What are dwarf planets — and how many are there?
In 2006, Pluto was famously demoted from a planet to a dwarf planet. It remains the most famous dwarf planet today, but there are others in our solar system, including potentially hundreds that haven't been discovered yet.
But what, exactly, is a dwarf planet? And how many dwarf planets are there?
A dwarf planet is a celestial body that is smaller than a planet but bigger than an asteroid or other small rock in the solar system. They're not planets because they only meet two of the three criteria for something in space to be considered a true planet.
A planet is defined by three qualities: It orbits the sun, it's mostly round, and it's massive enough for its gravity to have mostly kicked large objects from its orbit. Pluto and some other known dwarf planets meet the first two criteria but not the third because they orbit in the Kuiper Belt, a region beyond Neptune filled with small icy debris.
When Pluto was first discovered in 1930, it (and other similar objects in the Kuiper Belt) were so far away and faint that they were really hard to spot, even with the most powerful telescopes at the time. Indeed, the very qualities that make something a dwarf planet make those objects particularly hard to detect.
Related: James Webb telescope discovers 'a new kind of climate' on Pluto, unlike anything else in our solar system
"There are a few things that work against us spotting them," Mathew Yu, an astronomer at UCLA, told Live Science in an email. "They are far away from the sun. The reflected light from them is faint as a result. Some have low reflectivity, making light reflecting off them fainter."
Plus, "they move slowly across the sky due to their large distance from the sun," he added. "They go around the sun once every hundreds of Earth years. So their relative motions to the background stars are small. For astronomers with a limited observing time, these objects become hard to detect."
Astronomers got a lot better at finding objects in the Kuiper Belt in the 1990s and 2000s as telescope technology improved. And once they could see a bit better, they noticed there were a lot more rocks out there with orbits similar to Pluto's. Between 2002 and 2005, astronomers found seven more particularly large rocks: Haumea, Makemake, Quaoar, Sedna, Orcus, Eris and Salacia.
The International Astronomical Union (IAU) — the group of astronomers that decides on official names and terms for things in space — decided in 2006 that a new category was needed to describe these objects that were pretty big but not big enough to clear their orbits as a true planet does. Thus, the name "dwarf planet" was born.
With eight named large rocks in the Kuiper Belt, you might think that means there are eight dwarf planets. However, not all astronomers agree on the number.
"Accepted numbers range between around 10 to a few hundred in the Kuiper Belt alone," Yu said. "Some estimate that there may be up to tens of thousands of them beyond the Kuiper Belt."
The IAU has officially recognized only five dwarf planets: Pluto, Haumea, Makemake and Eris in the Kuiper Belt, plus Ceres in the asteroid belt. We've sent space probes to only two of these: Pluto (visited by NASA's New Horizons) and Ceres (visited by NASA's Dawn), both of which flew by those bodies in 2015.
Astronomers who observe dwarf planets, however, tend to recognize nine: the previous five, plus Quaoar, Sedna, Orcus and Gonggong. Gonggong was discovered in 2007 after the dwarf planet name change, but it wasn't confirmed until some new observations from NASA telescopes in 2016. The IAU is still considering proposals on these dwarfish bodies.
RELATED STORIES
—Watch newly discovered 'interstellar visitor' 3I/ATLAS shoot toward us in first livestream today (July 3)
—'A completely new phenomenon': Astronomers spot a planet causing its star to constantly explode
—James Webb telescope discovers tentacled 'jellyfish' galaxy swimming through deep space
There are at least a handful more objects that have been proposed but need more observations to confirm their size and, therefore, dwarf planet status.
And in June 2025, scientists proposed a new possible dwarf planet: 2017 OF201. Astronomers found this particularly faint object by searching through an old pile of data with new advanced algorithms.
If you count all of the currently proposed dwarf planets plus the newcomer, that makes eighteen or more dwarf planets in the solar system — and that's just the ones we've seen. There are likely more out there, perhaps even hundreds or thousands, someday to be revealed as our telescopes keep getting better.
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Yahoo
2 hours ago
- Yahoo
Bending Bones, Stretchy Ligaments: UT's 3D Printer Redefines Medical Implants
In a groundbreaking achievement that almost blurs the lines between science fiction and reality, researchers at The University of Texas at Austin have unveiled a new 3D printing technique that can combine soft and stretchable materials with other tough or rigid resins in a single, precise print. Inspired by the 'natural world,' think of the way bone transitions smoothly into cartilage: the new printing process allows engineers to create objects that can bend and flex when needed while also staying firm and supportive. Scientists at the University of Texas outlined to The Dallas Express that this breakthrough results in next-level prosthetics, modern flexible medical implants, and even wearable electronics that move and feel more like human tissue than ever before. 'By enabling precise control over both shape and material properties, our multimaterial 3D printing technology allows for the creation of devices that more closely mimic the complex mechanics of the human body,' Dr. Zak Page, Assistant Chemistry Professor at The University of Texas at Austin, told DX. 'Whether it's a prosthetic interface, a patient-specific surgical model, or a wearable health sensor, the ability to print gradual transitions between soft and rigid materials opens new possibilities for comfort, performance, and personalization across a wide range of medical applications,' Page added. The research results published earlier this week describe how the team achieved the 3D advancement using a custom-designed resin and a dual-light printing system. By simply changing the color of light during printing —violet for soft or rubbery parts and ultraviolet for more rigid sections —they were able to build objects with new gradients of flexibility and strength. A standout demo resulted in a tiny, functional 3D-printed 'knee joint,' complete with bending ligaments and sturdy bones that move together smoothly. Page said in the report that the first print was a surprise success. 'Honestly, what surprised me most was how well it worked on the first try. That almost never happens with 3D printing resins,' he said. 'We were also shocked by how different the properties were. The soft parts stretched like a rubber band and bounced back. The hard parts were as strong as plastics used in consumer products.' The new 3D printing technique also boasts faster speeds, and the necessary equipment isn't out of reach for smaller labs or hospitals worldwide. This could potentially result in easier access to medical equipment for isolated communities worldwide. 'This approach could make additive manufacturing more competitive for higher-volume production compared with traditional processes like injection molding. Just as important, it opens up new design possibilities,' added Keldy Mason, lead author of the university study and a graduate student in Page's lab.
Yahoo
2 hours ago
- Yahoo
Potentially Toxic Chemicals Are Reaching Toddlers Before Kindergarten, Study Finds
Young children nationwide are exposed to a large swath of possibly toxic chemicals before kindergarten, new research suggests 'Our study shows that childhood exposure to potentially harmful chemicals is widespread. This is alarming because we know early childhood is a critical window for brain and body development,' said the study's lead author, Deborah Bennett Researchers found that of the 111 chemicals they focused on, 48 were found in more than 50% of the childrenBefore ever stepping foot inside a kindergarten classroom, young children nationwide are already exposed to a large swath of possibly toxic chemicals, new research suggests. The study, published in Environmental Science and Technology on Monday, June 30, analyzed chemical exposure in 201 kids from the ages of 2-4 years old between 2010 and 2021, using urine samples from the children and most of their mothers during pregnancy. Researchers focused on 111 chemicals. 'Our study shows that childhood exposure to potentially harmful chemicals is widespread. This is alarming because we know early childhood is a critical window for brain and body development,' said the study's lead author, Deborah Bennett in a statement from UC Davis, where she is a professor. 'Many of these chemicals are known or suspected to interfere with hormones, brain development and immune function,' Bennett added. Researchers found that of the 111 chemicals, 96 were detected in at least five kids and 48 were found in more than 50% of the children. In addition, 34 were found in more than 90% of the kids — including nine substances "which have not been included in U.S. national biomonitoring." "This study reveals frequent exposure to multiple chemicals in young U.S. children, often exceeding prenatal levels," the authors wrote in a summary. "Expanded biomonitoring of emerging chemicals of concern and studies of their health effects in this vulnerable population are warranted." Never miss a story — sign up for to stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories. According to UC Davis, the study found children were exposed to phthalates, parabens, bactericides, and various other chemicals through "everyday activities, such as eating, drinking, breathing indoor and outdoor air and touching contaminated surfaces." 'Exposure to certain chemicals in early childhood, such as pesticides, plasticizers and flame retardants, has been linked to developmental delays, hormone disruption and other long-term health issues,' the study's first author, Jiwon Oh, told UC Davis. Read the original article on People
CNN
2 hours ago
- CNN
‘Jurassic World Rebirth' roars to top of the box office
Dinosaurs are alive and well at the box office as Universal's 'Jurassic World Rebirth' trampled competitors, grossing $147 million domestically over five days of the Fourth of July weekend. The fourth installment of the 'Jurassic World' series outperformed early estimates of nearly $80 million for the three days and $135 million for the five days. It nearly matched its predecessor from 2022, 'Jurassic World Dominion,' which grossed $145 million in its first three days before raking in over $1 billion worldwide. 'Jurassic World Rebirth' is another win for Hollywood, which has effectively rebounded from a sluggish start to 2025. The box office is up more than 14% year-to-date compared with last year, according to Comscore, which collects box office data. The summer season, which Comscore begins tracking on the first Friday in May, is faring even better — up 15% compared to 2024. 'Jurassic Park Rebirth' is the seventh film in the franchise, which began with Steven Spielberg's 'Jurassic Park' in 1993. The original movie would go on to gross $924 million worldwide, or $2 billion when adjusted for inflation. While 'Jurassic World' was a new era for the franchise, calling the fourth film 'Rebirth,' and casting Scarlett Johansson, likely reinvigorated the brand, according to Paul Dergarabedian, a senior media analyst at Comscore. 'This brand will never go extinct because it continues to thrill audiences,' he said. 'It's most impressive to have a franchise three decades old, topping the chart once again.' 'Jurassic World Rebirth' knocked Apple and Warner Bros. Pictures' 'F1' down a peg to No. 2. 'F1' grossed $26 million domestically this weekend, a 54% drop from the week prior. The racing movie starring Brad Pitt opened last weekend to roughly $55.6 million domestically and $144 million worldwide. Warner Bros. Discovery is the parent company of CNN. ''F1' is interesting because it's absolutely killing it at the international box office,' said Dergarabedian. '(It's) a sport that is more internationally centric than in the United States.' 'Jurassic World Rebirth' and 'F1' will face fierce competition next week when Warner Bros.' 'Superman' opens in theaters. Analysts expect 'Superman' to gross over $100 million in its opening weekend. 'The best thing for 'Superman' is the success of 'Jurassic' and 'F1.' The rising tide raises all ships,' said Dergarabedian. Shawn Robbins, director of analytics at Fandango and founder and owner of Box Office Theory, said the releases of 'Jurassic World Rebirth,' 'Superman,' and Disney's 'The Fantastic Four: First Steps' (July 25) could account for about a quarter of the domestic box office this summer. Robbins added that 'F1,' 'Jurassic World Rebirth' and 'Superman' will likely attract similar audiences of young men. 'Superman' could also appeal to families and younger audiences. 'It's summer. It's the time when multiple films can coexist, so if any of them are going to do it, this is a good set of movies to pull it off,' he said.
