The Time Now > Astronomy > Venus

The planet Venus

VenusThe planet Venus in real color. As seen by the space probe Mariner 10. © NASA/Ricardo Nunes

Venus is named after the Roman goddess of love, also called Aphrodite. Venus is similar in size to the Earth and has 80% of Earth’s mass. Venus is the second planet from the Sun and orbits every 224.7 Terran days. Because Venus produces its greatest reflection of sunlight near Earth sunrise and sunset, it is often called the morning star or the evening star. Unlike Earth, Venus doesn’t have any moons. And its day is slightly longer than its year.

Atmosphere of Venus

Atmosphere of Venus
Atmosphere of Venus. © European Space Agency/J. Whatmore

The atmosphere of Venus is so thick that the surface pressure is more than 90 times that of Earth. The atmosphere is primarily composed of sulfuric dioxide and carbon dioxide with traces of nitrogen. The greenhouse gas effect on Venus is so severe that the surface reaches an average temperature near 860°F. This is hot enough to melt tin and several Russian space craft sent to investigate the planet. The Venusian atmosphere does create lightening, as recorded by the European Space Agency probe Venus Express, which as of this writing, is still in orbit around Venus. Venus has almost no water vapor, but it does rain sulfuric acid.

Surface of Venus

The plate tectonics or movement of surface tectonic plates of Venus appears to have stopped. The surface of Venus has more than one hundred possible volcanoes which may or may not be dormant. The Venusian volcanoes have solidified lava flows on their sides. Venus also has more than a thousand impact craters. The craters are scattered in a random pattern that has been compared to a Monte Carlo simulation.

Surface of VenusSurface of Venus. Pictures taken by the Russian Venera-13 probe in 1982. It lasted only a couple of hours on the Venusian surface. © Venera probe

While Venus has a corrosive atmosphere, the hard rock of its surface has resisted erosion by wind and there is no erosion by water and rain as there is on Earth. This means that the impact craters are in pristine condition, with minimal weathering. This makes it harder to determine their age.

Maxwell Montes is the tallest mountain on the planet at roughly seven miles tall. Venus has two large highlands, similar to the continents on Earth if the planet had oceans. Maxwell Montes is located on the highland called Ishtar Terra, named after the Babylonian goddess of love, located on the Northern hemisphere of Venus. A second continental highland in the Southern hemisphere is called Aphrodite Terra.

Venus seems to be covered by a single tectonic plate that is much younger than the planet itself. Based on the estimated rate of asteroid strikes on the planet and slow weathering of the craters, it is estimated that the surface of Venus is 300 to 500 million years old. Remember that the planet is as old as the Earth, about 4.5 billion years old. This means that some cataclysmic event caused Venus to essentially renew its entire surface several hundred million years ago. Since there are only suggestive hints of a single tectonic plate on Venus and no active volcanoes as we’ve witnessed on Io and Titan, it has been theorized that Venus suffers horrific, planet wide break ups and reforming of its tectonic plate. We know that volcanic activity occurred after the formation of the Venus surface because there are impact craters partially or wholly covered by lava flows. Sif Mons shows what appear to be very recent lava flows, though they may be millions of years old.

Venus does not have a magnetic field like the Earth, though it has a similar surface gravity due to its similar size. It is theorized that Venus had an ocean early in its history, but there is no evidence of it today like the dry river channels of Mars. Venus is a very dry planet today with almost no water vapor in its atmosphere.

Exploration of Venus

Venus – morning star and the evening star
Venus reflected in the Pacific Ocean – the morning star and the evening star. © Brocken Inaglory

Both the United States and the former Soviet Union sent probes to explore Venus. Venera 9, a Russian / Soviet craft, landed on Venus in 1975 and sent the first photographs of Venus’ surface back to Earth before it began to melt. The former Soviet Union sent sixteen Venera probes to Venus. The Russian space agency is planning another probe to Venus planned to launch in 2016.

The first American craft to come close to Venus was Mariner 2. It and Mariner 5 and Mariner 10 only flew by and did not go into orbit around Venus. The first American spacecraft to enter Venus’ atmosphere was the Pioneer Venus Orbiter and Multiprobe. The Galileo probe flew by Venus in a gravity assist, a maneuver where it performed a slingshot around Venus to speed up its transit to Mars.

Most of our understanding of the Venus surface has not come from observation through telescopes, but the use of radar probes in orbit above the planet. Radar can pierce the thick, hazy atmosphere and reveal surface details telescopes cannot. The Magellan orbiter sent by the United States in the early 1990s spent four years in orbit around Venus mapping its surface using radar.

Is there life on Venus?

Structure of Venus
Cutaway diagram of possible internal structure of Venus. © NASA

Mars has received many unmanned probes in an effort to search for life, past or present. Mars we know had oceans and an atmosphere. Each generation of landers has searched for signs of water in its past that improve the odds that life existed or dig for fossils or chemical traces left behind by life.

While the iron core of Mars has cooled, there are small but steady geothermal or biochemical vents that may harbor microscopic life on Mars. Why has there been no similar search for life on Venus? And could there be life on Venus? The hot, toxic surface of Venus precludes life as we know it. However, the temperatures in the upper atmosphere are not as hot as the surface while the clouds receive light from the Sun. Thirty miles above the surface of Venus, the air pressure is similar to that of Earth with greater percentages of nitrogen and oxygen than exist near the surface.

There are bacteria on Earth that live among the clouds. There have been discussions of exploring the Venus atmosphere for similar cloud-living bacteria. Water vapor that is molecularly disassociated near the Venusian surface could exist in water vapor form among the sulfur dioxide clouds. While we do not have conclusive evidence of past or present life on Venus, the clouds of Venus are the most likely home for it if life is there.