VENUS (PLANET): DISCOVERY, CHARACTERISTICS, COMPOSITION, ORBIT - ARTE - 2025

Venus is the second closest planet to the Sun in the solar system and the most similar to Earth in size and mass. It is visible as a beautiful star, the brightest after the Sun and the Moon. Therefore, it is not surprising that it has attracted the attention of observers since ancient times.

Because Venus appears at sunset at certain times of the year and at sunrise at others, the ancient Greeks believed that they were different bodies. As the morning star they called it Phosphorus and during the evening appearance it was Hesperus.

Figure 1. Photograph of the planet Venus, top left, next to the Moon. Source: Pixabay.

Later Pythagoras assured that it was the same star. However, around 1600 BC the ancient astronomers of Babylon already knew that the evening star, which they called Ishtar, was the same one they saw at dawn.

The Romans knew it too, although they continued to give different names to the morning and evening apparitions. Also the Mayan and Chinese astronomers left records of the observations of Venus.

Each ancient civilization gave it a name, although in the end the name of Venus prevailed, the Roman goddess of love and beauty, equivalent to the Greek Aphrodite and the Babylonian Ishtar.

With the advent of the telescope, the nature of Venus began to be better understood. Galileo observed its phases in the early 17th century, and Kepler carried out calculations with which he predicted a transit for December 6, 1631.

A transit means that the planet can be seen passing in front of the Sun. In this way Kepler knew that he could determine the diameter of Venus, but he died before seeing his prediction fulfilled.

Later in 1761, thanks to one of these transits, scientists were able to estimate for the first time the Earth-Sun distance at 150 million kilometers.

General characteristics of Venus

Figure 2. Animation of the majestic rotational motion of Venus through radar-constructed images. Direct images of Venus are not easy to obtain, due to the thick cloud cover that surrounds it. Source: Wikimedia Commons. Henrik Hargitai.Although its dimensions are very similar to those of Earth, Venus is far from being a hospitable place, since to begin with, its dense atmosphere is composed of 95% carbon dioxide, the rest is nitrogen and trace amounts of other gases. Clouds contain droplets of sulfuric acid and tiny particles of crystalline solids.

That is why it is the hottest planet in the solar system, even if it is not the closest to the Sun. The marked greenhouse effect caused by the thick atmosphere rich in carbon dioxide is responsible for the extreme heat on the surface.

Another distinctive feature of Venus is its slow, retrograde spin. A traveler would observe the Sun rise in the west and set in the east, a fact discovered thanks to radar measurements.

Furthermore, if it were to stay long enough, the hypothetical traveler would be very surprised to realize that the planet takes longer to rotate around its axis than to rotate around the Sun.

The slow rotation of Venus makes the planet almost perfectly spherical and also explains the absence of a strong magnetic field.

Scientists believe that the planets' magnetic field is due to the dynamo effect associated with the movement of the molten metal core.

However, the weak planetary magnetism of Venus originates from the interaction between the upper atmosphere and the solar wind, the stream of charged particles that the Sun continuously emits in all directions.

To explain the lack of magnetosphere, scientists consider possibilities such as that Venus lacks a molten metallic core, or that it may have one, but that inside the heat is not transported by convection, a necessary condition for the existence of the dynamo effect.

Summary of the main physical characteristics of the planet

-Mass: 4.9 × 10 ²⁴ kg

-Equatorial radius : 6052 km or 0.9 times the radius of the Earth.

-Shape: it is almost a perfect sphere.

-Average distance to the Sun: 108 million km.

- Orbit inclination: 3,394º with respect to the Earth's orbital plane.

-Temperature: 464 ºC.

-Gravity: 8.87 m / s ²

-Own magnetic field: weak, 2 nT intensity.

-Atmosphere: yes, very dense.

-Density: 5243 kg / m ³

-Satellites: 0

-Rings: does not have.

Translation movement

Like all planets, Venus has a translational motion around the Sun in the form of an elliptical, almost circular orbit.

Some points in this orbit lead Venus to get very close to Earth, more than any other planet, yet most of the time actually spends quite far from us.

Figure 3. The translational motion of Venus around the Sun (yellow) compared to that of the Earth (blue). Source: Wikimedia Commons. Lookang many thanks to author of original simulation = Todd K. Timberlake author of Easy Java Simulation = Francisco Esquembre The mean radius of the orbit is around 108 million kilometers, therefore Venus is approximately 30% closer to the Sun than the earth. A year on Venus lasts 225 Earth days, since this is the time it takes for the planet to make a complete orbit.

Venus movement data

The following data briefly describe the motion of Venus:

-Mean radius of the orbit: 108 million kilometers.

- Orbit inclination: 3,394º with respect to the Earth's orbital plane.

-Eccentricity: 0.01

- Average orbital speed: 35.0 km / s

- Transfer period: 225 days

- Rotation period: 243 days (retrograde)

- Solar day: 116 day 18 hours

When and how to observe Venus

Venus is very easy to locate in the night sky; After all, it is the brightest object in the night sky after the Moon, since the dense layer of clouds that covers it reflects the sunlight very well.

To easily locate Venus, just consult any of the many specialized websites. There are also smartphone apps that provide your exact location.

Since Venus is within Earth's orbit, to find it you have to look for the Sun, looking east before dawn, or west after sunset.

The optimal moment for observation is when Venus is between the lowest conjunction, seen from Earth, and a maximum elongation, according to the following diagram:

Figure 4. Conjunction of a planet whose orbit is interior to that of the Earth. Source: Astronomy for Dummies.

When Venus is in lower conjunction, it is closer to the Earth and the angle it forms with the Sun, seen from Earth - elongation - is 0º. On the other hand, when it is in superior conjunction, the Sun does not allow it to be seen.

Hopefully Venus can still be seen in broad daylight and cast shade on very dark nights without artificial lighting. It can be distinguished from stars because its brightness is constant, whereas stars blink or twinkle.

Galileo was the first to realize that Venus goes through phases, as does the Moon - and Mercury - thus corroborating Copernicus' idea that the Sun, and not the Earth, is the center of the solar system.

Figure 5. The phases of Venus. Source: Wikimedia Commons. derivative work: Quico (talk) Phases-of-Venus.svg: Nichalp 09:56, 11 June 2006 (UTC).

Rotatory motion

Venus rotates clockwise as seen from Earth's north pole. Uranus and some satellites and comets also rotate in this same direction, while the other major planets, including Earth, rotate counter-clockwise.

In addition, Venus takes its time to run its rotation: 243 Earth days, the slowest among all planets. On Venus, a day lasts longer than a year.

Why does Venus rotate in the opposite direction as the other planets do? Probably in its beginnings, Venus rotated rapidly in the same direction as everyone else, but something must have happened for it to change.

Some scientists believe it is due to a catastrophic impact that Venus had in its remote past with another large celestial object.

However, mathematical computer models suggest the possibility that chaotic atmospheric tides have affected the planet's non-solidified mantle and core, reversing the direction of rotation.

Both mechanisms may have played a role during the stabilization of the planet, in the early solar system.

The greenhouse effect on Venus

On Venus, clear and clear days do not exist, so it will be very difficult for a traveler to observe the sunrise and sunset, which is what is commonly known as day: the solar day.

Very little light from the Sun makes it to the surface, as 85% is reflected off the cloud canopy.

The rest of the solar radiation manages to heat the lower atmosphere and reaches the ground. Longer wavelengths are reflected and retained by clouds, known as the greenhouse effect. This is how Venus became a gigantic furnace with temperatures capable of melting lead.

Virtually any place on Venus is this hot, and if a traveler were to get used to it, they would still have to withstand the enormous atmospheric pressure, which is 93 times greater than that on Earth at sea level, caused by the large 15 kilometer cloud layer. of thickness.

As if that were not enough, these clouds contain sulfur dioxide, phosphoric acid and highly corrosive sulfuric acid, all in a very dry environment, as there is no water vapor, just a small amount in the atmosphere.

So despite being covered in clouds, Venus is completely arid, and not the planet full of lush vegetation and swamps that science fiction authors envisioned in the mid-20th century.

Water on venus

Many scientists believe that there was a time when Venus had oceans of water, because they have found small amounts of deuterium in its atmosphere.

Deuterium is an isotope of hydrogen, which combined with oxygen forms so-called heavy water. Hydrogen in the atmosphere easily escapes into space, but deuterium tends to leave behind residues, which may be an indication that there was water in the past.

However, the truth is that Venus lost these oceans - if they ever existed - about 715 million years ago to the greenhouse effect.

The effect began because carbon dioxide, a gas that traps heat easily, concentrated in the atmosphere instead of forming compounds on the surface, to the point that the water evaporated completely and stopped accumulating.

Figure 6. Greenhouse effect on Venus: carbon dioxide clouds retain heat and warm the surface. Source: Wikimedia Commons. The original uploader was Lmb at Spanish Wikipedia. / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/).

Meanwhile the surface got so hot that the carbon in the rocks sublimated and combined with atmospheric oxygen to form more carbon dioxide, fueling the cycle until the situation got dire.

At present Venus continues to lose hydrogen, according to information provided by the Pioneer Venus mission, so it is unlikely that the situation will reverse.

Composition

There is little direct information about the composition of the planet, since seismic equipment does not survive for long on the corrosive surface, and the temperature is sufficient to melt lead.

Carbon dioxide is known to predominate in the atmosphere of Venus. In addition, sulfur dioxide, carbon monoxide, nitrogen, noble gases such as helium, argon and neon, traces of hydrogen chloride, hydrogen fluoride and carbon sulfide have been detected.

The crust as such is abundant in silicates, while the core surely contains iron and nickel, like that of the Earth.

The Venera probes detected the presence of elements such as silicon, aluminum, magnesium, calcium, sulfur, manganese, potassium and titanium on the surface of Venus. There are also possibly some iron oxides and sulfides, such as pyrite and magnetite.

Internal structure

Figure 7. Section of Venus showing the layers of the planet. Source: Wikimedia Commons. GFDL / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0).

Obtaining information on the structure of Venus is a feat, considering that the conditions of the planet are so hostile that the instruments stop working in a short time.

Venus is a rocky inner planet, and this means that its structure must be basically the same as that of Earth, especially when taking into account that both were formed in the same area of ​​the planetary nebula that gave rise to the solar system.

As far as is known, the structure of Venus is made up of:

-An iron core, which in the case of Venus is about 3000 km in diameter and consists of a solid part and a molten part.

-The mantle, with another 3000 km of thickness and sufficient temperature so that there are molten elements.

-The crust, with a variable thickness between 10 and 30 km, mostly basalt and granite.

geology

Venus is a rocky and arid planet, as evidenced by the images built by radar maps, the most detailed by data from the Magellan probe.

These observations show that the surface of Venus is relatively flat, as confirmed by the altimetry carried out by said probe.

In general terms, on Venus there are three well differentiated areas:

-Lowlands

–Deposition plains

-Highlands

70% of the surface is plains of volcanic origin, the lowlands constitute 20% and the remaining 10% are highlands.

There are few impact craters, unlike Mercury and the Moon, although this does not mean that meteorites cannot get close to Venus, but that the atmosphere behaves as a filter, disintegrating those that arrive.

On the other hand, volcanic activity probably erased the evidence of ancient impacts.

Volcanoes abound on Venus, especially shield-type volcanoes such as those found in Hawaii, which are low and large. Some of these volcanoes are likely to remain active.

Although there is no plate tectonics like on Earth, there are numerous accidents such as faults, folds and rift-type valleys (where the crust is undergoing deformation).

There are also mountain ranges: the most prominent is the Maxwell Mountains.

The terrae

There are no oceans on Venus to distinguish continents, however, there are extensive plateaus, called terra - the plural is terrae - that could be considered as such. Their names are of goddesses of love in different cultures, the main ones being:

-Ishtar Terra, from the Australian expanse. It has a great depression surrounded precisely the Maxwell Mountains, named after the physicist James Maxwell. The maximum height is 11 km.

-Aphrodite Terra, much more extensive, is located near the equator. Its size is similar to that of South America or Africa and shows evidence of volcanic activity.

Figure 8. Topographic map of Aphrodite Terra on Venus. Source: Wikimedia Commons. Martin Pauer (Power) / Public domain.

Missions to Venus

Both the United States and the former Soviet Union sent unmanned missions to explore Venus during the second half of the 20th century.

So far this century, missions from the European Space Agency and Japan have been added. It has not been an easy task due to the hostile conditions of the planet.

Scallop

The Venera space missions, another name for Venus, were developed in the former Soviet Union from 1961 to 1985. Of these, a total of 10 probes managed to reach the planet's surface, the first being Venera 7, in 1970.

The data collected by the Venera mission includes measurements of temperature, magnetic field, pressure, density and composition of the atmosphere, as well as images in black and white (Venera 9 and 10 in 1975) and later in color (Venera 13 and 14 in 1981).

Figure 9. Replica of the Venera probe. Source: Wikimedia Commons. Armael / CC0.

Among other things, thanks to these probes it was learned that the atmosphere of Venus consists mainly of carbon dioxide and that the upper atmosphere is made up of fast winds.

Mariner

The Mariner mission launched several probes, the first of which was Mariner 1 in 1962, which failed.

Next, Mariner 2 managed to reach the orbit of Venus to collect data from the planet's atmosphere, measure the intensity of the magnetic field and the surface temperature. He also noted the retrograde rotation of the planet.

Mariner 10 was the last probe on this mission to be launched in 1973, providing exciting new information from Mercury and Venus.

This probe managed to obtain 3000 photos of excellent resolution, since it passed very close, about 5760 km from the surface. It also managed to transmit video of the clouds of Venus in the infrared spectrum.

Pioneer Venus

In 1979 this mission carried out a complete map of the surface of Venus by means of radar through two probes in orbit over the planet: Pioneer Venus 1 and Pioneer Venus 2. It contained equipment to carry out studies of the atmosphere, measure the magnetic field, and perform spectrometry. and more.

Magellan

This probe sent by NASA in 1990, through the space shuttle Atlantis, obtained very detailed images of the surface, as well as a large amount of data related to the geology of the planet.

This information corroborates the fact that Venus lacks plate tectonics, as mentioned before.

Figure 10. The Magellan probe shortly before its launch at the Kennedy Space Center. Source: Wikimedia Commons.

Venus Express

It was the first of the European Space Agency's missions to Venus and lasted from 2005 to 2014, taking 153 to reach orbit.

The mission was in charge of studying the atmosphere, in which they detected abundant electrical activity in the form of lightning, as well as making temperature maps and measuring the magnetic field.

The results suggest that Venus may have had water in the distant past, as explained above, and also reported the presence of a thin layer of ozone and atmospheric dry ice.

Venus Express also detected places called hot spots, in which the temperature is even warmer than elsewhere. Scientists believe that they are places where magma rises to the surface from the depths.

Akatsuki

Also called Planet-C, it was launched in 2010, being the first Japanese probe directed at Venus. She has made spectroscopic measurements, as well as studies of the atmosphere and the speed of winds, which are much faster in the vicinity of the equator.

Figure 11. Artist's representation of the Japanese Akatsuki probe for the exploration of Venus. Source: NASA via Wikimedia Commons.

References

1. Bjorklund, R. 2010. Space! Venus. Marshall Cavendish Corporation.
2. Elkins-Tanton, L. 2006. The Solar System: the Sun, Mercury and Venus. Chelsea House.
3. Britannica. Venus, planet. Recovered from: britannica.com.
4. Hollar, S. The Solar System. The Inner Planets. Britannica Educational Publishing.
5. Seeds, M. 2011.The Solar System. Seventh Edition. Cengage Learning.
6. Wikipedia. Geology of Venus. Recovered from: es.wikipedia.org.
7. Wikipedia. Venus (planet). Recovered from: es.wikipedia.org.
8. Wikipedia. Venus (planet). Recovered from: en.wikipedia.org.