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June 6, 2022 • 16 minutes ago • 4 minutes reading • Join the conversation
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THE CONVERSATION
This article was originally published in The Conversation, an independent, non-profit source of news, analysis, and commentary from academic experts. Disclosure information is available on the original site.
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Author: Samantha Lawler, Assistant Professor, Astronomy, Regina University
Curious Kids is a series for kids of all ages. Do you have any questions that you would like an expert to answer? Send it to CuriousKidsCanadaâ † * theconversation.com.
Why does it matter if Pluto is a planet or a dwarf planet? Because for me it just makes it more confusing in our solar system. I know some things in space are planets and other stars and other names like moons or comets. Dwarf Planet is a different name and I think it just makes it more confusing. –
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Timmy, 11, Kitchener, Ontario.
“Comet”, “star” and “planet” are category names that immediately tell you something important about what they describe.
Our solar system is made up of the sun, planets (orbiting the sun) and small bodies (orbiting the sun or planets). The category of “small bodies” is divided into even smaller categories, depending mainly on the shape and size of the orbits.
In 1801, astronomers discovered Ceres, which was initially classified as a “planet”. Astronomers measured that it was much smaller than other known planets. Soon, many smaller objects were discovered in orbits very close to Ceres. These small bodies were classified as “asteroids” and since then we have discovered hundreds of thousands of them in the asteroid belt.
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New discoveries
A similar process of discovery and re-categorization occurred for smaller bodies further away from the solar system.
Pluto was discovered in 1930 and for many decades was called the ninth planet in our solar system. But astronomers soon learned that Pluto was quite different from the other eight planets: it is in an inclined orbit and is much smaller than the other planets.
Over the years, astronomers have discovered more and more small, planet-like objects that have crossed Pluto’s orbit. They are now classified as “Kuiper belt objects”. It seemed more and more that Pluto would fit better with the category of Kuiper Belt objects than with the planets.
In 2005, a new object was discovered in the outer solar system, Eris, which is even heavier than Pluto. This led astronomers to consider whether Eris and Pluto are planets or not. Astronomers thought this was an important enough decision that the International Astronomical Union voted on in 2006. Astronomers decided that instead of degrading Pluto to a simple object in the Kuiper belt, they would make a new small body category. called the “dwarf planet”. Pluto and Eris would be part of this new category.
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How planets form
Solar systems like ours are formed from large clouds of dust and gas collapsing into disks around young stars, but astronomers are still learning exactly how this process works. We use telescopes to look closely at how distant solar systems form, but they are so far away that it is very difficult to see the planets forming directly.
A planetesimal, a baby planet, is first formed from groups of dust in a disk orbiting a young star. Then the planetesimals pick up nearby pebbles, dust, and sometimes even smaller planetesimals with their gravity, which gets stronger as they get older. When they reach a few hundred kilometers in diameter, they have enough gravity to take on a round shape, which is the definition of a dwarf planet.
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Measuring small bodies in our solar system, including the dwarf planets, and comparing them to computer simulations is another way of looking at how our solar system formed. Our current theory is that there must have been many dwarf planets that formed in our solar system.
Ceres, in the asteroid belt, and Pluto, Eris, and a dozen other objects in the Kuiper belt are large enough to be in the dwarf planet category. This means that although they are planetesimals that grew large enough to be round, they did not develop a gravity strong enough to hold all the other planetesimals close to their orbit.
Other solar systems
Astronomers have now measured more than 5,000 exoplanets, planets from other solar systems. We won’t be able to measure dwarf planets there for long, but the ones we’ve found in our own solar system can teach us how planets form everywhere.
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Hello, curious children! Do you have any questions that you would like an expert to answer? Ask an adult to submit your question to CuriousKidsCanadaâ † * theconversation.com. Please tell us your name, age and the city where you live.
And since curiosity has no age limit: adults, let us know what you’re wondering. We will not be able to answer all the questions, but we will do our best.
Samantha Lawler receives funding from the Natural Sciences and Engineering Research Council of Canada.
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This article is republished from The Conversation under a Creative Commons license. Disclosure information is available on the original site. Read the original article:
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