Super fact 55 : The enormous Kuiper belt.
The Kuiper Belt is a vast torus/donut shaped region of space beyond Neptune, filled with icy, rocky bodies, including dwarf planets like Pluto. It shares a lot of similarities with the Asteroid belt, but it is much larger, and further out. The Kuiper belt is 20 times wider than the Asteroid belt, 1,000 larger by volume, and 20 to 200 times more massive than the Asteroid belt. It extends from roughly 30 to 50 astronomical units (AU) from the Sun.
I can add that one Astronomical Unit (AU) is the distance from the sun to Earth.
The Kuiper belt is like a giant Asteroid belt located further out, beyond Neptune. The Kuiper Object Pluto, formerly known as the Planet Pluto, is the most admired, the cutest and most beloved of all planets, and it was the first Kuiper object discovered in 1930. However, we did not know of the existence of the Kuiper belt at the time. The Kuiper belt was discovered in 1992 and predicted to possibly exist by Astronomer Gerard Kuiper in 1951. The discovery of the Kuiper belt was one of the reasons Pluto was demoted from its planet status in 2006. There are other dwarf planets in the Kuiper belt similar Pluto, including Makemake, Haumea, and Eris. However, there could be hundreds. Ceres is a dwarf planet located in the Asteroid belt. To read more about the Kuiper belt and verify the facts above, click here, or here, or here.
I selected this to be a super fact because the existence of the Kuiper belt drastically changed our view of our Solar system, so it is important, we know it exists, so it is a true fact, and despite its enormous size the Kuiper belt is much less known than the Asteroid belt, and its existence often comes as a surprise to people.
The Kuiper Belt Resides in Darkness
You may wonder why the Kuiper belt was discovered so late whilst the Asteroid belt has been known since the beginning of the 19th century (Ceres 1801, Pallas 1802, Vesta 1807, etc.) The reason is that the Kuiper belt resides in darkness. The Asteroid belt is 2.2AU to 3.2AU from the sun whereas the Kuiper belt is between 30 to 50AU from the sun.
Let’s say you take an object that is 2.5AU from the sun and place it at a distance that is 40AU from the sun. Due to the spreading of the light the object will now receive 16 X 16 = 256 times less sunlight. This is called Geometric dilution. In addition, this light needs to be reflected back to earth for us to see the object, and once again the light will spread resulting in 256 X 256 = 65,536 times less light reaching our telescopes. The Kuiper belt is huge, but it resides in darkness. Despite this fact, we have now discovered and catalogued more than 2,000 Kuiper belt objects. However, it is estimated that there are hundreds of thousands of Kuiper belt objects wider than 100 kilometers.
What is a Dwarf Planet?
A planet as well as dwarf planet is a celestial body that orbits the Sun and is nearly round due to its own gravity. Basically, it must be large enough to have compressed itself to a near spherical shape. To be classified as a planet and not a dwarf planet it must also have cleared its orbit of debris. So, a dwarf planet is therefore a celestial body that orbits the Sun, is nearly round due to its own gravity, but has not cleared the neighborhood around its orbit. Obviously, a planet in the Asteroid belt or the Kuiper belt is a dwarf planet. Just to make this complicated Astronomers have found giant exoplanets that have not cleared their orbit of debris . I wonder, are these exo-planets giant dwarf planets?
Oort Cloud
Astronomer and Author David Lee Summers (blog here) reminded me of the Oort cloud, which could be interesting to bring up in this context. The Oort Cloud is a vast spherical cloud of icy bodies, which is hypothesized to surround the solar system, extending from about 2,000 to 200,000 AU. It is thus thousands of times further out and wide than the Kuiper belt. I say hypothesized because the objects are so small, there’s really no direct observation of them and there’s some variation in numbers for its distance and extent, meaning it’s still not well defined yet. Still, its outer edge is believed to be the boundary between where the sun’s gravity dominates and the galaxy’s gravity dominates.
The Oort cloud is generally considered to be the outer edge of the solar system and believed to be the origin of most long period comets. The Oort cloud is thought to encompass two regions: a disc-shaped inner Oort cloud aligned with the solar ecliptic (also called its Hills cloud) and a spherical outer Oort cloud enclosing the entire Solar System.
Other Astronomy Related Super Facts
- We are Star Dust
- The Strange Worlds of Exoplanets
- The vastness of space and the beginning of infinity
- The Bizarre Reality of Black Holes
- That Earth is round was well known long before Columbus
Super Facts 