Makemake was one of the largest objects discovered in the outer Solar System in the early 21st century. Its discovery, along with Eris, led to the reclassification of Pluto in 2006, establishing the new category of plutoids. Makemake is an icy dwarf planet and a large member of the Kuiper Belt, a vast ring of objects beyond Neptune. Studying its composition requires sophisticated telescopic observations.
Makemake’s Place in the Solar System
Makemake resides in the Kuiper Belt, a zone of icy bodies extending beyond Neptune. Classified as a plutoid and a classical Kuiper Belt Object (KBO), its orbit is relatively stable. Makemake is about 45.8 astronomical units (AU) from the Sun on average, completing an orbit in approximately 305 Earth years.
The dwarf planet has an estimated average diameter of 1,430 kilometers, about two-thirds the size of Pluto. Its mass is estimated to be \(3 \times 10^{21}\) kilograms. Its bulk density is calculated to be 1.7 grams per cubic centimeter, slightly less dense than Pluto. This low density indicates the object is composed of a mixture of rock and various ices.
The Dominant Surface Ices
Spectroscopy has identified the materials covering Makemake’s surface. The dominant component is solid methane ice, stable at the frigid surface temperature of roughly -243 degrees Celsius (30 to 40 Kelvin). The surface is highly reflective, with a geometric albedo of about 0.77 to 0.81, indicating a relatively clean, icy covering.
The spectrum also reveals frozen hydrocarbons, including ethane and ethylene, which are products of methane broken down by solar radiation. This process creates complex organic molecules known as tholins, believed to be responsible for Makemake’s distinct reddish-brown hue. Although nitrogen is present, Makemake appears to have lost most of its nitrogen ice over time, leaving methane as the primary surface volatile.
Inferring Internal Makeup
The density measurement of 1.7 grams per cubic centimeter suggests the dwarf planet is composed of a mix of rock and water ice. Based on the densities of rock and water ice, the interior is likely a roughly equal mixture of these two materials by mass.
Scientists propose that Makemake is large enough to have undergone differentiation, where heavier materials sink to the center. This process would result in a dense, rocky core surrounded by a thick mantle of water ice. This layered structure is common among the largest KBOs, implying that Makemake’s formation involved enough internal heat to allow the materials to separate.
Atmospheric Conditions
Makemake does not possess a global atmosphere. This conclusion was reached following a stellar occultation in 2011, where the dwarf planet passed in front of a distant star. Scientists observed an abrupt disappearance and reappearance of the starlight, indicating the lack of a gradual fading effect that a global atmosphere would cause.
The occultation data set a very low upper limit on any global atmosphere’s surface pressure, at less than 4 to 12 nanobar. However, Makemake’s surface ices, particularly nitrogen and methane, are volatile and can sublimate into gas when the dwarf planet is closest to the Sun. This sublimation may create a temporary, localized atmosphere or surface haze that collapses and freezes back onto the surface as Makemake moves farther away.