A Visual Introduction to the Dwarf Planets in our Solar System
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A Visual Introduction to the Dwarf Planets in our Solar System

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A Visual Introduction to the Dwarf Planets of our Solar SystemA Visual Introduction to the Dwarf Planets of our Solar System

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Pluto and the Introduction of Dwarf Planets

Since its discovery in 1930, Pluto has been a bit of a puzzle.

For starters, not only is Pluto smaller than any other planet in the solar system, but it’s also smaller than Earth’s moon. It also has an extremely low gravitational pull at only 0.07 times the mass of the objects in its orbit, which is just a fraction of the Moon’s own strength.

At the same time, Pluto’s surface resembles that of terrestrial planets such as Mars, Venus or the Earth, yet its nearest neighbors are the gaseous Jovian planets such as Uranus or Neptune. In fact, Pluto’s orbit is so erratic that it led many scientists to initially believe that it originated elsewhere in space and the Sun’s gravity pulled it in.

These qualities have challenged the scientific view of Pluto’s status as a planet for years. It wasn’t until the discovery of Eris in 2005, one of many increasingly identified trans-Neptunian objects (objects beyond the planet Neptune), that the International Astronomical Union (IAU) defined criteria for classifying planets.

With Eris and other trans-Neptunian objects sharing similar characteristics with Pluto, the definition for dwarf planets was created, and Pluto got downgraded in 2006.

So what are dwarf planets, how do they differ from “true” planets and what are their characteristics?

The History of Dwarf Planets

A dwarf planet is a celestial body that almost meets the definition of a “true” planet. According to the IAU, which sets definitions for planetary science, a planet must:

  1. Orbit the Sun.
  2. Have enough mass to achieve hydrostatic equilibrium and assume a nearly round shape.
  3. Dominate its orbit and not share it with other objects.

Dwarf planets, along with not being moons or satellites, fail to clear the neighborhoods around their orbits. This is the primary reason why Pluto lost its status: because it shares part of its orbit with the Kuiper belt, a dense region of icy space bodies.

Based on this definition, the IAU has recognized five dwarf planets: Pluto, Eris, Makemake, Haumea, and Ceres. There are four more planetary objects*, namely Orcus, Sedna, Gonggong and Quaoar, that the majority of the scientific community recognize as dwarf planets.

Six more could be recognized in the coming years, and as many as 200 or more are hypothesized to exist in the Outer Solar System in the aforementioned Kuiper belt.

Ceres is the earliest known and smallest of the current category of dwarf planets. Previously classified as an asteroid in 1801, it was confirmed to be a dwarf planet in 2006. Ceres lies between Mars and Jupiter in the asteroid belt, and it is the only dwarf planet that orbits closest to Earth.

Here is a brief introduction to the most recognized dwarf planets:

NameRegion of the
Solar System
Orbital period
(in years)
Mean orbital
speed (km/s)
Diameter
(km)
Diameter
relative to
the Moon
Moons
OrcusKuiper belt (plutino)2474.7591026%1
CeresAsteroid belt4.617.994027%0
PlutoKuiper belt (plutino)2484.74237768%5
HaumeaKuiper belt (12:7)2854.531560≈ 45%2
QuaoarKuiper belt (cubewano)2894.51111032%1
MakemakeKuiper belt (cubewano)3064.41143041%1
GonggongScattered disc (10:3)5543.63123035%1
ErisScattered disc5583.62232667%1
SednaDetached~11,400~1.399529%N/A

Interesting Facts about Dwarf Planets

Here are a few interesting facts about the dwarf planets discovered in our solar system:

Ceres loses 6kg of its mass in steam every second

The Herschel Space Telescope observed plumes of water vapor shooting up from Ceres’ surface; this was the first definitive observation of water vapor in the asteroid belt. This happens when portions of Ceres’ icy surface warm up and turn into steam.

A day on Haumea lasts 3.9 hours

Haumea has a unique appearance due to its rotation, which is so rapid that it compresses the planet into an egg-like shape. Its rotational speed and collisional origin also make Haumea one of the densest dwarf planets discovered to date.

Makemake was named three years after its discovery in 2005

Makemake’s discovery close to Easter influenced both its name and nickname. Before being named after the creator of humanity and god of fertility in the mythos of the Rapa Nui (the native people of Easter Island), Makemake was nicknamed “Easter bunny” by its discoverer Mike Brown.

Eris was once considered for the position of the 10th planet

Eris is the most massive dwarf planet in the solar system, exceeding Pluto’s mass by 28%. As such, it was a serious contender to become the tenth planet but failed to meet the criteria set out by the IAU.

Pluto is one-third ice

The planet’s composition makes up two-thirds rock and one-third ice, mostly a mixture of methane and carbon dioxide. One day on Pluto is 153.6 hours, approximately 6.4 Earth days, making it one of the slowest rotating dwarf planets.

Exploratory Missions and New Planets on the Horizon

With newer technology rapidly available to the scientific community and new exploratory missions getting more data and information about trans-Neptunian objects, our understanding of dwarf planets will increase.

Nestled in the asteroid belt between Mars and Jupiter, the asteroid Hygiea remains a controversy. Hygiea is the fourth largest object in the asteroid belt behind Ceres, Vesta, and Pallas and ticks all the boxes necessary to be classified as a dwarf planet.

So what’s holding back Hygiea’s confirmation as a dwarf planet? The criterion for being massive enough to form a spherical shape is in contention; it remains unclear if its roundness results from collision/impact disruption or its mass/gravity.

Along with Hygiea, other exciting dwarf planets could be soon discovered. Here is a quick rundown of some serious contenders:

Potential Dwarf Planets Under Investigation

120347 Salacia

Discovered in 2004, it is a trans-Neptunian object in the Kuiper belt, approximately 850 kilometers in diameter. As of 2018, it is located about 44.8 astronomical units from the Sun. Salacia’s status is in contention because its planetary density is arguable. It is uncertain if it can exist in hydrostatic equilibrium.

(307261) 2002 MS4

With an estimated diameter of 934±47 kilometers, 2002 MS4 is comparable in size to Ceres. Researchers need more data to determine whether 2002 MS4 is a dwarf planet or not.

(55565) 2002 AW197

Discovered at the Palomar Observatory in 2002, it has a rotation period of 8.8 hours, a moderately red color (similar to Quaoar) and no apparent planetary geology. Its low albedo has made it difficult to determine whether or not it is a dwarf planet.

174567 Varda

Varda takes its name after the queen of the Valar, creator of the stars, one of the most powerful servants of almighty Eru Iluvatar in J. R. R. Tolkien’s fictional mythology. Varda’s status as a dwarf planet is uncertain because its size and albedo suggest it might not be a fully solid body.

(532037) 2013 FY27

This space object has a surface diameter of about 740 kilometers. It orbits the Sun once every 449 years. Researchers need more data on the planet’s mass and density to determine if it is a dwarf planet or not.

(208996) 2003 AZ84

It is approximately 940 kilometers across its longest axis, as it has an elongated shape. This shape is presumably due to its rapid rotation rate of 6.71 hours, similar to that of other dwarf planets like Haumea. Like Varda, it remains unknown if this object has compressed into a fully solid body and thus remains contentious amongst astronomers regarding its planetary status.

*Note: The IAU officially recognizes five dwarf planets. We include four additional dwarf planets widely acknowledged by members of the scientific community, especially amongst leading planetary researchers like Gonzalo Tancredi, Michael Brown, and William Grundy. There are many more potential dwarf planets not listed here that remain under investigation.

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Automotive

The Most Fuel Efficient Cars From 1975 to Today

This infographic lists the most fuel efficient cars over the past 46 years, including the current leader for 2023.

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The Most Fuel Efficient Cars From 1975 to Today

When shopping for a new car, what is the most important factor you look for? According to Statista, it’s not design, quality, or even safety—it’s fuel efficiency.

Because of this, automakers are always looking for clever ways to improve gas mileage in their cars. Beating the competition by even the slimmest of margins can give valuable bragging rights within a segment.

In this infographic, we’ve used data from the EPA’s 2022 Automotive Trends Report to list off the most fuel efficient cars from 1975 to today.

Editor’s note: This is from a U.S. government agency, so the data shown skews towards cars sold in North America.

Data Overview

All of the information in the above infographic is listed in the table below. Data was only available in 5-year increments up until 2005, after which it switches to annual.

Model YearMakeModelReal World Fuel Economy (mpg)Engine Type
1975HondaCivic28.3Gas
1980VWRabbit40.3Diesel
1985ChevroletSprint49.6Gas
1990GeoMetro53.4Gas
1995HondaCivic47.3Gas
2000HondaInsight57.4Hybrid
2005HondaInsight53.3Hybrid
2006HondaInsight53Hybrid
2007ToyotaPrius46.2Hybrid
2008ToyotaPrius46.2Hybrid
2009ToyotaPrius46.2Hybrid
2010HondaFCX60.2FCEV
2011BMWActive E100.6EV
2012Mitsubishii-MiEV109EV
2013ToyotaiQ EV117EV
2014BMWi3121.3EV
2015BMWi3121.3EV
2016BMWi3121.3EV
2017HyundaiIoniq Electric132.6EV
2018HyundaiIoniq Electric132.6EV
2019HyundaiIoniq Electric132.6EV
2020Tesla3138.6EV
2021Tesla3139.1EV

From this dataset, we can identify three distinct approaches to maximizing fuel efficiency.

Downsizing

Prior to 2000, the best way for automakers to achieve good fuel efficiency was by downsizing. Making cars smaller (lighter) meant they could also be fitted with very small engines.

For example, the 1985 Chevrolet Sprint was rated at 49.6 MPG, but had a sluggish 0-60 time of 15 seconds.

Hybrids

The 2000s saw the introduction of mass-market hybrid vehicles like the Honda Insight and Toyota Prius. By including a small battery to support the combustion engine, automakers could achieve good MPGs without sacrificing so heavily on size.

While the Insight achieved better fuel economy than the Prius, it was the latter that became synonymous with the term “hybrid”. This was largely due to the Prius’ more practical 4-door design.

The following table compares annual U.S. sales figures for both models. Insight sales have fluctuated drastically because Honda has produced the model in several short spans (1999-2006, 2009-2014, 2018-2022).

YearInsight SalesPrius Sales
2005666107,155
2006722106,971
20073181,221
2008-158,884
200920,572150,831
201020,962140,928
201115,549136,464
20126,619236,655
20134,802234,228
20143,965207,372
20151,458184,794
201667136,629
20173108,661
201812,51387,590
201923,68669,718
202015,93243,525
202118,68559,010
20227,62833,352

Source: goodcarbadcar.net

The Prius may have dominated the hybrid market for a long time, but it too has run into troubles. Sales have been declining since 2014, even setting historic lows in recent years.

There are several reasons behind this trend, with one being a wider availability of hybrid models from other brands. We also can’t ignore the release of the Tesla Model 3, which began shipping to customers in 2017.

Electric Vehicles

We’re currently in the middle of a historic transition to electric vehicles. However, because EVs do not use fuel, the EPA had to develop a new system called MPGe (miles per gallon of gasoline-equivalent).

This new metric gives us the ability to compare the efficiency of EVs with traditional gas-powered cars. An underlying assumption of MPGe is that 33.7 kilowatt-hours (kWh) of electricity is comparable to the energy content of a gallon of fuel.

The most fuel efficient car you can buy today is the 2023 Lucid Air, which achieves 140 MPGe. Close behind it is the 2023 Tesla Model 3 RWD, which is rated at 132 MPGe.

Check out this page to see the EPA’s top 10 most efficient vehicles for 2023.

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