What do mercury and venus have in common

Earth has one large moon, which orbits Earth once every The Moon is covered with craters; it also has large plains of lava. There is evidence that the Moon formed when a large object — perhaps as large as the planet Mars — struck Earth in the distant past Figure below. Besides its Moon, Earth is orbited by a great deal of space debris, the remains of satellites, and rocket stages.

The smallest planet, Mercury, is the planet closest to the Sun. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. However, the Mariner 10 spacecraft, shown in Figure below, visited Mercury from to The craft is currently in orbit around the planet, where it is creating detailed maps.

Also, with very little atmosphere, the processes of weathering and erosion do not wear down structures on the planet. Mercury is named for the Roman messenger god, who could run extremely quickly, just as the planet moves very quickly in its orbit around the Sun. A year on Mercury — the length of time it takes to orbit the Sun — is just 88 Earth days. Despite its very short years, Mercury has very long days.

A day is defined as the time it takes a planet to turn on its axis. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 57 Earth days long. In other words, on Mercury, a year is only a Mercury day and a half long! Mercury is close to the Sun, so it can get very hot. However, Mercury has virtually no atmosphere, no water to insulate the surface, and it rotates very slowly.

For these reasons, temperatures on the surface of Mercury vary widely. Although most of Mercury is extremely dry, scientists think there may be a small amount of water in the form of ice at the poles of Mercury, in areas that never receive direct sunlight. Mercury is one of the densest planets. Named after the Roman goddess of love, Venus is the only planet named after a female.

When it is visible, Venus is the brightest object in the sky besides the Sun and the Moon. When Venus rises just before the Sun rises, the bright object is called the morning star. When it sets just after the Sun sets, it is the evening star. Of the planets, Venus is most similar to Earth in size and density. Venus is also our nearest neighbor. But the resemblance between the two inner planets ends there.

Venus rotates in a direction opposite the other planets and opposite to the direction it orbits the Sun. This rotation is extremely slow, only one turn every days. This is longer than a year on Venus—it takes Venus only days to orbit the Sun. Venus is covered by a thick layer of clouds, as shown in pictures of Venus taken at ultraviolet wavelengths Figure below.

This ultraviolet image from the Pioneer Venus Orbiter shows thick layers of clouds in the atmosphere of Venus. Clouds on Venus are made mostly of carbon dioxide with a bit of sulfur dioxide — and they also contain corrosive sulfuric acid. Mercury is the closest to the Sun and the fastest, bears the name of the god of trade, travel, and communications. Mercury takes 88 Earth days to complete an orbit, and Venus takes days to orbit the Earth. Even though Mercury orbits closer to the Sun than Venus, it lacks an atmosphere.

The side facing the Sun is baked, with a temperature of degrees Celsius, the side facing away from the Sun cools down to degrees Celsius. Venus, on the other hand, has an incredibly thick atmosphere and traps the heat from the Sun. Begin typing your search term above and press enter to search.

Press ESC to cancel. However, these plains are older than the mare, so they have more craters on them remember, it took a while for the mare on the Moon to form, and there is less cratering there. Basically, the plains on Mercury are sort of in between the ages of the heavily cratered highlands of the Moon and the smooth lunar mare.

Also like the Moon, there is no atmosphere. This will, of course, cause there to be wide variations in temperature since heat is not retained at night. The daytime temperature is much greater than on the Moon due to Mercury's close proximity to the Sun. During the daytime on Mercury the temperature reaches K degrees F , while the nighttime temperature is similar to that found on the Moon, about K degrees F.

Figure 3. A side-by-side comparison of Mercury and the Moon left and right respectively. Note the lack of mare on Mercury, though the cratering isn't as densely concentrated as on the Moon's highland regions. Images from NASA. There are some features seen on the surface of Mercury that are also observed on the Moon. Amongst these are the scarps. These are long cliffs that stretch along the surface for hundreds of km and can be up to 3 km high, which is significantly larger than those seen on the Moon.

And while the Moon has the large impact basins that are now the mare, Mercury has older features that are not as smooth. The most prominent is the Caloris Basin , a multi-ringed feature that is about km in diameter. This means that if you took my astronomy course before , you learned the wrong size for the Caloris Basin - I told you astronomy was annoying! Just follow this link to see the full image of the Caloris basin, and the previous assumed size in yellow.

There are some puzzling features on Mercury that are a bit unexpected. First are the relatively large lava flow features visible near the planet's north pole. While this only covers a fraction of the surface, it is quite thick. Also there are a variety of features called "hollows" which appear to related to volcanic activity on the surface. Hollows appear as pitted features on the surface and they tend to be bluer than the other terrain, which makes them rather distinct.

It is also possible that these hollows may be currently changing, indicating that Mercury may still be geologically active. If you were to look at the side of the planet opposite of the Caloris Basin, you would see a region known as the Jumbled or Weird Terrain. This is a very hilly area covering about , square km. Is it a coincidence that these objects are on opposites of the planet? The likely scenario is that the impact which produced the Caloris Basin produced a big shock wave, which spread out from the impact site.

The shock wave would eventually run into itself on the other side of the planet, and when this happens the material in the area would suffer the consequences. This is sort of like the effect you get when two water waves come together and spray upward. Figure 4.

In the image on the left, various surface features are shown. The pink arrows show large, older craters that have experienced lava floods smoothed out. A scarp is visible running through a crater on the bottom blue arrow.

The yellow arrow shows some of the unusual bright material that has been observed in craters on Mercury, but have yet to be explaiend. Green arrows show chains of secondary craters, which were produced by other impacts which throw up a large amount of material. To the right is a false color image of the Caloris Basin showing the composition variation of the basin relative to the surrounding area.

The basin's area is shown as the yellow-ish terrain. These areas show relatively bright reflections from the IR instruments on the spacecraft was well as other indicators that water ice my exist on the surface in these dark craters. If that is the case, that would be another feature that Mercury shares with the Moon. That's not very good since Mercury is so close to the Sun, and the strong solar winds are able to flatten the field down significantly on the sun-facing side of the planet.

Large eruptions of particles from the Sun would have a much easier time getting to the the surface of Mercury than the Earth. By looking at Mercury's density and mass, we can determine the likely composition of its interior.

Mercury appears to have a very large iron-nickel core, making up a larger fraction of its interior than the Earth's core. Why is the magnetic field so weak? In part, because the planet is not a fast spinner remember, one rotation takes 59 of our days , and it is likely that this core is pretty rigid not liquid like part of the Earth's core.

Mercury is such a small planet that it would have cooled off very quickly in its history, while the Earth is still pretty hot. All of these effects make Mercury's magnetic field pretty weak.

Figure 5. Mercury's interior is compared to the Earth's. While the Earth is a larger planet, the fraction of the interior taken up be the iron rich core is much less than the fraction of Mercury's interior. There is a actually a problem with Mercury having such a large iron core.

There is just too much iron - objects in the solar system don't have such a large amount of iron in them, and it seems unlikely that the planet should have formed with that much iron in the first place.

Currently astronomrs theorize that Mercury in the past was a much larger object with a larger layer of rocky material. A large scale impact or several impacts would have resulted in the loss of a large fraction of the lower density surface material leaving behind a planet dominated by a large iron core. This is a reasonable theory since you have the Sun nearby and it tends to pull in a large number of objects, unfortunately for Mercury which may have gotten in the way of one of those objects.

Other theories think that the Sun's high temperature may have also stripped away some of the surface. The large iron core can also explain the presence of the scarps. Early in the planet's history, the rock layer above the iron core the mantle and crust would have cooled and solidified before the iron core would have cooled. Long after the crust solidified, the iron core started to cool down.

What happens when iron cools? In case you don't know, it contracts - gets smaller. There is so much iron in the interior of the planet that the contractions were pretty major possibly km of contraction in some areas. With the shrinking of the core the rock layers above it sort of lost their support, so they collapsed in various places forming long cliffs or, as we call them, scarps.

Recent observations from the Messenger spacecraft seem to support this theory, since detailed observations along with elevation data point to significant elevation differences across the surface. Overall the average contraction may be around 7 km 4. That might not seem to be a large amount, but it could certainly effect the surface features.

As mentioned above, Mercury lacks an atmosphere, while Venus has the thickest atmosphere of all the terrestrial planets. The temperatures and pressures are so extreme on the surface of Venus that spacecraft only last a few hours before being crushed and baked.

Both Venus and Mercury are within the orbit of Earth. They appear as the sky darkens, and then pass below the horizon within a few minutes.