Pluto could be set to regain its planetary status after 11 years in exile, if NASAscientists have their way.
A new definition of planets would add over 100 to our solar system, with even Earth’s moon due a promotion.
The International Astronomical Union (IAU) currently requires an object to be orbiting the Sun to be classified as a planet.
But the NASA team wants the IAU to drop that requirement, insisting that a world’s physical properties are more important than their interactions with stars.
“In keeping with both sound scientific classification and peoples’ intuition, we propose a geophysically-based definition of ‘planet’ that importantly emphasises a body’s intrinsic physical properties over its extrinsic orbital properties,” the researchers explain.
The proposal was made by a team of NASA scientists led by Alan Stern, principle investigator of the space agency’s New Horizons mission to Pluto.
Stern’s team suggests a new definition:
“A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.”
That might sound pretty broad, but it rules out a number of celestial objects, including white dwarfs, neutron stars and black holes.
Stern has previously spoken out about the IAU’s decision to demote Pluto to a dwarf planet in August 2006.
The decision was made after astronomer Mike Brown from the California Institute of Technology proposed a new definition of planets which required such worlds to clear the neighbourhood around their orbit.
Pluto fell foul of this rule.
In an interview with Business Insider in 2015, Stern said the move was “bullshit”.
“Why would you listen to an astronomer about a planet,” Stern, a planetary scientist, asked.
Astronomers focus on a wide variety of celestial objects and cosmic phenomena, while planetary scientists specialises in planets, moons and planetary system.
Stern compared asking the advice of an astronomer over a planetary scientist was like going to a podiatrist for brain surgery.
“Even though they’re both doctors, they have different expertise,” Stern said. “You really should listen to planetary scientists that know something about this subject. When we look at an object like Pluto, we don’t know what else to call it.”
Under the new definition, our moon, and other moons such as Titan, Enceladus, Europa and Ganymede would all be promoted to planetary status.
The proposal is at least partly motivated by the public’s perception of the importance of non-planetary worlds within our solar system.
The researchers write: “A common question we receive is, ‘Why did you send New Horizons to Pluto if it’s not a planet anymore?’”
There’s no guarantee the IAU will accept the new definition, and even if they do, it’s set to be some time before it becomes official.
Quelle: HUFFPOST TECH
It's been more than ten years since Pluto was cruelly stripped of its planetary status but the decision could be reversed if a group of scientists get their way.
Alan Stern, the head of Nasa's New Horizons mission to Pluto, and a host of other scientists from the space agency and universities have proposed a new definition for a planet. If it is adopted the change would make Pluto and another 109 objects in our solar system official planets.
Based on their studies, the team has created the following definition of what a planet is and published it in a short, easily digestible, paper.
"A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters," the proposed definition reads.
The team argues it is possible to make the definition simple enough for young children to understand. As part of this, the planetary scientists say it can be shortened to: "round objects in space that are smaller than stars."
"With the above definition of a planet, we count at least 110 known planets in our Solar System," Stern and colleagues write in the paper, which concludes by saying discussions with members of the public have shown there is support for a new definition.
However, for a 110 planet solar system to become official, the definition would have to be approved by the International Astronomical Union. The body, which was formed in 1919, is responsible for organising international space conferences and "the definition of fundamental astronomical and physical constants".
In 2006, it was the IAU that changed the definition of a planet and excluded Pluto from the list of eight known planets. Resolution 5A was revealed at the IAU's conference in 2006, and gave the following definition of a planet in our Solar System.
"A 'planet'  is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit."
The current definition means Pluto is currently known as a dwarf planet. WIRED has contacted the IAU asking whether the new proposal for a definition will be looked at by its researchers.
In the new paper, which the scientists plan to put forward to the IAU, the current definition is described as "technically flawed" - it only recognises planets as objects that are orbiting our Sun and not other stars. It also says the need for zone-clearing means "no planet in our Solar System" meets the criteria for planets.
The authors argue the new definition is "geophysical" and based on the physics of the world itself.
"Understanding the natural organisation of the Solar System is much more informative than rote memorisation," they explain.
When Stern was challenged on what a 110-planet Solar System would mean for children trying to memorise the planets, he said it was an outdated approach. "So 20th century," he said on Twitter.
"Do you have mnemonics for the names of all the stars or asteroids? Rivers/ Mountains? Course not."