The Mysteries of Dwarf Planets: Unraveling the Secrets of Pluto and Beyond

Outer space has plenty of mysteries that humankind is far from unraveling yet. One of these mysteries is the concept of dwarf planets. In 2006, the International Astronomical Union (IAU) introduced a fresh categorization for celestial bodies that revolve around the sun, and within this updated classification system, a specific grouping known as “dwarf planets” was incorporated. 

What is a Dwarf Planet?

To understand what dwarf planets are, let’s first understand the definition of planets. 

The International Astronomical Union outlines its planetary definition based on specific scientific criteria. A planet must: 

1. Orbit the sun
2. Possess enough gravitational force to shape itself into a rounded form (reaching hydrostatic equilibrium), and
3. Successfully eliminate other smaller objects from its orbital path.

It’s at this last point that planets and dwarf planets differ largely. While a planet’s gravity effectively either draws smaller bodies into its orbit or repels them away, a dwarf planet’s gravitational force lacks the capability to achieve this.

In other words, a dwarf planet is characterized as a celestial body that revolves around a star, possesses enough mass to attain hydrostatic equilibrium (resulting in an almost spherical configuration), yet has not managed to evacuate its orbital region of other celestial debris. These bodies fall short of meeting the criteria for full planetary status due to their size, but are substantial enough to have molded itself into an almost spherical shape through gravitational forces.

Read more: Seven Earth Sized Planets Discovered

Dwarf Planets in Our Solar System

There are five popular dwarf planets in our solar system that IAU has identified. These are:

1. Pluto
2. Eris
3. Ceres
4. Makemake
5. Haumea

Let’s dive deeper into the history and story of these planets individually.

Pluto

The discovery of Pluto in 1930 served as the catalyst for the emergence of the notion of dwarf planets. Following its discovery, Pluto held the status of the ninth planet in our solar system for several decades. 

Nevertheless, with the progression of technology and the exploration of additional celestial bodies situated beyond Neptune’s path, it gradually became evident that Pluto was just one of the many such objects. Pluto was officially reclassified as a dwarf planet in 2006.

Pluto, the most popularly known dwarf planet, holds the distinction of being the largest in terms of size and the second largest by mass. It boasts a system of five moons, with the most substantial one, Charon, encompassing over half of Pluto’s own size. 

In contrast to the predominantly circular orbits of the conventional planets, Pluto’s orbit deviates from circularity, occasionally intersecting with Neptune’s orbital path. Consequently, there are times when Pluto draws nearer to the Sun than Neptune does. Pluto’s journey around the Sun is an extended one, taking nearly 250 years to complete a single orbit.

In 2006, NASA launched the New Horizons spacecraft which took nearly nine years to reach its target: Pluto. This fly-by mission revealed that Pluto’s surface features plains and mountains made of nitrogen ice and water ice.

Dwarf Planet Eris

In 2005, astronomers made the discovery of an object named Eris located in the region beyond Neptune’s orbit. Initially, it was believed to be even larger than Pluto, leading to a reconsideration of Pluto’s planetary classification. However, the Eris dwarf planet is slightly smaller than Pluto but actually contains over 25% more matter. 

The Eris dwarf planet derives its name from the Greek goddess of discord, reflecting the controversy it triggered in the classification of Pluto and the introduction of the concept of dwarf planets. 

Due to its considerable distance from Earth, current instruments do not permit the observation of surface details on Eris. But astronomers have detected the presence of methane ice on Eris, suggesting its surface may resemble that of Pluto. Eris is accompanied by a natural satellite named Dysnomia, which completes a full orbit around Eris in 16 Earth days. Dysnomia’s name is derived from Greek mythology, representing the daughter of the goddess Eris: the inspiration behind the name of the Eris dwarf planet.

Dwarf Planet Ceres

Ceres stands as the largest object within the asteroid belt nestled between Mars and Jupiter. It is the only dwarf planet located in the inner solar system. Remarkably, this dwarf planet accounts for roughly one-third of the total mass within this region. Its nearly spherical form sets it apart from the typical rocky bodies known as asteroids. Ceres exhibits a significant number of craters on its surface, concealing substantial subterranean ice deposits.

Ceres takes 1,682 Earth days to complete one revolution around the Sun. It also lacks any moons or rings. 

Dwarf Planet Makemake

Makemake resides within the Kuiper Belt, alongside its compatriot dwarf planets: Pluto, Eris, and Haumea. The Kuiper Belt forms a donut-shaped region populated by icy objects situated past Neptune’s orbit. Makemake, marginally smaller than Pluto, holds the distinction of being the second-most luminous entity within the Kuiper Belt when viewed from Earth, with Pluto being the brightest. It requires approximately 305 Earth years to complete a single orbit around the Sun.

Makemake came into astronomers’ view for the first time in March 2005, thanks to the efforts of M.E. Brown, C.A. Trujillo, and D.L. Rabinowitz at the Palomar Observatory. It possesses a provisional moon known as S/2015 (136472) 1, affectionately referred to as MK 2. Despite displaying a reddish-brown hue akin to Pluto, Makemake’s surface features remain relatively concealed due to its substantial distance from Earth.

Dwarf Planet Haumea

In 2004, astronomers identified Haumea within the Kuiper Belt, a region located beyond Neptune’s orbital path. Despite requiring 285 Earth years to complete a single orbit around the Sun, Haumea rotates on its axis in less than four hours.

The Goblin Dwarf Planet

In the second half of 2015, astronomers discovered a new dwarf planet in the outer solar system – nicknamed as The Goblin, an addition to the several dwarf planets in our solar system. The Goblin’s orbital trajectory positions it within a category of diminutive, faraway celestial bodies known to astronomers as “Inner Oort Cloud objects.” 

In simpler terms, it dwells within the Oort Cloud, an expansive spherical region filled with icy entities encircling our sun. This area is commonly associated with comets and is located at a considerable distance beyond the paths of both Pluto and the nearer Kuiper Belt Objects. While Planet Nine remains undiscovered to date, there are strong indications that The Goblin is being gravitationally affected by a massive, hidden entity, potentially Planet Nine, reinforcing astronomers’ confidence in its existence.

This extremely distant dwarf planet, also known as 2015 TG387, is about 80 astronomical units (AU) from the sun, with one AU defined as the distance between the sun and Earth. In contrast, Pluto’s distance from the sun is approximately 34 astronomical units (AU), making the Goblin currently situated about two and a half times more distant from the sun than Pluto. 

How Many Dwarf Planets in Our Solar System?

Although these cover the known dwarf planets in our solar system, we are constantly learning more about our solar system and discovering more celestial bodies. 

There are a few more dwarf planets that have been observed. 

Among these dwarf planets are Sedna and Quaoar, both representing diminutive celestial bodies located in the distant reaches of our solar system, well beyond Pluto’s path. Additionally, there’s 2012 VP113, an entity believed to possess one of the most remote orbits ever detected, extending beyond the established boundaries of our solar system. Observations made in 2017 suggest that the object DeeDee may also meet the criteria for being classified as a dwarf planet.