The debate surrounding Pluto’s size has finally been settled, according to brand new results returned by NASA’s New Horizons spacecraft.
Pluto has been found to be about 2.370 kilometres (1,473 miles) in diameter, making it somewhat larger than previous estimates of the dwarf planet. Images taken by the Long Range Reconnaissance Imager (LORRI), confirms what astronomers already suspected: the dwarf planet is larger than all other known Solar System objects beyond the orbit of ice giant Neptune. “The size of Pluto has been debated since its discovery in 1930,” says Bill McKinnon, a New Horizons mission scientist. “We are excited to finally lay this question to rest.”
A new estimate of Pluto’s size means that the dwarf planet’s density is slightly lower than previously thought and the fraction of ice found in its interior is higher. The atmosphere that encompasses the world is also shallower than initially thought.
It’s because of Pluto’s atmosphere that astronomers have been unable to get a better idea of the dwarf planet’s size. Its largest moon Charon, on the other hand, doesn’t have a substantial atmosphere – that means that we’ve been able to determine just how big it is with relative ease using ground-based telescopes on Earth. Observations from New Horizons confirm previous estimates of 1208 kilometres (751 miles).
The spacecraft’s LORRI has also managed to zoom in on two of Pluto’s smaller moons, Nix and Hydra. Additionally it’s hoped that New Horizons will give us a better look at its other known moons Kerberos and Styx during the imminent flyby – but the spacecraft will have to be quick. “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,” says 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.”
Think you know everything about New Horizons? Watch our video for five amazing facts about the spacecraft.