Do you wonder how many dwarf planets are there? If so you’re not alone. There are more than a hundred! The list below includes Eris Haumea Varda Gonggong and many other lesser-known bodies. But how many of them are really worlds? And how far away are they? Fortunately we’ve studied enough to know some interesting details about most of them.
Scientists have confirmed that there are at least two dwarf planets orbiting other stars. Pluto and Ceres are also believed to have subsurface oceans and organic molecules have been found on both planets. Every dwarf planet has at least one moon and there are several more that may be candidates. Pluto’s moon Charon is almost half the size of Pluto. It is believed that there are more than a thousand dwarf planets orbiting other stars and astronomers are still determining their sizes and shapes.
The International Astronomical Union defined the term ‘dwarf planet’ in 2006 after Pluto was classified as a planet for several generations. Later other objects were discovered in the Kuiper belt including Eris. Astronomers realized that there were hundreds of Kuiper belt objects beyond Neptune so the IAU decided to create a new category called ‘dwarf planets.’
Ceres is the largest of these objects and is 1000 kilometers across. It orbits in the asteroid belt between Jupiter and Mars so it qualifies as a dwarf planet. While Ceres’ orbit is uncertain it is large enough to have a substantial self-gravity pulling it into a near-circular shape. Its orbital path is also filled with asteroids. The Dawn spacecraft was launched in 2007 and it took just a few days to study Ceres.
Eris was discovered in 2005 and was briefly considered a planet. However it was reclassified in 2007 and was considered the solar system’s tenth planet. Its discovery made astronomers reconsider the definition of ‘planet.’ Eris was named after the Greek goddess Eris who started the Trojan War. Eris’s moon is named Xena after her daughter. The answer to the question: How many dwarf planets are there?
The answer depends on the definition of a ‘dwarf planet’. These small objects orbit the Sun but are too small to be recognized as planets. Pluto was once considered a planet but was stripped of its status at the 26th IAU General Assembly. Today Pluto is considered a dwarf planet. Another known dwarf planet is Haumea an egg-shaped world located past Neptune’s orbit in the Kuiper Belt. Haumea’s discovery was debated by two teams of astronomers. Regardless it is recognized by the IAU only where it was discovered. The two moons orbit Haumea and are named for the Hawaiian goddess of childbirth and fertility. While no spacecraft have yet visited this system scientists are confident that it is a part of the solar system.
Other examples of dwarf planets are Pluto Eris Haumea Makemake and Plutooid. Plutooids are also known as ice dwarfs. Some plutoid-impacted outer planets display evidence of this collision. The tilt of Uranus for example may be attributed to plutoid impact. Ultimately the question is: How many dwarf planets are there?
Pluto was once considered a planet but was demoted in 2006 as the International Astronomical Union revised its definition of a planet. Scientists are still not sure which of the two objects meets this definition. Some astronomers believe that there are as many as eight dwarf planets in our solar system but this is not a final decision. There are many other possible objects. This is why Pluto was demoted.
Makemake the second-brightest object in the Kuiper belt was discovered in 2005. It is named after a Rapa Nui fertility god and was the primary reason behind Pluto’s reclassification. Despite its small size it has similar mass and diameter to Pluto and would have planet status if Pluto had not been stripped of the title. If Pluto were not removed from the name Makemake would also have qualified as a planet.
There are several candidates for dwarf planets and some of them are even asteroids. The IAU has an official list of these bodies. So far Ceres is the only round asteroid that is considered a dwarf planet and Pluto and Eris are both candidates for inclusion in this category. But what exactly does a dwarf planet look like? And which planets are most likely to be dwarf planets?
Haumea for example is a candidate. It’s not a typical spheroid but is shaped like an elongated sphere flattened by the angular momentum from its spin. But the gravitational pull of gravity on Haumea helps it qualify as a dwarf planet. Until then Haumea will remain a candidate.
Ceres’s surface may be similar to the current seafloors under the solar system’s moons. Astronomers have long wished to peer beneath the surface of Ceres because water is a prerequisite for life to develop. Ceres contains 25 percent water ice. It also contains all the other elements needed for habitability. If these conditions are present on Ceres it might be possible for life to exist there.
The Solar System is made up of eight known planets and four dwarf planets. Pluto is the most famous of these bodies. The smallest one is Ceres which is classified as an asteroid. However many other objects may be dwarf planets as well. While many of these objects are not officially recognized as planets scientists are confident that more than five of them exist. It may be too early to confirm how many of these objects are in our solar system.
Scientists have been looking at space since the early 1970s and have discovered at least 10 rocky objects that could possibly be dwarf planets. Although most are not confirmed some are including Pluto and Eris. Pluto is the largest but Eris is a little bigger than Pluto. The IAU currently only lists three dwarf planets: Pluto Eris and Charon. This list is not comprehensive however.
The term ‘dwarf planet’ was coined in 2006 by the International Astronomers Union. Objects similar to Pluto and Eris but that do not meet the formal criteria of a planet are now known as a dwarf planet. The IAU feared the discovery of more of these small bodies in the outer Solar System and the possible rise of a planet-sized list as large as forty or fifty.
While the IAU recognizes five dwarf planets researchers have yet to confirm the existence of more than half a dozen. There are about a thousand other objects orbiting the Sun including Pluto and Eris. The names Pluto and Eris have shifted a few times since then as more objects were discovered in the Kuiper belt region. And since the list is still growing there are many other candidates for dwarf planet status.
Haumea was discovered a few months after Pluto. It is 43 times farther from the Sun than Earth. Its fast rotation makes its shape elongated. The discovery of Makemake another dwarf planet in the Kuiper belt is another major milestone in the search for a new class of planets. It was discovered by a team of astronomers led by Michael Brown who created the ‘dwarf planet’ classification.
There is no definitive answer to the question ‘How many dwarf planets are there?’ But astronomers are finding them all the time and there are still a few candidates. It’s difficult to say exactly how many there are because the definition of a dwarf planet isn’t set in stone. In the next few years more candidates will likely be discovered as well. But for now the number is unknown and we won’t know until further research takes place.
There is no definite answer to the question ‘How many dwarf planets are there?’ However we do know that Pluto is one of the few known objects in the Kuiper belt. The resolution of Pluto remains in place despite evidence that it was not originally a planet. It’s a testament to the fluid nature of science which changes with new observations measurements and theories. As of the time of this writing there are approximately 200 trans-Neptunian objects in the Kuiper belt and several thousand more beyond it.
While Pluto is the prototypical dwarf planet there are other smaller worlds that aren’t quite as big. Some of these objects orbit in a spherical orbit in a region where many other objects are present. Ceres for instance orbits in the asteroid belt. But the most unusual ones sit in the Kuiper Belt and share basic characteristics with Pluto. For example the Plutoids have been detected through the use of Earth-based chemical detections.
Pluto is the first object to be classified as a dwarf planet by the International Astronomical Union (IAU). However more objects have since been discovered in the same region including Eris. Eris has been named after a Greek deity known for lawlessness. Pluto was later demoted to dwarf planet status. A recent Hubble Space Telescope image shows Eris’s satellite. The planet is believed to have a mass of 1.66 x 1022 kilograms which is 27% heavier than Pluto. However its orbital motion isn’t clear and it is classified as a dwarf planet although the precise distance is unknown.