<P> Determinations of Pluto's size had been complicated by its atmosphere, and hydrocarbon haze . In March 2014, Lellouch, de Bergh et al. published findings regarding methane mixing ratios in Pluto's atmosphere consistent with a Plutonian diameter greater than 2360 km, with a "best guess" of 2368 km . On July 13, 2015, images from NASA's New Horizons mission Long Range Reconnaissance Imager (LORRI), along with data from the other instruments, determined Pluto's diameter to be 2,370 km (1,470 mi), which was later revised to be 2,372 km (1,474 mi) on July 24, and later to 7006237400000000000 ♠ 2374 ± 8 km . Using radio occultation data from the New Horizons Radio Science Experiment (REX), the diameter was found to be 7006237660000000000 ♠ 2376. 6 ± 3.2 km . </P> <P> Pluto has a tenuous atmosphere consisting of nitrogen (N), methane (CH), and carbon monoxide (CO), which are in equilibrium with their ices on Pluto's surface . According to the measurements by New Horizons, the surface pressure is about 1 Pa (10 μbar), roughly one million to 100,000 times less than Earth's atmospheric pressure . It was initially thought that, as Pluto moves away from the Sun, its atmosphere should gradually freeze onto the surface; studies of New Horizons data and ground - based occultations show that Pluto's atmospheric density increases, and that it likely remains gaseous throughout Pluto's orbit . New Horizons observations showed that atmospheric escape of nitrogen to be 10,000 times less than expected . Alan Stern has contended that even a small increase in Pluto's surface temperature can lead to exponential increases in Pluto's atmospheric density; from 18 hPa to as much as 280 hPa (three times that of Mars to a quarter that of the Earth). At such densities, nitrogen could flow across the surface as liquid . Just like sweat cools the body as it evaporates from the skin, the sublimation of Pluto's atmosphere cools its surface . The presence of atmospheric gases was traced up to 1670 kilometers high; the atmosphere does not have a sharp upper boundary . </P> <P> The presence of methane, a powerful greenhouse gas, in Pluto's atmosphere creates a temperature inversion, with the average temperature of its atmosphere tens of degrees warmer than its surface, though observations by New Horizons have revealed Pluto's upper atmosphere to be far colder than expected (70 K, as opposed to about 100 K). Pluto's atmosphere is divided into roughly 20 regularly spaced haze layers up to 150 km high, thought to be the result of pressure waves created by airflow across Pluto's mountains . </P> <P> Pluto has five known natural satellites: Charon, first identified in 1978 by astronomer James Christy; Nix and Hydra, both discovered in 2005; Kerberos, discovered in 2011; and Styx, discovered in 2012 . The satellites' orbits are circular (eccentricity <0.006) and coplanar with Pluto's equator (inclination <1 °), and therefore tilted approximately 120 ° relative to Pluto's orbit . The Plutonian system is highly compact: the five known satellites orbit within the inner 3% of the region where prograde orbits would be stable . Closest to Pluto is Charon, which is large enough to be in hydrostatic equilibrium and to cause the barycenter of the Pluto--Charon system to be outside Pluto . Beyond Charon there are four much smaller circumbinary moons, Styx, Nix, Kerberos, and Hydra . </P>

How many miles is it from earth to pluto