"Long before it's in the papers"
January 28, 2015


Protest over new planet definition

Sept. 5, 2006
Special to World Science  
Updated Sept. 6

More than 300 sci­en­tists have signed a pe­ti­tion protest­ing a new def­i­ni­tion of plan­et that an or­gan­i­za­tion of world as­tronomers adopt­ed last month. The pe­ti­tion­ers pledge not to use the de­fi­ni­tion. 

On Aug. 24, the In­ter­na­tion­al As­tro­nom­i­cal Un­ion Gen­er­al As­sem­bly in Prague passed a res­o­lu­tion redefining the plan­ets of our so­lar sys­tem. The new def­i­ni­tion ex­clud­ed dis­tant Plu­to, known as a plan­et since 1930.

But on­ly 428 of the IAU’s near­ly 10,000 mem­bers were in­volved in the vote, crit­ics of the move point out. Some as­tronomers al­so claim that the new def­i­ni­tion is as vague and con­fus­ing as old­er ones it was meant to clear up.

Crit­ics point out oth­er per­ceived flaws in the proc­ess. A pro­pos­al crafted over the past year by a spe­cial com­mit­tee of the or­gan­i­za­tion would have ex­pand­ed the num­ber of ob­jects des­ig­nat­ed as plan­ets in the so­lar sys­tem to 12, with the po­ten­tial for more. But at the meet­ing, that rec­om­men­da­tion was axed in fa­vor of new word­ing with­in days.

“Nei­ther def­i­ni­tion was sub­jected to crit­i­cal re­view by the broader plan­etary sci­ence com­mu­ni­ty pri­or to the as­sem­bly,” said a state­ment re­leased last week from the Cen­ter for Space Ex­plo­ra­tion Pol­i­cy Re­search in Boul­der, Col­o­rad­o, crit­i­cal of the move.

“A more open proc­ess” is needed, said Mark Sykes, di­rec­tor of the Plan­e­tar­y Sci­ence In­sti­tute in Tuc­son, Ariz., who started the pe­ti­tion. 

The pe­ti­tion states: “We, as plan­etary sci­en­tists and as­tronomers, do not agree with the IAU’s def­i­ni­tion of a plan­et, nor will we use it. A bet­ter def­i­ni­tion is need­ed.” The pe­ti­tion is on­line at www

The In­ter­na­tion­al As­tro­nom­i­cal Un­ion changed lead­ers at the time of the meet­ing where the vote took place. The in­com­ing pre­si­dent, Cath­er­ine Ce­sarsky, was al­so a mem­ber of the def­i­ni­tion com­mit­tee whose rec­om­men­da­tion was dropped. 

None­the­less, she de­fen­ded the de­ci­sion. She wrote in an e­mail that the group ri­go­rous­ly fol­lowed its own rules, which say that only mem­bers present can vote. They had a “healthy de­bate,” she added, then passed the re­de­fi­ni­tion and agreed on two re­la­ted re­so­lu­tions by wide ma­jo­ri­ties. The new word­ing al­so has broad support from many cor­ners in­clud­ing the Ame­ri­can As­tro­no­mi­cal So­cie­ty, she wrote. 

Out­go­ing pre­s­i­dent Ron Ek­ers wrote in an e­mail that the leadership “will take these comments seriously,” but there is no formal process to respond to a petition as resolutions of this kind are only considered at General Assemblies every three years.

* * *

Send us a comment on this story, or send it to a friend


Sign up for

On Home Page         


  • St­ar found to have lit­tle plan­ets over twice as old as our own

  • “Kind­ness curricu­lum” may bo­ost suc­cess in pre­schoolers


  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?


  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

More than 300 scientists have signed a petition protesting a new definition of planet that an organization of world astronomers adopted last month. On Aug. 24, a session of the International Astronomical Union General Assembly in Prague passed a resolution re-defining the planets of our solar system. The new definition excluded distant Pluto, known as a planet since 1930. But only 428 of the IAU’s nearly 10,000 members were involved in the vote, critics of the move point out. Some astronomers also claim that the new definition is as vague and confusing as older ones it was meant to clear up. Critics point out other perceived flaws in the process. A proposal crafted over the past year by a special committee of the organization would have expanded the number of objects designated as planets in the solar system to 12, with the potential for more. But at the meeting, that recommendation was axed and a new definition adopted within days. “Neither definition was subjected to critical review by the broader planetary science community prior to the assembly,” said a statement released last week from the Center for Space Exploration Policy Research in Boulder, Colorado, critical of the move. “A more open process” is needed, said Mark Sykes, director of the Planetary Science Institute in Tucson, Az, who started the petition. The International Astronomical Union changed leaders at the time of the meeting where the vote took place. Neither the outgoing president, Ron Ekers, nor the incoming one, Catherine Cesarsky, responded immediately to emails seeking comment. Cesarsky was also a member of the special planet definition committee whose recommendation was dropped. The petition states: “We, as planetary scientists and astronomers, do not agree with the IAU’s definition of a planet, nor will we use it. A better definition is needed.” The petition is online at http://www.ipetitions.com/petition/planetprotest.