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:
- Orbit the Sun.
- Have enough mass to achieve hydrostatic equilibrium and assume a nearly round shape.
- 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:
|Name||Region of the|
|Orcus||Kuiper belt (plutino)||247||4.75||910||26%||1|
|Pluto||Kuiper belt (plutino)||248||4.74||2377||68%||5|
|Haumea||Kuiper belt (12:7)||285||4.53||1560||≈ 45%||2|
|Quaoar||Kuiper belt (cubewano)||289||4.51||1110||32%||1|
|Makemake||Kuiper belt (cubewano)||306||4.41||1430||41%||1|
|Gonggong||Scattered disc (10:3)||554||3.63||1230||35%||1|
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:
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.
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.
Visualized: The World’s Population at 8 Billion
Our population will soon reach a new milestone—8 billion. These visualizations show where all those people are distributed around the world
Visualized: The World’s Population at 8 Billion
At some point in late 2022, the eight billionth human being will enter the world, ushering in a new milestone for humanity.
In just 48 years, the world population has doubled in size, jumping from four to eight billion. Of course, humans are not equally spread throughout the planet, and countries take all shapes and sizes. The visualizations in this article aim to build context on how the eight billion people are distributed around the world.
For extended coverage of this moment and what it means to the world, you can get access to our full report and webinar by signing up to VC+, our premium newsletter.
Now, here’s a look at each country’s population as of September 2022:
|Global Rank||Country/Region||Population (2022)|
|3||🇺🇸 United States||335,391,957|
|16||Democratic Republic of Congo||96,104,525|
|92||United Arab Emirates||10,164,747|
|97||Papua New Guinea||9,342,727|
|104||Hong Kong SAR||7,635,279|
|125||Central African Republic||5,025,077|
|136||Bosnia and Herzegovina||3,235,985|
|154||Trinidad and Tobago||1,409,672|
|173||Micronesia (Fed. States of)||561,300|
|188||Sao Tome and Principe||228,652|
|196||Saint Vincent and the Grenadines||111,732|
|199||United States Virgin Islands||104,083|
|200||Antigua and Barbuda||99,773|
|202||Isle of Man||86,049|
|208||Northern Mariana Islands||58,336|
|211||Saint Kitts and Nevis||54,052|
|214||Turks and Caicos||39,924|
|220||British Virgin Islands||30,687|
|227||Wallis and Futuna||10,818|
|230||Saint Pierre & Miquelon||5,732|
Below are regional breakdowns of population.
Africa’s Population by Country
As of 2022, Africa’s total population stands at 1.4 billion people. Many of the countries with the fastest growth rates are located in Africa and by 2050, the population of the continent is expected to jump to 2.5 billion.
Nigeria is Africa’s most populous country and its largest economy. Based on current growth rates, Nigeria’s largest city, Lagos, could even emerge as the world’s top megacity by the end of the century.
Africa has by far the lowest median age of any of the other continents.
Asia’s Population by Country
With 4.7 billion people in 2022, Asia is by far the world’s most populous region.
The continent is dominated by the two massive population centers of China and India. In 2023, a big shift will occur, with India surpassing China to become the world’s most populous country. China has held top spot for centuries, but the mismatch between the two countries’ growth rates made it only a matter of time before this milestone arrived.
Asia is a region of contrast when it comes to population growth. On the one end are countries like Singapore and Japan, which are actually shrinking. On the other, are Middle Eastern nations like Oman and Qatar, which have robust population growth rates of 4-5%.
Vietnam is on the cusp of becoming the 15th country to surpass the 100 million population mark.
Europe’s Population by Country
Europe’s population in 2022 is 750 million people—more than twice the size of the United States.
A century ago, Europe’s population was close to 30% of the world total. Today, that figure stands at less than 10%. This is, in part, due to population growth throughout other regions of the world.
More importantly though, Europe’s population is contracting in a number of places—Eastern Europe in particular. Many of the countries with the slowest growth rates are located in the Balkans and former Soviet Bloc countries.
Russia remains Europe’s largest country by population. Although the country’s landmass extends all the way across Asia, three-quarters of Russia’s people live on the European side of the country.
Germany is the second largest country in Europe, followed by the UK, France, and Italy.
Ukraine is the seventh largest population center in Europe, but it remains to be seen how the current conflict with Russia impacts the country’s long-term population prospects.
North America’s Population by Country
North America’s population is 602 million people as of 2022.
The continent is dominated by the United States, which makes up more than half of the total population. America’s population is still growing modestly (by global standards), but perhaps more interesting are the internal migration patterns that are occurring. States like Texas and Florida are seeing an influx from other states.
Canada has one of the highest population growth rates of major developed economies thanks to international migration.
Mexico is currently the 10th most populous country, but will eventually be bumped from the top 10 list by fast-growing African nations.
South America’s Population by Country
The population of South America in 2022 is 439 million. Brazil makes up nearly half of that total.
Sometime this decade, Colombia’s capital, Bogotá, will become the region’s fifth megacity (which is defined as having a population of 10 million or more). São Paulo, Rio de Janeiro, Buenos Aires, and Lima are South America’s current megacities.
Oceania’s Population by Country
The population of the Oceania region is 44 million people—just slightly higher than the population of California.
Australia, New Zealand, and Papua New Guinea make up the lion’s share of the population of this region.
Interestingly, many of the smallest countries by population can also be found in this region.
When Will Earth’s Population Hit 9 Billion?
The next global population milestone—nine billion—will likely be hit sometime in the 2030s.
In fact, Earth’s population is expected to continue growing until it hits a peak at some point in the 2080s—possibly over the 10 billion mark.
Explainer: The Basics of DNA and Genetic Systems
All living things have a genetic system made up of DNA. This graphic explores the basics of DNA composition and structure.
Explainer: The Basics of DNA and Genetic Systems
While there is great diversity among living things, we all have one thing in common—we all rely on a genetic system made up of DNA and/or RNA.
But how do genetic systems work, and to what extent do they vary across species?
This graphic by Anne-Lise Paris explores the basics of DNA and genetic systems, including how they’re structured, and how they differ across species.
Composition of Genetic Systems: DNA and RNA
A genetic system is essentially a set of instructions that dictate our genetic makeup—what we look like and how we interact with our environment.
This set of instructions is stored in nucleic acids, the two main types being deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA is made up of four molecules, known as nucleotides: Adenine (A), Thymine (T), Cytosine ( C), and Guanine (G). These nucleotides are grouped in sets of two, which are called base pairs.
Size of Genomes Across Different Organisms
Human DNA is made up of approximately 3.2 billion base pairs that are tightly wound up and stored in our cells. If you were to unwind and measure the DNA stored in a single human cell, it would be about 2 meters (6.5 feet) long!
This lengthy DNA is stored in pairs of chromosomes. A full collection of chromosomes, or an entire set of genetic information, is referred to as a genome.
Genomes vary in size, depending on the organism. Here is a look at 24 different species and the size of their genomes, from animals and plants to bacteria and viruses:
|Organism||Kingdom||Size of genomes (number of base pairs)|
|Hepatitis D virus||Virus||1,700|
The Marbled Lungfish has the largest known animal genome. Its genome is made up of 130 billion base pairs, which is about 126.8 billion more than the average human genome.
Comparatively, small viruses and bacteria have fewer base pairs. The Hepatitis D virus has only 1,700 base pairs, while E. coli bacteria has 4.6 million. Interestingly, research has not found a link between the size of a species’ genome and the organism’s size or complexity.
In fact, there are still a ton of unanswered questions in the field of genome research. Why do some species have small genomes? Why do some have a ton of redundant DNA? These are still questions being investigated by scientists today.
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