Tuesday, March 21, 2017

A Proposed Simpler Definition of Planet



On August 24th, 2006, The International Astronomical Union (IAU), which has the last word on all things astronomical, redefined the word “planet.” Technically, they gave the first actual definition of a planet. Prior to that, “planet,” Greek for “wanderer,” meant any celestial object whose position in the sky changed relative to the background stars. Humans knew of seven planets since long before written history: Mercury, Venus, Mars, Jupiter and Saturn, but also two other perhaps surprising planets, the sun and the moon. They, too, changed positions relative to the background stars. That’s not so much a definition as a description.

In more modern times, since the invention of the telescope, three other objects joined the ranks of planets: Uranus, Neptune, and Pluto, this last one added in 1930. That’s the way things stood until January 5, 2005. On that date, Cal Tech astronomer Mike Brown and his colleagues Chad Trujillo and David Rabinowitz discovered a Trans-Neptunian Object, TNO, they called Zena, but whose name would officially be changed to Eris. The rest of the world learned about Eris on July 29th that same year when the astronomers announced their discovery. TNO’s exist in the region of our solar system beyond Neptune, also called the Kuiper Belt, the realm of Pluto.

Early analysis indicated the Eris was about 10% larger than Pluto and thus, if Pluto deserves the moniker planet, Eris did, too. But Brown and his colleagues began finding other not-quite-so-large TNO’s in the Kuiper Belt and eventually decided that Pluto was just one among many objects roughly equal in size and so, their thinking went, represented a large class of similar objects that don’t fit with the other planets. Also, astronomers had begun to regularly discover plant-sized objects orbiting other stars, known as extra-solar planets. They didn’t wander in our skies, so astronomers needed a physical definition of planet.

Partly due to Brown’s team’s discovery of Eris, the IAU meeting in Prague, Czechoslovakia, two years later redefined the word planet. A resolution passed on the final day of the conference, after 3/4ths of the delegates had already left, created a new definition:

      A Planet:
  1. Is in orbit around the Sun but is not a satellite (moon) of another object,
  2. Has sufficient mass to assume hydrostatic equilibrium (shape is determined by gravity overcoming the rigidity of the body of the object), and
  3. Has "cleared the neighborhood" around its orbit.

Because Pluto orbited in the Kuiper Belt, it couldn’t satisfy provision #3. Pluto became the first of a new class of objects called Dwarf Planets, and Eris would be classified one as well. Almost immediate controversy followed the vote, particularly regarding the last point. Jupiter, the largest planet in the solar and indisputably a planet, has thousands of asteroids, known as Trojan asteroids, at the L4 and L5 points in its orbit around the sun. Even Earth has asteroids that are near to or cross its orbit. In a sense, no object in our solar system fits that part of the definition. Also, the clause that states “A planet is in orbit around the sun” excludes all the known extra-solar planets.

Speculation mounted that many of those voting didn’t want the number of planets to blow up to unreasonable numbers. Our solar system would suddenly contain dozens or hundreds of objects called planets, to the chagrin of some astronomers. Since then, several persons or groups have proposed new definitions of planet. None of the proposed counter-definitions include a “clear the neighborhood” clause.

Most start with a statement “In orbit around a star (not necessarily our sun).” Many proposals also add something to the effect that it can’t itself be a star, an object which sustains nuclear fusion. I believe that needs further clarification. A brown dwarf is a star-like object much larger than a planet and often called a failed star, and is large enough to have initiated limited fusion reactions. Our suns, as do virtually all stars in the sky, generate energy by fusing four hydrogen atoms to create one helium atom, neutrinos, and energy, essentially the same energy source tapped by a hydrogen nuclear bomb.

Prior to the initiation of this hydrogen fusion stage, also known as a star’s main sequence stage, all stars contain some limited amount of lithium. It’s considerably easier to fuse than hydrogen and most brown dwarfs spend a brief amount of time sporting lithium fusion. That process essentially demarcates brown dwarfs from large gas giant planets, like Jupiter. Brown dwarf is a in a classification distinct from stars and planets.

All planet definitions include the “hydrostatic equilibrium” clause, and many stop there. That would mean our and every other round or nearly round moon in our solar system becomes a planet. Along with the largest asteroids, that makes the total planet count in our solar system over 100. While I abhor making emotional statements like “That’s just too many planets” to become a part of a scientific definition, I think it muddies the planetary waters.

Some planet definitions include the “not a satellite (or natural moon) of another object,” but that also lacks precision. What makes something a satellite of another object? That lack of precision leads me to propose this definition of natural satellite: when two non-stellar objects co-orbit each other, if the barycenter (the center of mass) is within the body of the more massive one, the smaller one is a moon. The barycenter of the Earth-moon system is only 2,900 miles from the center of Earth, barely half way to Earth’s surface. Our moon is truly a moon.

Charon, the largest object orbiting Pluto is so massive, the barycenter of the Pluto-Charon, while close to Pluto, is in space between the two, making Pluto and Charon a double planet. No other Moon in our solar system meets that criteria.



So I propose this definition of “planet:”

     A planet:
  1. Is in orbit around a star (an object capable of supporting on-going fusion of hydrogen or heavier elements) or originally formed around a one,
  2. Is not itself a star, regular or brown dwarf,
  3. Is not a satellite (moon) of another object (see definition of moon),
  4. Has sufficient mass to assume hydrostatic equilibrium.

This definition brings Pluto back as a planet and adds Charon, Eris and all the currently recognized Dwarf Planets, of which there four others, and a few other asteroids. That definition also lets us unequivocally define the planet status of those 4000+ know extra-solar planets. The extra clause “or originally formed around a one” also allows us to also include the many millions of Rogue Planets that don’t orbit a star because they were gravitationally torn from their parent by the gravity of a close encounter with another star.

In order to makes the classification simpler, I propose we divide planets into types. Terrestrial planets include Mercury, Venus, Earth, and Mars, because they’re like Earth, mostly composed of rock and metals, and not frozen volatiles, although if too close to their star the rock/metal could be molten. Gas Giant planets, like Jupiter and Saturn are composed almost entirely of gasses. Although we usually group Uranus and Neptune in that category, they and extra-solar planets like them will be classed as Ice Giant planets, as their interiors include a large proportion of ices. Finally, those planets composed of mostly frozen volatiles, like Pluto and Ceres, will be classed as Ice Dwarf planets. Although in our solar system, the classification seems to follow the distance from the sun, that’s not necessarily true elsewhere. Our list of known extra-solar planets contains a large percentage of “hot Jupiters,” gas giant planets in close proximity to their parent star. It’s virtually impossible that they formed there, but due to their stellar system dynamics, they migrated inward towards their star. One of these categories should apply to all rogue planets, too, despite their orphan status.

Welcome back, Pluto.

Tuesday, January 17, 2017

Writing Children’s Picture Books



So you want to write a children’s picture book. Here are some things that might help you.

Think in pages. A typical picture book runs 24 story pages, although some publishers want or will accept 28 pages. Pages in a book are added in groups of four only, so don’t try to write a 26-page book. That will make life hard for a publisher and they don’t like writers who make life hard.

Shoot for 400-1000 words, the low end being for the youngest readers. Six to eight hundred is a happy medium for older picture book readers. “Where the Wild Things Are,” one of the best-known children’s books that also became a movie, had only 336 words. “Green Eggs and Ham” contains 641 words but it has a fantastic twist. Dr. Seuss, Theodore Geisel, had a bet with his publisher that he couldn’t write a complete, interesting story using only 50 unique words. He won that bet, and the book became one of the 5 most popular children’s picture books ever written.

If it sounds easy to write a 600-word story, think again.

With only 600 words in the story, each one must count. In an 80,000-word novel, you can get by some poorly chosen words. If, say, only 5% of your words are weak, the story contains 4000 bad words. Using that same metric, your 600-word book contains 30, and that breaks down to one or two per page. With each page containing on average 12-13 words, one weak or useless word stands out like a sore thumb.

Kids who read picture books take things literally and they want those stories to move along. Using passive verbs is the best way to kill that story movement. Passive verbs don’t show action. Here’s a list of passive verbs to avoid when possible: be, being, been, am, is, are, was, were, been, has, have, had, do, did, does, can, could, shall, should, will, would, might, must, may. Write and rewrite every sentence you create to avoid using them. It’s particularly weak writing to use the verb phrase ‘had + verb.’ Instead of writing “She had started to read the book” say “She read the book every chance she got.” Other words to avoid adverbs like seem(-s, -ed), really, just, very. In general, try to find active verbs that don’t require adverbs to describe them. All this is true of writing in any genre.

Whether you illustrate it yourself or not, and you won’t if you plan on submitting it to a traditional publisher because they’ll provide one who meets their preferred style, every single page needs to be uniquely illustratable. The story must create pictures that can be added and each illustration must be sufficiently different from all the others or the reader gets bored. The illustrator may not create the pictures you imagine. Mine usually don’t, but the readers likely won’t either, so the illustrator uses her own experience in creating the images like you did in stringing the words together.

As you contemplate writing a picture book, think action story, one that makes sense to the age you are writing for. The young reader must be able to identify with the main character and her problem must be one the reader can identify with, even if your main character is an animal or an inanimate object, although you better know what you’re doing to try and anthropomorphize, say, a bed. Kids love the rhythm and sound of a rhyming picture book story. But if you aren’t good at poetry, your book will sound and feel forced to the reader and, more importantly, to the editor. As a beginning picture book writer, write it out in narrative form, not poetry. You still want to think of stanzas, as in the words on each page, and rhythm, but don’t force rhymes.

My now 9-year-old daughter is my first reader, since my first picture book 5 years ago. If you can find a captive picture book reader, let them read it or read it to them. They’ll let you know if it’s any good.

These represent just a few of the basics of picture book writing. More to come in this space in the future.