Interesting Facts and Features of the Planet Venus

Venus
Credit: Remastered Soviet Venera probe Image of Venus by Don P. Mitchell

We all know that Venus is so hellishly hot that lead melts on its surface, that it is enveloped in a thick, massive, mostly sulfurous atmosphere, and that by standing on its surface you would feel a similar amount of pressure as being at least a mile under the ocean back on Earth. In fact, so many Top 10 lists on Venus exist today that compiling a new one is no easy task, but here’s a list containing at least some items that should be new to you.

Quick Facts

Diameter: 3,032 miles (12,104 km) (0.95% Earth)
Age: 4.503 billion years
Mass: 81.5% Earth
Distance from Sun: 67.24M miles (108.2M kms) (0.73 AU)
Orbit Period (Day): 243.02 days
Revolution period (Year): 224.7 days
Equatorial Rotation Velocity: 6.52 km/h (1.81 m/s)
Surface Temperature: 735 K (462 °C, 863.6 °F)
Atmosphere: CO2 (96%), Nitrogen (3%), Sulfur Dioxide (0.015%),  argon, water vapour,

Earth-like Two Billion Years Ago

Ancient VenusUsing computer models designed to map climate changes on Earth, scientists at the Goddard Space Flight Center have “played back” the evolution of Venus’ atmosphere and have concluded that for the first 2 billion years or so after its formation, Venus was surprisingly Earth-like. The simulation shown above shows a shallow ocean and the continents as they are thought to have been in the planets’ early history.

However, since Venus received about 40% more sunlight that Earth did at this time, the ocean boiled away, or more precisely, evaporated, with ultraviolet radiation breaking the water molecules apart to allow the hydrogen component of the water molecules to escape into space. With no liquid water present, this process caused carbon dioxide to accumulate, which 600 million to a few billion years ago eventually triggered the runaway greenhouse effect that we observe today.

Entire Surface gets Recycled

Despite diligent analysis of the planet’s surface, no tectonic plate boundaries have been identified. Moreover, most scientists agree that in view of the relative scarcity of cratering, the planet’s surface is substantially less than 500 million years old, which suggests that violent and prolonged volcanism “recoats”, or resurfaces the entire planet every few hundred million years or so. The planet’s surface therefore consists of relatively smooth volcanic plains, with the exception of two large elevated “continents” that take up about 8% of the planet’s surface, one about the size of Africa located south of the equator called Aphrodite Terra, and the other roughly the size of Australia in the north called Ishtar Terra, which also contains Maxwell Montes, the planet’s tallest mountain at 11 km (7 miles) high.

Ishtar and Aphrodite Terra

Most Geological Features Named after Women

According to a dictate issued by the International Astronomical Union in the early 1990’s, all surface features on Venus will eventually be named after famous women, with the proviso that if a woman’s name is proposed, that actual woman must have been dead for at least three years, and she must be worthy of the honor” in some way. These include Artermis Chasma, Phoebe Regio, and Guinivere Planitia, with many more examples to be found in the image above. Note, however, that while the names of famous goddesses from all mythologies are welcomed, the names of female military or religious leaders from the 19th and 20th centuries are not, nor are the names of female leaders of the six chief religions that are practiced or observed today, as well as the names of any females that hold a special politically inspired nationalist significance.

Most Venusian Volcanoes Squashed Flat

Pancake Volcanoes on Venus

Venus has numerous volcanoes spread out across its surface, the tallest of which is Maat Mons, a 5 mile (8 km) high shield volcano named after the ancient Egyptian truth goddess. Since the atmospheric pressure on Venus is about 90 times higher than on Earth, however, viscous lava flows are squashed flat as they emerge from volcanic vents acros the planet. The structures in the image opposite, for instance, shows what is commonly known as “Pancake Volcanoes” or Carmenta Farra, that can be up to 1,000 meters high, and several kms in diameter. They are often found in groups near to coronae, which are oval-shaped trench features surrounding an elevated plain, with the surface of the pancake volcanoes usually folded, fractured and covered with cracks and faults. Interestingly, corona have so far only been found to exist on Venus, and the smallest and innermost moon of Uranus called Miranda.

Longest River Channel in Solar System

Located on Venus is the Baltis Vallis, which is an average of 1-3 kms in width, and almost 7,000 kilometers in length, making it the longest river channel yet found in the solar system. This long, meandering feature was discovered by the Soviet Venera 15 and 16 orbiters in 1983, and is believed to have once held a river of lava. It is named after the Arabian goddess Baltis, who in ancient times was revered by the people of Carrhae in north-west Mesopotamia, where she was associated with the planet Venus.

No Small Craters

Mead CraterAlthough there are more than 1,000 known meteorite impact sites on Venus, none are smaller than 1.25 miles in diameter. This is because meteorites smaller than about 50 meters across break up in the dense Venusian atmosphere before they can reach the surface, which seems to be borne out by the fact that even the planet’s large craters are clustered together. The largest known crater on Venus, known as the Mead crater, is a huge 280 kilometers (174 miles) in diameter, and consists of multiple rings, with the innermost (C) scarp and outer (D) ring believed to be the result of the original meteor’s impact. Mead’s flat brighter inner floor (A) is likely to have resulted from the original crater’s infilling by impact melt and volcanic lavas, which contrasts with darker looking surrounding plain (G) which is covered in fine debris.

No Magnetic Field

Although Venus’ core is electrically conductive and thought to be molten, no magnetic field has been detected on the planet. This suggests that the dynamo effect that causes magnetic fields on other planets is either missing, or there are no convection currents between the planets’ core and mantle. Planetary scientists are therefore puzzled, to say the least. One school of thought holds that Venus has no solid core, or that the core is not cooling due to a lack of plate tectonics, while another holds that the planets’ inner parts have already solidified, which means that convection would not be possible. A third school of thought holds that a global resurfacing event had locked possible tectonic plates in place, which would have the effect of reducing heat loss through the crust. Investigations are continuing, but since the state of the planets’ core depends on the amount of sulfur it contains, a definitive explanation of the lack of a magnetic field on Venus will remain elusive until this is known with any degree of certainty.

Planet’s Orbit Forms a Pentagram

Pentagram of VenusAs seen from above, the orbit of Venus forms a near-perfect pentagram, with the five lobes of the figure each representing the closest approach of the planet to Earth. However, the pentagram is not perfect, due to a slight mismatch in the roughly 13:8 Venus-Earth orbital resonance (gravitational influence), but is nevertheless close enough to be endlessly fascinating. A cool animation showing how the planetary orbital motions that produces the pentagram work is available here.

Almost Universally Hot

Despite its long rotation period of 243 days, Venus shows almost the same average 462 °C temperature everywhere on its surface, as well as between its poles and equatorial regions. This is thought to be caused by constant surface winds that carry heat from the sunlit side to the side facing away from the Sun. The only measurable temperature variations occur with altitude, with the highest point on the planet, Maxwell Montes, having a temperature of about 380 °C. It is worth noting that since the average surface temperature on Venus is high enough to melt lead, the white substance observed on Maxwell Montes is thought to be “snow” formed by precipitated lead sulfide, or perhaps elemental tellurium.

Rotation is Slowing Down

While it has long been known that it takes Venus longer to rotate once around its axis (243 earth-days) than it takes to revolve once around the Sun (224.7 earth-days), what was unknown until recently was that the planet’s rotation has been slowing in a dramatic fashion. It turns out that in the 16 years between the Magellan spacecraft (1990) and Venus Express satellite (2006) visits, Venus’ rotation had slowed by a massive 6.5 minutes per Venusian sidereal day. The exact reason for this remains a mystery.

Retrograde Motion Now Explained

There have been many theories put forward to explain why Venus spins in the “wrong” direction. Some theories hold that a giant impact was responsible, however, it is more likely to be the result of a combination of factors, which do not include the possibility of impacts. Recent studies have shown that Venus is close enough to the Sun to be tidally locked to it, in much the same way that the Moon is tidally locked to Earth. This has played a major part in slowing down the planet’s rotation, but the main factor in reversing its rotation is the effects of thermal heating of the planet’s thick atmosphere, which has been shown to produce a retrograde torque moment. Thus, Venus’ slow retrograde rotation is now in equilibrium between Sun-Venus tidal interactions, and atmospheric influences that are spinning the planet in the “wrong” direction.

Easily Spotted in Daytime

Venus in DaytimeVenus can be spotted in the day, and records of many such historical sightings exist, such as Edmund Halley in 1716 using the opportunity to calculate its maximum possible brightness. Another recorded historical daytime sighting of the planet occurred in March of 1865, during the inauguration of President Abraham Lincoln, in Washington D.C, which became apparent to all in attendance, and as Sergeant Smith Stimmel, one of Lincoln’s bodyguards stated at the time:

“It was a little after midday at the time I saw it, possibly near one o’clock; the sun seemed to be a little west of the median, the star a little east. It was a strange sight. I never saw a star at that time in the day before or since. The superstitious had many strange notions about it, but of course it was simply owing to the peculiarly clear condition of the atmosphere and the favorable position of the planet at that time. The President and those who were with him in the carriage noticed the star at the same time.”

The photo opposite was taken by Martin J. Powell from a location in the UK, with Venus seen to the right of the Moon. In general, however, Venus, also known as the “evening star” or “morning star”, is usually visible up to 3 hours before sunrise or sunset, when it can attain an apparent visual magnitude of -4.9, especially during its crescent phase. That is when the planet is situated nearest to the Earth, and less than 45 million miles, or around half an AU away, which produces more illumination than its full phase when it is on the other side of the Sun and around 1.7 AU distant, and shining with a magnitude of -3.

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