Interplanetary medium

The heliospheric current sheet.

Along with light, the Sun radiates a continuous stream of charged particles (a plasma) known as the solar wind. This stream of particles spreads outwards at roughly 1.5 million kilometers per hour, creating a tenuous atmosphere (the heliosphere) that permeates the Solar System out to at least 100 AU. This is known as the interplanetary medium. Geomagnetic storms on the Sun’s surface, such as solar flares and coronal mass ejections, disturb the heliosphere, creating space weather. The Sun’s rotating magnetic field acts on the interplanetary medium to create the heliospheric current sheet, the largest structure in the solar system.

Aurora australis seen from orbit.

Earth’s magnetic field protects its atmosphere from interacting with the solar wind. Venus and Mars do not have magnetic fields, and the solar wind causes their atmospheres to gradually bleed away into space. The interaction of the solar wind with Earth’s magnetic field creates the aurorae seen near the magnetic poles.

Cosmic rays originate outside the Solar System. The heliosphere partially shields the Solar System, and planetary magnetic fields (for those planets that have them) also provide some protection. The density of cosmic rays in the interstellar medium and the strength of the Sun’s magnetic field change on very long timescales, so the level of cosmic radiation in the Solar System varies, though by how much is unknown.

The interplanetary medium is home to at least two disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes zodiacal light. It was likely formed by collisions within the asteroid belt brought on by interactions with the planets. The second extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt.

III. Answer the questions:

1. What elements does the Solar System consist of?

2. How many planets are there in the Solar System? Make a list of them.

3. How many planets have natural satellites? List them.

4. What is a planet?

5. Is Pluto a planet? Why?

6. What is the difference between a planet and a dwarf planet?

7. What small Solar System bodies do you know?

8. How do the astronomers measure the distance within the Solar System?

9. What is the distance between the Sun and the Earth?

10. How do different objects within the Solar System move?

11. Why do most of them move around the Sun?

12. What is the Sun?

13. How are the stars classified?

14. What is the future of the Sun?

15. How did the Sun form?

16. What is the interplanetary medium?

17. How many regions of the interplanetary medium do you know? What are they?

IV. Do you agree or disagree with the following statements? Prove your point of view.

1. The Solar System consists of the Sun and those celestial objects bound to it by gravity.

2. The Solar System includes terrestrial planets only.

3. There is only one natural satellite in the Solar System.

4. Objects orbiting the Sun are divided into three classes: planets, dwarf planets, and small Solar System bodies.

5. There is no difference between different objects of the Solar System.

6. One light-year, the best known unit of interstellar distance.

7. The Earth, Pluto and Venus are the largest bodies orbiting the Sun.

8. Objects travel around the Sun following Kepler’s laws of planetary motion.

9. The Sun is the Red gas giant.

10. The sun-light is the visible consequence of the nuclear fusion within the Sun.

11. The stars which are closer to the Sun hotter and brighter than the distant ones.

12. Now the Sun is halfway through its life cycle.

13. The interplanetary medium is the stream of the charged particles.

14. There is no activity on the Sun.

15. Heliosphere protects our system from cosmic radiation.