Asteroids: Crash Course Astronomy #20

Summary

This script explores the fascinating world of asteroids, from their discovery in the gap between Mars and Jupiter to the diverse types found in the solar system. It delves into the composition of these celestial bodies, the Kirkwood Gaps, asteroid families, and the largest asteroid, Ceres. It also discusses the concept of asteroid belts, their actual sparseness, and the various classifications of asteroids, including Near-Earth Asteroids and Trojan asteroids. The script concludes with the naming conventions of asteroids and their importance in astronomical studies.

Takeaways

• 📅 The discovery of Ceres in 1801 marked the beginning of the recognition of a new class of solar system objects, initially thought to be the 'missing planet' between Mars and Jupiter.
• 🌌 The term 'asteroids' was coined for these celestial bodies, which are like stars in appearance but are smaller and rocky or metallic in composition.
• 🔍 Over time, the number of known asteroids has grown exponentially, with hundreds of thousands identified and potentially billions larger than 100 meters across in the solar system.
• 🪨 Asteroids are categorized into types based on their composition: carbonaceous, silicaceous, and metallic, with the majority being carbonaceous.
• 💫 The region where most asteroids are found between Mars and Jupiter is known as the Main Belt, which has a structure influenced by gravitational interactions with Jupiter.
• 🚀 Spacecraft like Dawn have visited and are studying asteroids, providing new insights into their composition and history, such as the presence of water on Ceres.
• 🌑 Asteroids can form families with similar orbits, suggesting a common origin from a disrupted larger body, like the Eunomia family.
• 🌐 The Main Belt is not densely packed; asteroids are spaced millions of kilometers apart, contrary to popular depictions in media.
• 🌍 Some asteroids have orbits that bring them close to Earth, categorized as Near-Earth Asteroids, with some being Mars-crossing or even Earth-approaching.
• 🌑 Asteroids are remnants from the early solar system, possibly once part of larger bodies that were broken apart by collisions and gravitational disturbances.
• 🌐 Trojan asteroids, found in Lagrange points, share an orbit with planets like Jupiter, and even Earth, maintaining a relative position due to balanced gravitational forces.

Q & A

What significant event occurred on January 1, 1801, related to the solar system?

On January 1, 1801, Italian astronomer Giuseppi Piazzi discovered a point of light moving at the right speed to be the desired planet between Mars and Jupiter, which was later named Ceres.

What is the term used to describe the celestial bodies found between Mars and Jupiter, and what does it mean?

The term used to describe these celestial bodies is 'asteroids', which literally means 'star-like', as they were points of light like stars when viewed through telescopes.

How many asteroids are known to exist in the solar system today?

Today, we know of hundreds of thousands of asteroids, with estimates suggesting there could be billions of them larger than 100 meters across in the solar system, and over a million larger than 1 km in size.

What is the general definition of an asteroid?

An asteroid is generally defined as a class of smaller bodies that are rocky or metallic, orbiting the Sun out to Jupiter.

What are the three main compositions of asteroids?

The three main compositions of asteroids are carbonaceous, which contains lots of carbon; silicaceous, which is heavy on silicon-based materials or rock; and a catch-all category dominated by metallic objects rich in iron, nickel, and other metals.

What is the Kirkwood Gap and how is it formed?

The Kirkwood Gap is a region in the asteroid belt where very few asteroids are found, approximately 425 million kilometers from the Sun. It is formed due to Jupiter's gravity repeatedly pulling asteroids out of that orbit, as any asteroid there would have an orbital period that is a simple fraction of Jupiter's period.

What is the significance of the Ceres asteroid, and what spacecraft is currently visiting it?

Ceres is the largest asteroid, about 900 km across, and is nearly spherical due to its own gravity. It is currently being visited by a spacecraft named Dawn, which may provide new insights into its composition and structure.

What are asteroid families, and how do they form?

Asteroid families are groups of asteroids that have similar orbits and are thought to have formed from a larger parent asteroid that was disrupted by an impact.

Why is the asteroid belt mostly empty space, and how far apart are asteroids on average?

The asteroid belt is mostly empty space because, on average, decent-sized asteroids are millions of kilometers apart, so far that if you stood on an asteroid, you likely wouldn't be able to see another one with the naked eye.

What are Near-Earth Asteroids, and how are they categorized?

Near-Earth Asteroids are asteroids whose orbits bring them close to Earth. They include Apollo asteroids, which cross Earth's orbit, and Aten asteroids, which have orbits almost entirely inside Earth's orbit.

What are Trojan asteroids, and how are they named?

Trojan asteroids are those that occupy the Lagrange points along the same orbit as a planet, but 60° ahead or behind. They are named after Greek and Trojan figures from the Trojan War, with the first found being named Achilles.

What is the current naming convention for asteroids, and how does it relate to the International Astronomical Union?

Originally, asteroids were named after female goddesses, but as more were discovered, astronomers were allowed to name them through a lengthy proposal and acceptance process governed by the International Astronomical Union. They are also assigned a number.

What is the role of observatories and surveys in monitoring Near-Earth Asteroids, and why is it important?

Observatories and surveys scan the skies to monitor Near-Earth Asteroids to assess the potential risk they pose to Earth. This is important because some of these asteroids have orbits that intersect with Earth's, posing a potential impact threat.