That which we call a planet

Tetsunori Koizumi, Director

July 14, 2015 will probably go down in the history of space exploration as the “encounter day”, the day a man-made spacecraft came closest to Pluto. At 7:50 am EDT, the New Horizons spacecraft launched by NASA from Cape Canaveral on January 19, 2006 came within 7,800 miles of Pluto’s surface as it flew past at the speed exceeding 30,000 mph. The day is a triumphant day for Alan Stern (1967- ), a planetary scientist and an aeronautic engineer, who has been pushing for a NASA mission to Pluto for nearly 25 years, recruiting scientists, senators, and even children to lobby the Congress for funding the mission.1

At three billion miles from the Sun, Pluto is invisible to the naked eye, and was not discovered until 1930. The honor of naming Pluto, for the Roman god of underworld, goes to Venetia Burney, an 11-year old British girl, who suggested this name while she was discussing the discovery with her grandfather. The name was unanimously adopted by the staff at the Lowell Observatory, named after Percival Lowell (1855-1916) who had started searching for what he called “Planet X” as early as 1905 whose existence was finally confirmed by Clyde Tombaugh (1906-1997) in February 1930.

Planetary scientists now know that Pluto is but one of many small frozen bodies at the far edge of the solar system circling around the Sun. With the discovery of so many similar objects in the Kuiper Belt—Quaoar, Haumea, Eris, and others—where Pluto is located, it became increasingly problematic to maintain that Pluto is a planet. With the size of only 1,430 miles across (found to be 1,473 miles across by the New Horizons spacecraft), it is clear that Pluto does not come close to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune whose status as planets is well recognized. At a meeting held in Prague in August 2006, the General Assembly of the International Astronomical Union (IAU), which is responsible for naming and classifying celestial objects, decided to adopt the name of “dwarf planets” for a class of objects similar in size as Pluto. The decision to demote Pluto’s status from a planet to a dwarf planet was a bitterly disappointing one for Alan Stern, for dwarf planets are a different category of celestial objects from planets. One of the arguments IAU scientists used against calling Pluto a planet was that increasing the number of planets in the solar system to 20 or more beyond the eight universally recognized ones would be inconvenient. Indeed, we are tempted to paraphrase Juliet’s words to infer what Alan Stern must have felt: “What’s in a name? that which we call a planet by any other name would look as planetary”.2

The controversy surrounding the naming and categorizing of a celestial object like Pluto reminds us of the importance we humans attach to our activity of naming and categorizing things in the world around us. To give a thing a name is important because having a name already suggests that we know something about that thing, for a name captures some property of a thing, be it its color, shape, or constituent substances. For scientists, naming a thing comes with the honor of having his/her name attached to it, as in Halley’s comet, Comet Hale-Bopp, and the Doppler effect. In some cases, it takes the poet’s imagination to give a name to a thing, as Shakespeare writes in his Midsummer Night’s Dream:

“The poet’s eye, in a fine frenzy rolling,/ Doth glance from heaven to earth, from earth to heaven;/ And, as imagination bodies forth/ The forms of things unknown, the poet’s pen/ Turns them to shapes, and gives to airy nothing/ A local habitation and a name.”

The world where a thing has “a local habitation and a name” is, according to Buddhist thought, the world of conventional reality, or the world of “name and form”. A thing, which always appears as a composite entity called sankhara, or “that which has been put together”, is given a name for its form to distinguish it from other things. But a form, being subject to the laws of impermanence and non-self, comes and goes without any entity that can be called its own self. “Form is nothing other than emptiness, emptiness is nothing other than form. Form is but emptiness, emptiness is but form.” These lines are well known to Buddhist practitioners as they appear in the short yet profound sutra known as the Prajnaparamita, or the Heart Sutra. It reminds us of the illusionary nature of things in the world of conventional reality, behind which lies the world of ultimate reality, or the world of “airy nothing” in Shakespeare’s words, accessible only to the insight of an enlightened Buddha or a poet like Shakespeare. Since the world of conventional reality is the observable world for the rest of us, the debate about what name to give to a distant celestial object will continue as scientists keep pushing out the boundary of the observable universe we inhabit. As for Pluto, it will continue to have “a local habitation and a name” until a sankhara in the universe, that which we call the solar system, is reduced to “airy nothing”, when the Sun runs out of its energy and collapses itself to a dwarf. By that time, no scientists will be around to debate whether a dwarf planet is a planet or not.

  1. For details about Stern’s involvement in the New Horizon mission and his passion for Pluto, see Lemonick, Michael, “Plutonic Love”, Smithsonian, June 2015.
  2. “What’s in a name? that which we call a rose by any other name would smell as sweet”, Shakespeare, The Tragedy of Romeo and Juliet, Act II, Scene II.