New Horizons delivers the exact size of Pluto as it approaches. The small planet is not so small afterall.
NASA has new information from New Horizons as it approaches Pluto. The closest distance will be reached tomorrow on July 14. Today NASA can reveal the size of Pluto and its larger than thought. New Horizons settles a dispute that goes back to 1930.
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Mission scientists have found Pluto to be 1,473 miles (2,370 kilometers) in diameter, somewhat larger than many prior estimates. Images acquired with the Long Range Reconnaissance Imager (LORRI) were used to make this determination. This result confirms what was already suspected: Pluto is larger than all other known solar system objects beyond the orbit of Neptune.
“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.
Pluto’s newly estimated size means that its density is slightly lower than previously thought, and the fraction of ice in its interior is slightly higher. Also, the lowest layer of Pluto’s atmosphere, called the troposphere, is shallower than previously believed.
Measuring Pluto’s size has been a decades-long challenge due to complicating factors from its atmosphere. Its largest moon Charon lacks a substantial atmosphere, and its diameter was easier to determine using ground-based telescopes. New Horizons observations of Charon confirm previous estimates of 751 miles (1208 km) kilometers) across
LORRI has also zoomed in on two of Pluto’s smaller moons, Nix and Hydra.
“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 and Hydra were discovered using the Hubble Space Telescope in 2005. Even to Hubble, they appeared as points of light, and that’s how they looked to New Horizons until the final week of its approach to Pluto. Now, the latest LORRI images show the two diminutive satellites not as pinpoints, but as moons seen well enough to measure their sizes. Nix is estimated to be about 20 miles (about 35 kilometers) across, while Hydra is roughly 30 miles (roughly 45 kilometers) across. These sizes lead mission scientists to conclude that their surfaces are quite bright, possibly due to the presence of ice.
What about Pluto’s two smallest moons, Kerberos and Styx? Smaller and fainter than Nix and Hydra, they are harder to measure. Mission scientists should be able to determine their sizes with observations New Horizons will make during the flyby and will transmit to Earth at a later date.
Knowledge for Geeks
It is getting exciting for NASA's Pluto flyby mission team. After a more than nine-year, three-billion-mile journey to Pluto, the New Horizons spacecraft will at the closest distance on July 14 at 7:49:57 am EDT. New Horizons will be approximately 7,800 miles (12,500 kilometers) above the surface at this time.
NASA has started daily briefings about the final approach to Pluto on NASA TV airing daily now at 11:30am EDT until July 14. On July 14 the Pluto Countdown Program will air from 7:30am to 8am. The images of the Pluto Flyby will be released on Wednesday July 15 at 3 to 4pm.
To get educated on Pluto watch NASA's Pluto in a minute video series below.
New Horizons is an interplanetary space probe that was launched as part of NASA's New Frontiers program. Built by the Applied Physics Laboratory and the Southwest Research Institute, with a team led by S. Alan Stern, the spacecraft was launched to study Pluto, its moons and the Kuiper Belt, performing flybys of the Pluto system and one or more Kuiper Belt Objects (KBOs). The goal of the mission is to understand the formation of the Pluto system, the Kuiper Belt, and the transformation of the early Solar System.
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The spacecraft will study the atmospheres, surfaces, interiors and environments of Pluto and its moons. It will also study other objects in the Kuiper Belt. Find more on the historic space mission background on Wikipedia and on the New Horizons Mission page on NASA.