THE HINDU Editorial Vocabulary - September 19, 2018 - Topic 2

Celestial misfit

After years of arguing over whether Pluto is a planet, in 2006 the International Astronomical Union (IAU) voted to remove Pluto’s planetary status. Now some researchers are challenging this decision, citing the manner in which scientific tradition has dealt with the taxonomy of planets. The IAU, in 2006, designated Pluto a ‘dwarf planet’ along with Ceres in the asteroid belt and Xena, an object in the Kuiper belt, which is an icy ring of frozen objects that circle the solar system beyond Neptune’s orbit. It was a bid to overcome sentiment and go by scientific rationale. 

The meeting defined three conditions for a celestial object to be called a planet: one, it must orbit the Sun; two, it should be massive enough to acquire an approximately spherical shape; three, it has to ‘clear its orbit’, that is, be the object that exerts the maximum gravitational pull within its orbit. Owing to this third property, if an object ventures close to a planet’s orbit, it will either collide with it and be accreted, or be ejected out. However, Pluto is affected by Neptune’s gravity. It also shares its orbit with the frozen objects in the Kuiper belt. Based on this, the IAU deemed that Pluto did not ‘clear its orbit’. Dwarf planets, on the other hand, need only satisfy the first two conditions.

This rationale has been questioned by Philip Metzger, a planetary physicist who has worked with the U.S. National Aeronautics and Space Administration, and others who have studied the history of classifying planets and come up with several exceptions to the third rule. In a paper published in the journal Icarus, they point out that the only work in history that used this rule to classify planets was an article by William Herschel in 1802. They also argue that this work was based on reasoning and observations that have since been disproved. However, the last argument does not build up a strong enough case to give up what is, in fact, a sensible rule. Physics has many examples where an idea was once discarded for being incorrect, and much later emerged in a different form and gained acceptance — the concept of photons, for instance. And then again, if Pluto were to be re-designated a planet, many more complications would arise. For one thing, Charon, Pluto’s moon, is much too large to be called a satellite. Judging by this, the Charon-Pluto system should then rightly be called a binary planet system. This would then lead to classifying several other sets of bodies as binary planets. Recent research shows that both the Kuiper Belt and the Oort cloud, a shell of objects that surrounds the entire solar system far beyond the Kuiper belt, contain objects that can then be called planets, thereby complicating the issue. Denying planetary status to Pluto is then nothing less than a sweep of Occam’s razor, and Pluto remains a dwarf planet, albeit an exceptional one.

Vocabulary

Tradition: the transmission of customs or beliefs from generation to generation, or the fact of being passed on in this way.

Example: Every shade of color is fixed by tradition and governed by religious laws

Synonyms: historical convention, unwritten law, mores, oral history

Rationale: a set of reasons or a logical basis for a course of action or a particular belief.

Example: He explained the rationale behind the change

Synonyms: reason(s), reasoning, thinking, logic, grounds, sense, principle, theory

Celestial: positioned in or relating to the sky, or outer space as observed in astronomy.

Example: A celestial body

Synonyms: space, heavenly, astronomical, extraterrestrial, stellar

Acquire: buy or obtain an object or asset for oneself.

Example: Instead, tax will become payable automatically 30 days after the date that the purchaser acquires the property or land.

Synonyms: obtain, come by, get, receive, gain, earn, win, come into, be given

Venture: dare to do something or go somewhere that may be dangerous or unpleasant.

Example: She ventured out into the blizzard

Synonyms: set out, go, travel, journey

Accrete: grow by accumulation or coalescence.

Example: Ice that had accreted grotesquely into stalactites

Deemed: regard or consider in a specified way.

Example: The event was deemed a great success

Synonyms: consider, regard as, judge, adjudge, hold to be, view as, see as

Exception: a person or thing that is excluded from a general statement or does not follow a rule.

Example: The drives between towns are a delight, and the journey to Graz is no exception

Synonyms: anomaly, irregularity, deviation, special case, isolated example

Complication: a circumstance that complicates something; a difficulty.

Example: There is a complication concerning ownership of the site

Synonyms: difficulty, problem, obstacle, hurdle, stumbling block, drawback