Submitted by GeoGeoGeoGeo t3_yf5p66 in science
Reply to comment by Dendad6972 in Magma on Mars Likely - Until now, Mars has been generally considered a geologically dead planet. An international team of researchers led by ETH Zurich now reports that seismic signals indicate volcanism still plays an active role in shaping the Martian surface. by GeoGeoGeoGeo
We don't know for sure, but was assume they all formed around 4.5-4.6 billion years ago. They where spinning around in a giant debris cloud collecting more and more material and slamming into each other until we had what we see today... or something like that.
So that means they are potentially made up of significantly different materials, perhaps like seams of materials in a mine the cloud was not likely to be evenly distributed and it's hard to say what's really on the inside. It's not like the planet are just blobs ejected from the sun that just happened to turn out that way, much of what they became is based on how they spun around that early cloud of debris and what they run into or what ran into them.
The bigger a protoplanet got the more stuff it could suck in until it was a planet and it was big enough to even absorb smaller planets and protoplanets or get absorb.
It was a game of absorb or get absorbed until they carved the relatively empty space you see today.
The average density of mars is about 70% that of earth. so we'd expect that its made of relatively less metal than earth and more light elements like carbon, oxygen, and silicon. (this is complicated somewhat by compression, but you can do some complicated modelling which suggests that Mars is indeed a slightly different composition than the Earth (its more similar to the Moon)
Are the planets largely less dense as you get further away? Like the elements were light enough to make it further out in larger quantities? Considering it’s rocky planets, then gas planets, it seems that way. I’m sure there’s a huge margin of error when taking material accumulation and how those materials interact with one another to then make larger atoms, especially the more massive planets.
The closer you get to the sun -- or in this case, the protostar that became the sun -- the hotter it gets. Obviously. That's important because it means that when you're close to the sun, it's too hot for many molecules to stay solid, and they'll evaporate (or rather, sublimate). It's very difficult for forming planets to accrete gases, so planets that form close to the sun will generally be denser.
Outside a certain radius, it will be cool enough for water to form ice, and the average density of solid material will plummet. The moons of the gas giants, and Kuiper Belt objects like Pluto are much less dense than Earth because they're made of much more water than Earth, by mass. Planetesimals in this part of the solar system can even grow large enough to start accreting the gases in the forming solar system and grow to incredible masses.
Of course, formation is not the end of the story. Our solar system is not static, and the planets can radically change their position with time. There are many examples of Jupiter sized exoplanets that orbit their stars further in than Mercury!
If you’re further in than mercury you would have a good chance of being tidally locked right?
I wonder about mercury too since it has like no crust compared to the earth. I had heard one theory that mercury had a big collision and it stripped away most of that crust. Sucks mercury is so hard to get to. I wish we knew more about it.
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