Just How Big Is Pluto? Now We Know Thanks To New Horizons
Measurements of Pluto's size from ground-based telescopes have a lot of uncertainty due to the presence of an atmosphere on Pluto but thanks to NASA's New Horizons we now know that Pluto is 2,370 kilometers (1,473 miles) in diameter, confirming that Pluto is indeed the largest known Kuiper Belt Object - larger than dwarf planet Eris.
"The size of Pluto has been debated since its discovery in 1930. We are excited to finally lay this question to rest," said mission scientist Bill McKinnon, Washington University, St. Louis.
New Horizons also observed Nix and Hydra, two of Pluto's smaller moons. "We knew from the time we designed our flyby that we would only be able to study the small moons in detail for just a few days before closest approach," said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado. "Now, deep inside Pluto’s sphere of influence, that time has come."
Nix is estimated to be about 35 kilometers (20 miles) wide with Hydra at about 45 kilometers (30 miles) wide. The sizes of the two smallest moons of Pluto - Kerberos and Styx - will be measured during the flyby and available later.
NASA's New Horizons is now less than 1 million kilometers (620,000 miles) from Pluto. It will flyby the system on July 14 at 7:49 AM EDT and obtain the highest resolution images yet. I can't wait!