Tag Archives: planets

Scientists propose new planet definition that reinstates Pluto

Unhappy since 2006 with the definition of “planet” imposed by the International Astronomical Union (IAU) that demoted Pluto, planetary scientists, including New Horizons principal investigator Alan Stern, have now proposed a new definition that they think is more appropriate and would reinstate Pluto.

The scientists suggest planets should constitute as “round objects in space that are smaller than stars,” thus excluding white dwarfs, neutron stars, and black holes from the planetary status. “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 proposal elaborates, noting that the Earth’s moon would constitute as a planet under the new definition.

Stern and his colleagues note that the IAU’s definition of a planet is too narrow and recognizes planets only as objects that orbit our sun and “requires zone clearing, which no planet in our solar system can satisfy since new small bodies are constantly injected into planet-crossing orbits.”

Make sense to me as well as a lot of people. The definition created in 2006 was never very satisfactory, and I know many planetary scientists who have never accepted it.

The planet debate continues

In a public debate about the scientific definition of a planet, the IAU’s definition, imposed about eight years ago to expressly prevent Pluto from being called one, was soundly defeated when the votes were counted.

Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, presented the historical viewpoint. Dr. Gareth Williams, associate director of the Minor Planet Center, presented the IAU’s viewpoint [which is the definition that is presently considered official by scientific bureaucrats]. And Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, presented the exoplanet scientist’s viewpoint.

Gingerich argued that “a planet is a culturally defined word that changes over time,” and that Pluto is a planet. Williams defended the IAU definition, which declares that Pluto is not a planet. And Sasselov defined a planet as “the smallest spherical lump of matter that formed around stars or stellar remnants,” which means Pluto is a planet.

After these experts made their best case, the audience got to vote on what a planet is or isn’t and whether Pluto is in or out. The results are in, with no hanging chads in sight.

According to the audience, Sasselov’s definition won the day, and Pluto IS a planet.

Notice that two of the three debaters considered Pluto a planet even before the vote was taken. Notice also that the first debater, Gingerich, was on the very committee that the IAU had created to come up with a definition and then ignored completely when its definition decided that Pluto was a planet.

In the end, it will be the people who speak the language that will decide, not IAU bureaucrats. This little public relations event and vote tells me that the bureaucrats will lose.

Astronomers have found what they believe is the first evidence of a planet consumed by its star as the star expanded and aged.

Astronomers have found what they believe is the first evidence of a planet consumed by its star as the star expanded and aged.

Sadly, for those of you out there who like the idea of watching planets getting destroyed, the event happened a long time ago, and all the astronomers have is circumstantial evidence that is most likely explained by such an event.

When is an Asteroid Not an Asteroid?

When is an asteroid not an asteroid?

The layered structure of Vesta (core, mantle and crust) is the key trait that makes Vesta more like planets such as Earth, Venus and Mars than the other asteroids, McCord said. Like the planets, Vesta had sufficient radioactive material inside when it coalesced, releasing heat that melted rock and enabled lighter layers to float to the outside. Scientists call this process differentiation.

This question immediately demonstrates once again the terrible mess the International Astronautical Union made when it decided several years ago to define what makes a planet, and came up with a definition that simply doesn’t work. For if Vesta should be considered a planet, why not Pluto?

A lean future for U.S. planetary missions

Planetary scientists make their recommendations for the kinds of planetary missions they think the United States should do for the next decade. And it looks like a lean future, as the scientists also note that their primary recommendations, missions to Mars and Europa, should only be built if their budgets can be trimmed significantly:

NASA’s top priority, according to the survey’s recommendations, should be the Mars Astrobiology Explorer Cacher, or MAX-C, which could help determine whether Mars ever supported life and offer insight on its geologic and climate history. It would also be the first step in an effort to get samples from Mars back to Earth. However, the report said this mission should only be undertaken if NASA’s cost is about $2.5 billion, which is $1 billion less than independent estimates provided to the panel. The mission would be run jointly by NASA and the European Space Agency, according to the survey.

A mission to Europa and its subsurface ocean — which might support life — should be the second priority mission, the experts said. But its estimated price tag of $4.7 billion may make it too expensive without an increase in NASA’s planetary science budget or a paring of the mission’s costs. [emphasis mine]