Venus — Planet Second-Closest to the Sun


Venus is the planet second-closest to the the sun in our solar system and Earth’s nearest neighbor. The cloudy rocky planet orbits the sun at an average distance of 67,238,251 mi (108,209,475 km) at a mean orbital velocity of 78,339 mph (126,074 km/h). For us Earthlings, Venus also the second-brightest object in the night sky, with the first being the moon.

Venus is almost the same size as Earth and has an atmosphere that scientists believe closely resembles primeval Earth’s. Because of that, Venus is often called Earth’s twin, although it’d be more of a murderous evil twin. The Venusian atmosphere is very thick, much thicker than Earth’s, and its atmospheric pressure much higher. If a human were to stand on the planet’s surface, they’d be crushed like a lemon under a sledge hammer because of the high atmospheric pressure, similar to the way humans would if they went unprotected into the deepest parts of the Earth’s oceans. On Venus, however, atmospheric pressure would be the least of a human’s problems. There is also the corrosive sulfuric acid rain and the extreme heat, which combined would turn a human visitor into a pile of crispy, tangy, jerky.

Venus is an odd planet for a number of other reasons and not just because it would render a person into a pile of dehydrated carbon. It spins very slowly on its axis, so slowly that a day on Venus is equal to 243 Earth days. It is also one of two planets that spins on its axis in the opposite direction (west to east instead of east to west like Earth). Scientists believe that this was caused by a collision with another large object at some point in Venus’ distant past that may have reversed its spin, made it spin slower, or both. What’s even stranger is that a Venusian day is longer than a Venusian year; it takes Venus 225 Earth days to make a single orbit around the sun, so its day is longer than its year by 18 Earth days. Unlike Earth and most other planets there is little tilt to Venus’ axis so there are no seasons.

Extreme Atmosphere

Even though it is not the planet closest to the sun, Venus is the hottest planet in the solar system with an average surface temperature of about 900°F (465°C). That’s hot enough to melt lead and fry the circuit boards on any electronics that aren’t protected and cooled. The few space probes that have managed to soft-land on its surface only survived for 1-2 hours before melting. The high surface temperature is the result of an extreme greenhouse effect due to the chemical make-up of its atmosphere, which is primarily carbon dioxide and nitrogen. Venus does not have a magnetic field like the Earth, which has a very strong one. The Venusian magnetic field is very weak almost non-existent, which allows solar rays to hit the upper atmosphere with little to stop it. It is only Venus’ thick clouds and atmosphere that prevents rays from raining down on the surface. One of the more discussed theories as to why there is little in the way of a magnetic field there is that Venus spins too slowly for the core to generate any friction on itself and thereby wouldn’t generate enough magnetism as a result.

This slow rotation is in direct contrast to the winds on Venus, the top levels of which fly around the planet at about 225 mph. Largely due to convection within the Venusian atmosphere, the clouds on the planet are believed to circle the planet every 4 Earth days, a phenomenon known as a super-rotation — the atmosphere rotates faster than the surface. The only other place in the solar system where this has been recorded is on the Saturnian moon Titan.

Closer to the surface the wind speed slows considerably to only a few miles per hour, but the weather itself is harsh. Instead of water, very corrosive sulfuric acid rains down on the surface from the clouds above, which along with the heat and pressure makes putting a working probe there a very difficult thing to do. One somewhat puzzling aspect of the Venusian climate are the cold poles. It stands to reason that they would be cooler than the parts of the planet near the equator, but what scientists didn’t expect was the temperature at the poles to be colder than any place on Earth.

What gives Venus its bright white and gray color are its clouds. The entire planet is shrouded in thick clouds, which originally made scientists believe that there was water there. However, when Soviet and U.S. probes reached the planet in the early 1960s, data sent back showed that there was very little water or humidity in the atmosphere. Scientists today believe that Venus once had water but that it had burned off the planet millions of years ago, although it is quite possible that some could exist underground.

Surface Features

The surface of Venus is varied and rocky. There are tall mountains, extinct volcanoes, features that look like river beds, and mountains. The highest mountain is Maxwell Montes, which rises to about 28,900 ft (8.8 km). It is believed that Venus had many active volcanoes back in the day — about 500 million years ago — which covered the surface and gave it many of its distinctive features. There are several large highland areas and valley along with structures that look like river beds, along with many impact craters most of which are quite large. Because of its thick atmosphere it is only large meteorites that can reach the surface causing huge craters to form on impact; smaller rocks burn up before they can get anywhere near the surface so finding “small” impact craters isn’t likely.


Venus Exploration

Mars has always been a planet of fascination especially with the popularity of H.G. Wells’ 1898 book War of the Worlds, but it was Venus not Mars that was the first planet visited by a human space probe. About 40 or so successful probes have been sent to or by Venus over the years, most of which conducted observations from orbit, while others dropped probes into the atmosphere, and only a few that actually soft-landed on the surface. Whichever probe was first to visit the planet depends on how we define “visit”. The Soviet Union sent the Venera 1 craft toward Venus in 1961, but the scientists on Earth lost contact with the probe about a week after launch so they really had no idea where it went. If however the initial trajectory was correct, Venera 1 may technically be the first human-made probe to fly by a planet — any planet. Although it wasn’t a very useful flyby since there was no information sent back. It was during the following year in December 1962 when a useful flyby was conducted by the NASA probe Mariner 2 as it went hurtling by Venus. Unlike the Venera 1, Mariner 2 sent back quality data about the planet, mostly about the Venusian magnetic field or lack thereof and atmospheric conditions.

But the Soviet Union by and large led the charge toward Venus with its Venera series of probes, and it was the Soviet Union that put the first probes into the Venusian atmosphere and onto the surface. The Venera 3 probe in 1966 may have been the first probe to crash into Venus, but since there was no telemetry or data of any kind sent back, nobody can be sure. Venera 4 became the first probe to transmit data from within another planet’s atmosphere as it parachuted to the surface. Much of what the probe detected confirmed data that previous probes had sent back, but some of its more surprising readings were of the surface temperature and atmospheric density. Scientists did not anticipate such a dense atmosphere, which greatly slowed the probe’s parachute descent toward the surface. As a result, Venera 4‘s batteries ran out of juice before the probe could reach the surface.

Venera 7 was a huge success for planetary explorers. In 1970, it became the first spacecraft to transmit data from the surface of another planet although it was garbled and almost incomprehensible. After some computer processing of the radio signals it sent back, mission specialists found that there was some surface temperature and atmospheric information included in there with all the noise.

Composite picture of the surface of Venus, taken by the Venera 9 probe in 1975. Elements of this composite were the first images taken from the surface of a planet other than Earth. (NASA)

Venera 9 was arguably the most important probe ever sent to Venus. It parachuted to a soft-landing on the planet on October 22, 1975, and returned the long-awaited first photos of the Venusian surface (one of which you can see above). Those first photos were the first ever taken from the surface of another planet and, despite the fact they didn’t really show much beyond the immediate area, they were considered a huge advancement for planetary exploration. The craft lasted only 53 minutes on the surface before it it finally succumbed to the heat, pressure, and acidic clouds. Venera 10 was the twin to Venera 9, and it arrived at Venus three days after Venera 9 landed. It too sent back pictures of the surface and functioned there for about 65 minutes before it too melted into a pile of junk.

Other U.S. and Soviet probes visited Venus throughout the 1970s and 80s including several more Venera probes, a few Mariner (U.S.) missions, Pioneer Venus (U.S.), and a few others. Most involved making radar surveys of the planet, and taking atmospheric and orbital readings. The last two probes to land safely on the planet were Venera 13 and Venera 14 in March 1982. Since then no landers have been sent as most interplanetary surface research has been focused on the much-easier-to-land-on Mars. When it comes to planetary exploration and robotics, extreme cold is easier to deal with than extreme heat and pressure.

In the 1990s, NASA’s Magellan spacecraft mapped the entire surface of Venus using cloud-piercing radar. The images produced from those radar surveys present a varied landscape with many surface features unseen by previous probes. Later in the 2000-aughts the European Space Agency’s Venus Express craft spent nearly a decade studying the planet’s atmosphere compiling an enormous amount of data regarding atmospheric conditions, including evidence for possible recent and current volcanic activity — although no such activity has been directly detected.

Venusian Blimps?

Since Venus is such a hellish place for humans to go, most space enthusiasts consider Mars to be a better option  for sending humans (of course, Mar isn’t exactly a welcoming environment either). Unless a whole mess-load of technology gets invented to cope with high atmospheric pressures, intense heat, and acid raining down, it’s not likely that a human will ever walk on the surface of Venus. But at least according to the smart people over at NASA, such issues really shouldn’t stop people from visiting Earth’s closest neighbor. By visit, they don’t mean just sending a few astronauts over into Venusian to orbit. They came up with an idea to actually put humans into the Venusian atmosphere.

Artist’s concept of a floating cloud city above Venus. (Advanced Concepts Lab at NASA Langley Research Center)

Since atmospheric pressure and temperatures at the surface are so forbidding, the crazy kids at the Advanced Concepts Lab at NASA Langley Research Center came up with the idea of building a floating settlement high above all the hell that is Venus and in an area that would be surprisingly pleasant. The settlement would be composed of helium-filled airships lashed together providing support for habitation modules and landing pads, kinda like Cloud City in The Empire Strikes Back. Once you get over the absurd visual of silvery blimps flying too and fro above a very cloudy world below, it actually makes a lot of sense. Right away it alleviates the temperature and atmospheric pressure issues. At 30 miles up from the surface, the atmospheric pressure is like that of the Earth at sea level, and though the temperature is still high — about 167°F (75°C) — it’s far more manageable for humans and it wouldn’t require any significant advances in materials technology. There would still be tiny droplets of sulfuric acid floating around that could be problematic, that too could be alleviated by a protective coating over all surfaces of the settlement in contact with the outside atmosphere. What’s even better about this concept is that the gravity of Venus is roughly that of Earth so astronauts living there for extended periods shouldn’t experience the same radical bone and muscle loss due to reduced gravity or weightlessness. True they will lose a significant amount just getting there, it would still be less of an issue than for astronauts visiting a place like Mars, where the gravity is about 40% of the Earth’s.

None of this is likely to happen in the near future. There’s little reason for humans to operate in the clouds of Venus although it would probably be cool to see.

Venus vs. Earth vs. Mars

The table below presents facts about Venus along with Earth and Mars facts for comparison. I didn’t include Mercury because it compares more to the Earth’s moon than it does the other planets.

Equatorial Circumference
23,627.4 mi (38,024.6 km)24,873.6 mi (40,030.2 km)13,233.3 mi (38,024.6 km)
Volume222,738,686,740 mi.3 (928,415,345,893 km3)259,875,159,532 mi.3 (1,083,206,916,846 km3)39,133,515,914 mi3 (163,115,609,799 km3)
Average Distance from the Sun
67,238,251 mi (108,209,475 km)92,956,050 mi (149,598,262 km)141,637,725 mi (227,943,824 km)
Surface Gravity29.1 ft/s2 (8.87m/s2)32.041 ft/s2 (9.80665m/s2 )12.2ft/s2 (3.71m/s2)
Average Length of a Day (time it takes for the planet to rotate on its axis)243 Earth days24 hours24.6 Earth hours
Average Length of a Year224.7 Earth days365.25 Earth days686.6 Earth days
Atmospheric Compositioncarbon dioxide, nitrogennitrogen, oxygen, carbon dioxidecarbon dioxide, nitrogen
Escape Velocity23,175 mph (37,296 km/h)25,031 mph (40,284 km/h)11,252 mph (18,108 km/h)

Seeing Venus

Being the second brightest object in the night sky it’s usually not a problem identifying Venus. However, the planet isn’t always visible. Because its orbit lies between the Earth’s and the sun, Venus at certain times of the year can “disappear” behind the sun. If it’s either directly between the Earth and the sun or way over on the opposite side of the sun from Earth, it cannot be observed. But then as it keeps going along in its orbit, Venus later pops out from the sun’s glare and can be visible either in the morning or night sky. You can find out where and when in the sky to look for Venus and other planets here.

The photos below are some different views of Venus. Please click to enlarge.