Background

Students may not think of the Solar System as dynamic, but gravitational interactions involving small Solar System objects have caused changes to their orbital motions, and these changes are still taking place. Asteroid orbits are changed by close encounters with more massive objects (especially the Sun and Jupiter). New comets making their first journey sunward often experience orbital and physical changes.

Studying the orbital properties and compositions of small Solar System objects provides clues to the formation and evolution of the Solar System. Near-Earth objects (NEOs) are detected and monitored for the purpose of protecting our planet. A long-term goal is to mine NEOs for valuable metals.

Openstax Astronomy textbook: Comets and Asteroids

Teacher Notes

1. Our investigations are designed so that students cannot proceed to the next page without answering each question. If you would like to quickly preview the entire investigation, you can use “educator mode” on the Start page. Enter the passphrase: 3ducatorMod3 to activate it.
   
   

2. The newly discovered objects on pp. 22-24 of the investigation are randomized, so every student gets unique objects to view.
   
   

3. This investigation emphasizes three orbital elements: eccentricity, inclination, and semi-major axis. However, in order for an orbit to be accurately defined, six elements are necessary. More background about the orbital elements may be found here.
   
   

4. The semi-major axis of an orbit is used as a proxy for its distance from the Sun. This is a standard practice used for objects in the Solar System.
   
   

5. A variety of objects are included in the data for this investigation. They are officially designated by the International Astronomical Union as small Solar System bodies. The four main groups used here are near-Earth objects (NEOs), main belt asteroids (MBAs), comets, and trans-Neptunian objects (TNOs). In this investigation, all small Solar System bodies (with the exception of comets) at the orbit of Neptune and beyond are collectively referred to as TNOs. This includes objects in the Kuiper Belt and the inner Oort Cloud. Likewise, all asteroids between the orbits of Mars (1.5 au) and Jupiter (5.2 au) are considered to be part of the main asteroid belt, even though the majority of main belt asteroids are located between 2.1 au - 3.3 au.
   
   

6. In the current version of this investigation, the positions of comets in their orbits are not accurate. (The positions of other Solar System bodies are correct.) Comets and asteroids discovered in the last several years may not appear in the data.
   
   

7. Solar System objects that appear to move faster across the background stars are closer to Earth and the Sun than objects that appear to move slowly. The observed motion is due to the object’s orbital speed and distance from the Sun, its distance from Earth, and Earth’s orbital speed around the Sun. This rule is generally true except for the brief period of time each year when the Earth passes a more distant object.