Venus

Venus

Overview

When Venus was first studied in modern times, scientists saw a beautiful world that was almost the size of Earth, and it had a thick cover of clouds. The picture to the right shows what Venus looks like when seen in ultra-violet light (UV shows more contrast in the clouds). For years, Venus was called Earth's Sister Planet, and much popular science and science fiction literature was devoted to what might lie below the huge clouds. All that changed once scientists were able to measure what those lovely clouds were made of: Poisonous gases.

Venus' atmosphere is so thick that a barometric reading (a measure of pressure) would be between 90 to 100 times higher than Earth's, which is the equivalent on Earth of being underneath 1 km of water. Its atmosphere is 97% carbon dioxide. This green-house gas retains almost all of the heat Venus' surface gets from the sun, and its surface temperature of 480 °C (896 °F) is the same on both sides of the planet due to the insulating nature of the clouds. This temperature is hot enough to melt lead. The clouds are rich in sulfuric acid, so any type of precipitation would "burn" with acidity.

Scientists have mapped more of Venus' surface than that of the Earth. While we cannot see beneath the clouds in visible light, we can bounce radar off the planet's surface. The radar that is reflected can then be used construct a map of the surface. This is the same principle that bats use to see in the dark, dolphins use to communicate, and we use to map Earth's ocean floor. There is only a small section of Venus that has not been mapped. The image to the left is a false-color image of what Venus would look like if stripped of its clouds. The darker colors indicate lower features, and the brighter colors indicate higher features.

From the data currently available, Venus is a world composed of mountains, flatlands, and valleys -- much like the rugged terrain found on Earth. The surface has relatively few craters, which suggests that there was either recent or current volcanic activity that has erased older craters.

Atmosphere

As can be seen in the planetary data table below, Venus' atmosphere is nearly 100 times as massive as Earth's, and its thick cloud layers block the surface from view. It exerts a pressure of approximately 92 bars at the surface. Its composition is nearly all CO₂:

• CO₂: 96.5%
• N₂: 3.5%
• SO₂: 0.015%
• Ar: 0.007%
• H₂O: 0.002%
• CO: 0.0017%
• He: 0.0012%
• Ne: 0.0007%

The density at the surface is 65,000 g/m³. Wind speeds range from 1-4 km/sec (0.5-2 mph) at the surface. The scale height of the atmosphere is about 15.9 km.

Venus is the case of a runaway greenhouse effect. The temperature and pressure of the atmosphere decrease with height, so water vapor rises in the atmosphere and encounters conditions that cause it to condense back into liquid water and fall back to the surface - a region called the "cold trap." On Earth, this is at a height of 9-15 km (5-9 miles) above the surface, but on Venus it lies at an altitude around 50 km (31 miles) due to the planet's closer proximity to the sun.

On Earth, the ozone layer is several kilometers above this, and the ozone prevents ultraviolet light from destroying water in our atmosphere. On Venus, there is no ozone layer, and the atmosphere doesn't become opaque to ultraviolet light until a depth is reached below the cold trap. This allows ultraviolet light to destroy water between this height and the cold trap's.

So, as water rises in Venus' atmosphere and reaches this region, UV light dissociates it into two hydrogen atoms and one oxygen atom. The hydrogen is much lighter than the water molecule was, and so it easily escapes Venus' atmosphere. The water will usually quickly recombine with a carbon or carbon monoxide molecule to form carbon monoxide or carbon dioxide. This is probably one reason why there is so much carbon dioxide in Venus' atmosphere today.

Heavy water, however, which is composed of one oxygen, one hydrogen, and one deuterium (a proton and one neutron), cannot reach the requisite height as easily. If it does, it can still be dissociated just like normal water, but this happens at a much slower rate. Thus, a measurement of how much deuterium compared with how much hydrogen today shows that Venus has much more deuterium in its atmosphere for each hydrogen atom than Earth does. This is the strongest evidence that Venus has lost a massive amount of water in its history.

This process is a runaway one in that once less water is available to wash CO₂ from the atmosphere, the CO₂ level rises. This results in a stronger greenhouse effect, so the temperature rises. The higher temperature moves the cold trap higher, and the cycle continues at an accelerated rate because there is a larger region where water can become dissociated.

Geology

[To be inserted.]

Time Line

Venus' surface is very young. Based upon models for how long it should take to accumulate the 967 craters that are observed on its surface, it is estimated that the planet was completely resurfaced about 700 million years ago. And the craters are distributed randomly, so there is currently no way to determine whether one part or feature is older than another. As a result, it is nearly impossible to create a meaningful timeline of Venus' history.

Spacecraft that Have Visited or Will Visit

1. Sputnik 7 - attempted Venus impact in 1961
2. Venera 1 - Venus flyby (contact lost) in 1961
3. Mariner 1 - attempted Venus flyby (launch failure) in 1962
4. Sputnik 19 - attempted Venus flyby in 1962
5. Mariner 2 - 1 flyby in 1962
6. Sputnik 20 - attempted Venus flyby in 1962
7. Sputnik 21 - attempted Venus flyby in 1962
8. Venera 1964A - attempted Venus flyby (launch failure) in 1964
9. Venera 1964B - attempted Venus flyby (launch failure) in 1964
10. Cosmos 27 - attempted Venus flyby in 1964
11. Zond 1 - Venus flyby (contact lost) in 1964
12. Venera 2 - Venus flyby (contact lost) in 1965
13. Venera 3 - Venus lander (contact lost) in 1965
14. Cosmos 96 - possibly an attempted Venus lander in 1965
15. Venera 1965A - attempted Venus flyby (contact lost) in 1965
16. Venera 4 - Venus probe in 1967
17. Mariner 5 - 1 flyby in 1967
18. Cosmos 167 - attempted Venus probe in 1967
19. Venera 5 - Venus probe in 1969
20. Venera 6 - Venus probe in 1969
21. Venera 7 - Venus lander in 1970
22. Cosmos 359 - attempted Venus probe in 1970
23. Venera 8 - Venus probe in 1972
24. Cosmos 482 - attempted Venus probe in 1972
25. Mariner 10 - 1 flyby in 1974
26. Venera 9 - Venus orbiter and lander in 1975
27. Venera 10 - Venus orbiter and lander in 1975
28. Pioneer 12 AKA Pioneer Venus Orbiter - orbited from 1978-1992
29. Pioneer 13 AKA Pioneer Venus Multiprobe Mission - orbited in 1978 and released 3 probes into the atmosphere
30. Venera 11 - Venus orbiter and lander in 1978
31. Venera 12 - Venus orbiter and lander in 1978
32. Venera 13 - Venus orbiter and lander in 1981
33. Venera 14 - Venus orbiter and lander in 1981
34. Venera 15 - Venus orbiter and lander in 1983
35. Venera 16 - Venus orbiter and lander in 1983
36. Vega 1 - Venus lander and balloon in 1985
37. Vega 2 - Venus lander and balloon in 1985
38. Magellan 4 - orbited from 1990-1994
39. Venus Express - ESA Venus orbiter launched in 2005 with a planned orbit insertion in 2006
40. Planet-C - ISAS Venus Orbiter with a planned launch in 2008

Mythology and Naming Schemes

Venus is named after the ancient Roman goddess of love. When scientists first spotted it, they saw beautiful swirls of clouds, and thought that they hid a world of beauty that was Earth-like, and would contain life. They couldn't have been more wrong.

Since Venus is the only planet named for a female, every surface feature of Venus is named for a female, too; however, there is one exception: The largest mountain range on Venus is called Maxwell Montes, which is commonly referred to as "The Only Man on Venus."

Other features are given names as:

• Astra (radial patterns), fluctus (flow terrain), labyrinthi (complex intersecting valleys), montes (mountains), and tholi (small domical mountain or hill) are named after goddesses and other miscellaneous females.

• Chasmata (deep, elongated, steep-sided depressions) are named after goddesses of the hunt and moon.

• Colles (small hills or knobs) are named after sea goddesses.

• Coronae (ovoid-shaped features) are named after fertility and Earth goddesses.

• Craters that are larger than 20 km are named after dead women who have made fundamental contributions to their field, while craters that are smaller than 20 km are given common female first names.

• Dorsa (ridges) are named for sky goddesses.

• Farra (pancake-like structures or a row of them) are named after water goddesses.

• Fossae (long, narrow, shallow depressions) and Lineaeare (dark or bright elongated marking) named for goddesses of war.

• Paterae (irregular crater or a complex one with scalloped edges) are named for famous women.

• Planitiae (low plains) are named for mythological heroines.

• Plana (plateau or high plain) are named for goddesses of prosperity.

• Regiones (large area marked by reflectivity or color distinctions from surrounding areas, or a large geographic area) are for giantesses and titanesses, though two are named after the first two letters of the Greek alphabet.

• Rupes (scarps) are named for goddesses of hearth and home.

• Tesserae (tile-like, polygonal terrain) are named for goddesses of fate and fortune.

• Terrae (extensive land masses) are named for goddesses of love.

• Undae (dunes) are named for desert goddesses.

• Valles (valleys) longer than 400 km are named after various words for the planet Venus in other languages, while those shorter than 400 km are named after river goddesses.

Data for the Planets

	Mercury	Venus	Earth	Mars	Jupiter	Saturn	Uranus	Neptune
Perihelion (106 km)	46.00	107.5	147.09	206.62	740.52	1352.55	2741.30	4444.45
Mean Orbital Distance (106 km)	57.91	108.2	149.60	227.92	778.57	1433.53	2872.46	4495.06
Aphelion (106 km)	69.82	108.9	152.10	249.23	816.62	1514.50	3003.62	4545.67
Average Orbital Velocity (km/s)	47.87	35	29.78	24.13	13.07	9.69	6.81	5.43
Orbital Inclination (from Earth's Orbit)	7.00°	3.4°	0.0°	1.850°	1.304°	2.485°	0.772°	1.769°
Orbital Eccentricity	0.2056	0.007	0.0167	0.0935	0.0489	0.0565	0.0457	0.0113
Equatorial Radius (km)	2439.7	6051.8	6378.1	3397	71,492	60,268	25,559	24,764
Polar Radius (km)	2439.7	6051.8	6,356.8	3375	66,854	54,364	24,973	24,341
Volume (1010 km3)	6.083	92.843	108.321	16.318	143,128	82,713	6833	6254
Ellipticity (Variation from Sphere)	0.0000	0.000	0.00335	0.00648	0.06487	0.09796	0.02293	0.01708
Axial Tilt (from Earth's geographic North)	0.01°	177.4°	23.45°	25.19°	3.13°	26.73°	97.77°	28.32°
Mass (1024 kg)	0.3302	4.87	5.9736	0.64185	1898.6	568.46	86.832	102.43
Density (water=1)	5.427	5.243	5.515	3.933	1.326	0.687	1.27	1.638
Escape Velocity (km/s)	4.3	10.36	11.19	5.03	59.5	35.5	21.3	23.5
Gravity (m/s2)	3.70	8.802	9.78	3.716	23.1	9	8.7	11
Surface Pressure (bars)	≈ 10-15	92	1.014	0.000636	N/A	N/A	N/A	N/A
Total Mass of Atmosphere (kg)	< 1000	4.8x1020	5.1x1018	2.5x1016	N/A	N/A	N/A	N/A
Sidereal Rotation Period (hours)	1407.6	-5832.5	23.9345	24.6229	9.9250	10.656	-17.24	16.11
Length of Day (hours)	4222.6	2802	24	24.6597	9.9259	10.656	17.24	16.11
Tropical Orbital Period (days)	87.968	224.7	365.256	686.980	4330.595	10,746.94	30,588.740	59,799.9
Bond Albedo	0.119	0.750	0.306	0.250	0.343	0.342	0.300	0.290
Visual Geometric Albedo	0.106	0.65	0.367	0.150	0.52	0.47	0.51	0.41
Visual Magnitude	-0.42	-4.40	-3.86	-1.52	-9.40	-8.88	-7.19	-6.87
Solar Irradiance (W/m2)	9126.6	2613.9	1367.6	589.2	50.50	14.90	3.71	1.51
Black-Body Temperature (K)	442.5	231.7	254.3	210.1	110.0	81.1	58.2	46.6
Average Surface Temperature (Celsius)	167°	464°	15°	-65°	-110°	-140°	-195°	-200°
Number of Moons
Rings?	No	No	No	No	Yes	Yes	Yes	Yes
Global Magnetic Field Strength (Gs) / Tilt	0.0033 / 169°	- / -	0.3076 / 11.4°	- / -	4.28 / 9.6°	0.210 / <1°	0.228 / 58.6°	0.142 / 46.9°
Discoverer	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	William Herschel	Johann Gottfried Galle
Discovery Date	Prehistory	Prehistory	Prehistory	Prehistory	Prehistory	Prehistory	March 13, 1781	September 23, 1846