Tag: planets

Planetary scientists fight back: “Pluto is a planet!”

6:04 pm

A group of eminent and active planetary scientists have just published a new peer-reviewed paper documenting how moons and asteroids were routinely referred to as planets from Galileo until 2006 when a very small number of scientists at an International Astronomical Union (IAU) meeting decided arbitrarily that the definition must be changed.

That IAU definition, which required an object to have a solar orbit and the vague ability of the object to clear that orbit, somehow made Pluto a non-planet. It has also never been accepted by planetary scientists, who consider it inconsistent, vague, and useless in their research as well as in teaching students about planetary science. I know this attitude is real because of what planetary scientists have told me consistently in many interviews since 2006.

The new paper appears to be part of a new aggressive campaign by planetary scientists to get that IAU definition dumped, and replace it with the definition planetary scientists have been using forever, which is that if the object is large enough for gravity to shape it into a spherical shape, it is a planet. This is still the definition they routinely use when discussing large moons like the Moon or the large Galilean moons of Jupiter or the larger moons of Saturn or Pluto itself.

It also appears, based on information at the link, that this campaign is beginning to make headway. To that I say, Hallelajuh!

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Astronomer discovers newest farthest solar system object

8:16 am

Worlds without end: An astronomer leading a team looking for a large planet beyond Pluto has broken their own record and found a new solar system object that is the farthest known from the Sun.

That’s when he saw it, a faint object at a distance 140 times farther from the sun than Earth — the farthest solar system object yet known, some 3.5 times more distant than Pluto. The object, if confirmed, would break his team’s own discovery, announced in December, of a dwarf planet 120 times farther out than Earth, which they nicknamed “Farout.” For now, they are jokingly calling the new object “FarFarOut”. “This is hot off the presses,” he said during his rescheduled talk on 21 February.

I like the names for both.

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Science paper slams IAU planet definition

10:26 am

Worlds without end! A paper published August 29 in the science journal Icarus has hurled serious criticisms of the definition of planets imposed on the world by International Astronomical Union in 2006 that also robbed Pluto of planetary status.

“The IAU’s definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets,” said Dr. Kirby Runyon, from the Johns Hopkins University Applied Physics Laboratory. “We showed that this is a false historical claim. It is therefore fallacious to apply the same reasoning to Pluto.”

According to the team, the definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet’s orbit. “Dynamics are not constant, they are constantly changing. So, they are not the fundamental description of a body, they are just the occupation of a body at a current era,” Dr. Metzger said. “We recommend classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape.”

I must also note that the IAU’s definition had ignored the recommendations of its own committee on coming up with a new planetary definition and was voted on at the very end of a conference when almost everyone had left.

In other words, the IAU’s actions in 2006 were purely political, were bad science, and should be dumped as quickly as possible. And now the scientists are saying this, in peer-reviewed papers.

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Planetary scientists protest use of term “Planet Nine” for unknown planet

9:13 am

A group of planetary scientists have protested the recent use by some of the term “Planet Nine” for the unknown large planet some believe remains undiscovered in an orbit beyond Pluto.

“We the undersigned wish to remind our colleagues that the IAU planet definition adopted in 2006 has been controversial and is far from universally accepted. Given this, and given the incredible accomplishment of the discovery of Pluto, the harbinger of the solar system’s third zone — the Kuiper Belt — by planetary astronomer Clyde W. Tombaugh in 1930, we the undersigned believe the use of the term ‘Planet 9’ for objects beyond Pluto is insensitive to Professor Tombaugh’s legacy.

“We further believe the use of this term should be discontinued in favor of culturally and taxonomically neutral terms for such planets, such as Planet X, Planet Next or Giant Planet Five.”

The planetary scientist community, the people who really should be the ones to determine the proper definition of a planet, has never accepted the IAU planet definition. This protest letter is just more evidence of this fact.

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Pluto is a planet

9:51 am

In an op-ed today, the principal investigator for the New Horizons’ mission as well as his co-author for the history of that mission explained in detail why the definition for planet as imposed by the International Astronomical Union (IAU) is flawed and unworkable.

In 2006, the International Astronomical Union (IAU) announced an attempted redefinition of the word “planet” that excluded many objects, including Pluto. We think that decision was flawed, and that a logical and useful definition of planet will include many more worlds.

We find ourselves using the word planet to describe the largest “moons” in the solar system. Moon refers to the fact that they orbit around other worlds which themselves orbit our star, but when we discuss a world like Saturn’s Titan, which is larger than the planet Mercury, and has mountains, dunes and canyons, rivers, lakes and clouds, you will find us — in the literature and at our conferences — calling it a planet. This usage is not a mistake or a throwback. It is increasingly common in our profession and it is accurate.

Most essentially, planetary worlds (including planetary moons) are those large enough to have pulled themselves into a ball by the strength of their own gravity. Below a certain size, the strength of ice and rock is enough to resist rounding by gravity, and so the smallest worlds are lumpy. This is how, even before New Horizons arrives, we know that Ultima Thule is not a planet. Among the few facts we’ve been able to ascertain about this body is that it is tiny (just 17 miles across) and distinctly nonspherical. This gives us a natural, physical criterion to separate planets from all the small bodies orbiting in space — boulders, icy comets or rocky and metallic asteroids, all of which are small and lumpy because their gravity is too weak for self-rounding.

They go on to explain the flawed history of the IAU definition, and how it has simply not been accepted by astronomers and planetary scientists alike. The definition makes no sense, and excludes the thousands of exoplanets discovered orbiting other stars. They also point to a proposed new definition that is simple and admits to reality.

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.

Whether or not the stuffed shirts at IAU ever officially endorse this definition, it is the one that human beings are using now, and it will be the one they use into the never-ending future.

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Recent Kuiper Belt discoveries cast doubt a big planet exists there

9:03 am

The uncertainty of science: Despite predictions by some scientists that a big planet exists in the Kuiper Belt beyond Neptune, recent new discoveries of new objects there cast doubt on its existence.

If the additional big planet existed, the newly discovered objects would have shown some clustering, shepherded by its gravity.

“We find no evidence of the orbit clustering needed for the Planet Nine hypothesis in our fully independent survey,” says Cory Shankman, an astronomer at the University of Victoria in Canada and a member of the Outer Solar System Origins Survey (OSSOS), which since 2013 has found more than 800 objects out near Neptune using the Canada-France-Hawaii Telescope in Hawaii. In a paper posted to arXiv on 16 June and soon to be published in The Astronomical Journal, the OSSOS team describes eight of its most distant discoveries, including four of the type used to make the initial case for Planet Nine.

“I think it’s great work, and it’s exciting to keep finding these,” says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was among the first to suspect a large planet in the distant solar system. But he says three of the four new objects do have clustered orbits consistent with a Planet Nine. The fourth, an object called 2015 GT50, seems to skew the entire set of OSSOS worlds toward a random distribution. But that is not necessarily a knockout blow, he says. “We always expected that there would be some that don’t fit in.”

Note that I do not consider “Planet Nine” to be an accurate name for this theorized planet. Either it is #10, after Pluto, or one of a large number far more than nine, based on a new proposed and more logical planetary definition. The present definition however does not work.

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Scientists propose new planet definition that reinstates Pluto

6:03 pm

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.

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The planet debate continues

8:22 am

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.

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

5:33 pm

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.

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When is an Asteroid Not an Asteroid?

10:32 pm

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?

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A lean future for U.S. planetary missions

10:24 pm

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]

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