Featured Article Summary #159

Makemake is a dwarf planet that orbits the Sun far beyond Neptune. It is about 60% the diameter of Pluto, making it one of the largest trans-Neptunian objects and the biggest in the classical Kuiper belt. It was discovered in 2005 by astronomers at Palomar Observatory, and its discovery helped lead to Pluto being reclassified as a dwarf planet in 2006. Makemake’s surface is very reflective and is mostly frozen methane, with reddish-brown material, and it has one known moon. Scientists think it may have extreme seasons due to its moon’s orbit, and evidence of possible cryovolcanism suggests it could contain a hidden ocean of liquid water. Because no spacecraft has visited it yet, scientists only see it as a point of light from Earth, and they want to send a probe to learn more. Makemake was discovered in 2005 by American astronomers Mike Brown, Chad Trujillo, and David Rabinowitz while searching for large objects beyond Neptune. They took images with a telescope at Palomar Observatory on March 31, 2005, but Brown noticed and identified Makemake as very bright on April 3. The team originally planned a later announcement, but after another group announced Haumea early, Brown feared their discoveries could be made public first. He contacted the Minor Planet Center, which posted announcements for Makemake and Eris in July 2005, and the discovery of these large bodies helped lead the International Astronomical Union to redefine “planet,” reclassifying Pluto as a dwarf planet in 2006. The dwarf planet was named Makemake after the Rapa Nui creator god of fertility, and it also received the minor planet number 136472. Before the formal name, it had provisional and computer-generated designations, including “Easterbunny.” The IAU approved and announced “Makemake” in 2008, and its symbol was added to Unicode in 2022 (U+1F77C), though planetary symbols are generally discouraged in scientific work. Makemake orbits the Sun beyond Neptune at an average distance of 45.5 AU, taking about 307 years to complete one orbit. Its path is moderately stretched and tilted, ranging from 38.2 AU at its closest to 52.8 AU at its farthest, and it is currently near its farthest point (aphelion), which it will reach in May 2033. Makemake is part of the “dynamically hot” classical Kuiper belt population, meaning its orbit is generally tilted and not strongly locked in resonance with Neptune. Astronomers classify it as a dwarf planet—more specifically a plutoid—because it is round from its own gravity but has not cleared other objects from its orbit. Makemake is a nearly spherical dwarf planet about 1,430 km across, making it the fourth-largest known dwarf planet and trans-Neptunian object in the Solar System. Measurements from a 2011 stellar occultation suggest it is slightly flattened at the poles (around 1,420 km pole-to-pole and 1,434 km at the equator), consistent with a shape caused by its rotation. Its mass is estimated at about 2.5 to 2.9 kg (from the orbit of its moon), giving it surface gravity of roughly 3.6% of Earth’s and an escape speed of a few hundred meters per second.