The Dwarf Planet is officially the Largest in Solar System

This image shows an artist impression of the Dwarf Planet Eris.

Since Eris is larger than the Dwarf Planet Pluto, it is presented as the tenth planet.

However, a long-lasting debate over the status of Pluto forced the International Astronomical Union (IAU) to develop a precise definition of the term planet. 

On August 24, 2006, the IAU adopted a resolution, under which both Pluto and Eris were classified as "dwarf planets" and subsequently added to the Minor Planet Catalogue.

Our universe is full of mysteries but there are a few things we know for certain.

For instance, that the Earth orbits the Sun and not vice versa, or that there are eight planets in the solar system. If you still believe in the latter, you probably have not heard of Eris.

This is an image of the dwarf planet Eris (center) and its companion satellite Dysnomia (at 9 o'clock position) taken with NASA's Hubble Space Telescope on Aug. 30, 2006. Hubble observations were obtained on Dec. 3, 2005 and Aug. 30, 2006 using the Advanced Camera for Surveys.

Credit: Hubblesite

Eris is the largest dwarf planet discovered in 2005 using the Hubble Telescope and was initially described by NASA as the Solar System's tenth planet.

Eris is 27% larger than Pluto, has a diameter of 2.3 kilometers and one companion satellite (moon) called Dysnomia.

The planet orbits the sun at a distance of 96.4 astronomical units, taking 557 years to complete one lap.

Whilst it sounds like a fully-fledged planet, the word 'dwarf' tends to instill confusion. Eris is what astronomers call a plutoid; a trans-Neptunian object located in the part of the solar system known as the Kuiper belt.

A dwarf planet is now officially defined as a "celestial body in direct orbit of the Sun that is massive enough for its shape to be controlled by gravity, but that unlike a planet has not cleared its orbit of other objects."

The number of known planets in the solar system was therefore reduced to eight, as it was before Pluto's discovery in 1930.

With the new status Eris was granted its present name. Previously, the newly discovered space object was informally called Xena after a character from the popular television series Xena: Warrior Princess, but given the discord it caused in the astronomical community, the name of the Greek goddess Eris, a personification of strife, suits this planet like no other.

Mars name-a-crater scheme runs into trouble: IAU Stops sales

This NASA handout image released February 5, 2014 shows a dramatic, fresh impact crater, captured by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter on November 19, 2013

The world's paramount astronomical authority on Tuesday slapped down a bid to hawk the names of Mars' craters, saying the Red Planet's monickers are not up for sale.

"Such initiatives go against the spirit of free and equal access to space, as well as against internationally recognised standards," the Paris-based International Astronomical Union (IAU) said in a press release.

"Hence no purchased names can ever be used on official maps and globes."

IAU spokesman Lars Lindberg Christensen told reporters the move came after US crowdsourcing website Uwingu said the public could name craters on its map of Mars for a fee.

Founded in 1919, the IAU holds the official mission of naming all planets, satellites, comets and asteroids in the Solar System.

The topographical features of Mars, named after the Roman god of war, for instance, carry Latin names like "mons" for mountain and "planitia" for plain.

In half a century, the union has named only a thousand of the estimated half-a-million craters on Mars, each decided in a cautious vetting process.

Large craters wider than 60 kilometres (37.5 miles) have been named after deceased scientists, explorers and writers who have added to Martian lore.

Smaller ones carry the names of Earthly cities with populations of fewer than 100,000.

Name game
Uwingu said the money generated through its scheme, launched two weeks ago, will be used as "grants for space researchers, educators, and entrepreneurs in this time of government cutbacks".

Prices range from $5 to (3.6 euros) to $5,000, depending on the size of the crater, and the website lists a $10-million goal for 2014.

Those who purchase a name will have it listed on Uwingu's database, which also includes monickers already given by the IAU. The purchase only gives rights to the entry in the database, not to the crater itself.

"Once you've completed the checkout process, your name is accepted," says the website.

"And unless it's later found to be profane, pejorative, or otherwise offensive (in which case it'll be removed), it'll remain approved."

In an article posted Monday on the specialist website The Space Review, Uwingu's founders, planetary scientists Alan Stern and Mark Sykes, said 7,000 craters had been named by people in 78 countries in 10 days.

The IAU said the public can get involved in naming when a space agency or the discoverer of a new feature or object asks for ideas.

"This was the case for NASA's Magellan Venus mapping mission launched in 1989: the public was invited to offer names of women who had made outstanding or fundamental contributions to their fields, for the names of Venusian craters," it said.

"A more recent example was the naming of the two most recently discovered satellites of Pluto in 2013, which was the result of a public vote."

The moons were named after a many-headed guard dog, Kerberos, and an underworld goddess, Styx, in Greek mythology.

NASA Messenger: Mercury impact crater was named after John Lennon

This Mercury impact crater was named after John Lennon.

Credit: NASA/USGS

Beatles legend John Lennon, "Breakfast at Tiffany's" author Truman Capote and sculptor Alexander Calder are among the 10 artists and writers now immortalized on Mercury with impact craters bearing their names.

The International Astronomical Union (IAU), the global authority for all planetary and satellite nomenclature, approved the new monikers this week.

The names were proposed by the science team for NASA's Messenger spacecraft, which has beamed back hundreds of pictures of Mercury from its orbit around the tiny planet.

According to the IAU's naming rules, craters on Mercury can only be named after creative types, or more specifically, "deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field and have been recognized as art historically significant figures for more than 50 years."

The IAU has been arbitrating cosmic names since 1919 and it has strict guidelines for different celestial bodies and planetary features.


Pluto's satellites, for example, must be named after mythological deities associated with the underworld (thus, Styx and Kerberos).

Moons of Jupiter, meanwhile, are named for Jupiter's lovers and descendants (such as Europa and Io).

Messenger — which stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging — launched in 2004 and arrived in orbit around Mercury in March 2011.

The spacecraft completed its first flyby of our solar system's smallest planet in January 2008, and since then, more than 100 craters on Mercury have been named.

"The Messenger team is delighted that the IAU has named an additional 10 impact craters on Mercury," the mission's principal investigator, Sean Solomon of Columbia University, said in a statement.

"We are particularly pleased that eight of the 10 individuals honored made all or many of their artistic contributions in the Twentieth Century, the same century in which the Messenger mission was conceived, proposed, and approved for flight."