© NASA/JPL

Venus, the hottest planet in the Solar System, even though Mercury is twice as close to the Sun and receives four times more solar energy. The second planet in our solar system has a thick, carbon dioxide atmosphere causing a runaway greenhouse effect. On the surface, Venus boasts an atmosphere 50 times more dense than Earth’s, and experiences average surface temperatures of 470 degrees Celsius (878 degrees Fahrenheit) — a heat intensity capable of melting lead.

The scorching terrestrial (rocky) type planet is named after the Roman goddess of love and beauty and is the only solar system planet named after a female following the International Astronomical Union designation of names that the astronomy community uses as a convention.

However, Venus’s “real” colour is impossible to see from orbit due to the sulfuric acid clouds surrounding the planet. Images of Venus are only discernible if a spacecraft in orbit possesses the capability to penetrate through the dense cloud cover. For a human explorer to glimpse the surface, they would need to descend and endure the scorching temperatures and extreme pressures prevalent there. This harsh environment implies that, at present, we’ll rely on robotic explorers to observe Venus on our behalf.

No other planet comes as close to Earth as Venus; at its nearest approach, it is the nearest sizable celestial body to Earth, second only to the Moon. Because Venus orbits closer to the Sun than Earth, the planet is typically located in roughly the same direction in the sky as the Sun, and can be observed only during the hours around sunrise or sunset. When visible, it shines as the brightest planet in both the sky and the entire solar system. Venus has earned the moniker of Earth’s twin due to the resemblances in their masses, sizes, densities, and their proximity in the solar system.

Given that they likely formed from similar rocky planetary building blocks in the solar nebula, they probably share comparable overall chemical compositions. Early observations through telescopes revealed a perpetual shroud of clouds, indicating a substantial atmosphere and leading to popular speculation that Venus might have been a warm, moist world, potentially akin to Earth during its ancient era of swampy carboniferous forests and prolific life. Scientists now understand, however, that Venus and Earth have evolved surface conditions that are strikingly disparate. Venus is exceedingly hot, arid, and in various other aspects, so hostile that it is improbable for life as we know it on Earth to have originated there.

ABOUT THE PLANET – VENUS

Venus is counted among the four terrestrial planets in the Solar System, signifying that it is a rocky celestial body akin to Earth. It shares similar dimensions and mass, often earning it the label of Earth’s “sister” or “twin”. Venus’s nearly spherical shape is primarily due to its slow rotation. Venus has a diameter of 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth’s—and its mass is 81.5% of Earth’s. Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.

The surface pressure on Venus stands at 9.3 megapascals (93 bars), and the average surface temperature is 737 K (464 °C; 867 °F). This surpasses the critical points of both major constituents, rendering the surface atmosphere a supercritical fluid, primarily composed of supercritical carbon dioxide and some supercritical nitrogen.

INTERNAL STRUCTURE

Venus shares a significant similarity in size and density with Earth, leading scientists to propose that they possess a comparable internal structure, comprising a core, mantle, and crust. Much like Earth, Venus’s core likely harbors partially liquid elements, as both planets are undergoing cooling at a similar pace. The slightly smaller size of Venus results in pressures within its deep interior being 24% lower than those within Earth, curbing heat loss and impeding cooling.

While the core of Venus, like that of Earth, is presumed to be primarily composed of iron and nickel, its marginally lower density suggests the possibility of some additional, less-dense material, such as sulfur. The absence of an intrinsic magnetic field on Venus means there’s no direct proof of a metallic core, as found on Earth. Estimates of Venus’s internal structure place the outer boundary of the core at just over 3,000 km (1,860 miles) from the planet’s center.

Beneath the crust but above the core lies Venus’s mantle, constituting the majority of the planet’s volume. Despite the extreme surface temperatures, temperatures within the mantle are likely akin to those in Earth’s mantle. Even though the material in a planetary mantle is solid rock, it can slowly deform or flow, akin to glacial ice, allowing for substantial convective movements. If temperatures in Venus’s depths were significantly higher than those within Earth, the viscosity of the rocks in the mantle would drop significantly, expediting convection and expelling heat more swiftly. Thus, the deep interiors of Venus and Earth are anticipated to exhibit only minor differences in temperature.

As previously mentioned, the Venusian crust is believed to be predominantly composed of basalt. Gravity data implies that the thickness of the crust remains relatively consistent across much of the planet, with typical estimates ranging from 20 to 50 km (12 to 30 miles). The Tessera highlands may present exceptions, potentially featuring a significantly thicker crust.

SURFACE

Venus exhibits a diverse range of geological features, including volcanoes, extensive impact craters, and landforms shaped by aeolian erosion and sedimentation. Its topography is characterized by a single, robust crustal plate, resulting in an unimodal elevation distribution where over 90% of the surface lies between -1.0 and 2.5 km. Despite its similarities to Earth in size, mass, density, and potentially composition, Venus boasts a unique geology distinct from our own. Despite being much older than Earth, Venus’ surface is relatively youthful compared to other terrestrial planets, likely due to a large-scale resurfacing event that concealed much of the previous rock record.

Surface conditions on Venus are significantly harsher than on Earth, with temperatures ranging from 453 to 473 °C and pressures of 95 bar. The absence of water strengthens crustal rock, contributing to the preservation of surface features. These observed features offer valuable evidence of the geological processes at play.

PLAINS

Plains cover a vast portion of Venus, displaying relatively flat topography at varying elevations. Lowland plains, or planitiae, lie within 1–3 km of the datum, while highland plains, or plana, are situated above this range. These plains, unlike those found on other silicate planets, are extensively faulted or fractured. They encompass an array of features, including wrinkle ridges, grabens (fossa and linea), fractures, scarps (rupes), troughs, hills (Collis), and dikes at both local and regional scales. Many plains exhibit discernible flow patterns, indicating an origin from volcanic lava flows. Prominent lava flow fields are known as fluctūs.

The presence of surface flow patterns, combined with intersecting valleys, suggests that these plains likely formed through global lava flows over a short period, later experiencing compressional and extensional stresses. Structurally, plains often display deformation in belts of ridges (dorsa) or fractures of varying orientations and morphologies.

CHANNELS

The surface of Venus contains over 200 channel systems and named valles, resembling terrestrial rivers. These channels vary in size and are frequently found in planar regions of the planet. They range from the minimum resolution of Magellan imaging to over 6800 km long (e.g., Baltis Vallis) and up to 30 km wide. The distribution of these channels across the planet is not uniform, tending to concentrate near the equatorial region, particularly around volcanic structures. Channels likely formed in extraordinarily short time frames (1–100 years), indicating swift movement and erosion of lavas. These Venusian channels are classified by morphology into three types: simple, complex, and compound.

Simple channels are single-channel valleys with little to no branching or anastomosing. Various types of straightforward channels seen on Venus encompass sinuous rilles, simple channels with flow margins, and Canali. Sinuous rilles, akin to those found on the Moon, are slender erosive channels that originate from regions of volcanic collapse, such as coronae. Simple channels with flow margins are situated in conspicuous flow areas, lacking a clearly defined source and end, and are thought to supply large flows from surrounding volcanic activity. Canali, exemplified by the Baltis Vallis, are extensive flows maintaining a consistent width and depth. They may encompass deserted channels, bends, and levees, indicative of their origin from substantial quantities of dense lavas.

Complex channels are channels that can be braided, anastomosing, or in distributary patterns. They commonly form on lava flow deposits but also occur elsewhere. Complex channels without flow margins may form part of a larger flow system, and form as channels of lava flows erode into the crust. Complex channels exhibiting flow margins manifest as non-erosive, with distinct channels divided by sections of crust exhibiting varying radar properties.

Compound channels display a combination of simple and complex channel structures. Typically commencing as straightforward channels, they eventually split and meander as the energy of the flow diminishes towards its farthest reaches.

VOLCANOES

More than 1,100 volcanic formations exceeding 20 kilometers in diameter have been identified on Venus. It’s believed that the number of smaller structures likely surpasses this count by a considerable margin. These formations encompass extensive volcanic constructs, fields of shield volcanoes, and individual calderas. Each of these structures represents a center of extrusive magma eruption and differences in the amount of magma released, depth of the magma chamber, and rate of magma replenishment effect volcano morphology. When compared to Earth, the number of preserved volcanic zones is staggering, and this is based on Venus’ strong crust due to a lack of water.

Volcanic centers on Venus are not distributed evenly, as over half of the centers are found in and around the Beta-Atla-Themis region, which covers 30% of the planet’s surface. Volcanic features on Venus fall into two primary categories based on their ability to generate a shallow magma reservoir: either through the creation of extensive regions with numerous small eruption sites clustered together or by large flows originating from a single edifice.

Single volcanoes refer to a single, substantial edifice. These can include large volcanoes (often named mons and measuring around 100 km in diameter, examples being Theia Mons and Maat Mons), intermediate volcanoes (with diameters ranging from 20 to 100 km), and calderas. These single-eruption-center volcanoes are sustained by a shallow magma chamber within the crust, replenished by magma from mantle upwelling and decompression melting, leading to the pooling and trapping of a reservoir. The retention of a magma chamber allows for long-term eruptions, resulting in the formation of significant volcanic domes and flow deposits.

The extrusion of magma to the surface is often linked to rifting or extensional tectonics in the region, with the shape of the dome or magma flow field being influenced by the chemistry and viscosity of the magma. Each of these types of volcanoes can be further classified based on factors such as the shape of the dome created, the number of edifices present, the presence of rifting along the dome, radial fracturing, or collapse of the magma chamber. Intermediate volcanoes with domical surface cones are referred to as tholus, while pancake-shaped volcanoes are known as farrum.

Calderas are circular depressions on the surface believed to have formed by deformation above a cooling magma chamber. Calderas on Venus are characterized as simple, single depressions, called coronae, and complex, radially fractured zones, called arachnoids. Some caldera are named patera.

Shield fields are expansive regions spanning 100–200 km in diameter that house numerous small, mostly shield, volcanoes typically around 20 km in size. These fields can boast tens to hundreds of these volcanoes, occasionally earning individual shield volcanoes the name “colles”. They form in areas where the rate of magma replenishment is too low to generate a magma reservoir in the crust, leading to several small eruptions on a regional scale. The prevalence of shield-type volcanoes in these regions has led to the term “shield fields”.

CORONAE

Coronae, on the other hand, are geological features shaped by the influence of hot, buoyant material masses—known as diapirs—rising from deep within Venus. These diapirs can fracture the surface in a radial pattern as they approach the surface, creating a characteristic starburst of faults and fractures, often situated atop a broad, gently sloping topographic rise. After nearing the surface and cooling, a diapir loses its buoyancy, causing the initially elevated crust to sag under its own weight, resulting in concentric faults. This process yields a circular-to-oval pattern of faults, fractures, and ridges.

Volcanism can occur at all stages of corona formation, with late-stage volcanism tending to obscure the radial faulting seen in the early stages. Coronae typically measure a few hundred kilometers in diameter. The radially fractured domes seen in the early stages are relatively rare, while the concentric scars characteristic of mature coronae are among the most abundant large tectonic features on the planet.

RIFTS

Rifts, among the most striking tectonic features on Venus, are most prominently found atop broad, elevated areas like Beta Regio. They sometimes radiate outward from their centers, resembling the spokes of a colossal wheel. Regions like Beta Regio appear to be sites where extensive sections of the lithosphere have been forced upward from below, resulting in the surface splitting to form vast rift valleys. These rifts are comprised of countless faults, with their floors typically lying 1–2 km below the surrounding terrain.

In many respects, the rifts on Venus share similarities with major rifts elsewhere, such as the East African Rift on Earth or Valles Marineris on Mars. For instance, volcanic activity appears to be associated with all these features. Nevertheless, the Venusian rifts differ from those on Earth and Mars in that little erosion has occurred within them, due to the absence of water.

TESSERAE

Tesserae, an exclusive characteristic of Venus, exemplify the most complex geological zones. They are described as expanses with continent-like dimensions, boasting elevated topographies (ranging from 1 to >5 km above the datum), and showcasing extensive deformation, often featuring intricate ridges. These formations arise from the intersection of at least two structural elements. The deformation in tessera terrain can be so intricate that it is sometimes challenging to discern the types of stresses in the lithosphere that were responsible for their formation. Tesserae typically exhibit very bright characteristics in radar images, indicating an extremely rugged and blocky surface at meter scales. They are categorized based on their structural components, with examples including Ishtar Terra and Aphrodite Terra.

IMPACT CRATERS

The Venusian surface bears the marks of both extraplanetary objects and internal forces. Meteorites entering the atmosphere and impacting the surface have left behind numerous craters. In the solar system, nearly all solid celestial bodies show signs of meteoritic impacts, with smaller craters typically outnumbering larger ones. Venus hosts nearly 1000 impact craters. However, its dense atmosphere acts as a robust shield, slowing down, flattening, and sometimes fragmenting incoming objects. Consequently, the Venusian surface lacks small craters (≤30–50 km in size) due to the atmosphere’s influence on smaller objects. Depending on factors like impact angle, velocity, size, and composition, the atmosphere may disintegrate and crush the incoming object, essentially causing it to melt in mid-air.

The significant craters on Venus exhibit distinctive features compared to those on other planets. While most impact craters, both on Venus and elsewhere, display ejecta surrounding them, Venusian ejecta is peculiar in that its outer rim often showcases a lobed or petal-like pattern. This suggests that a substantial portion of it flowed outward close to the ground, rather than following a ballistic trajectory high above the surface before falling back down.

If craters were concentrated in specific regions, scientists could deduce that a wide range of surface ages were represented across the planet. However, due to a nearly random distribution of craters worldwide, it leads to the inference that essentially the entire planet has undergone geological resurfacing in the last billion years or less, with a significant portion of this resurfacing occurring over a relatively short span of time.

CHARACTERISTICS

MASS	4.8675×1024 kg
VOLUME	9.2843×1011 km3
SURFACE AREA	4.6023×108 km2
MEAN RADIUS	6,051.8 km
SURFACE PRESSURE	9.3 MPa
DENSITY	5.243 g/cm3
ESCAPE VELOCITY	10.36 km/s
SURFACE GRAVITY	8.87 m/s2
ABSOLUTE MAGNITUDE	-4.4
SATELLITES	0
RINGS	NO
MEAN TEMPERATURE	-41°C
SEMI-MAJOR AXIS	108,208,000 km
ORBIT PERIOD	224.701 days
PERIHELION	107,477,000 km
APHELION	108,939,000 km
MEAN ORBITAL VELOCITY	35.02 km/s
MAXIMUM ORBITAL VELOCITY	35.26 km/s
MINIMUM ORBITAL VELOCITY	34.78 km/s
ORBIT INCLINATION	3.395°
ORBIT ECCENTRICITY	0.2056
SIDEREAL ROTATION PERIOD	-5832.6 hours
LENGTH OF DAY	116.75 days
MINIMUM DISTANCE FROM EARTH	38.2 ×106 km
MAXIMUM DISTANCE FROM EARTH	261 ×106 km
MAXIMUM VISUAL MAGNITUDE	-4.8

ORBIT AND ROTATION

Venus orbits the Sun at an average distance of about 108 million kilometers (67 million miles). It takes approximately 225 Earth days to complete one orbit around the Sun. Venus rotates on its axis very slowly and in the opposite direction to most planets as viewed from above Earth’s north pole. This means Venus has a retrograde rotation, taking about 243 Earth days for one complete rotation. As a result, a day on Venus (from sunrise to sunrise) is longer than a year on Venus. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus’s opaque clouds prevent observing the Sun from the planet’s surface.

While all planetary orbits possess some degree of ellipticity, Venus currently maintains the orbit closest to a circle, with an eccentricity of less than 0.01. Computer simulations of the early solar system’s orbital dynamics suggest that Venus’ orbit might have been considerably more elliptical in the past, potentially reaching values as high as 0.31, which could have influenced the planet’s early climate evolution.

Venus likely assumed its present state, including its rotation period and axial tilt, through a process of chaotic spin variations driven by interactions with other planets and the gravitational effects of its dense atmosphere. This transformation would have unfolded over billions of years. The rotation period of Venus likely represents a balance between being tidally locked to the Sun’s gravitational pull, which tends to slow rotation, and experiencing atmospheric tides generated by the Sun’s heating of the thick Venusian atmosphere.

Within the orbital region of Venus exists a cloud of dust particles, thought to have originated from various sources, including asteroids trailing behind Venus, interplanetary dust migrating in waves, or remnants of the original circumstellar disc that formed the planetary system.

Earth and Venus maintain a near orbital resonance of 13 orbits for Venus to every 8 orbits for Earth. This leads to their periodic close approaches and their alignment at inferior conjunctions occurring approximately every 584 days on average. When Venus is positioned between Earth and the Sun during an inferior conjunction, it comes closest to Earth, typically at an average distance of 41 million km (25 million mi). Although Venus approaches Earth the most closely, Mercury more frequently becomes the closest planet to Earth. Among all planets, Venus exerts the lowest gravitational potential difference to Earth. In terms of tidal forces, Venus ranks third, following the Moon and the Sun, though its influence is significantly less.

ATMOSPHERE

Venus possesses the most substantial atmosphere among the terrestrial planets, including Mercury, Earth, and Mars. This gaseous envelope primarily consists of over 96.5 percent carbon dioxide and approximately 3.5 percent molecular nitrogen. It also contains trace amounts of other gases like carbon monoxide, sulfur dioxide, water vapor, argon, and helium. The atmospheric pressure at the planet’s surface varies with elevation; at the mean radius elevation, it reaches about 95 bars, equivalent to 95 times the atmospheric pressure at Earth’s surface. This mirrors the pressure encountered at approximately 1 km (0.6 miles) beneath the surface of Earth’s oceans. Additionally, the atmosphere of Venus possesses a mass 92 times that of Earth’s.

Comparatively, Venus’s atmosphere is abundant in ancient noble gases when compared to Earth’s, suggesting an early divergence in their evolutionary paths. The origin of this enrichment has been attributed to a substantial comet impact or the accretion of a more massive primary atmosphere from the solar nebula. However, the atmosphere lacks radiogenic argon, indicative of a swift cessation of significant magmatic activity.

Scientific studies propose that billions of years ago, Venus’s atmosphere may have resembled the early Earth‘s, with substantial amounts of liquid water on the surface. Over a span of 600 million to several billion years, factors like heightened solar radiation from the Sun’s increasing luminosity and potentially extensive volcanic resurfacing led to the evaporation of the original water, shaping the current atmosphere. This resulted in a runaway greenhouse effect when a critical level of greenhouse gases (including water) was introduced into the atmosphere.

While the surface conditions on Venus are now unsuitable for Earth-like life that might have existed before these events, there is conjecture about the potential existence of life in the upper cloud layers of Venus, situated approximately 50 km (30 mi) above the surface. In this region, the atmospheric conditions most closely resemble those of Earth in the Solar System, with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being comparable to Earth’s surface, albeit with acidic clouds and an atmosphere primarily composed of carbon dioxide.

Above the main body of Venus’s atmosphere lies the ionosphere, which, as its name suggests, is composed of charged particles or ions. These ions result from the absorption of ultraviolet solar radiation and the interaction of the solar wind—the stream of charged particles emanating from the Sun—with the upper atmosphere. The predominant ions in Venus’s ionosphere are various forms of oxygen (O+ and O2+) and carbon dioxide (CO2+).

MAGNETIC FIELD

In 1967, Venera 4 found Venus has a very weak and virtually non-existent global magnetic field. Unlike Earth, which has a strong and protective magnetic field generated by its liquid iron-nickel core, Venus’s internal structure and dynamics are different, leading to the absence of a significant magnetic field. The absence of a native magnetic field on Venus was unexpected, especially considering its Earth-like size, leading scientists to anticipate the presence of a core-based dynamo. For a dynamo to function, three essential elements are needed: a conductive fluid, rotational motion, and convective activity.
The lack of a global magnetic field on Venus can be attributed to a combination of factors:

SLOW ROTATION

Venus rotates very slowly on its axis, taking about 243 Earth days for one complete rotation. This slow rotation rate affects the generation of a dynamo effect, which is responsible for creating and sustaining magnetic fields on planets like Earth.

CORE COMPOSITION

While Venus likely has a solid iron-nickel core like Earth, its core may not have the same degree of convective motion as Earth’s core. Convection currents in Earth’s liquid outer core are crucial for generating its magnetic field.

CORE SIZE AND STRUCTURE

The size and structure of Venus’s core might be different from Earth’s, further impacting the generation of a magnetic field. Additionally, it is believed that Venus’s core is less differentiated than Earth’s, which means it has not separated into distinct layers as much.

MANTLE CONVECTION

Earth’s magnetic field is also influenced by the convection currents in its mantle. The mantle is the layer of semi-solid rock beneath the crust. It is possible that the mantle dynamics on Venus are not conducive to sustaining a strong magnetic field.

MAGNETOSOPHERE STRIPPING

Venus’s weak magnetic field, combined with the intense solar wind and lack of a protective atmosphere, allows the solar wind to interact more directly with the planet’s upper atmosphere. This interaction can lead to the stripping away of ions from the upper atmosphere, further weakening any potential magnetic effects.

Although Venus lacks a global magnetic field, it does exhibit localized magnetic anomalies in some regions. These anomalies have been observed by spacecraft orbiting the planet, indicating the presence of localized magnetic fields associated with certain geological features. However, these magnetic anomalies are not strong enough to form a global magnetic shield comparable to Earth’s, which makes Venus more vulnerable to the harsh effects of solar wind and cosmic radiation, reaching elevations of 54 to 48 km Earth-like levels.

GRAVITY

Venus is often referred to as Earth’s “sister planet” due to its similar size, composition, and proximity to the Sun. The picture above depicts the gravity waves on Venus. Venus’s gravity is similar to Earth’s, The gravitational acceleration on Venus is approximately 8.87 meters per second squared (8.87 m/s²), compared to Earth’s 9.81 m/s². This means that objects on the surface of Venus weigh approximately 90.7% of what they would weigh on Earth.

GRAVITATIONAL ACCERLATION

The gravitational pull experienced on the surface of a planet is influenced by both its mass and radius. Venus possesses a mass roughly 81.5% that of Earth and a radius about 95% of Earth’s. Consequently, the gravitational acceleration on Venus amounts to roughly 90.7% of that on Earth.

EFFECTS ON HUMAN ACTIVITY

WEIGHT

On Venus, a 100-kilogram object would weigh about 90.7 kilograms. This difference in weight has implications for human exploration and colonization. Astronauts on Venus would experience a significantly different environment compared to Earth, affecting things like mobility and physical strain.

ENERGY REQUIREMENTS

Due to the lower gravity, it would require less energy for activities like walking or lifting objects on Venus compared to Earth. However, this may also lead to challenges in adapting to the differences in muscle usage and coordination.

COMPARISON WITH OTHER PLANETS

When comparing Venus’s gravity to other planets, it has stronger gravity than Mars (which has only about 38% of Earth’s gravity) but is significantly weaker than Earth’s. This makes Venus a potentially interesting target for future human exploration, though the challenges posed by its harsh environment are considerable.

Previous Planet – “Mercury“

Next Planet – “Earth“