Your comment got me to look up the number of objects considered planets over the years, this has ranged from 5-23. Data since 1543 is available here: https://dx.doi.org/10.1038%2Fscientificamerican0107-34
For fun I did a linear regression of year vs # planets and found that the while the slope was 1.8 planets/century, this was not significantly different from zero. The evidence appears to be consistent with a constant number of planets.
Your comment got me to look up the number of objects considered planets over the years, this has ranged from 5-23. Data since 1543 is available here: https://dx.doi.org/10.1038%2Fscientificamerican0107-34
For fun I did a linear regression of year vs # planets and found that the while the slope was 1.8 planets/century, this was not significantly different from zero. The evidence appears to be consistent with a constant number of planets.