How many planets are there after all?
We talk about the first tiny moments of our Universe after the Big Bang discussing the emergence of structure in it, we try to solve the mystery of galaxies’ spiral ends moving faster than expected, or invent a totally new source of (negative) energy – dark energy – to explain the Universe’s accelerating expansion. At the same time we find it difficult to tell how many planets our Solar system has after all. With Pluto being discarded from the list of objects with planetary status we should be certain that there are eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune which was discovered in the XVIII century as a consequence of accounting for irregularities of Uranus’ rotation. There are also two belts: the rocky asteroid belts between Mars and Jupiter and the Kuiper belt. The latter is the circumstellar disc of the outer of our Solar system reaching from Neptune (which is 30 times more distant from the Sun than Earth) to roughly 50 astronomical units (1 astronomical unit equals 150,000,000 km or the distance from Earth to the Sun).
We may not be entirely right about the number of planets, though. In January 2016, Konstantin Batygin and Michael E. Brown proposed the existence of a ninth planet in the Solar System. They calculations were based on irregularities (or rather incredible regularities) spotted among the objects constituting the Kuiper belt. In 2020 Batygin and Brown recalculated their models. The ninth planet was supposed to be 10 times larger than Earth with an orbital period of 20,000 years. After the recalculations it turns out that the ninth planet is only 5 times heavier than Earth and its orbital period makes only 10,000 years. It is still extremely challenging to detect this planet in the sky. In 2022 the Large Synoptic Survey Telescope (LSST) currently under construction in Chile will be operational and there is an expectation that we would be able to see the ninth planet and figure out what consequences its rotation around the Sun might have on our planet. We are all afraid of cosmic cataclysms and for a good reason – we do not have power yet to avoid or block them.
We all know of Milankovitch cycles - cyclical movements of our planet related to the Earth’s orbit around the Sun. There are three of them: eccentricity, axial tilt, and precession with 100,000, 51,000 and 26,000 year periods respectively. Do we have to now believe that the ninth planet may add an additional cyclic disturbance to what happens to our planet? If you have your own opinion on this matter please let us know by writing at email@example.com