The surface of Venus is hidden beneath a thick, highly reflective cloud cover Venus is similar to the Earth in its size, mass, average density, and surface gravity It is covered by unbroken, highly reflective clouds that conceal its other features from Earth- based observers
Venus’s murky past (and atmosphere) Because it was similar is size and solar system position, many people have called it the twin of Earth. Because we couldn’t see through the clouds, a great number of interesting hypotheses came into existence about its surface. None of those hypotheses were correct.
Early Discovery – From Afar Motion in our sky Orbit and rotation Atmosphere (atmosphere and cloud composition, cloud motion)
Venus can be seen in the eastern sky in the hours before dawn for several months around the greatest western elongation. It can be seen in the western sky in the hours after dusk for several months around greatest eastern elongation. At its greatest eastern and western elongations, Venus is about 47° from the Sun. Greatest Elongations of Venus
East (evening)West (morning) 2013Nov12014Mar22 2015Jun62015Oct26 2017Jan122017Jun3 2018Aug172019Jan6 2020Mar242020Aug13 2021Oct292022Mar20 2023Jun42023Oct23 2025Jan102025Jun1 2026Aug152027Jan3 2028Mar222028Aug10 Greatest Elongations of Venus
The upper cloud layers of the Venusian atmosphere move rapidly (300 km/hr) around the planet in a retrograde direction (with rotation), with a period of only about 4 Earth days.
The circulation of the Venusian atmosphere is dominated by two huge convection currents in the cloud layers, one in the northern hemisphere and one in the southern hemisphere
Then we went exploring! Venus ExpressVenus Express - ESA Venus Orbiter (2006) (Currently in Orbit) MESSENGER MESSENGER - NASA Mercury Orbiter (2004) (Two Venus Flybys in 2006 and 2007) MagellanMagellan - NASA Venus Radar Mapping Mission (1989-1994) Pioneer Venus Pioneer Venus - NASA Orbiter/Probes to Venus (1978-1992) Galileo Galileo - NASA Mission to Jupiter (Venus flyby - 1990) Vega 1 Vega 1 - Soviet mission to Venus and Comet Halley (Venus flyby - 1985) Vega 2 Vega 2 - Soviet mission to Venus and Comet Halley (Venus flyby - 1985) Venera Venera - Soviet Venus Missions (1-16) (1961-1983) Mariner 10 Mariner 10 - NASA Mission to Venus and Mercury (1973-1975) Mariner 5 Mariner 5 - NASA Venus flyby (1967) Mariner 2 Mariner 2 - NASA Venus flyby (1962)
In 1962 the unmanned U.S. spacecraft Mariner 2 made the first close flyby of Venus Scientific discoveries made by Mariner 2 included a slow retrograde rotation rate for Venus, hot surface temperatures and high surface pressures, a predominantly carbon dioxide atmosphere, continuous cloud cover with a top altitude of about 60 km, and no detectable magnetic field.
Venus’s rotation is slow and retrograde Venus rotates clockwise, with period slightly longer than orbital period. Possible reasons: Off-center collision with massive protoplanet Tidal forces of the sun on molten core
Venus rotates slowly in a retrograde direction with a solar day of 117 Earth days and a rotation period of 243 Earth days There are approximately two Venusian solar days in a Venusian year.
Spectra Comparison Spectra taken of Venus showed mostly Carbon Dioxide in the atmosphere. The clouds were shown to be sulfuric acid! This is a comparison showing Carbon Dioxide in the Venusian, Terran, and Martian atmospheres
Venera 16 Venera 16 - Soviet Venus Orbiter (1983) Venera 15 - Soviet Venus Orbiter (1983) Venera 14 - Soviet Venus Lander (1981) (Images and soil samples – similar to oceanic basalts) Venera 15 Venera 14 Venera 13 Venera 13 - Soviet Venus Lander (1981) (Images and soil samples) Venera 12 Venera 12 - Soviet Venus Lander (1978) Venera 11 Venera 11 - Soviet Venus Lander (1978) Venera 10 Venera 10 - Soviet Venus Orbiter and Lander (1975) Preliminary results provided: (A) profile of altitude (km)/pressure (earth atmospheres)/temperature (deg C) of 42/3.3/158, 15/37/363, and 0/92/465, (B) successful TV photography showing large pancake rocks with lava or other weathered rocks in between, and (C) surface wind speed of 3.5 m/s. Venera 9 Venera 9 - Soviet Venus Orbiter and Lander (1975) Preliminary results indicated: (A) clouds 30-40 km thick with bases at 30-35 km altitude, (B) atmospheric constituents including HCl, HF, Br, and I, (C) surface pressure about 90 (earth) atmospheres, (D) surface temperature 485 deg C, (E) light levels comparable to those at earth midlatitudes on a cloudy summer day, and (F) successful TV photography showing shadows, no apparent dust in the air, and a variety of 30-40 cm rocks which were not eroded. Venera 8 Venera 8 - Soviet Venus Lander – 1972 Venus atmospheric probe and lander. Confirmed high surface temperature. Ran 50 min. Cloud layer floor. Rock similar to granite? Venera 7 Venera 7 - Soviet Venus Lander – 1970 first man-made object to return data after landing on another planet, hit at 38 mph at 50 angle, bumpy ride and parchute rip, got temp, was barely functional 23 min after landing Venera 6 Venera 6 - Soviet Venus Probe – 1969, chemical readings Venera 5 - Soviet Venus Probe – 1969, chemical readings Venera 4 - Soviet Venus Probe – 1967, 95% CO 2, crashed after battery died. Venera 5 Venera 4 Venera 3 Venera 3 - Soviet Venus Lander (Contact Lost) - 1965 Venera 2 - Soviet Venus Flyby (System Failed) - 1965 Venera 1 - Soviet Venus Flyby (Contact Lost) – 1961, data on magnetic fields, cosmic rays and solar plasma. Venera 2 Venera 1 Venera Atmospheric Studies Results reported included evidence of lightning and thunder, a high Ar36/Ar40 ratio, and the discovery of carbon monoxide at low altitudes. Radar Mapping
The Atmosphere of Venus Spacecraft measurements reveal that 96.5% of the Venusian atmosphere is carbon dioxide Most of the rest of the atmosphere is nitrogen. The bottom 30 km is clear of clouds or haze. There is 150 x more Deuterium per H atom than on Earth. New data shows atmosphere up to 90 km on night side!
Venus has a hot, dense atmosphere and corrosive cloud layers Venus’s clouds consist of droplets of concentrated sulfuric acid. The haze is also sulfuric acid. The surface pressure on Venus is 90 atm, and the surface temperature is 460°C (close to 900°F)! Both temperature and pressure decrease as altitude increases
Cold Layer found! A new analysis based on five years of observations using ESA’s Venus Express, scientists have uncovered a very chilly layer at temperatures of around –175ºC in the atmosphere 125 km above the planet’s surface. The curious cold layer is far frostier than any part of Earth’s atmosphere, for example, despite Venus being much closer to the Sun. The discovery was made by watching as light from the Sun filtered through the atmosphere to reveal the concentration of carbon dioxide gas molecules at various altitudes along the terminator – the dividing line between the day and night sides of the planet. Armed with information about the concentration of carbon dioxide and combined with data on atmospheric pressure at each height, scientists could then calculate the corresponding temperatures. 1 October 2012 Venus Express has spied a surprisingly cold region high in the planet’s atmosphere that may be frigid enough for carbon dioxide to freeze out as ice or snow.
Ozone Layer found! 6 October 2011 ESA’s Venus Express spacecraft has discovered an ozone layer high in the atmosphere of Venus. The ozone was detectable because it absorbed some of the ultraviolet from the starlight. These atoms are then swept around to the nightside of the planet by winds in the atmosphere: they can then combine to form two-atom oxygen molecules, but also sometimes three-atom ozone molecules. Its ozone layer sits at an altitude of 100 km, about four times higher in the atmosphere than Earth's and is a hundred to a thousand times less dense.
The Atmosphere of Venus Venus is the victim of a runaway greenhouse effect – just kept getting hotter and hotter as infrared radiation was reabsorbed
Venera 13 - terrainVenera 14 - terrain Venera-13 revealed rolling hills with layered slabs of rock and soil. From high resolution radar imaging of the landing site, Russian geologists concluded that Venera-13 probably landed on the most common type of Venusian terrain, plains with wrinkle ridges. These are the oldest volcanic plains, formed about 750 million years ago, fractured and buckled by tectonic pressures in the crust. Potassium-rich basalts. Venera-14 saw a flat expanse of rock with no soil. Radar imaging of the site reveals a younger volcanic plain with lobate flows of lava, probably formed a few million years ago. The rock is actually layered and crunchy. One new theory suggests it is a pumice-like material, formed out of volcanic ash or dust from meteorite strikes. Similar to ocean floor basalts. Credit: Don P. Mitchell
Ishtar Terra, topographic, data from Venera and Magellan
Surface Features on Venus Smooth lowlands Highland regions: Maxwell Montes are ~ 50 % higher than Mt. Everest!
Radar Best mapping technique: use radar to penetrate clouds –Radar systems emit a short burst of radio waves and then detect the reflected burst to determine a target's distance and (through the Doppler effect) motion. –Interpreting radar images: brighter regions are more reflective of radar waves, meaning they are rougher. Darker regions are smoother. Radar Map of Venus (Pioneer, 1981)
Volcanic Features on Venus Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!) Aine Corona Pancake Domes: Associated with volcanic activity forming coronae Coronae: Circular bulges formed by volcanic activity Some lava flows collapsed after molten lava drained away
The density of craters suggests that the entire surface of Venus is no more than a few hundred million years old. According to the equilibrium resurfacing hypothesis, this happens because old craters are erased by ongoing volcanic eruptions
Lakshmi Planum and Maxwell Mountains Radar image Wrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.
How do you get mountains? If it is so hot, how do the mountains stay upright and not flow away as they start to melt? If you bake rock, you make it harder!
The Surface of Venus Venus’s largest impact crater, named after Margaret Mead:
Incoming! Craterless Splotch Crater Cluster Dark Halo
Craters on Venus ~900 impact craters on Venus’s surface: Surface not very old. No water on the surface Thick, dense atmosphere (filters out 90% of objects smaller than 9 km in diameter) No erosion Craters appear sharp and fresh (86% pristine)
The Crater Story Pristine Craters Randomly scattered (with respect to elevation, terrain type, etc.) Relatively few craters –Resurfacing Event! About 91.5% resurfaced between 500 and 750 million years ago!
The climate on Venus followed a different evolutionary path from that on Earth Venus’s high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight. The early atmosphere of Venus contained substantial amounts of water vapor This caused a runaway greenhouse effect that evaporated Venus’s oceans and drove carbon dioxide out of the rocks and into the atmosphere Almost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere. The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earth’s oceans and chemically bound into its rocks
Volcanic eruptions are probably responsible for Venus’s clouds Venus’s clouds consist of droplets of concentrated sulfuric acid Active volcanoes on Venus may be a continual source of this sulfurous material
Venus’s Magnetic Field and Internal Structure No magnetic field, probably because rotation is so slow (or because core is solid?) No measurements available that would give clues to internal structure Gravity data by Magellan is controversial
Solar wind and atmosphere interaction During normal solar wind During reduced solar wind
A History of Venus Complicated history; still poorly understood. Very similar to Earth in mass, size, composition, density, but no magnetic field Core solid? Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail. Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail. CO 2 produced during outgassing remained in atmosphere (on Earth: dissolved in water). Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.) Any water present on the surface rapidly evaporated → feedback through enhancement of greenhouse effect
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