How Big Is Pluto? New Horizons Settles Decades-Long Debate

Pluto and its moon Charon (brought nearer together, but sizes kept same) Credit: NASA With less than 24 hours to go before closest approach, NASA’s New Horizons spacecraft is seeing Pluto at a level of detail that grows sharper literally by the minute — not surprising when you consider that it is closing in on its target at nearly 31,000 miles per hour. Late Monday morning, members of the mission science team held a news briefing at the Johns Hopkins University Applies Physics Lab in Laurel, Maryland, site of mission operations. Principal Investigator Alan Stern broke some major discoveries from the past few days. Perhaps most importantly, the science team has refined Pluto’s radius to 736 miles (plus or minus 6 miles). This is on the high end of previous estimates and, when combined with the ice dwarf planet’s known mass, implies a lower density than thought and thus a ...