Samantha Lawler (opens in a new tab), Assistant Professor, Astronomy, University of Regina “Why does it matter if Pluto is a planet or a dwarf planet? Why for me it makes it more confusing in our solar system. I know some things in space are planets and other stars and some are other names like moons or comets. The dwarf planet is a different name and I think it just makes it more confusing. ” – Timmy, 11, Kitchener, Ont. “Comet”, “star” and “planet” are category names that immediately tell you something important about what they describe. Our solar system consists of the sun, planets (orbiting the sun) and small bodies (either orbiting the sun or planets). The “small bodies” category is divided into even smaller categories (opens in a new tab), mainly depending on the shape and size of the tracks. In 1801, astronomers discovered Demeter, who was initially categorized as a “planet.” (opens in new tab) Astronomers have estimated that it was much smaller than the other known planets. Soon, many smaller objects were discovered in orbits very close to Dimitra. These tiny bodies have been categorized as “asteroids” and we have since discovered hundreds of thousands of them in the asteroid belt (opens in a new tab). Anniversary of Pluto Flight: The Most Amazing Photos from NASA’s New Horizons
New discoveries
A similar process of discovery and reclassification occurred for small bodies further out into the solar system. Pluto was discovered in 1930 (opens in a new tab) and was named the ninth planet in our solar system for many decades. But astronomers soon learned that Pluto was quite different from the other eight planets: it is in a sloping orbit and is much smaller than the other planets. Over the years, astronomers have discovered more and more small objects that look like planets orbiting Pluto. These are now categorized as “Kuiper Belt Objects (opens in a new tab).” He looked more and more like Pluto, which could be a better fit in the Kuiper belt category than the planets. In 2005, a new object was discovered in the outer solar system, Eris (opens in a new tab), which is even heavier than Pluto. This has led astronomers to wonder whether both Dispute and Pluto are planets. The astronomers considered that this was a very important decision that the International Astronomical Union passed in 2006 (opens in a new tab). Astronomers have decided that instead of reducing Pluto to a simple old object in the Kuiper Belt, they will create a new class of small bodies called a “dwarf planet (opens in a new tab).” Pluto and Eris would both be part of this new category.
Ceres, as seen from NASA’s Dawn spacecraft. (Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA)
How planets are formed
Solar systems like ours are formed by large clouds of dust and gas that collapse into disks around young stars, but astronomers are still learning exactly how this process works. We use telescopes to look closely (opens in a new tab) at the formation of solar systems far away, but it is so far away that it is really difficult to see the planets forming directly. A planet – a small planet – is initially formed by clusters of dust on a disk that revolves around a young star (opens in a new tab). The planetariums then grab nearby pebbles, dust and sometimes even smaller planetariums by their gravity, which becomes stronger as they grow older. When they reach a few hundred kilometers in diameter, they have enough gravity to pull themselves into a round shape, which is the definition of the dwarf planet (opens in a new tab).
The two images at the top reveal debris disks around young stars unearthed in archival images taken by NASA’s Hubble Space Telescope. The image below each image shows the orientation of the debris disks. (Image credit: (NASA / ESA, R. Soummer, Ann Feild (STScI)) Measuring small bodies in our solar system, including dwarf planets, and comparing them to computer simulations is another way to see how our solar system formed. Our current theory is that there must have been many dwarf planets formed in our solar system (opens in a new tab). Demeter, in the asteroid belt, and Pluto, Eris, and about a dozen other Kuiper Belt objects (opens in the new tab) are large enough to belong to the dwarf planet category. This means that while they are planetary that have grown large enough to be round, they have not developed a gravity strong enough to grab any other planetary near their orbit.
Other solar systems
Astronomers have now counted more than 5,000 exoplanets (opens in a new tab), planets in other solar systems. We will not be able to count dwarf planets there for long, but those we have found in our own solar system can teach us how planets form everywhere. This article is republished by The Conversation (opens in a new tab) with Creative Commons permission. Read the original article (opens in a new tab). Follow all of the Expert Voices topics and discussions – and join the discussion – on Facebook and Twitter. The views expressed are those of the author and do not necessarily reflect the views of the publisher.
