* Surface Temperature: This depends on how close a planet is to the sun and its atmosphere.

* Internal Heat: This is generated by a planet's core and can be significant, even for planets farther from the sun.

Here's a breakdown based on both definitions:

By Surface Temperature:

1. Venus: The hottest planet in our solar system, with a surface temperature of about 867°F (464°C) due to a dense, toxic atmosphere that traps heat.

2. Mercury: While closest to the sun, Mercury has a very thin atmosphere, causing extreme temperature swings between day and night. Its average temperature is about 333°F (167°C).

3. Earth: Our home planet has an average surface temperature of 59°F (15°C).

4. Mars: Much colder than Earth, with an average temperature of about -81°F (-63°C).

5. Jupiter: A gas giant with no solid surface, but its upper atmosphere averages around -234°F (-148°C).

6. Saturn: Another gas giant with an average temperature of about -288°F (-178°C).

7. Uranus: This ice giant has an average temperature of -320°F (-195°C).

8. Neptune: The furthest planet from the sun, Neptune has an average temperature of -353°F (-214°C).

By Internal Heat:

* Jupiter: While its surface is incredibly cold, Jupiter generates more heat internally than it receives from the sun. This is due to its rapid rotation and gravitational pressure.

* Saturn: Saturn also generates significant internal heat, though less than Jupiter.

* Neptune: Neptune's internal heat is thought to be surprisingly high for a planet so far from the sun.

Therefore:

* Based on surface temperature, the 6th, 7th, and 8th hottest planets are: Saturn, Uranus, and Neptune, respectively.

* Based on internal heat, the 6th, 7th, and 8th hottest planets are more difficult to rank, but Neptune likely falls within the top 3 for internal heat generation.

It's important to remember that these rankings are based on current scientific understanding, and more information about the internal structure and heat generation of these planets may be revealed in the future.