Could an Earth like exoplanet with complex life exist if it has a high enough mass but only 75% Earths radius? Would the smaller radius effect life?
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Could an Earth like exoplanet with complex life exist if it has a high enough mass but only 75% Earths radius? Would the smaller radius effect life?
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I can't think of any physical reason why that would impact the development of life.
STARGAZING: All I see are the lights of a billion places I'll never go. --Howard Tayler, Schlock Mercenary
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75 % radius would increase the gravity of the planet by by ruoghly 1.8 times so things probably would be shorter as a result but they can be still be life.
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Perhaps it would affect life. A smaller radius implies a larger surface to volume ratio, and that should cause the planet to cool down more rapidly after it's initial formation. So, I think it could have an effect but there are other factors to consider also.Originally Posted by willstaruss22
Order of Kilopi
No, an Earthlike planet with 75% radius would have decresed surface gravity--roughly 75% of Earth's gravity. More important would be the decrease in escape velocity, which is also decreased by 75%. This means that this planet would more readily lose its atmosphere.
However, this 75% decrease isn't really all that much. Life on this planet could be much like life here on Earth.
A planet with an internal composition similar to Mercury could be denser, and could have a surface gravity more like Earth's. However, such a planet might not have water or air suitable for life.
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By "enough mass" do you mean the same mass as Earth? If so, a smaller planet would be denser. If it has the same density as Earth but smaller size, it would have less mass and therefore less gravity.
STARGAZING: All I see are the lights of a billion places I'll never go. --Howard Tayler, Schlock Mercenary
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That's what I thought he meant and appears to be what TOS thought he meant when he said the gravity would be higher.
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How long did Mars have dense atmosphere and liquid water flows eroding valleys? Did Mars have water and atmosphere for 500 million years and then spend 4 milliard years as cold and arid desert, or did Mars have flowing water and oceans for 4 milliard years and became the desert only for the last 500 million years?
Mars is just 53 % Earth radius. Mercury has much bigger compressed density than Mars.
Could a planet just the size of Mars but slightly denser have retained dense atmosphere and flowing water till now, and support complex life?
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Actually gravity varies as in inverse square so the closer to the object the higher the gravity. Yes I assumed the plant would have the same mass as the Earth.
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Early Mars fo what I remeber was more geologically active and more carbon was released into the atmosphere through volcanoes and other geological processes and so it had a greenhouse effect. Over time the core become colder and colder and cold not power the volcanoes and the carbon dioxide leaked into space and eventually the surface got colder and colder.
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You can't just magically compress Earth into a mere 42% of its original volume.
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For a small planet to be denser than Earth it would have to have a different internal composition, which would affect surface chemistry and tectonic and volcanic activity.
STARGAZING: All I see are the lights of a billion places I'll never go. --Howard Tayler, Schlock Mercenary
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Earth is more massive than Mars, yet has less carbon dioxide.
Order of Kilopi
Really? I figured that could be true for Venus but Mars too?
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Most of the core is actually iron and nickel which is more dense then the crust therefore it would have more of the mass of the Earth then the crust and the mantle.
I have a feeling this is a Planet made up for a problem in physics or astronomy class. I have done enogh homework for someone else this week.
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Mars - total pressure 6,7 mbar or so, 97% or so carbon dioxide, so say 6,5 mbar carbon dioxide
Earth - total pressure 1013 mbar, under 0,04 % carbon dioxide, so under 0,4 mbar carbon dioxide
QED.
Has carbon dioxide escaped from Earth into space?
Order of Kilopi
No, it's sequestered. Look at the numbers in the table here:
http://en.wikipedia.org/wiki/Carbon_...ain_Components
The atmosphere only accounts for a small part of the total carbon budget. It's thought that as the sun gets hotter over billions of years, the Earth will eventually develop an atmosphere similar to what Venus has now.
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Earth at Sea level has 0.4 millibars of carbon dioxide in the atmosphere. The surface of Mars averages about 4.5 millibars of carbon dioxide so the mass of carbon dioxide in Mars' atmosphere is greater, because less gravity increases the mass. The heighth of the atmosphere is about 100 miles for both planets. Likely Earth has far more chemically combined carbon dioxide as carbonate rock than Mars has frozon carbon dioxide, because Earth has about double the surface area of Mars. Neil
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More like triple (3.5x) the surface area or Mars (.284 Earth's), according to wikipedia.
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Okay, I'm not sure how valid this is. Using NASA factsheets, I took the mass of the atmosphere of each planet and multiplied it by the percentage of CO2 in the atmosphere by volume. I know there is probably a problem using mass and volume that way, but feel free to play with moles.
CO2 mass in Martian Atmosphere 2.383 x1016 (2.5 x1016 kg * .9532)
CO2 mass in Earth Atmosphere 1.9737 x1015 (5.1 x1018 kg * .000387)
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If you took a planet of Earth's mass and made it 75% the radius its density would be 13g/cm3 which is above that predicted for a theoretical solid iron planet. Infeasible.
However upping the density by 30% to 7.2g/cm3 and dropping the mass to .55 Earths gives a reasonable looking set of environment numbers (and 75% radius). Gravity 0.98G, Escape Velocity 9.6km/s which is acceptable for atmosphere holding. It imples a much more metal rich planet though. (numbers obtained by playing with this web tool)
I assume a higher metallicity planet with a bigger and denser core would have a stronger magnetic field - as long as the core is still molten - I assume that helps reduce solar radiation better than Earth's does, which might be better for life - though would that slow evolution?
If it had Earths surface water volume, which I believe is mostly from early asteroid bombarment, and only half Earth's surface area (56%), would its entire surface be underwater?
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I've heard (one of Richard Pogge's iTunesU recordings) that the minimum mass for a planet to maintain a molten outer core after 4.5 billion years is about half the mass of the Earth (other estimates are higher, at about 60% of the mass of the Earth). Without a molten core, the planet's magnetic field will collapse and it's probable that plate tectonics will stop. The latter will terminate the carbon dioxide cycle.
Assuming Earth's density (in reality, somewhat smaller planets will probably have lower densities), a planet of 50% Earth mass will have about 80% of the Earth's radius. One of 75% Earth's radius will have about 42% of the Earth's mass. I'd have to do some math to see how long a planet of that size will retain a molten core, and any such calculation is fraught with assumptions (planet mass, internal heat transfer rates, percentage of radioactives, etc).
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How does the carbon dioxide cycle critically depend on plate tectonics?
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When it rains, carbon dioxide dissolves in water. Some of the carbon dioxide will then be take up by carbonate rock; some will be taken up (indirectly) by animals, like molluscs, with carbonate-based shells. When these are carried to subduction zones, the carbon dioxide is released when the carbonates are sufficiently heated. See http://earthobservatory.nasa.gov/Fea...ycle/page2.php , among other sources.
With no plate tectonics, the carbon dioxide that gets dissolved in rain and deposited in carbonate rocks is permanently lost to the atmosphere.
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Then has any carbon dioxide on Mars turned into carbonates?
Mars lacks magnetic field - but Mercury has it (and so has Ganymede).that the minimum mass for a planet to maintain a molten outer core after 4.5 billion years is about half the mass of the Earth (other estimates are higher, at about 60% of the mass of the Earth). Without a molten core, the planet's magnetic field will collapse and it's probable that plate tectonics will stop. The latter will terminate the carbon dioxide cycle.
Mars has no sign of having had plate tectonics, ever. There are volcanoes, there is the Vallis Marineris rift zone - but are there any traces of subduction zones in a subsequently stopped plate tectonics? Earth has plenty of inactive subduction zone seams across continents.
When Olympus Mons and the other shield volcanoes of Tharsis and Elysium erupt, do they emit carbon dioxide into atmosphere?
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Erupted. iirc, the current estimate is that Mars has had no volcanism for 600 million [Earth] years. Currently, I believe that the consensus is that Olympus Mons is considered an example of hot spot volcanism, in the same way as the Hawai'ian Islands. As for subduction zones on Mars? I think that the other consensus is that Mars never had plate tectonics (it is unlikely Olympus Mons could have formed if the plate it's on was moving -- see the Hawai'ian Islands), but I think that we need to get a few (dozen?) seismographic stations on Mars to do a proper investigation.
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Wouldnt a density of 7.2g/cm3 make it less habitable because of greater proportions of heavy elements or would it be ok to still support life even with that density? Im Just boarderline on the great of density.
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Assuming similar heat capacity and conductivity for the denser planet, it would take longer to cool as there's more heat energy to dissipate, and the only way for it to leave the planet is radiation from the surface. Then, too, a planet with more heavy metals may have more radioactive elements. iirc, the current estimate is that about 40% of the Earth's internal heat is from radioactive decay, with the other 60% being residual heat of formation.
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Meaning that the volcanism lasted for 3,9 milliards years and just happened to shut down 600 million years ago....
How much more massive would Mars have to be in order to reach complete shutdown of all volcanism in 4,9 milliard years (400 million years into future) instead of 3,9 milliard?
Look at Io. The large amount of rock erupted to surface has to be balanced by rock going down somehow.
Does Io have subduction zones and plate tectonics?
Order of Kilopi
Perhaps Io is shrinking. Or maybe it's not shrinking and its interior is expanding via phase change or crystals with larger lattice structures.
Et tu BAUT? Quantum mutatus ab illo.
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