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.
Mapped: Human Impact on the Earth’s Surface
This detailed map looks at where humans have (and haven’t) modified Earth’s terrestrial environment. See human impact in incredible detail.
Mapped: Human Impact on the Earth’s Surface
With human population on Earth approaching 8 billion (we’ll likely hit that milestone in 2023), our impact on the planet is becoming harder to ignore with each passing year.
Our cities, infrastructure, agriculture, and pollution are all forms of stress we place on the natural world. This map, by David M. Theobald et al., shows just how much of the planet we’ve now modified. The researchers estimate that 14.6% or 18.5 million km² of land area has been modified – an area greater than Russia.
Defining Human Impact
Human impact on the Earth’s surface can take a number of different forms, and researchers took a nuanced approach to classifying the “modifications” we’ve made. In the end, 10 main stressors were used to create this map:
- Built-Up Areas: All of our cities and towns
- Agriculture: Areas devoted to crops and pastures
- Energy and extractive resources: Primarily locations where oil and gas are extracted
- Mines and quarries: Other ground-based natural resource extraction, excluding oil and gas
- Power plants: Areas where energy is produced – both renewable and non-renewable
- Transportation and service corridors: Primarily roads and railways
- Logging: This measures commodity-based forest loss (excludes factors like wildfire and urbanization)
- Human intrusion: Typically areas adjacent to population centers and roads that humans access
- Natural systems modification: Primarily modifications to water flow, including reservoir creation
- Pollution: Phenomenon such as acid rain and fog caused by air pollution
The classification descriptions above are simplified. See the methodology for full descriptions and calculations.
A Closer Look at Human Impact on the Earth’s Surface
To help better understand the level of impact humans can have on the planet, we’ll take a closer look three regions, and see how the situation on the ground relates to these maps.
Land Use Contrasts: Egypt
Almost all of Egypt’s population lives along the Nile and its delta, making it an interesting place to examine land use and human impact.
The towns and high intensity agricultural land following the river stand out clearly on the human modification map, while the nearby desert shows much less impact.
Intensive Modification: Netherlands
The Netherlands has some of the heavily modified landscapes on Earth, so the way it looks on this map will come as no surprise.
The area shown above, Rotterdam’s distinctive port and surround area, renders almost entirely in colors at the top of the human modification scale.
Resource Extraction: West Virginia
It isn’t just cities and towns that show up clearly on this map, it’s also the areas we extract our raw materials from as well. This mountainous region of West Virginia, in the United States, offers a very clear visual example.
The mountaintop removal method of mining—which involves blasting mountains in order to retrieve seams of bituminous coal—is common in this region, and mine sites show up clearly in the map.
You can explore the interactive version of this map yourself to view any area on the globe. What surprises you about these patterns of human impact?
Interactive Map: Tracking Global Hunger and Food Insecurity
Every day, hunger affects more than 700 million people. This live map from the UN highlights where hunger is hitting hardest around the world.
Interactive Map: Tracking Global Hunger and Food Insecurity
Hunger is still one the biggest—and most solvable—problems in the world.
Every day, more than 700 million people (8.8% of the world’s population) go to bed on an empty stomach, according to the UN World Food Programme (WFP).
The WFP’s HungerMap LIVE displayed here tracks core indicators of acute hunger like household food consumption, livelihoods, child nutritional status, mortality, and access to clean water in order to rank countries.
After sitting closer to 600 million from 2014 to 2019, the number of people in the world affected by hunger increased during the COVID-19 pandemic.
In 2020, 155 million people (2% of the world’s population) experienced acute hunger, requiring urgent assistance.
The Fight to Feed the World
The problem of global hunger isn’t new, and attempts to solve it have making headlines for decades.
On July 13, 1985, at Wembley Stadium in London, Prince Charles and Princess Diana officially opened Live Aid, a worldwide rock concert organized to raise money for the relief of famine-stricken Africans.
The event was followed by similar concerts at other arenas around the world, globally linked by satellite to more than a billion viewers in 110 nations, raising more than $125 million ($309 million in today’s dollars) in famine relief for Africa.
But 35+ years later, the continent still struggles. According to the UN, from 12 countries with the highest prevalence of insufficient food consumption in the world, nine are in Africa.
|Country||% Population Affected by Hunger||Population (millions)||Region|
|Burkina Faso 🇧🇫||61%||19.8||Africa|
|South Sudan 🇸🇸||60%||11.0||Africa|
|Sierra Leone 🇸🇱||55%||8.2||Africa|
|Syria 🇸🇾||55%||18.0||Middle East|
|Yemen 🇾🇪||44%||30.0||Middle East|
Approximately 30 million people in Africa face the effects of severe food insecurity, including malnutrition, starvation, and poverty.
Although many of the reasons for the food crisis around the globe involve conflicts or environmental challenges, one of the big contributors is food waste.
According to the United Nations, one-third of food produced for human consumption is lost or wasted globally. This amounts to about 1.3 billion tons of wasted food per year, worth approximately $1 trillion.
All the food produced but never eaten would be sufficient to feed two billion people. That’s more than twice the number of undernourished people across the globe. Consumers in rich countries waste almost as much food as the entire net food production of sub-Saharan Africa each year.
Solving Global Hunger
While many people may not be “hungry” in the sense that they are suffering physical discomfort, they may still be food insecure, lacking regular access to enough safe and nutritious food for normal growth and development.
Estimates of how much money it would take to end world hunger range from $7 billion to $265 billion per year.
But to tackle the problem, investments must be utilized in the right places. Specialists say that governments and organizations need to provide food and humanitarian relief to the most at-risk regions, increase agricultural productivity, and invest in more efficient supply chains.
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