Марс пен астероид белдеуі арасындағы бесінші планета гипотезасы

Hypothetical fifth plant that existed between Mars and the asteroid belt

Planet V is a hypothetical fifth terrestrial planet posited by NASA scientists John Chambers and Jack J. Lissauer to have once existed between Mars and the asteroid belt. In their hypothesis the Late Heavy Bombardment of the Hadean era began after perturbations from the other terrestrial planets caused Planet V's orbit to cross into the asteroid belt. Chambers and Lissauer presented the results of initial tests of this hypothesis during the 33rd Lunar and Planetary Science Conference, held from March 11 through 15, 2002.

In the Planet V hypothesis, five terrestrial planets were produced during the planetary formation era. The fifth terrestrial planet began on a low eccentricity orbit between Mars and the asteroid belt with a semi major axis between 1.8 and 1.9 AU. While long lived, this orbit was unstable on a time scale of 600 Myr. Eventually perturbations from the other inner planets drove Planet V onto a high eccentricity orbit which crossed into the inner asteroid belt. Asteroids were scattered onto Mars crossing and resonant orbits by close encounters with Planet V. Many of these asteroids then evolved onto Earth crossing orbits temporarily enhancing the lunar impact rate. This process continued until Planet V was lost most likely by impacting the Sun after entering the ν6 secular resonance. In a later article published in the journal Icarus in 2007, Chambers reported the results of 96 simulations examining the orbital dynamics of the Solar System with five terrestrial planets. In a quarter of the simulations Planet V was ejected or impacted the Sun without other terrestrial planets suffering collisions. This result was most frequent if Planet V's mass was less than 0.25 of Mars. The other simulations were not considered successful because Planet V either survived for the entire 1 billion year length of the simulations, or collisions occurred between planets. The terrestrial Planet V hypothesis was examined by Ramon Brasser and Alessandro Morbidelli in 2011. Their work was the first to focus on the magnitude of the bombardment caused by Planet V. Brasser and Morbidelli calculated that to create the Late Heavy Bombardment Planet V would have to remove 95% of the pre LHB main asteroid belt or 98% of the inner asteroid belt (semi major axis < 2.5 AU). Depleting the main asteroid belt by 95% with a 0.5 Mars mass Planet V was found to require it remain in an orbit crossing the entire asteroid belt for 300 million years. This orbital evolution was not observed in any simulations; Planet V typically entered an Earth crossing orbit resulting in a short dynamic lifetime before entering such an orbit. In a few percent of simulations Planet V remained in the inner belt long enough to produce the LHB. However, producing the LHB from the inner asteroid belt would require the inner asteroid belt to have begun with 4–13 times the mass, and 10–24 time the orbital density, as the rest of the asteroid belt.

An impact of Planet V onto Mars, forming the Borealis Basin has recently been proposed as an explanation for the Late Heavy Bombardment. Debris from this impact would have a different size distribution than the asteroid belt with a smaller fraction of large bodies and would result in a lower number of giant impact basins relative to craters.