Makemake
Makemake is a dwarf planet in the Kuiper belt, a disk of icy bodies beyond the orbit of Neptune. It is the fourth largest trans-Neptunian object and the largest member of the classical Kuiper belt, having a diameter 60% that of Pluto. It was discovered on March 31, 2005 by American astronomers Michael E. Brown, Chad Trujillo, and David Rabinowitz at Palomar Observatory. As one of the largest objects found by this team, the discovery of Makemake contributed to the reclassification of Pluto as a dwarf planet in 2006.
Makemake is similar to Pluto with respect to its surface: it is highly reflective, covered largely by frozen methane, and stained reddish-brown by tholins. Makemake has one known satellite, which has not been named. The orbit of this satellite suggests that Makemake's rotation has a high axial tilt, which implies that it experiences extreme seasons. Makemake shows evidence of geochemical activity and cryovolcanism, which has led scientists to suspect that it might harbor a subsurface ocean of liquid water. Gaseous methane has been found on Makemake, although it is unclear whether it is contained in an atmosphere or comes from temporary outgassing.
No high-resolution images of Makemake's surface exist because it has not been visited up close by a space probe. Makemake is so far from Earth that it appears as a star-like point of light even when viewed through a telescope. Scientists have expressed desire to send a space probe to explore Makemake because of its geological activity and potential subsurface ocean.
History
Discovery
Makemake was discovered in 2005 by a team of American astronomers consisting of Michael E. Brown, Chad Trujillo, and David Rabinowitz during their search for large objects beyond the orbit of Neptune. The team's search for trans-Neptunian objects, which begun in 2001, involved routinely imaging the night sky using a charge-coupled device camera attached to the Samuel Oschin telescope at Palomar Observatory in California, United States. The discovery images of Makemake were taken by this telescope on March 31, 2005, but it was not until April 3, 2005 that Mike Brown found the object in his inspection of the images and identified it as exceptionally bright.Several months before Makemake's discovery, Brown and his team had discovered the exceptionally large trans-Neptunian objects and, which were thought to be at least the size of the then-ninth planet Pluto. As they were in the process of planning further observations for both objects, the team originally planned to delay the announcement of Makemake to sometime after Eris's planned announcement in October 2005. However, this plan was upended when a team led by José Luis Ortiz Moreno at Sierra Nevada Observatory in Spain announced their own discovery of Haumea on July 27, 2005. Brown realized that his team's observing logs containing the positions of Haumea, Eris, and Makemake were unintentionally public and had been accessed by a computer at Ortiz's institution. Fearing that his team's discoveries of Eris and Makemake would be similarly scooped, Brown contacted Brian G. Marsden of the Minor Planet Center on July 29, 2005, to announce their discovery. The MPC issued the discovery announcements for Eris and Makemake on its website at noon California time, followed by the Central Bureau for Astronomical Telegrams later that evening. The announcement of these Pluto-sized objects prompted widespread debate over what should be considered a planet, which motivated the International Astronomical Union to create a new definition of planet that reclassified Pluto as a dwarf planet in August 2006.
Name and symbol
This dwarf planet is named after Makemake, the creator of humanity and god of fertility in the myths of the Rapa Nui people native to Easter Island. It has the minor planet catalog number of 136472, which was given by the MPC on September 7, 2005 after the object's orbit became well determined. Before Makemake was named, it was known by its provisional designation, which was given by the MPC when its discovery was announced. Makemake was also previously known by its nickname "Easterbunny", given by Brown's team as a reference to the object's time of discovery shortly after Easter, and the codename "K05331A", which was automatically assigned by Brown's computer software when he discovered it.In his personal writings and interviews, Brown recounted that deciding on Makemake's name was difficult because the object's known characteristics at the time were not relatable to mythology. Wanting to preserve the object's connection with Easter, Brown had thought about naming the object after either the Anglo-Saxon goddess Ēostre or the Anishinaabe trickster rabbit Manabozho, but found both names unusable. Brown and his team finally settled on the name Makemake, which satisfied both the object's connection with Easter and the IAU's rule for naming classical Kuiper belt objects after creator deities. The name of Makemake was approved and announced by the IAU in July 2008.
A symbol for Makemake was introduced to Unicode in January 2022, as U+1F77C. The use of planetary symbols in scientific publications is discouraged by the IAU, so the symbol for Makemake is mostly used by astrologers. However, the symbol was used once by NASA, in an infographic published in 2015. The symbol for Makemake was designed by Denis Moskowitz and John T. Whelan; it represents a traditional petroglyph of Makemake's face, stylized to resemble the letter 'M'. Other astrologers have designed and used their own symbols for Makemake, such as.
Orbit and classification
Makemake orbits the Sun beyond Neptune at an average distance of 45.5 astronomical units. It completes one orbit every 307 years. With an orbital eccentricity of 0.16, Makemake follows a moderately elliptical orbit that comes as close as to the Sun to as far as from the Sun. Makemake has a relatively high orbital inclination of 29° with respect to the ecliptic.Makemake is currently near aphelion, the farthest point of its orbit. It is away from the Sun, and will reach aphelion in May 2033. Makemake is currently positioned far above the ecliptic and will remain so at aphelion, where its ecliptic latitude will be 25.9°. Makemake will cross the ecliptic in 2103 and will come to perihelion –26° below the ecliptic in 2186. N-body simulations show that Makemake's orbit is stable on a scale of billions of years and is unlikely to change significantly over the remaining life of the Solar System.
Makemake shares its orbital characteristics with many other small icy bodies beyond Neptune, which together to a region known as the Kuiper belt. Makemake specifically belongs to the "dynamically hot" population of classical Kuiper belt objects, whose orbits have high inclinations, relatively low eccentricities, and are not in orbital resonance with Neptune. Makemake is the largest member of the classical Kuiper belt, although it only constitutes a small fraction of the total mass off the belt. The hot classical Kuiper belt objects are believed to have been gravitationally scattered by Neptune in the Solar System's early history, hence astronomers have also termed Makemake a "scattered" object.
The scientific consensus is that Makemake is a dwarf planet: that is, that it is massive enough for its own gravity to make its shape spherical, but not massive enough to clear other objects away from its orbit, as demonstrated by its location in the Kuiper belt. It was the first object named by the IAU under new procedures for naming objects expected to be dwarf planets, and the fourth object announced as a dwarf planet since that category had been established in 2006. Makemake is more specifically a plutoid: the subcategory of dwarf planets that orbit beyond Neptune.
Size, shape, and mass
Makemake is a nearly spherical object with an average diameter of around, which is about 60% the diameter of Pluto or 11% the diameter of Earth. This makes Makemake the fourth-largest known dwarf planet and trans-Neptunian object in the Solar System, after Pluto, Eris, and Haumea. Observations of a stellar occultation in 2011 showed that Makemake is slightly oblate or flattened at its poles, with an upper limit in its polar diameter of around and an equatorial diameter of around. These dimensions are consistent with Makemake having a flattened spherical shape known as a Maclaurin spheroid, which occurs when an object is in hydrostatic equilibrium and is deformed by its rotation.Makemake has a mass of between approximately and, a number determined from the orbital period and distance of its moon. This makes Makemake the fourth-most massive known dwarf planet and trans-Neptunian object in the Solar System, again after Eris, Pluto, and Haumea. Compared to other Solar System objects, Makemake is about 3.7% the mass of Earth's moon and around 20% the mass of Pluto. Given Makemake's mass and average diameter, its average surface gravity is about m/s2 and its surface escape velocity is about km/s.
Rotation
The rotation period of Makemake is uncertain, with measurements giving either . These rotation period measurements were made by monitoring changes in Makemake's brightness over time, which is plotted as a light curve. Makemake exhibits very little variation in brightness presumably due to small albedo variations across its surface, which makes it difficult for telescopes to measure Makemake's light curve and rotation period. For example, studies prior to 2019 suggested possible rotation periods of 7.77, 11.24, 11.5, and 22.48 hours. For measurements, it is unclear whether Makemake's brightness peaks once or twice per rotation, so it is unclear whether the rotation period is 11.4 hours or double that value at 22.8 hours.The axial tilt of Makemake has not been measured, although it can be reasonably assumed that its rotation axis is aligned with the pole of its moon's orbit. In that case, Makemake would have a high axial tilt somewhere between with respect to its orbit around the Sun, with its equator facing toward the Sun and Earth at the time its moon was discovered. This high axial tilt together with its eccentric orbit can give rise to major seasonal changes in Makemake's surface temperature and terrain, similar to those seen on Pluto. Makemake's moon was predicted to eclipse Makemake sometime during 2009–2013 or 2023–2027, so Makemake may have passed equinox during either of those year ranges if its rotation is aligned with its moon's orbit.