The Fifth Giant Planet

By | November 4, 2017

Strange things happened in our Solar System when it was young and forming. During the later stages of Solar System formation, massive protoplanets and planetesimals (the building blocks of planets) performed a chaotic gravitational ballet that caused many planetesimals to be rudely tossed into new and dangerous orbits by some of their dancing partners. This dangerous dance resulted in angular-momentum exchange between planets and planetesimals, which caused migration–either outward or inward-

-of the unlucky baby planet. For example, the outward migration of the ice-giant Neptune (the most distant major planet from our Sun) is believed to be responsible for the resonant capture of the ice dwarf planet Pluto–and others of its frozen kind, termed Plutinos–into a 3.2 resonance with Neptune. In October 2015, a team of astrophysicists at the University of Toronto in Canada, proposed that a close encounter of the worst kind with the enormous gas-giant planet Jupiter–that occurred about 4 billion years ago–may have resulted in a long-lost giant planet’s unceremonious eviction from our Solar System into the space between stars.

During this fierce and ancient chaos, that resembled a kind of cosmic playground for kindergarten planets during recess, strange games were played by all of the young attendees. Planetary migration occurs when a planet or other body in orbit around a star, such as our own Sun, interacts with either a primordial disk of gas or playful planetesimals. This strange gravitational game results in the alteration of

the young planetary body’s orbital parameters–especially with its semi-major axis. In planetary systems beyond our own, planetary migration is thought to be the most likely explanation for the existence of roasting hot Jupiters. Hot Jupiters are exoplanets with hefty masses similar to our own Solar System’s behemoth Jupiter, that hug their parent-stars fast and close in searing-hot orbits of only a few days. Most theories of planetary formation from a protoplanetary accretion disk of gas and dust, whirling around a young star, predict that hot Jupiters cannot form so close to their roasting, fiery, roiling stellar parent. This is because there is insufficient mass and the temperature is too high to permit the birth of rocky or icy planetesimals. It has also become obvious that terrestrial, rocky planets such as Earth, may be subject to rapid inward migration if they are born while the gas disk is still lingering around its young star.

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