Makemake

• 1. Introduction

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  Makemake is a dwarf planet drifting in the frozen outer reaches of the Solar System, so far from Earth that even the most powerful telescopes see it only as a pinprick of light. That light, however, hints at something extraordinary. Makemake's surface shines with an albedo of 82 percent, brighter than Pluto, blanketed in freshly deposited methane ice and stained reddish-brown by strange organic compounds called tholins. Beneath that glittering crust, something may be stirring. Scientists suspect a liquid ocean, active geochemistry, and volcanic eruptions of ice. How did a world this remote end up so geologically alive? And how did its discovery in 2005 help reclassify one of the most famous objects in the solar system? Those questions will carry us from Palomar Observatory to the edge of the known Solar System.

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• 2. The Discovery Scramble

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  On the 31st of March 2005, the 1.22 m Samuel Oschin telescope at Palomar Observatory in California captured the images that would contain Makemake. Astronomers Michael E. Brown, Chad Trujillo, and David Rabinowitz had been systematically photographing the night sky since 2001 using a charge-coupled device camera, hunting for large objects beyond Neptune's orbit. Brown did not spot the new object until the 3rd of April, when he reviewed the plates and noted its exceptional brightness.

  The team had originally planned to keep Makemake quiet until after the scheduled October 2005 announcement of another find, Eris. That plan collapsed on the 27th of July 2005, when a team led by José Luis Ortiz Moreno at Sierra Nevada Observatory in Spain announced their discovery of Haumea. Brown realized that his team's observing logs, including the positions of Haumea, Eris, and Makemake, had been left unintentionally public and had been accessed by a computer at Ortiz's institution. Two days after the Haumea announcement, on the 29th of July 2005, Brown contacted Brian G. Marsden of the Minor Planet Center to announce the discoveries before anyone else could. The Minor Planet Center issued its announcements at noon California time that same day, followed by the Central Bureau for Astronomical Telegrams later that evening.

  The public announcement of multiple Pluto-sized objects in the outer Solar System forced a reckoning. The International Astronomical Union convened to answer what a planet actually is, and in August 2006 issued a new definition that reclassified Pluto as a dwarf planet, the same category Makemake would officially join.

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• 3. A Name From Easter Island

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  Brown has written and spoken about how difficult it was to find a suitable name for the new dwarf planet. At the time of its discovery, Makemake's known characteristics did not easily connect to mythology. The team had been calling it by two informal names: the nickname "Easterbunny", chosen because the discovery came shortly after Easter, and the automated codename "K05331A" assigned by Brown's computer software.

  Brown considered naming the object after Ēostre, the Anglo-Saxon goddess of spring, or after Manabozho, the Anishinaabe trickster rabbit. He found both names unusable. The team finally settled on Makemake, the creator of humanity and god of fertility in the myths of the Rapa Nui people of Easter Island. The choice satisfied the IAU's requirement that classical Kuiper belt objects be named after creator deities, and it preserved the Easter connection that had inspired the original nickname. The IAU approved the name in July 2008.

  The Minor Planet Center had already assigned the catalog number 136472 on the 7th of September 2005, once Makemake's orbit was well enough determined. A symbol for Makemake entered Unicode in January 2022 as U+1F77C, designed by Denis Moskowitz and John T. Whelan to resemble both the letter 'M' and a traditional Rapa Nui petroglyph of Makemake's face. NASA used the symbol once in an infographic published in 2015, though the IAU discourages planetary symbols in scientific literature.

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• 4. An Icy, Reddening Surface

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  Astronomical spectroscopy has shown that Makemake's surface is dominated by frozen methane, with smaller amounts of ethane, ethylene, acetylene, and high-mass alkanes such as propane. Unlike Pluto and Eris, which share this methane-rich character, Makemake apparently lacks both carbon monoxide and nitrogen ices. The James Webb Space Telescope found less than 3 percent nitrogen and less than 1 part per million of carbon monoxide on its surface.

  Ultraviolet sunlight and cosmic rays break down that methane in a cascade of photochemical reactions, converting it first to ethane, then ethylene, then acetylene, and eventually leaving behind a dark reddish mixture of complex hydrocarbons called tholins. Tholins give Makemake its reddish-brown color. Makemake is less red than Pluto but redder than Eris, a difference astronomers attribute to differing concentrations of tholins on each body. Despite constant production of dark tholins, the surface stays bright because fresh methane ice continuously covers them over.

  Phase curve measurements made by the New Horizons spacecraft suggest the regolith on Makemake's surface consists of smooth, snow-like grains. Observations of a stellar occultation in 2011 showed the body is slightly oblate, with a polar diameter of around 1420 km and an equatorial diameter of around 1434 km, consistent with a flattened shape called a Maclaurin spheroid. Planetary scientists William M. Grundy, Alex H. Parker, and colleagues have proposed that Makemake's abundant volatile methane may produce geography similar to Pluto's, potentially including bladed terrain or convecting glaciers resembling Pluto's Sputnik Planitia.

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• 5. Heat From Within

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  Makemake has a bulk density of about 1.76, similar to other trans-Neptunian dwarf planets, which suggests an interior mostly composed of water ice and rock with a differentiated rocky core. Planetary scientists suspect that radionuclides and primordial heat inside Makemake may be sustaining a subsurface liquid water ocean, either today or in the past.

  Evidence for internal activity came from JWST spectroscopy, which detected heavy isotopologues of methane containing deuterium and carbon-13. The measured deuterium-to-hydrogen ratio is 2.9, much lower than the D/H ratios of methane in comets but similar to the D/H ratios of water in comets. Scientists have interpreted this as a sign that Makemake's methane inherited its hydrogen from geochemical reactions in subsurface water at temperatures of around 150 degrees Celsius, a level of heat that only its rocky core could sustain.

  Since 2008, when the Spitzer Space Telescope first reported it, Makemake has emitted an unusually high amount of mid-infrared radiation relative to far-infrared. In 2025, Csaba Kiss and collaborators proposed that this excess could come from a cryovolcanic hotspot reaching about 150 K, covering an area of roughly 350 square kilometers, equivalent to a circle about 10 km in radius. That hotspot may release a similar amount of heat as the south pole geysers of Saturn's moon Enceladus. Alternatively, an orbiting ring of tiny carbonaceous dust grains could explain the emission, though that hypothesis is disfavored because such a ring would be destroyed by solar radiation pressure within a decade.

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• 6. Gas, Moon, and Mystery

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  Analysis of JWST spectroscopy published in 2025 confirmed the presence of gaseous methane on Makemake, making it the second trans-Neptunian object confirmed to have gas, after Pluto. Whether that gas constitutes a true atmosphere or is simply escaping from the surface remains unresolved. If the methane is entirely atmospheric, the surface pressure would be roughly 10 picobars, or 100 billion times less than Earth's atmospheric pressure and 1 million times less than Pluto's. The 2011 stellar occultation found no evidence for a substantial global atmosphere above 4-12 nanobars, supporting the picture of an extremely thin or patchy gas layer. If the methane is outgassing rather than atmospheric, Makemake may be releasing roughly 266 kg of methane per second from 4-30 percent of its surface, a rate comparable to the water output of Enceladus's plumes.

  Makemake's one known satellite, provisionally designated S/2015 (136472) 1 and nicknamed "MK 2", was found in Hubble Space Telescope images taken on the 27th of April 2015, by astronomers Alex H. Parker, Marc W. Buie, William M. Grundy, and Keith S. Noll. The moon is about 175 km in diameter, roughly 1,300 times fainter than Makemake in visible light, and follows a likely circular orbit with a period of 18 days and a semi-major axis of 22,250 km. The orbit of MK 2 implies that Makemake has a high axial tilt somewhere between 46 and 63 degrees relative to the ecliptic, which would produce extreme seasons on the dwarf planet. The moon is predicted to have eclipsed Makemake during 2009-2013, and may be doing so again during 2023-2027, though no such eclipse has yet been reported.

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• 7. A Target for the Future

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  Despite being the second brightest trans-Neptunian object in the sky after Pluto, Makemake was discovered relatively late because its highly inclined orbit of 29 degrees carries it far above the ecliptic, outside the zones where earlier sky surveys had concentrated their searches. The earliest known image of Makemake is a photographic plate taken at Palomar Observatory on the 29th of January 1955, predating its official discovery by just over 50 years. From discovery sites scattered across South America, only one stellar occultation has ever been successfully observed, on the 23rd of April 2011, yielding 7 positive detections out of 16 participating telescopes.

  No spacecraft has ever visited Makemake up close. A 2011 study by Ryan McGranaghan and colleagues calculated that a flyby mission launching on the 24th of August 2036 and using a Jupiter gravity assist could reach Makemake in just over 16 years. A 2024 study by the University of Tennessee suggested that a powered Jupiter gravity assist could shorten the journey to 9.6-16.4 years, depending on payload mass, with optimal launch dates of the 22nd of August 2036 and the 27th of September 2048. The New Horizons spacecraft observed Makemake from afar in October 2007 and again in January 2017, from distances of 52 AU and 70 AU respectively, measuring the light-scattering properties of its surface at angles that cannot be achieved from Earth. A probe that actually reached Makemake would arrive at a world still completing only 16 percent of one orbit since the first photograph of it was ever taken.

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