Final answer:
Dr. Tyson's reasoning for Pluto being America's favorite planet is not definitively provided, but cultural significance and the number 'nine' could play roles. Pluto was reclassified as a dwarf planet by the IAU in 2006 because it did not meet the criterion of having cleared its orbit.
Step-by-step explanation:
In "Astrophysicist Chronicles Battle over Pluto," Dr. Tyson suggests that Pluto's status as America's favorite planet might be related to the Disney character that shares its name. This affinity could stem from the tournament concept of identifying the ninth planet, rooted in the fact that Pluto was once considered the ninth planet in our solar system. Moreover, the cultural impact and sentimental attachment to the number nine as the count of planets in our solar system also play a role. However, it must be noted that the information provided does not clearly state which of the choices is the reason given by Dr. Tyson. Therefore, based on the context provided, we cannot definitively conclude the reason for Pluto's favored status among Americans.
As for Pluto's reclassification, in 2006, the International Astronomical Union (IAU) introduced three criteria for a celestial body to be considered a planet. Pluto did not meet the third criterion, which stipulates that a planet must have cleared its orbit of other debris. This led to Pluto being reclassified as a dwarf planet. This decision was met with various reactions ranging from scientific acceptance to public disappointment, highlighting sentimental and educational attachments to the former ninth planet.