Why is the Earth's size not odd?

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In summary: However, it is interesting to know that it may have been a touch of luck that the Earth was the right size for life to evolve. Additionally, it is interesting to know that the atmosphere on Earth is necessary for organisms to live. Lastly, it is interesting to know that water must be at a certain pressure to be liquid.
  • #1
AtomicJoe
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It is bigger than all it's neighbours, which is odd.
Obviously it is not as big as the gas giants but they are not real solid planets.


[PLAIN]http://blrdb.com/images/BlrDb_Astronomy_Planet_Sizes.gif
 
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  • #2
I don't accept your premise: it is only 5% bigger than Venus, so that's not odd.
 
  • #3
Well, Earth was a bit smaller until something the size of Mars made a glancing collision, donating its iron core, and their crustal debris congealed as our Moon...
 
  • #4
russ_watters said:
I don't accept your premise: it is only 5% bigger than Venus, so that's not odd.

That is the diameter, the volume is 15% bigger, but nonetheless it is curious we are the biggest small planet.


What determined our size? And indeed the sizes of the other planets?

Somebody must know.
 
  • #5
AtomicJoe said:
That is the diameter, the volume is 15% bigger, but nonetheless it is curious we are the biggest small planet.


What determined our size? And indeed the sizes of the other planets?

Somebody must know.
Chance determined the size. Things collide. Things collect together. Things get destroyed.

http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System
 
  • #6
AtomicJoe said:
It is bigger than all it's neighbours, which is odd.
Obviously it is not as big as the gas giants but they are not real solid planets.[PLAIN]http://blrdb.com/images/BlrDb_Astronomy_Planet_Sizes.gif[/QUOTE]

The Earth may be close to the limit a rocky body can be and still have been stable during its formation in terms of the tidal forces in the inner solar system. Look up the Roche limit.
 
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  • #7
AtomicJoe said:
It is bigger than all it's neighbours, which is odd.
Obviously it is not as big as the gas giants but they are not real solid planets.


[PLAIN]http://blrdb.com/images/BlrDb_Astronomy_Planet_Sizes.gif[/QUOTE]

In the context of the universe, it's pretty damn small.
 
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  • #9
One may perhaps even speculate that there may be a touch of Anthropic Principle [1] at work here. For instance, it may conceivably be that it is more rare for life to evolve on a smaller planet that a large planet because smaller planets are less able to hold on to the heavier elements in an atmosphere. Or one could speculate that during solar system formation planets that form in the habitable zone [2] have a tendency to be "larger" rather than "smaller" through some mechanism.

[1] http://en.wikipedia.org/wiki/Anthropic_principle
[2] http://en.wikipedia.org/wiki/Habitable_zone
 
  • #10
As an above user said, a large Mars-sized body crashed into the Earth during its early development.

Also, being made of iron, naturally, gravity attracts the lighter elements.
 
  • #11
jduster said:
As an above user said, a large Mars-sized body crashed into the Earth during its early development.

Also, being made of iron, naturally, gravity attracts the lighter elements.

Gravity affects all elements almost equally. Until you get to a large fraction of the Earth's mass, the acceleration due to gravity on the surface is still about 9.8 m/s^2.
 
  • #12
What Filip Larsen mentioned may be interpreted as a form of natural selection. The Earth is the size it is because if it was much smaller, it could not allow us to come into existence.

Earth organisms need liquid water to metabolize and grow in, and water will not be liquid below its triple-point pressure. So there must be something creating that pressure, and on the Earth, it's the atmosphere. If the Earth was much smaller and less massive, its escape velocity would be much less, and its atmosphere would escape into outer space.
 
  • #13
^ which is what happened with the hydrogen and helium in our atmosphere during the early Earth
 
  • #14
I suspect that if Earth was the smallest planet in the solar system, you would be saying:

"It is smaller than all it's neighbours, which is odd.
Obviously it is not as small as the moons but they are not real planets."

There is nothing odd about the Earth's size. Or at least, we cannot say anything at this time with regards to it's oddness.
 

FAQ: Why is the Earth's size not odd?

1. Why is the Earth so much bigger than other planets?

The Earth is bigger than other planets in our solar system because it is located in the habitable zone, also known as the "Goldilocks zone". This means that it is the perfect distance from the sun to have temperatures that allow for liquid water to exist on its surface. This liquid water, along with other factors such as a solid surface and a protective atmosphere, make Earth ideal for supporting life. Other planets in our solar system either lack these conditions or are too close or too far from the sun to sustain life.

2. What factors determine the size of a planet?

The size of a planet is determined by its mass and the materials it is made up of. Planets with a larger mass and more dense materials tend to be bigger in size. Additionally, the location of a planet in its solar system and the amount of gravitational force it experiences from its star can also impact its size. Planets that are closer to their star tend to be smaller due to the intense heat and gravity they experience.

3. How does the Earth's size affect its gravitational pull?

The Earth's size directly affects its gravitational pull. The larger the mass of an object, the stronger its gravitational pull. This is why the Earth has a stronger gravitational pull than other smaller objects, such as the moon. This gravitational pull is what keeps us and other objects on the Earth's surface, and also helps to maintain the Earth's atmosphere.

4. Can the Earth's size change over time?

The Earth's size does change over time, but these changes are very gradual and can only be observed over long periods. The Earth is constantly being bombarded by meteorites and other space debris, which adds to its mass and may cause it to grow slightly. However, the Earth also loses mass through processes such as evaporation and erosion. Overall, these changes do not significantly alter the Earth's size.

5. How does the Earth's size compare to other planets in the universe?

The Earth is relatively small compared to other planets in the universe. In fact, it is considered a "small" or "terrestrial" planet, meaning it is mostly made up of rock and metal and has a solid surface. Larger planets in the universe, known as gas giants, are mainly composed of gas and have no solid surface. These gas giants, such as Jupiter and Saturn, can be thousands of times larger than the Earth in terms of mass and size.

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