Hunting for Planet Nine by its Influence on Neptune BY ALEX GAVITT '23 Cover image: Artist’s impression of Planet Nine. The yellow ring around the Sun is Neptune’s orbit. Source: Wikimedia Commons/ nagualdesign and Tomruen, CC-BY-SA 4.0
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Abstract
What is a Planet?
As more and more Kuiper belt objects have been discovered, astronomers have begun to notice that many of their orbits are aligned contrary to the expected random distribution around the Sun. Furthermore, some have extremely long or highly inclined orbits that cannot be explained by the gravitational influence of known objects. As a result, some astronomers have suggested that there may be a ninth planet, orbiting far beyond Neptune, that is influencing the orbits of these Kuiper belt objects. This paper provides scientific background for the Planet Nine hypothesis and describes a calculation of the transit timing variation (TTV) it would introduce in Neptune’s orbit. Ultimately, it finds that the TTV would be too small and occur over too long a timescale to be useful in finding Planet Nine.
Wanderers The word “planet” comes from the ancient Greek word for “wanderer.” This definition offers a profound insight into humanity’s original understanding of the planets: they clearly move through the sky independent of the slow and fixed movement of the other stars. Under the geocentric model of the solar system, astronomers counted seven planets that fit this definition: Mercury, Venus, Mars, Jupiter, and Saturn, as well as the Sun and the Moon. The advent of the heliocentric solar system, then, was the first nail in the coffin of this definition, for it stripped the wandering Sun and Moon of the title “planet,” while also adding the Earth to the planetary ranks, despite its apparent lack of motion (Brown, 2010, pp. 18–21). What sealed the fate of the “wanderer” definition was the discovery of Uranus in 1781 DARTMOUTH UNDERGRADUATE JOURNAL OF SCIENCE
