physics question #3570



steve abel, a 51 year old male from Seattle, WA, USA asks on August 24, 2006,

Q:

Can you explain the meaning of the phrase: " has cleared the neighbourhood around its orbit.” I have read that Pluto is no longer considered a planet because its orbit overlaps with that of Neptune, behavior which is contrary to the above criteria. Why then isn't Neptune also eliminated from the list of bodies considered to be planets since it has not cleared its neighbourhood of Pluto?

viewed 14193 times

the answer

Leigh Palmer, Physics professor, Simon Frasser University, Burnaby, BC Canada answered on October 4, 2006, A:

This business is a mess, and it's not science. Look at the image below and decide whether Pluto has "cleared its orbit" or not. NOTE: click on image for larger version.

Orbital diagram showing orbits of Neptune and Pluto. It is clear everywhere by more than 2 Astronomical Units (the mean distance between the Earth and the Sun) from Neptune's orbit (its nearest neighbor), something that can't be said for Earth, Venus, Mercury, or Mars. Words like "overlaps" and "crosses" when applied to the orbits of Neptune and Pluto simply indicate that two dimensional geocentric thinking is going on.

Add to or comment on this answer using the form below.
(required)
(required if you would like a response)
Note: All submissions are moderated prior to posting.
If you found this answer useful, please consider making a small donation to science.ca.