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They have similar size, mass, and interiors, making the two planets look nearly the same if you never bother to look at their different surfaces.
Of course, when you do take their atmospheres into consideration, then the two planets couldn't be any more different. Short of flying straight into a gas giant or landing onto the surface of Sun, the Venusian surface might be the most extreme and inhospitable place for a human in the entire solar system. And it isn't just that the atmospheres are composed of very different combinations of chemicals. Planetary scientists long thought that the underlying mechanics of the two atmospheres were fundamentally different, which is why the discover of very Earth-like lightning on the planet is such a shock.
Indeed, some theorists thought Venusian lightning was an impossibility, because the clouds there are essentially smog clouds, which don't usually generate lightning on Earth. By comparing the electromagnetic waves produced at the two planets, we found stronger magnetic signals on Venus, but when converted to energy flux we found very similar lightning strength. So what caused these seemingly Earth-like planets to become so resolutely, well, not?
Was it some accident of composition, or millions of years spent in an inhospitable environment? Getting to the bottom of these questions, and understanding the diversity of rocky planets, is of paramount importance for astronomy. Part of the problem is that the innermost planets are incredibly hard to visit.
Only two spacecraft have ever made it to Mercury and of the numerous Venus landers, none survived longer than 90 minutes. While both photography and radar imaging work by collecting radiation that has bounced off an object, the difference lies in the forms of radiation collected.
Mercury, not Venus, is the closest planet to Earth - Tech Explorist
Photography collects visible light radiation, and radar mapping collects microwave radiation. The first radar mappings of the Venusian surface via spacecraft came in when the Pioneer Venus spacecraft began orbiting the planet. What the resulting maps revealed was a surface consisting primarily of plains formed by ancient lava flows, with only two highland regions, Ishtar Terra and Aphrodite Terra.
In , the Magellan spacecraft began orbiting Venus. In addition to performing radar mapping similar to that of Pioneer Venus, Magellan also undertook a more advanced radar imaging that gathered much finer details. What Magellan found was approximately impact craters. Interestingly, none of the craters seen were less than 2 km in diameter. This suggest that any meteroid small enough to create a crater having a diameter less than 2 km would have broken apart and burned up during its passage through the dense Venusian atmosphere.
What this tells us is that the surface has been formed since the period of heavy bombardment, a span of 3.
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Thus, geologically speaking, the Veunsian surface is relatively young. As noted above, the first of these features is the enormous plains caused by ancient lava flows. In addition to shield volcanoes similar to those found on Earth e. After such an eruption, the lava then spreads outwardly in a uniform, circular manner. On one hand, because Venus and Earth are so alike, it is reasonable to conclude that since Earth has a liquid core, Venus does as well.
On the other hand, there is also evidence to suggest the Venusian core is solid.
Simply put, planetary magnetic fields are a result of the transfer of heat from inside a planet to its surface. A necessary component of this transfer is a liquid core. The argument is since Venus lacks a substantial magnetic field, it cannot possess a liquid core.
Indeed, with an eccentricity of only. The reason for this is presently unknown, but there are two popular theories.
Why Mars, and not another planet?
The first points to the spin-orbit resonance of Venus with the Earth. Instead, they have looked to the early Solar System when the planets were being formed to provide an explanation. Taking approximately Earth days to complete a single rotation, a day on Venus is longer than on any other planet. This alone is noteworthy.