Scientists make the case to restore Pluto's planet status
Johns Hopkins University scientist Kirby Runyon wants to make one thing clear: Regardless of what one prestigious scientific organization says to the contrary, Pluto is a planet.
|The Long Range Reconnaissance Imager aboard NASA's New Horizons spacecraft captured this photo |
of Pluto's surface in 2015 [Credit: NASA/JHUAPL/Southwest Research Institute]
The definition approved by the International Astronomical Union in 2006 demoted Pluto to "non-planet," thus dropping the consensus number of planets in our solar system from nine to eight. The change -- a subject of much scientific debate at the time and since -- made no sense, says Runyon, lead author of a short paper making the pro-Pluto argument that will be presented next week at a scientific conference in Texas.
Icy, rocky Pluto had been the smallest of the nine planets, its diameter under three-quarters that of the moon and nearly a fifth of Earth. Still, says, Runyon, who is finishing his doctorate this spring in the Department of Earth and Planetary Sciences, Pluto "has everything going on on its surface that you associate with a planet. ... There's nothing non-planet about it."
The other authors are S. Alan Stern and Kelsi Singer of the Southwest Research Institute in Boulder, Colorado; Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona; Will Grundy of the Lowell Observatory in Flagstaff, Arizona; Michael Summers of George Mason University in Fairfax, Virginia. All the authors are science team members on the New Horizons mission to Pluto, operated for NASA by the Johns Hopkins University Applied Physics Laboratory. In the summer of 2015, the New Horizons spacecraft became the first to fly by Pluto, some 4.67 billion miles from Earth, passing within 8,000 miles and sending back the first close-up images ever made of Pluto.
Runyon and his co-authors argue for a definition of "planet" that focuses on the intrinsic qualities of the body itself, rather than external factors such as its orbit or other objects around it. They define a planet as "a sub-stellar mass body that has never undergone nuclear fusion" and that has enough gravitational heft to maintain a roughly round shape. (Even if it bulges at the equator because of a three-way squeeze of forces created by its own gravity and the influence of both a star and a nearby larger planet.)
|In the center left of Pluto’s vast heart-shaped feature lies a vast, craterless plain that appears to be no more|
than 100 million years old and is possibly still being shaped by geologic processes
[Credit: NASA/JHUAPL/SOUTHWEST RESEARCH INSTITUTE]
Stern, the principal investigator for the New Horizons mission, has argued in the past that the IAU definition also excludes Earth, Mars, Jupiter and Neptune, which share their orbits with asteroids.
The proposed new geophysical definition omits stars, black holes, asteroids and meteorites, but includes much of everything else in our solar system. It would expand the number of planets from eight to approximately 110.
The new definition, which does not require approval from a central governing body, is also more useful to planetary scientists. Most of them are closely affiliated with geology and other geosciences, thus making the new geophysical definition more useful than the IAU's astronomical definition.
He has some reason to be optimistic, as the new definition has already been adopted by Planet Science Research Discoveries, an educational website founded by scientists at the University of Hawaii.
"I want the public to fall in love with planetary exploration as I have," Runyon said. "It drives home the point of continued exploration."
Author: Arthur Hirsch | Source: Johns Hopkins University [March 17, 2017]