Eli5: How does the core of the Earth (or any planets) not cool and still give off tons of heat energy? Where is this energy coming from?
In: 202
The core is 19,400,000,000,000,000,000,000,000 kilograms. That does cool down if you give it a few billion years.
I had also read that the pull of gravity by the moon and sun cyclically deforms the earth, creating internal friction that also contributes to added heating. Somebody more knowledgeable on the topic can expand on this.
As rest said, they cool off. Smaller planets cool off faster (still 100s of millions to billions of years).
That happened to Mars: core cooled, because of that magnetic field dissipated (no circling core to generate it), and that exposed surface of the planet to the Solar wind. It is assumed that is how Mars was stripped of water. Solar wind blew off atmosphere (no magnetic field to protect it), lowered pressure, water evaporated and subsequently was blown off as well.
It is stipulated that hot circling core and magnetic field due to that might be important for sustainability of the life on the planets. So smaller planets might not be good places long term as they cool off faster.
I’d say the earths impact with the moon billions of years ago would be the attributing factor for the amount of heat it’s been able to hold in comparison to the other planets that are pretty much dead or dying
The core is 19,400,000,000,000,000,000,000,000 kilograms. That does cool down if you give it a few billion years.
I’d say the earths impact with the moon billions of years ago would be the attributing factor for the amount of heat it’s been able to hold in comparison to the other planets that are pretty much dead or dying
Since space is mostly empty space, the process of losing heat is very slow. Typically heat transfer happens through conduction and convection, that is a warmer object is bleeding off heat to surrounding matter, which is typically a gas or fluid surrounding it. In space, this effectively doesn’t happen, since there’s very little matter in between bodies to transfer that heat to. So most of the heat is transferred through infrared radiation. This is a much slower process than the other two, and in the case of planets their cooled outer shell acts as further insulation which means that the rate at which a planetary body cools gets slower as the outside is cooling. In the case of Earth there’s even more insulation because of the atmosphere.
So the Earth is cooling, just very very slowly.
The planet is cooling off, although very slowly. Heat in the inner planet has three sources:
Original heat present when the planet formed
Heat given off via radioactive decay
Heat given off when liquid outer core iron crystallizes at the inner/outer core boundary.
Eventually the latter two will subside and Earth will slowly cool down permanently.
Since space is mostly empty space, the process of losing heat is very slow. Typically heat transfer happens through conduction and convection, that is a warmer object is bleeding off heat to surrounding matter, which is typically a gas or fluid surrounding it. In space, this effectively doesn’t happen, since there’s very little matter in between bodies to transfer that heat to. So most of the heat is transferred through infrared radiation. This is a much slower process than the other two, and in the case of planets their cooled outer shell acts as further insulation which means that the rate at which a planetary body cools gets slower as the outside is cooling. In the case of Earth there’s even more insulation because of the atmosphere.
So the Earth is cooling, just very very slowly.
It’s a function of volume and surface area.
Think about it this way:
If you’ve got a cup of normal-sized ice cubes, they’ll melt in a handful of minutes.
If you’ve got a cup with a cup with a single, big ice cube in it, it’ll last much much longer. Hours maybe. Even if it’s technically the same amount of ice.
And if you’ve got a bunch of crushed ice or snow, it’ll melt in an instant. Once again, even if it’s the same amount of ice, just crushed up.
This is because the only part of a thing that can melt (or cool, if it’s hot) is the part on the outside. So the more outside a thing has relative to the total volume (the more surface area it has), the faster it will warm up or cool down.
For example, back before refrigeration, people used to harvest ice for the summer months. They’d take enormous ice blocks, pile them up in huge insulated “ice houses” and cover them in saw dust to insulate them further. But mainly because these huge piles of ice had a lot more “inside” (volume) than “outside” (surface area) they would last for *months or years,* even though it was really just a big ice cube slowly melting.
Intuitively, we think that if a block of ice is twice as big, it’ll take twice as long to melt, but this isn’t true. It’ll take much longer.
—-
Now if we talk about the Earth:
Yes, there’s radioactive elements slowly decaying deep inside it, and this creates heat.
And yes, the tidal pull of the moon stretches and squishes the Earth somewhat, generating heat. No idea off the top of my head how significant either of these things are.
But the main reason it’s still hot is simply that it started out really hot a long time ago, and it’s really really really big. It has enormous volume relative to its surface area, and it takes an enormous amount of time for all of that heat to slowly slowly bleed away. And meanwhile, the cooler outer layers act like insulation, further slowing the process.
**TL:DR: A red hot ball of iron a thousand miles in diameter, insulated by thousands of miles of solid rock, will stay hot for billions of years. Because it’s big.**
Latest Answers