Planet Nine was at about 1,000 AU, it would seem 1 million times weaker, notes the report. "There's really a brick wall, basically, at 1,000 AU," said Kevin Luhman, of Pennsylvania State University.
However, there is enough evidence that a planet, specifically a rocky one -- four times the size of Earth and 10 times as dense -- is out there. BP519 is one such Extreme Trans-Neptunian Object (ETNO) which is about 450 AU, being influenced by this mysterious object.
