Is the Earth so active due to the moon

[tony67]

Hi all,

my first post. My knowledge of astronomy comes totally from TV (Discovery and History) and some Wikipedia reading, so I may be missing some bits. OK here goes.

I've been reading about the planets and life ect. From what I've read found a major reason for life is to do with plate tectonics. So my question is why is the earth so volcanically active? From what I've read Mars is inactive, due to it's small size. Venus, thought many people think it should be is not showing any real evidence. Even though Venus is the same size it shows no evidence for volcanoes erupting all the time, like earth. Also it has no/little magnetic field. From what I've read of Earth core, magnetic fields ect are caused by radioactive decay at the Earth's core. If Venus is the same size why are we not seeing the same evidence? While thinking about this I watched a programme about Jupiter and it's inner moons, one I think is very active, the others have possible liquid oceans under ice. The reason for this it claimed is tidal gravity stretching the moons causing internal heat.

This made me think that the possible reason why Earth is so active and Venus not is due to tidal activity of the moon, Venus having no near by object to cause the tidal effect. The moon is not active perhaps because it is a big ball of ash, the remains of a collision, with no real core to heat.

[SteveL]

From what I've read of Earth core, magnetic fields ect are caused by radioactive decay at the Earth's core

The magetic field is caused my the rotation of the earth molten iron core. This is why the earth is active. Mars probaby had a molten iron core at some point, propviding a magnetic field to protect its atmosphere from the solar wind, but as the planet is amsller and further away from the sun, it cooled fater than the earth, the core solidified, the magnetic field collapsed, and the atmosphere slowly got stripped away by the solar wind.

The moons overall effect of gravity on the earth is enough to create the tides, but not really much in the way of generationg heat within the rocks due to deformation.

[acey]

Various effects keep Earth active, one is radioactive heat released by uranium and other heavy metals in the core, which is what has kept the core molten long after it would otherwise have become solid. Another is magnetism as SteveL says, and another is tidal influence of the Moon as you suggest, Tony. I don't know the relative ratios, nor what other effects there are, nor why the cores of other planets should have cooled since they presumably also have internal radioactive heat: my guess would be that it's simply because they're smaller than Earth so have radiated heat into space much more quickly. Maybe the insulating effect of the atmposphere plays a role too.

The Moon, as you say, lacks a significant metallic core, because it's basically made of stuff blown out of the outer region of the proto-Earth by collision.

The bottom line, as I understand it, is that heat convection is what gives rise to plate techtonics.

[tony67]

Thanks everyone, but I'm still unsure on a couple of things

SteveL, I think I understand your Mars points, but that doesn't account for why Venus isn't massively volcanically active? Also why does Mercury appear to have a magnetic field? It's smaller than Mars.

Acey Shouldn't Venus be made out of the same stuff as Earth? So have about the same level of radioactive elements. Also as far as I can see it has a a very thick atmosphere. Again that means it should be massively volcanic.

Sorry for the questions I have tried to look this us on web sites but facts just seem to contradict themselves, if it's size why does Mercury show evidence of a core? If it's radioactive decay why doesn't Venus appear to have one? :icon_scratch:

[acey]

Fair enough - I'm afraid I can't offer any more thoughts on that one. You raise an interesting question and I'd like to know the answer too!

[Capricorn]

Just put "vulcanism venus" into a search engine and get pages of information on volcanoes on Venus. One mentioned 57 identifiable volcano types on Venus.

Seems to be very active.

Venus doesn't need to be made out of the same stuff as the earth, similar but not the same, and especially not in the same proportions. Have a read on separating elements and chemicals by using a centrifuge.

Haven't looked but the tidal forces from the sun probably causes Mercury to generate heat and so have a molton core and therefore have a magnetic field. Jupiter causes tidal effects in the surface material on one of it's satellites and Jupiter is small then the sun.

Extract from Wikipedia:

Volcanism on Venus

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The 8-km-high volcano Maat Mons is displayed in this perspective view of the surface of Venus, with the vertical scale multiplied by 22.5. Based on Magellan probe radar images.The surface of Venus is dominated by volcanism and has produced more volcanoes than any other planet in the solar system. It has a surface that is 90% basalt, and about 80% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface.

[toml42]

We don't currently have any observations of active volcanoes on the surface of Venus, but expect this to change later this year - the japanese space agency has a probe en-route to look for evidence of current vulcanism, my expectation is that they will find some. lookup 'Akatsuki' for more info. The main barrier preventing study of the Venusian surface is that pesky thick atmosphere and its proximity to the sun when viewed from Earth. Akatsuki should be able to make detailed infra-red observations which should settle the debate.

As far as we can tell, Venus is of very similar composition to the Earth, and whilst there is evidence of at least past vulcanism, it appears to be of a very different flavour to that on Earth - there seems to be no evidence of plate tectonics, so the volcanoes we have found are not as localised as they are on Earth.

This is a big mystery, but one hypothesis is the lack of surface water on venus, that we obviously have in abundance. The idea is that liquid water on earth creates different pressure and compositional 'zones' in the earths crust rather than being homogenous (ocean crust is thinner and denser than continental crust), and the interaction between these different zones gives us plate tectonics. plate tectonics gives us a more active planet than venus, despite our other similarites.

perhaps Akatsuki will give us answers this december. science is about asking questions, and yours are good ones. hope this helps

[nicnac]

dont forget that venus is not in the so called life belt, its closer to the sun than us (who are) so heat radiating from the sun will have an effect on venus.

mars is at the opposite end, out of the "life belt" but further away so less heat from the sun.

some scientists say that in a few thousand years earth will be like venus, as the sun expands

[toml42]

just to expand on a couple of points, venus likely has no magnetic field for 2 reasons:

1. Very slow rotation rate. as you probably know, venus takes 243 days to rotate once. the 'dynamo effect' thought to be the cause of planetary magnetic fields requires the metal core to be spinning at a decent rate

2. in the earth the dynamo effect is bolstered by plate tectonics and convection currents in the mantle making everything slosh about, venus is not so lucky