Who gets to name the plethora of planets being discovered outside our solar system? Two groups of astronomers are engaged in a heated public argument about whose extraterrestrial turf that responsibility is.

In recent years, hundreds of planets have been confirmed outside our solar system. Most newly discovered ones get a scientific name that includes the star they orbit and some letters or numbers. In many case, the name appears as a string of letters and numbers such as KOI-172 or HD 85512 b.

Uwingu, a non-profit company that raises money for space research and education, launched a contest on March 19 to give a popular name to Alpha Centauri Bb, the closest planet ever discovered outside our solar system, at just about four light years away.

Participants can suggest a name for $4.99 and vote on the existing nominations for $0.99, and nominators will be eligible for prizes if their name gets at least 100 votes.

The person who suggests the name with the most votes will receive a commemorative plaque from Uwingu, which is named after the Swahili word for "sky" and is run by a group of planetary scientists and science educators.

The contest is raising money for a fund for space education projects for which the organization expects to start accepting grant applications later this year. Uwingu says the contest has been endorsed by Xavier Dumusque, the planetary scientist who discovered the Alpha Centauri Bb.

However, on Friday, the International Astronomical Union, an organization that organizes scientific meetings for professional astronomers around the world, issued a news release with the headline: "Can one buy the right to name a planet?"

"In the light of recent events, where the possibility of buying the rights to name exoplanets has been advertised, the International Astronomical Union (IAU) wishes to inform the public that such schemes have no bearing on the official naming process," the release said.

Validity, credibility questioned by IAU

The release did not name Uwingu, but mentioned the fact that the public had been invited to "purchase both nomination proposals for exoplanets, and the right to vote for the suggested names" in return for a "certificate commemorating the validity and credibility of the nomination."

It said such certificates would be "misleading" as they will not lead to an "officially recognized" name.

The IAU added that it acts as the "single arbiter" of the process of naming exoplanets and other astronomical objects, as it must be clear and systematic, and any naming system is "a scientific issue."

"As an international scientific organization, it dissociates itself entirely from the commercial practice of selling names of planets, stars or even 'real estate' on other planets or moons," the release said. "These practices will not be recognized by the IAU and their alternative naming schemes cannot be adopted."

Reputation damaged, Uwingu says

Uwingu CEO Alan Stern, a planetary scientist who is a former associate administrator for NASA's science mission directorate and an IAU member, told the space news website Space.com that the IAU wrongly implied that Uwingu was "conducting a scam." He added, "They basically put us out of business, and they've ruined our reputation."

Uwingu shot back at the IAU in its own release Monday, saying the group "significantly mis-characterized" the contest and Uwingu itself.

It added that the IAU "has no purview — informal or official — to control popular naming of bodies in the sky or features on them."

It added that informal names for astronomical objects, such as our Milky Way galaxy, are common; many objects such as the North Star (also known as Alpha Ursa minori, Polaris and HD8890) have multiple names;  and many astronomical features and objects have been given names by astronomers without an IAU process.

Uwingu's contest was supposed to close on April 15, but following the IAU's news release,  the organization announced it had decided to extend the deadline to April 22.

Stern told CBCNews.ca in an email Monday that while the IAU's statements initially hurt Uwingu, many people sprang to the group's defence over the weekend, including senior astronomers who have written to the IAU in protest. The contest was doing much better Monday, he added. "So in the end, this may end up being very positive for us."

As of Monday afternoon, the contest had received more than 1,200 nominations and more than 4,000 votes. 

The most popular name at the time was Rakhat, a planet from Mary Doria Russell's science fiction novel The Sparrow.