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| About Venus |
| Past Missions to Venus |
| Atmosphere of Venus |
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| Chronology of Venus Exploration |
About Venus
View Dr. David Grinspoon's Presentation about Venus
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Solar System Seminar on Venus @ DPS, 2006 |
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| Presenter: Dr. David Grinspoon | |
| Length: 00:46:35 | |
| Number of slides: 40 | |
| View Presentation |
Venus' celebrity is far from a recent phenomenon. Throughout history, numerous (at least 30) cultures have observed, been enthralled by and found their own name for Earth's sister planet. Often depicted as a female (although in some Native American stories, it is a male character), Venus the planet and its atmosphere present an extremely hot and hostile environment. The planet's sheer radiance may be a key to its sway on the imagination - Venus surface is completely shrouded in highly reflective clouds, making it the most brilliant object in the night sky other than the moon. Additionally, because its orbit is inside the Earth's, Venus can be seen shortly after sunset and before sunrise at different times of the year. These appearances occur in an eight-year cycle, an observation the ancient Mayans of Central American used to construct a highly accurate Maya Calendar.
Venus' brightness and periodic proximity to the Earth have also made it useful in some of history's most significant astronomical advances. Venus has been in the sights of telescopes since the beginning, when Galileo discovered the planet's moon-like phases. Galileo's discovery was a milestone in the modern understanding of the Sun-centered (heliocentric) solar system. In addition, Venus has played a very crucial role in many modern advances in science. Early measurements of the speed of light were derived from observations of the transit of Venus across the solar disk. In the late 1960s, Venus was hit by the first radar signals to bounce off a solar system object. And in 1983 the former Soviet Union's Venus orbiter, Venera 15 made the first radar observations of another planet from an orbiting platform.
The Atmosphere of Venus
Of all the terrestrial planets, Venus has the thickest atmosphere and the slowest rotation rate. One day on Venus is equal to 243.16 Earth days. This puts Venus in a class of its own, with Titan, the atmosphere-bearing moon of Saturn, as its only companion (rotation rate of about 16 days). Because Venus has no oceans to vary the surface heating, no tilt to its rotation axis, a nearly circular orbit around the Sun, no large scale topography, and a nearly uniform, global cloud cover, it seems its atmosphere would be easy to understand using only incoming solar radiation. Early models of the Venusian atmosphere suggested the winds should blow from the day side to the night side, and the day-night temperature difference could be large indeed.
Ground- and spacecraft-based observations tell us otherwise: the winds blow in essentially the same direction planet's rotation (with a slight poleward component) at all observed latitudes and at all altitudes to about 100 km. It is only in the atmosphere above 100 km that the winds blow from the day-side to the night-side. Furthermore, the east winds and the poleward component generally increase with latitude to about 45 degrees. Poleward winds at this latitude in both the hemispheres and the east-west (zonal) and the north-south (meridional) winds decrease towards the pole. There is thus a peak in the angular speed of the atmosphere in two bands about mid-way between the equator of Venus and its poles - the equivalent of the terrestrial jet stream.
This global structure of the atmospheric motion organizes the Venus atmosphere in the form of two giant hemispheric vortices , one centered over each pole.
Past Missions to Venus
Venus has been observed by reconnaissance spacecraft such as Mariner 5, Mariner 10, Galileo, and by the Soviet "Mother Spacecrafts" Veneras 8, 9, and 10. Other spacecrafts investigated Venus on their way to exploring other objects, including Mariner 10 (Mercury), the VeGa 1 and VeGa 2 crafts (Comet Halley), and Galileo (Jupiter and its moons). More intense investigation of Venus has been carried out by orbiters (Veneras11-15, Pioneer, and Magellan), entry probes (Venera 4, 5, 6, and Pioneer Venus Small Probes and one Large Probe), landers (Venera 6, 7, 8, 9, 10, 11, 12, 13, and 14), and even balloons (VeGa 1 and VeGa 2).
1962
The 1962 launch of the Mariner 2 spacecraft commenced the modern era of Venus exploration by spacecraft. Mariner 2 established Venus' high surface temperature, and was the first successful mission to another planet. The history of Venus exploration contains other such landmarks: the Soviet Venera 4, launched in 1967, was the first successful probe to enter and return data from another planet (though, the transmission stopped before the probe reached the surface), and in 1970 the Venera 7 lander became the first craft to successfully land on another planet.
1974
In 1972 Venera 8 first established the rapid rotation of the deep atmosphere from ~ 62 km down to the surface as being in the same direction as the planet's backward spin. Mariner 10 returned the first images of Venus from a fly-by trajectory in 1974, enabling determination of the global atmospheric circulation and its organization into two hemispheric vortices (Suomi and Limaye, 1978). Allen and Crawford (1983) discovered features in the night side infrared emission from Venus that could arise from the existence of spectral windows in the near infrared region.
1975
In 1975 Venera 9 and Venera 10 landers returned the first images taken from the surface of another planet. Pioneer Venus (1978) was the first orbiter around Venus and carried the first radar to observe another planet. The Vega 1 and Vega 2 missions were the first to successfully deploy balloons in another planet's atmosphere. In 1990, the Magellan orbiter followed the successful missions of Venera 15 and 16 orbiters (1983) to provide the first high resolution mapping by radar of another planet. The Near Infared Mapping Spectrometer (NIMS) on the Galileo Orbiter (1990), building on the work of Allen and Crawford, discovered additional spectral windows and utilized them to observe emissions from the deep atmosphere of Venus. This enabled the detection of surface features from infrared emissions (at 1.18 micron wvelength) that matched the radar topography.
1990
The most recent observations of Venus are from the Galileo spacecraft, which flew past Venus in February 1990 on its roundabout journey to Jupiter. The Cassini Orbiter, currently in orbit around Saturn, also observed Venus briefly and sent home some useful data.
Present
European Space Agency's Venus Express mission arrived at Venus on 11 April 2006, and has since been observing Venus through a capable suite of instruments. While past space missions have substantially changed our view of Venus and enhanced our knowledge, some fundamental questions about Venus and its atmosphere remain unanswered:
- The most frustrating puzzle for atmospheric scientists is the rapid rotation of its atmosphere, many times faster than that of the underlying planet.
- Geologists want to know how Venus loses its heat.
- And for chemists, the burning question is whether the surface of Venus is in equilibrium with its atmosphere.
The findings of the European Space Agency's Venus Express mission will provide insight into these questions. On November 9th of 2005, Venus Express was launched on a Russian rocket, with support from NASA. Successful insertion into orbit around Venus took place on April 11, and data analysis is well underway. The mission is expected to provide data on the Venus atmosphere for several of the planet's days.
