cover of the August 28, 1971 issue

The diminishing mass of PlutoScience News, August 28, 1971

Pluto was the last of the earths to be uncovered (in 1930). If astronomers remain to make it lighter, it might be the very first to vanish.… [The latest measurement] brings Pluto to 0.11 of Planet’s mass, much less than an eighth of its previous self.… The large disparities amongst the numbers provided for the mass of Pluto show the specific problems of determining its mass.… If an earth has satellites, its mass can be established from researching their activities.… Yet Pluto has no recognized satellites.


The discovery of Pluto’s moon Charon in 1978 (SN: 7/15/78, p. 36) lastly enabled astronomers to properly compute the earth’s mass: concerning 0.2 percent of Planet’s mass. Years after researchers dealt with Pluto’s heft, the earth obtained probably the best downgrading of all — a downgrade to dwarf planet (SN: 9/2/06, p. 149). Some astronomers have actually because suggested alternative interpretations for the term “earth” that, if extensively taken on, would certainly restore Pluto to its former rank.