Instruct: Given a question, retrieve passages that can help answer the question.
Query: What is Venus' atmosphere made of?
The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740K (467°C, 872°F), and the pressure is 93bar (9.3MPa), roughly the pressure found 900m (3,000ft) underwater on Earth.[1] The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible. Information about the topography has been obtained exclusively by radar imaging.[1] Aside from carbon dioxide, the other main component is nitrogen. Other chemical compounds are present only in trace amounts.[1]
The atmosphere of Venus is known to have undergone substantial evolution over geologic time. Evidence for this includes the present remarkable contrast between Venus’ atmosphere and the Earth’s: Venus has very little water, a 95% CO atmosphere, a surface temperature of 750 K, and a surface pressure of 90 bar. The early Venusian atmosphere is thought to have undergone either a moist or runaway greenhouse heating episode to produce these conditions, and this would have included hydrodynamic escape of light gases from the upper atmosphere to deplete possibly as much as an ocean of water. Support for this scenario comes from the measured ratio of D/H in Venus' atmosphere of roughly 1.6% from the Pioneer Venus mass spectrometer, orbiting ion mass spectrometer (OIMS) data, and IR spectra of the night-side atmosphere. This large enhancement over cosmic abundances is consistent with the loss of an ocean's worth of HO over geologic time.
The refined density of TRAPPIST-1b, along with the planet's transmission spectrum, indicate that its atmosphere is made mainly of vaporized water. The atmosphere has likely risen the planet's surface temperature to about 750-1500 K, which would require an atmospheric pressure between 10 (10) to 10 (10,000) bar, potentially thicker than Venus's atmosphere. TRAPPIST-1b's atmosphere is likely very similar to that of Venus.
Unfortunately, it was impossible to time the exact moment of the start and end of the transit because of the phenomenon known as the "black drop effect". This effect was long thought to be due to Venus's thick atmosphere, and initially it was held to be the first real evidence that Venus had an atmosphere. However, recent studies demonstrate that it is an optical effect caused by the smearing of the image of Venus by turbulence in the Earth's atmosphere or imperfections in the viewing apparatus.
Venus Atmospheric Maneuverable Platform (VAMP) is a mission concept by the aerospace companies Northrop Grumman and LGarde for a powered, long endurance, semi-buoyant inflatable aircraft that would explore the upper atmosphere of planet Venus for biosignatures as well as perform atmospheric measurements. The inflatable aircraft has a trapezoidal shape that is sometimes called delta wing or flying wing, and would have dual electric-driven propellers that would be stowed during atmospheric entry.
The same principle applies to planets. Many scientists think the early Earth had a reducing atmosphere, along with Mars and Venus. This would have proven to be a good environment for "Cyanobacteria" to evolve the first photosynthetic metabolic pathways which gradually increased the oxygen portion of the atmosphere, changing it to what is known as an oxidizing atmosphere. With increased levels of oxygen, the evolution of the more efficient aerobic respiration might have been enabled, allowing animal life to evolve and thrive.
The upper atmosphere of Venus can be measured from Earth when the planet crosses the sun in a rare event known as a solar transit. The last solar transit of Venus occurred in 2012. Using quantitative astronomical spectroscopy, scientists were able to analyse sunlight that passed through the planet's atmosphere to reveal chemicals within it. As the technique to analyse light to discover information about a planet's atmosphere only first showed results in 2001,[70] this was the first opportunity to gain conclusive results in this way on the atmosphere of Venus since observation of solar transits began. This solar transit was a rare opportunity considering the lack of information on the atmosphere between 65 and 85km.[71] The solar transit in 2004 enabled astronomers to gather a large amount of data useful not only in determining the composition of the upper atmosphere of Venus, but also in refining techniques used in searching for extrasolar planets. The atmosphere of mostly CO2, absorbs near-infrared radiation, making it easy to observe. During the 2004 transit, the absorption in the atmosphere as a function of wavelength revealed the properties of the gases at that altitude. The Doppler shift of the gases also enabled wind patterns to be measured.[72]
Venus' atmosphere is mostly composed of carbon dioxide. It contains minor amounts of nitrogen and other trace elements, including compounds based on hydrogen, nitrogen, sulfur, carbon, and oxygen. The atmosphere of Venus is much hotter and denser than that of Earth, though shallower. As greenhouse gases warm a lower atmosphere, they cool the upper atmosphere, leading to compact thermospheres. By some definitions, Venus has no stratosphere.
The renowned astronomer Carl Sagan proposed the planetary engineering of Venus in an article published in the journal "Science" in 1961. Sagan imagined seeding the atmosphere of Venus with algae, which would convert water, nitrogen and carbon dioxide into organic compounds. As this process removed carbon dioxide from the atmosphere, the greenhouse effect would be reduced until surface temperatures dropped to "comfortable" levels. The resulting carbon, Sagan supposed, would be incinerated by the high surface temperatures of Venus, and thus be sequestered in the form of "graphite or some involatile form of carbon" on the planet's surface. However, later discoveries about the conditions on Venus made this particular approach impossible. One problem is that the clouds of Venus are composed of a highly concentrated sulfuric acid solution. Even if atmospheric algae could thrive in the hostile environment of Venus's upper atmosphere, an even more insurmountable problem is that its atmosphere is simply far too thick—the high atmospheric pressure would result in an "atmosphere of nearly pure molecular oxygen" and cause the planet's surface to be thickly covered in fine graphite powder. This volatile combination could not be sustained through time. Any carbon that was fixed in organic form would be liberated as carbon dioxide again through combustion, "short-circuiting" the terraforming process.
Venus could also be cooled by placing reflectors in the atmosphere. Reflective balloons floating in the upper atmosphere could create shade. The number and/or size of the balloons would necessarily be great. Geoffrey A. Landis has suggested that if enough floating cities were built, they could form a solar shield around the planet, and could simultaneously be used to process the atmosphere into a more desirable form, thus combining the solar shield theory and the atmospheric processing theory with a scalable technology that would immediately provide living space in the Venusian atmosphere. If made from carbon nanotubes or graphene (a sheet-like carbon allotrope), then the major structural materials can be produced using carbon dioxide gathered "in situ" from the atmosphere. The recently synthesised amorphous carbonia might prove a useful structural material if it can be quenched to Standard Temperature and Pressure (STP) conditions, perhaps in a mixture with regular silica glass. According to Birch's analysis, such colonies and materials would provide an immediate economic return from colonizing Venus, funding further terraforming efforts.
The thinning of the Venerian atmosphere could be attempted by a variety of methods, possibly in combination. Directly lifting atmospheric gas from Venus into space would probably prove difficult. Venus has sufficiently high escape velocity to make blasting it away with asteroid impacts impractical. Pollack and Sagan calculated in 1994 that an impactor of 700 km diameter striking Venus at greater than 20 km/s, would eject all the atmosphere above the horizon as seen from the point of impact, but because this is less than a thousandth of the total atmosphere and there would be diminishing returns as the atmosphere's density decreases, a very great number of such giant impactors would be required. Landis calculated that to lower the pressure from 92 bar to 1 bar would require a minimum of 2,000 impacts, even if the efficiency of atmosphere removal was perfect. Smaller objects would not work, either, because more would be required. The violence of the bombardment could well result in significant outgassing that would replace removed atmosphere. Most of the ejected atmosphere would go into solar orbit near Venus, and, without further intervention, could be captured by the Venerian gravitational field and become part of the atmosphere once again.
"Venus Express" was a mission by the European Space Agency to study the atmosphere and surface characteristics of Venus from orbit. The design was based on ESA's "Mars Express" and "Rosetta" missions. The probe's main objective was the long-term observation of the Venusian atmosphere, which it is hoped will also contribute to an understanding of Earth's atmosphere and climate. It also made global maps of Venerean surface temperatures, and attempted to observe signs of life on Earth from a distance.
The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.
Unfortunately, the knowledge of Venus' atmosphere was still inexact in 1961, when Sagan made his original proposal for terraforming. Thirty-three years after his original proposal, in his 1994 book "Pale Blue Dot", Sagan conceded his original proposal for terraforming would not work because the atmosphere of Venus is far denser than was known in 1961:
There is also a pattern of air circulation found flowing in the direction of Titan's rotation, from west to east. Observations by "Cassini" of the atmosphere made in 2004 also suggest that Titan is a "super rotator", like Venus, with an atmosphere that rotates much faster than its surface.
The first vortex on Venus was discovered at the north pole by the Pioneer Venus mission in 1978.[27] A discovery of the second large 'double-eyed' vortex at the south pole of Venus was made in the summer of 2006 by Venus Express, which came with no surprise.[26]
Venus's atmosphere is made mostly out of carbon dioxide, which, after filtering from sulfuric acid, can be used to grow food. Because nitrogen and oxygen are lighter than the carbon-dioxide that makes the atmosphere, breathable-air-filled balloons will float at a height of about . At this height, the temperature is a manageable ; or if we could get higher (see ). 
The troposphere on Venus contains 99% of the atmosphere by mass. Ninety percent of the atmosphere of Venus is within 28km of the surface; by comparison, 90% of the atmosphere of Earth is within 10km of the surface. At a height of 50km the atmospheric pressure is approximately equal to that at the surface of Earth.[20] On the night side of Venus clouds can still be found at 80km above the surface.[21]
Glaze was the Principal Investigator for a proposed NASA Discovery mission to Venus, Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI). This mission would send a probe on a journey through Venus' atmosphere, descending over the planet's roughest and most geologically complex terrain. The DAVINCI probe would explore the planet's atmosphere from top to bottom, including the deep atmospheric layers largely hidden from Earth-based instruments and orbiting spacecraft. DAVINCI would be the first U.S. probe in nearly four decades to target Venus' atmosphere.
Prior to the early 1960s, the atmosphere of Venus was believed by astronomers to have an Earth-like temperature. When Venus was understood to have a thick carbon dioxide atmosphere with a consequence of a very large greenhouse effect, some scientists began to contemplate the idea of altering the atmosphere to make the surface more Earth-like. This hypothetical prospect, known as terraforming, was first proposed by Carl Sagan in 1961, as a final section of his classic article in the journal "Science" discussing the atmosphere and greenhouse effect of Venus. Sagan proposed injecting photosynthetic bacteria into the Venus atmosphere, which would convert the carbon dioxide into reduced carbon in organic form, thus reducing the carbon dioxide from the atmosphere.
In 1761, Russian polymath Mikhail Lomonosov observed an arc of light surrounding the part of Venus off the Sun's disc at the beginning of the egress phase of the transit and concluded that Venus has an atmosphere.[67][68] In 1940, Rupert Wildt calculated that the amount of CO2 in the Venusian atmosphere would raise surface temperature above the boiling point for water.[69] This was confirmed when Mariner 2 made radiometer measurements of the temperature in 1962. In 1967, Venera 4 confirmed that the atmosphere consisted primarily of carbon dioxide.[69]
Venus In Situ Atmospheric and Geochemical Explorer (VISAGE) is a proposed Venus lander mission that would perform atmospheric and surface science investigations.
Balloons cannot work on the Moon because it has no atmosphere. Mars has a very thin atmosphere – the pressure is only 1/160th of earth atmospheric pressure – so a huge balloon would be needed even for a tiny lifting effect. Overcoming the weight of such a balloon would be difficult, but several proposals to explore Mars with balloons have been made.[4] Venus has a CO2 atmosphere at the surface. Because CO2 is about 50% more dense than Earth air, ordinary Earth air could be a lifting gas on Venus. This has led to proposals for a human habitat that would float in the atmosphere of Venus at an altitude where both the pressure and the temperature are earthlike. In 1985, the Soviet Vega program sent two balloons to float in Venus' atmosphere at 54km altitude. Titan, Saturn's largest moon, has a dense atmosphere of mostly nitrogen that is appropriate for ballooning. A use of Aerobots was proposed on Titan. Also the Titan Saturn System Mission included a balloon to circumnavigate Titan.
A runaway greenhouse effect involving carbon dioxide and water vapor may have occurred on Venus. In this scenario, early Venus may have had a global ocean. As the brightness of the early Sun increased, the amount of water vapor in the atmosphere increased, increasing the temperature and consequently increasing the evaporation of the ocean, leading eventually to the situation in which the oceans boiled, and all of the water vapor entered the atmosphere. On Venus today there is little water vapor in the atmosphere. If water vapor did contribute to the warmth of Venus at one time, this water is thought to have escaped to space. Some evidence for this scenario comes from the extremely high deuterium to hydrogen ratio in Venus' atmosphere, roughly 150 times that of Earth, since light hydrogen would escape from the atmosphere more readily than its heavier isotope, deuterium. Venus is sufficiently strongly heated by the Sun that water vapor can rise much higher in the atmosphere and be split into hydrogen and oxygen by ultraviolet light. The hydrogen can then escape from the atmosphere and the oxygen recombines. Carbon dioxide, the dominant greenhouse gas in the current Venusian atmosphere, owes its larger concentration to the weakness of carbon recycling as compared to Earth, where the carbon dioxide emitted from volcanoes is efficiently subducted into the Earth by plate tectonics on geologic time scales.
The bus was targeted to enter the Venusian atmosphere at a shallow entry angle and transmit data until destruction by the heat of atmospheric friction. The objective was to study the structure and composition of the atmosphere down to the surface, the nature and composition of the clouds, the radiation field and energy exchange in the lower atmosphere, and local information on atmospheric circulation patterns. With no heat shield or parachute, the bus made upper atmospheric measurements with two instruments:The spacecraft operated down to an altitude of about 110 km before disintegrating.