Venus
Venus is the second planet from the Sun. It is similar to Earth in size and mass, but conditions at its surface are radically different. Beneath an unbroken cloud layer lie scorching plains, mountains and volcanoes. A dense carbon-dioxide atmosphere maintains a surface temperature of about 464 °C, the highest of any planet in the Solar System.[2]
Size and physical characteristics
Venus has a diameter of approximately 12,104 km, only about 640 km less than Earth's mean diameter. Its equator measures roughly 38,000 km around. On an imaginary road encircling the planet, a car travelling at 100 km/h would need almost 16 days to complete the journey without stopping.[3]
The planet has a mass of approximately 4.87 × 1024 kg, or 81.5% of Earth's mass, and a mean density of about 5.24 g/cm³. Surface gravity is only slightly weaker than on Earth: an object exerting a force of 100 newtons on its support on Earth would exert about 90 newtons on Venus.[3]
Orbit and rotation
Venus completes one orbit around the Sun in approximately 225 Earth days. Its orbit is nearly circular, with the distance from the Sun changing from about 107.5 million km to 108.9 million km. The mean orbital speed is close to 35 km/s; in one minute, the planet travels more than 2,100 kilometres.[1]
Venus rotates very slowly and in the direction opposite to the rotation of Earth and most other planets. One rotation relative to the stars takes about 243 Earth days, longer than a Venusian year. Radar measurements also show that the rotation rate changes slightly over time.[4]
A solar day, measured from one sunrise to the next, lasts about 117 Earth days. Slightly fewer than two solar days pass during one Venusian year.[1]
Atmosphere and temperature
Surface pressure reaches approximately 92 bar, about 90 times the pressure at sea level on Earth. A similar pressure occurs in Earth's oceans at a depth of roughly 900 metres. Every square centimetre of the surface experiences a force of about 920 newtons, comparable to the weight of a 94-kilogram mass on Earth.[2]
Carbon dioxide makes up most of the atmosphere. It absorbs and re-emits infrared radiation, restricting the loss of heat from the surface to space. The powerful greenhouse effect maintains a temperature of about 464 °C, above the melting point of lead. The surface remains extremely hot on the nightside despite the exceptionally long night.[5]
There are no terrestrial-style oceans, and water vapour occurs only in trace quantities in the atmosphere. Modern Venus is a dry planet where water cannot persist as open seas or lakes.[2]
Clouds and atmospheric circulation
Venus is completely covered by clouds containing droplets of sulphuric acid. They reflect most incoming sunlight and conceal the surface at visible wavelengths. The bright disk seen in an ordinary photograph therefore shows the cloud envelope rather than the rocky terrain.[6]
The upper cloud layers circle the planet far faster than the surface rotates, completing a revolution in only several Earth days. This phenomenon is known as atmospheric super-rotation. Winds at high altitude reach about 400 km/h, whereas winds near the surface are much slower.[6][7]
Ultraviolet images reveal bands, vortices and dark areas that are almost invisible in ordinary light. Venus Express observations showed that circulation on the nightside differs from that on the dayside, and that some atmospheric waves are connected with highland regions below.[8]
Surface and terrain
Volcanic plains cover most of Venus. Large highland regions, mountain belts and numerous volcanoes rise above them. The surface also contains tesserae, areas of complex terrain crossed by intersecting ridges, folds and faults.[2]
Radar made detailed mapping possible because radio waves pass through the clouds. The Magellan spacecraft mapped about 98% of the surface. Its images reveal solidified lava flows, impact craters and deformations of the crust.[9]
Magellan data from coronae, large circular geological structures, indicate possible continuing activity. Coronae are associated with hot material rising through the interior and deforming the planet's outer shell.[10]
Volcanic activity
Volcanism changed the surface of Venus in the geologically recent past. Radar images from the early 1990s show changes near Sif Mons and in Niobe Planitia. The most likely explanation is that new lava flows appeared between the observations.[11]
A volcanic vent on Maat Mons enlarged and changed shape between February and October 1991. Its area approximately doubled in eight months, indicating an eruption between the two Magellan observations.[12]
Magnetic environment
Venus has no detected intrinsic global magnetic field comparable to Earth's. The solar wind interacts directly with the upper atmosphere and its ionised component, producing an induced magnetosphere around the planet.[13]
This environment changes with solar-wind conditions. Venus Express observed the planet's ionosphere stretching far into the nightside and forming a long tail when the pressure of the solar wind weakened.[13]
Observation from Earth
Venus is one of the brightest objects in Earth's sky. It shines by reflected sunlight and appears either after sunset or before sunrise, giving rise to its traditional descriptions as the evening star and the morning star.[2]
Through a telescope, Venus displays phases ranging from an almost full disk to a narrow crescent. As it approaches Earth, its apparent disk grows, while the illuminated portion may become thinner. Its changing brightness therefore depends both on distance and on the fraction of the dayside facing the observer.[14]
Spacecraft exploration
In 1962, Mariner 2 became the first spacecraft to study Venus successfully during a flyby. Soviet spacecraft of the Venera programme later measured the atmosphere and reached the surface. Venera 7 made a soft landing on 15 December 1970 and transmitted data from the ground—the first successful transmission from the surface of another planet.[15][16]
On 22 October 1975, Venera 9 returned the first photograph from the Venusian surface. The image showed rocky ground and fragments of rock. The lander operated for 53 minutes after reaching the surface.[17]
The American Magellan spacecraft studied Venus from orbit between 1990 and 1994, producing detailed radar maps.[9] The European Venus Express orbited the planet from 2006 to 2014 and investigated its clouds, atmospheric circulation and interaction with the solar wind.[8]
See also
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 Venus Fact Sheet // NASA, National Space Science Data Center.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Venus Facts // NASA Science.
- ↑ 3.0 3.1 Planetary Fact Sheet — Metric // NASA, National Space Science Data Center.
- ↑ Margot J.-L. et al. Spin state and moment of inertia of Venus // Nature Astronomy. 2021.
- ↑ Greenhouse effect, clouds and winds // European Space Agency.
- ↑ 6.0 6.1 Destination: Venus // European Space Agency.
- ↑ Variable clouds and hazes at Venus // European Space Agency.
- ↑ 8.0 8.1 Cloudy Venus // European Space Agency.
- ↑ 9.0 9.1 Magellan Mission to Venus // NASA, National Space Science Data Center.
- ↑ NASA's Magellan Mission Reveals Possible Tectonic Activity on Venus // NASA. 14 May 2025.
- ↑ Ongoing Venus Volcanic Activity Discovered With NASA's Magellan Data // NASA. 27 May 2024.
- ↑ NASA's Magellan Data Reveals Volcanic Activity on Venus // NASA Jet Propulsion Laboratory. 15 March 2023.
- ↑ 13.0 13.1 When a planet behaves like a comet // European Space Agency.
- ↑ Phases of Venus // NASA Science, Astronomy Picture of the Day. 21 May 2020.
- ↑ Venus Exploration // NASA Science.
- ↑ Deep Space Robotic Firsts // NASA Science.
- ↑ First Look: Venus // NASA Science.