Venus

Is Venus similar to Earth?

they are similar in size, mass, density, and escape speed, they are the same age, orbit the same star, but they aren’t really similar at all

Does Venus have phases?

yes - when Venus is closest to us, it is a very thin crescent (new) and when it’s furthest away, it’s full

Can we see Venus when it’s at its closest to us?

not usually, because its night side is facing us - occasionally the orbits line up so that Venus passes between the Earth and the Sun, producing a solar transit

How often do transits usually occur?

in pairs a few years apart, ~120 years between pairs

Does Venus have craters?

yes - images of Venus’ surface show the presence of numerous craters, which are also very evenly distributed (no older or younger regions)

What does Venus’ surface age tell us?

Venus must have entirely resurfaced itself within the last billion years given that it’s surface age isn’t super old or young

Does Venus have volcanoes?

yes - has numerous widely-distributed volcanoes of the shield type, some of which show recent activity

Does Venus have plate tectonics?

no - lack of strato volcanoes; evidence suggests Venus is made up of small “fields” that slide around like packed ice

What does Venus’ internal structure look like?

similar density to Earth (must have dense core), but lacks a strong magnetic field; also has no Moon to cause tides and a slow rate of rotation, meaning Venus’ interior is relatively static compared to Earth’s

Where does a planet’s internal heat come from?

heat from accretion process that formed the planets, gravitational energy released by sinking of heavier elements to the core, decay of radioactive elements, tidal friction from an orbiting moon

Does Venus and Earth have similar internal heat behaviors?

yes - heat should gradually leak out through the surface to maintain a steady internal temperature; if it leaks faster than the rate of production, the planet cools off; if slower, the planet heats up

What does Earth’s internal heat production look like?

relatively balanced w/ heat loss

What does Mars’ internal heat production look like?

it loses heat faster than it produces, so the planet cooled off

What does Venus’ internal heat production look like?

steady increase in internal temperature over the first 3.5-4 billion years (heat produced faster than leakage rate), leading to a global resurfacing event about 0.5-1 billion years ago that erased all previous impact craters

What does Venus’ atmosphere look like?

denser, hotter, and drier than Earth - cloudy but the clouds are composed of sulfur dioxide and sulfuric acid

What did Venus’ early atmosphere look like?

atmospheres of rocky planets are formed by an accumulation of volcanic gases, so it’s assumed that Earth and Venus initially had similar atmospheres w/ similar composition, even though they’re so different now

What is the greenhouse effect?

H2O and CO2 are greenhouse gases that trap heat and raise the temperature - sunlight can filter inward to some extent (even in cloudy atmosphere), but infrared radiation (heat) emitted by the surface cannot escape back into space because it’s absorbed (so, an atmosphere of volcanic gases will cause a strong greenhouse effect)

How did Venus lose its water?

solar ultraviolet light has broken up (photo-dissociated) the water - hydrogen would leak into space