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š¬ Think about it
Imagine eight friends standing at different distances from a bonfire. The closest feels hot, the farthest feels cold. The planets are like that around the Sun. But there is a surprise — one planet breaks the rule. Let us find out which.
What are the planets of our solar system?
- Eight planets go around the Sun in nearly circular orbits.
- In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- Mercury, Venus, Earth and Mars are small rocky planets.
- Jupiter, Saturn, Uranus and Neptune are large gas planets.
Rocky planets
Gas planets
Small and made of rock
Large and mostly gas
Mercury, Venus, Earth, Mars
Jupiter, Saturn, Uranus, Neptune
Closer to the Sun
Farther from the Sun
In this Activity, we will collect information about the temperature, size and atmosphere of the planets in the solar system.
Materials needed
Library books or trusted websites, notebook and Table 13.2.
Procedure
1. Collect information about the temperature and size of the planets.
2. Check if each planet has an atmosphere.
3. Use school library books, trusted websites, or ask your teacher.
4. Fill out the missing information in Table 13.2.
2. Check if each planet has an atmosphere.
3. Use school library books, trusted websites, or ask your teacher.
4. Fill out the missing information in Table 13.2.
Table 13.2 — Planets in our solar system
| S.No. | Planet | Average temperature (°C) | Radius, compared to the Earth | Has an atmosphere? |
|---|---|---|---|---|
| 1. | Mercury | 170 | 0.38 | No |
| 2. | Venus | 450 | 0.95 | Yes |
| 3. | Earth | 15 | 1 | Yes |
| 4. | Mars | −65 | 0.53 | Yes |
| 5. | Jupiter | −110 | 11 | Yes |
| 6. | Saturn | −140 | 9 | Yes |
| 7. | Uranus | −195 | 4 | Yes |
| 8. | Neptune | −200 | 4 | Yes |
Observation
Generally, planets closer to the Sun are hotter and far ones are colder. But Venus is the hottest, not Mercury.
Explanation
All planets get energy from the Sun, so closeness should mean more heat. Venus breaks this rule because its thick atmosphere traps heat.
ā Summary
- Planet data collected
- Closer means hotter
- Venus is hottest
- Atmosphere traps heat
Why is Venus the hottest planet, not Mercury?
- Mercury is closer to the Sun, so we expect it to be hottest.
- But Venus has a thick atmosphere of carbon dioxide gas.
- This gas does not let the heat escape.
- So heat is trapped, making Venus hotter than Mercury.
Why Venus Is the Hottest
Sun warms Venus
↓
Thick atmosphere
Venus has air almost all carbon dioxide.
↓
Heat trapped
The gas stops heat from escaping.
↓
Venus stays hotter than Mercury
What is the greenhouse effect?
- Gases like carbon dioxide in the air trap heat.
- They absorb the radiation given off by the warmed planet.
- This trapping of heat is called the greenhouse effect.
- On Earth, it helps keep just the right temperature.
Example:
The greenhouse effect is like a blanket that keeps the warmth in on a cold night.
š” A step further
- A planet's greenhouse effect is not the same as a plant greenhouse.
- On Venus or Earth, gases like carbon dioxide trap heat by absorbing radiation.
- A plant greenhouse traps warm air because it is a closed glass space.
- It heats up by day, but the warm air cannot escape.
- So both keep things warm, but in different ways.
Important Points
- The solar system has eight planets orbiting the Sun.
- Closer planets get more heat from the Sun.
- The greenhouse effect traps heat in a planet's atmosphere.
ā Test Yourself
-
How many planets are in the solar system?
View Answer
Eight planets. -
Which is the hottest planet?
View Answer
Venus, because its thick atmosphere traps heat. -
Name the four rocky planets.
View Answer
Mercury, Venus, Earth and Mars. -
What gas mostly makes up Venus's air?
View Answer
Carbon dioxide. -
Is the greenhouse effect helpful on Earth?
View Answer
Yes, it keeps Earth at just the right temperature.
Important Definitions
- Solar system — the Sun together with the eight planets that orbit it.
- Greenhouse effect — the trapping of heat by gases like carbon dioxide in a planet's atmosphere.
