Earth’s twin: No oxygen, no water, scorching temperatures and a runaway greenhouse effect. What else do we know about our closest neighbour, Venus?
Arizona State University’s AST111
Introduction to Solar System Astronomy
Design Project evidence
Describe the origins, structure, contents, and evolution of our solar system.
“Venus favours the bold” – Ovid
Describe the planet Venus, how it became so hot and examine the scientific impact resulting from the many missions to Venus, otherwise known as Freya’s planet.
Image courtesy of http://www.space.com/images/i/000/044/599/original/venus-surface-magellan-spacecraft.jpg
Venus fact file
- Second planet from the Sun, 67 million miles apart (0.72 AU)
- Second brightest object in the night sky, behind the Moon. Venus’ clouds are highly reflective, making it shine bright in the night sky
- Named after the Roman Goddess of love and beauty
- Has no moons or rings
- Spins very slowly in a clockwise direction (retrograde rotation), backwards to the other planets in the solar system. Backwards spin is probably due to a cosmic collision early in its history
- Venus is very nearly a perfect sphere, thanks slow rotation!
- 80% size of Earth, similar mass and both rocky worlds
- Hottest world in our system, 480 degrees celsius on the surface, hot enough to melt lead
- Runaway greenhouse effect. It is thought Venus used to have oceans but due to extra heat from the Sun these oceans evaporated and the water vapour trapped more heat in the atmosphere warming the planet further, trapping more heat until the oceans were no more
- Has a cratered and volcanic surface
- 1 year on Venus is equal to 225 Earth days, and 1 day on Venus lasts 243 Earth days – making a day last longer than a year on Venus
- Atmosphere consists mainly of carbon dioxide (~96%), Nitrogen (~4%)
- More than 40 spacecraft have explored Venus
Venus in culture
The Venus de Milo is ancient Greek statue created between 130 and 100 BC. It depicts Aphrodite, the Greek goddess of love and beauty, known as Venus to the Romans. It is on permanent display at the Louvre in Paris.
Men are from Mars, Women are from Venus. This book published in 1992 has sold over 50 million copies around the world. It states that common relationship problems between men and women are a result of fundamental psychological differences between the sexes because they are from ‘different planets’.
Beyond Apollo – Barry M. Malzberg. A novel about a 2 man mission to Venus which is aborted and when the mission returns to Earth the captain is missing and the other man cannot explain what happened to him. The novel tries to get to the bottom of this mystery and overall it represents humanity’s incompetence at the enormity of space exploration. The book is listed as in development on IMDb so look out for a motion picture soon. (http://www.imdb.com/title/tt2403823/?ref_=fn_al_tt_1)
For a twin planet, Venus is very different to Earth
4 billion years ago Venus was thought to be a lot like Earth, with evidence pointing towards Venus supporting bodies of water (H2O), perhaps even oceans. However, 4 billion years ago the Sun was less powerful that it is today and was only 70% as bright. Over time as the Sun became much hotter any bodies of water on Venus evaporated and water vapour was driven into the atmosphere, causing major greenhouse changes. Water vapour can trap heat, acting as a blanket around a body. At the top of the Venus atmosphere water molecules were split into hydrogen (H) and oxygen (O), under the full intensity of sunlight and ultraviolet rays. Much of the hydrogen (H) escaped into space whilst the oxygen (O) combined with carbon to form carbon dioxide (CO2), a great absorber of heat. Oxygen also bound with sulphur (S) and created sulphur dioxide (SO2) which created droplets of sulphuric acid (H2SO4). Could this runaway greenhouse effect ever happen here on Earth?
The Venus atmosphere is extremely dense and hot. It is mainly composed of carbon dioxide with clouds of sulphuric acid, which gives Venus its yellow colour. It does rain sulphuric acid, but drops never reach the surface due to the extreme heat. The thick atmosphere traps heat and the tremendous amount of carbon dioxide adds to the runaway greenhouse effect on the planet. The weight of the thick, dense atmosphere creates enormous pressure on the surface of 90 times heavier than standing on the surface of Earth. The equivalent pressure on Earth is about 1 km beneath the surface of an ocean. The atmosphere is slowly being stripped away by the solar wind, a million tonne per second stream of material coming from the Sun. About 300 kg of the atmosphere is being lost every day from Venus.
Venus has an iron core approx. 3000 km in radius. This is similar to all terrestrial planets because of the effects of gravity, causing heavier material to sink to the middle of the planet whilst lighter material floated to the top. Venus does not have a magnetic field as it rotates too slowly.
Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/InteriorOfVenus.png
Missions to Freya
Over 40 missions have explored Venus. The first craft to land on the surface was Venera 7 and was actually the first craft to land on another planet, after 15 failed missions. This Soviet mission in 1970 successfully landed on the surface and was able to send back 23 minutes worth of data, including a surface temperature reading of 475 degrees celsius and a pressure reading of 90. Not a very pleasant place to be!
Image courtesy http://solarsystem.nasa.gov/missions/venera_07/galleries
There is presently an active Venus mission called Akatsuki. The goal of the mission is to study weather patterns, confirm the presence of lightning in thick clouds and search for signs of active volcanism. This mission suffered a huge blow early on in its mission when thrusters failed to fire and the craft ended up on a journey around the Sun rather than Venus. Over the next five years JAXA (the Japanese Space Agency) tested the various thrusters and came up with a strategy to fix the craft and send it back to Venus. To do this they dumped fuel from the broken thrusters and used the secondary control thrusters to orient the probe towards Venus. This happened in December of 2015 and the probe entered the orbit of Venus as originally planned.
Image courtesy http://solarsystem.nasa.gov/galleries/space-tourism-posters
Magellan – mapping the surface of Venus. Launched in 1989 by NASA, the Magellan deep space orbiter was designed to map the surface of Venus down to a resolution of 120 to 300 metres. On 15 September 1990 the craft began to send high resolution radar images of the surface clearly showing signs of vulcanism, tectonic movement, surface winds, lava channels and pancake shaped domes. During its first cycle it mapped 83.7% of the surface returning 1200 GB of data, an incredible amount at that time. After the second cycle it had mapped 96% of the surface and the third mapped 98%. Contact with the probe was lost on 12 October 1994 after it had plunged into the atmosphere to collect further aerodynamic data.
- 85% of the surface is covered with volcanic flows
- Complete lack of water
- Extremely slow erosion process
- Surface features persist for hundreds of millions of years
ESA goes express to Venus in 2005! The ESA sent the Venus Express to Venus in 2005 with the primary goal of studying the atmosphere. This was the ESA’s first mission to Venus and it was named Express due to the quick time the mission took to prepare and execute.
Image courtesy http://www.esa.int/spaceinimages/Images/2007/11/Artist_s_concept_of_lightning_on_Venus
The magnetometer (MAG) on board ESA’s Venus Express detected wave signals that show evidence of lightning in the atmosphere.
Major achievements of Venus Express include:
- Discovery of a shape-shifting southern solar vortex. It can take almost any shape indicating complex weather patterns due to centre of vortex being offset to geographical pole
- Evidence of recent volcanism, perhaps in the last few thousand to ten thousand years
Double volcano on Venus. Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/Ast105week08.html
A ten-fold increase in sulphur dioxide in the atmosphere has led scientists to question whether volcanos are still active today.
- Venus’ rotation is slowing down, found by comparing data collected by the Magellan mission. Features monitored by Express could only be lined up with Magellan if the length of a day on Venus is on average 6.5 minutes longer than when Magellan tracked the same features
- Discovery of a cold area 125 km above the surface where snow or ice could exist. The temperature of -175 degrees celsius means the carbon dioxide can freeze
- Detection of a thin ozone layer approx. 90 to 120 km above the surface, far higher than on Earth where ozone exists at 15 to 50 km above the surface
- Water loss due to splitting of water molecules in upper atmosphere by ultraviolet radiation from the Sun. The process creates two hydrogen atoms and one oxygen atom which are carried into space by the solar wind. Venus does not generate a magnetic field which can protect its atmosphere from the solar wind
- Discovered mean wind speed of 400 km/h, an increase of 100 km/h over the 8 year mission
Pancake domes on Venus. Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/Ast105week08.html
Images from the surface – Venera 13. On 1 March 1982 Venera 13, a Soviet mission, set down on the surface of Venus and began relaying data back to Earth. It was able to transmit data for 127 minutes, far longer than the expected 32 minutes before the craft was crushed and melted by the extreme pressure and heat on the surface of Venus. It successfully relayed the first colour pictures of the surface of Venus, something previous missions had failed to do. It sent 8 panoramas showing fields of orange-brown rocks and loose soil. Soil analysis showed soil similar to terrestrial leucitic basalt with high potassium content.
Image above shows Venus surface.
Future Venus missions?
1. The clockwork Venus rover. The solution to Venus landers not lasting longer than 2 hours could be a clockwork lander with no electronics. To send messages back home it would record data on a phonograph and then loft it on a balloon to rendezvous with a spacecraft overhead. (https://www.newscientist.com/article/mg23030693-600-our-top-5-wacky-nasa-missions-that-might-just-happen/)
The phonograph is a machine invented by Thomas Edison in 1877. It is a machine for recording sound on tinfoil coated cylinders. It has 2 needles, one for recording and one for playback. It is incredible to think that over one-hundred year old technology could be used to explore the solar system today.
2. Can sound help us detect ‘earthquakes’ on Venus? (http://www.astrobio.net/topic/solar-system/venus/can-sound-help-us-detect-earthquakes-on-venus/)
Researchers are planning to deploy an array of balloons in the atmosphere of Venus that could detect seismic activity on the surface using sound. A team of experts at the Keck Institute for Space Studies began thinking of ways to use infrasonic observations to get a better look at the geological dynamics of Venus. If we can get a better idea of the seismic activity on the planet this can tell us more about the history of the planet and its interior.
Escape velocity of Venus
During the course the mathematical labs have not been my strongest area, but I have learnt so much from attempting the challenges, something I really enjoyed doing. I would like to finish with a math problem I can do – the escape velocity of Venus. So here goes…
What is the escape velocity from the Venus exosphere, which begins about 220 km above the surface?
mass = 4.867 x 10^24 kg
radius = 6.05 x 10^6 m
height = 2.2 x 10^5 m
= 2 x 6.67 x 10^11 x 4.867 x 10^24 / (6.05 x 10^6 + 2.2 x 10^5) = 1.03 x 10^8
v = sqrt (1.03 x 10^8) = 10148 m/s = 10.1 km/s ~ 10 km/s
Please check the math and let me know if I have made a mistake along the way.
Watch BBC The Sky at Night Venus documentary https://www.youtube.com/watch?v=82fS9C9koxU for more information.
Huge thanks go to Dr Frank Timmes for being an outstanding teacher during this course, your videos and notes were amazing, thank you sooo much! You have inspired me to learn more about the universe. Big thanks also go to the rest of the team at Arizona State University for putting together an amazing course and for all their support. This has been the best course I have enrolled in on edX and I would highly recommend it to anyone interested in astronomy.
Thanks for reading, bye bye!