why are interiors of planets very hot??

Question

there are 3 options:
1. sunlight during planetary day penetrates the surface
2. gravitational energy released when particles accreted to form the planet and natural radioactivity within da planet.
3.nuclear fusion going on at the core like inside the sun but on a smaller scale.

Answer 1

There are plenty of options really, although 1 out of the three of your options are essentially correct.

#1 Doesn't make sense, it would be physically impossible (the inside of your body does not heat up more than your skin does when you stand in the sun). Though sunlight does give the earth a balmy 55 degree average temperature (and rising!).

#3 For fusion to occur, you need a much, much, much larger density of material (meaning larger overall mass). The minimum required is about 0.08 times the mass of the sun (the earth's mass is about 0.000003 times the mass of the sun, so it would have to be about 26,773 times heavier!).

Anyway, answer #2 is essentially correct. When the earth first formed from swirling clouds of dust, they spiraled inward, and the materials gravitational potential energy is converted into kinetic energy, which essentially heats it up. When the earth formed it was really a molten blob of elements, over time, these settled out, and a crust formed on top (like the skin on pudding). The reason it is still hot so long after the fact is twofold: A) really dense material holds onto heat longer than something that is less dense (tinfoil versus a cast iron pan), and B) the radioactive decay of such fun things as potassium-40, uranium-238, and thorium-232, whose half lives are over a billion years (meaning that after a billion years, only half of them will have decayed). So, although the process slows down with time, its still going to stay hot for a while longer.

Added little bit of info: As far as part A of the answer goes, some think that the reason that mars is a desolate wasteland is because its core has turned solid (thanks to its smaller mass), which knocked out the magnetic field and allowed the atmosphere to boil off into space. So, you have that to look forward to in who knows how long.

Answer 2

#2 is the best choice. As the planets condensed out of dust, the infalling matter brought energy from descent in a gravitational field. The earth, and I suppose the other rocky planets, gets some heat from the radioactive decay of long lived isotopes (U238 being the dominant), but this is a relatively small contribution.

Answer 3

Charley M is pretty right except that from the info that I have read the decay of heavy metals is more than a minor effect.

If it wasn't for this decay we would be a solid ball of ice. There is a lot of heavy metals in the core, much more than on the surface. This is due to the heavier elements sinking to the core during the aggregation of the earth.

Answer 4

None of the above...

take any material you wish and stand it in a pile roughly 4,000 miles high. The bottom of the pile will be so unbelieveably hot you will be utterly amazed. This heat comes from the intense pressure from all that weight pushing down. And, that is exactly what happens on moons, planets, and stars.

Probably you won't be able to make a pile 4,000 miles high, so make one with pencil and paper. Figure out the weight of one cubic foot of any material you choose. Multiply that figure by 5,280 feet in a mile...then multiply that by 4,000 miles...see what you get...

That is the pressure pushing down on one square foot of core. That pressure is so immense that it causes extremely high temperatures to be generated, and those high temperatures change the material into a molten state. That is how you get lava, and things like that...

Answer 5

"Simple question simple answer".....they are all near to the sun....its only our planet earth, which is at the perfect location that is neither too far from the sun nor too close to the sun.This phenomenon makes life possible on this planet...this everybody learns in School in Geography
There may be some more scientific reason for the interior planets to be hot but the answer i gave is comfortable enough for a common man to understand

Answer 6

The answer is most definitely B. Pressure from gravity and radioactivity are the two most likely reason listed for why the Earth still has a molten core. Word-

Answer 7

as gravity acts on a system of particles, it brings them closer and starts spinning them around...now, as more and more matter gets pulled in, you generate more heat (particle movement) and they get more dense, which in turn creates a superheated center

Answer 8

because it is not exposed to the cooler outer space .when everything blasted out from the nebula , both outer and inner surfaces were hot. but due to the above mentioned reasons, the inner thing is still hot.

Answer 9

because of the enormous pressure at the core.

Answer 10

Sounds like someone is trying to get homework done...