Terraforming Venus

Terraforming is the process of changing the global environment of a planet  in such a way as to make it suitable for human habitation. Because it is so far beyond our current technological capabilities, most articles about terraforming have been written by science fiction writers rather than scientists.  For example, there is  an entry for a terraformed Venus in the science fiction work “Encyclopaedia Galactica” which is set thousands of years in the future.

Originally a hot dry greenhouse world, (Cytherian Type) with an atmosphere consisting mostly of carbon dioxide with a surface pressure 94 times greater than that of Earth. The planet was shrouded with clouds of sulphuric and hydrochloric acid and the mean surface temperature was 480 C, making the world extremely hostile to terragen and carbon-based life. Because of this the planet was sparsely populated for many thousands of years; recently it has been successfully terraformed.

(Kazlev et al 2006).

Even though I know of very few references to a terraformed Venus in serious scientific writing, there is no reason why – given sufficient resources and time – an advanced human civilisation wouldn’t be able to terraform Venus. In this post I’ll talk about the challenges to making Venus habitable so that humans can live and work on the planet without any need for protective equipment such as space suits or oxygen supplies.


What a terraformed Venus might look like – Image from Wikimedia Commons

High Temperatures and Pressures.

The surface temperature of Venus is around 500 degrees Celsius and the atmospheric pressure is a crushing  92 times that of the Earth. The atmosphere consists of 97%  carbon dioxide (Williams 2015), a powerful greenhouse gas which traps the Sun’s heat. In order to make the planet habitable the surface temperature would need to be around 0 to 35 degrees and the atmospheric pressure similar to that on the Earth.

One way to cool Venus would be to build a giant sunshade to block most of the Sun’s rays from hitting the planet. This was described in detail in a paper written by the late British science writer Paul Birch (1991).

Venus Sunshade

The shade would orbit the Sun at a specific point about 1 million km above the planet’s surface called the L1 Lagrange point, shown as L in the diagram above (see note 1). It would need to be slightly larger than the diameter of Venus, 12,100 km, to fully shade the planet. The cost and technological challenge of building such a shade would enormous. It would need to be 100 billion times larger in surface area than the International Space station, shown below, which is the largest object ever built in space.


It is likely that such a shade would be built up from thousands or even millions of smaller individual shades and would take many decades to complete from start to finish. As the shade neared completion, and most of the Sun’s rays were blocked from hitting the planet, the surface of Venus would begin to cool.  Interestingly, when the shade was complete, because Venus would no longer be lit up by the Sun, to an observer on Earth Venus would go from being the third brightest object in the sky (after the Sun and the Moon) to being invisible.

After about 100 years the temperature of Venus would drop to 31 degrees (see note 2). At this temperature, known as the critical point of carbon dioxide, some of the carbon dioxide in the atmosphere would start to condense from gas to liquid and the low-lying areas of the surface of Venus would begin to be covered in seas and oceans of liquid carbon dioxide, in the same way that much of the Earth’s surface is covered by seas and oceans of water. As it condensed into liquid, the amount of carbon dioxide left in the atmosphere would start to fall and with it the atmospheric pressure.

Eventually the temperature would drop to the freezing point of carbon dioxide (-57 degrees) and the seas, oceans and lakes of liquid carbon dioxide would begin to freeze. Much of the remaining carbon dioxide in the atmosphere would fall as snow.

This entire cooling process would take hundreds of years from start to finish. When it had completed the next step would be to ensure that when the shade was removed, allowing the planet to warm up, the frozen carbon dioxide wasn’t released back into the atmosphere. One way this could be achieved would be to cover up the frozen carbon dioxide oceans with an insulating material and provide some sort of refrigeration system to keep it cool. Once the carbon dioxide was safely locked away the sunshade could then be removed to allow the planet to warm up again. Because nearly all the carbon dioxide would have been removed from the atmosphere it would no longer provide such a powerful greenhouse gas.

No Water

Venus is a very dry planet. Its atmosphere contains only a small trace of water and there is no water on its surface. By comparison, on Earth 71% of the planet’s surface is covered by water and  there are about 1.39 billion cubic kilometers of water on the planet.  The breakdown of how this water is distributed is shown in the tables below (U.S. Department of the Interior 2015)

Earth Water

As water is essential for life, it would be necessary to import water to Venus to make the entire planet habitable for plant and animal life. A lot of water would be needed, but it would not be necessary to have most of the planet covered with deep oceans of water. Probably around 30-50 million cubic kilometres of water would be sufficient. Even so, this is a still a huge amount of water to shift.

How could we get a large amount of water to Venus?

There various ways of doing this. One way would be to transport it from the seas and oceans of Earth. The cost of this would we be prohibitive and even if there are huge advances in technology it would be extremely difficult to transport a huge amount of water by this method.

Another possibility, again prohibitively expensive, would be to import hydrogen by scooping it up on an orbiting ring from one of the giant planets in the outer Solar System. The hydrogen would then be sent onto Venus by a cargo-carrying spacecraft. The hydrogen would produce water by chemical reaction with the remaining carbon dioxide in the planet’s atmosphere.

A fascinating alternative way of getting all the water needed to Venus was suggested in Birch’s paper.  It involves moving one of Saturn’s ice moons into orbit around Venus and then breaking it up, thus releasing all the water needed onto the planet.

Saturn has a number of ice moons such as Hyperion (shown below), an irregularly shaped object 360 by 260 km which consist mainly of ice, covered in a thin layer of rock.


Image from NASA

The proposal is that we could build a huge structure on Hyperion which would use the Sun’s heat, concentrated by mirrors, to put out a jet of steam into space in the same direction as it orbits Saturn. This is shown in the diagram below.

Hyperion Steam Engine


This jet of steam will provide a force which will gradually slow down Hyperion in its orbit causing it to gradually spiral inwards towards Saturn. After about 30 years Hyperion will be in an oval-shaped orbit which will cause it to pass close to the giant moon Titan.

Hyperion Steam Orbit Decay

Titan is much larger than Hyperion and the near collision between the two objects will give Hyperion so much speed that it will be ejected from orbit around Saturn.  If the speed and angle are just right, after it escapes from Saturn it will be on a path which will take it close to the giant planet Jupiter. This technique is known as a slingshot and NASA uses it to send spacecraft to the outer Solar System.

As Hyperion passes Jupiter, the giant planet’s gravity will hurl it into the inner Solar System. If the angle of approach to Jupiter is just right it will be possible to send it on such a path that it will approach Venus slowly enough to be captured by Venus’s gravity and go into orbit around the planet. Once in orbit Hyperion would be gradually broken up and its water transferred to the planet’s surface.

Although this somewhat convoluted plan might appear to be something out of an exotic science fiction story, it obeys all the laws of physics and could potentially be achieved by an advanced human civilisation which devoted the resources to do it.

No oxygen

In order to be habitable Venus would need a similar level of oxygen in its atmosphere to that on the Earth. On Earth oxygen makes up about 21% of the atmosphere, whereas Venus’s atmosphere has almost no oxygen.  Compared to the other challenges this would be relatively easy to resolve. The oxygen concentration could be increased by plant life which, as you may remember from your high school biology lessons, uses a process called photosynthesis to convert carbon dioxide and water into carbohydrates and oxygen.


Image from Wikimedia Commons

Long day/night cycle

On Venus the slow rotation of the planet means that a day lasts 116.8 Earth days. Most Earth lifeforms would struggle to adapt to such a long day/night cycle. A shorter day could be created by means of orbiting shades and mirrors.

No magnetic field

On the Earth its magnetic field forms a protective shield around the planet which protects its surface from electrically charged particles from the Sun (the solar wind) and from outer space (cosmic rays). Without a magnetic field  there would be an increased risk of cancer for anyone who ventured outdoors for any significant period of time.  To make Venus completely habitable it would need to be given an artificial magnetic field. This is actually quite difficult to do, even for an advanced civilisation, and will merit its own blog post in due course!


The Science Geek



1) At this point the shade would orbit the Sun in exactly the same time, 224.7 days, that it takes Venus to orbit the Sun. Therefore it would always be shading the planet once it was put in place.

2) Any timescales here should be treated as very approximate. The actual values depend on the properties of the Venusian atmosphere during the cooling scenario.


Birch, P. (1991) Terraforming Venus quickly, Available at:http://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf (Accessed: 6 February 2016).

Kazlev, M.A., Sandberg M., Bowers, S., Parisi M (2006) Encyclopaedia Galactica -Venus, Available at: http://www.orionsarm.com/eg-article/48e7ce77477af (Accessed: 11th February 2016).

U.S. Department of the Interior (2015) How much water is there on, in, and above the Earth?, Available at: http://water.usgs.gov/edu/earthhowmuch.html (Accessed: 7 February 2016).

Williams D R (2015) Venus fact sheet, Available at:http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html (Accessed: 6 February 2016).



Living on Venus

In this post I’ll look into the distant future and talk about humans living and building settlements on the planet Venus. Because it is well beyond what we can achieve with our current technology, it is a topic that been more in the realm of science fiction rather than factual scientific writing. However, even though there are many difficult obstacles in the way, I think it is very likely to happen at some point in the distant future.


Venus as seen through a telescope – image from NASA.

Why would we want to live on Venus?

There are a number of reasons why humans would want to colonise Venus.  The first three also apply to the Moon, Mars or Mercury.

  • To ensure the continuation of humanity. While the human species is restricted to life on a single planet it is vulnerable to extinction caused by natural or man made disasters.  If humans could live in a self supporting colony outside the Earth then this would provide a Plan B to allow the continuation of our species. Indeed the British physicist Stephen Hawking recently said:

“I believe that the long term future of the human race must be space and that it represents an important life insurance for our future survival, as it could prevent the disappearance of humanity by colonising other planets.”

Stephen Hawkins NASA

Image from NASA

  • To spread human civilisation to other places.  Since humans first evolved, they have constantly sought to expand to new territories. It seems to be almost a biological imperative to find other places to live.  There are not many uninhabited places on Earth, so humans may one day extend their civilisation beyond our planet.
  • To stimulate the economy.  Despite the enormous cost, building colonies outside the Earth would give a huge stimulus to the Earth’s economy. There may well be spin-offs in the same way that the Apollo programme in the sixties and early seventies led to huge technological developments unconnected to space travel.
  • It is relatively easy to get to. Compared to Mars and Mercury, Venus gets closer to the Earth (Williams 2015 a,b). At its closest approach it is 40 million km away from Earth, whereas Mars at its closest approach is still around 80 million km away. It is therefore easier to reach.
  • Larger surface area. Venus is almost the same size as the Earth (ibid). This means that it has almost 4 times the surface area of Mars and 15 times the surface area of the Moon, giving a greater area to colonise.

Earth Venus Mars

  • Similar gravity to the Earth. When astronauts spend long periods of time in a low gravity environment, such as the International Space Station, their bones and muscles weaken. It is not known if the weak gravity on the Moon (16% of the Earth’s gravity) or Mars (38% of the Earth’s gravity) would be sufficient to prevent this happening. The surface gravity on Venus is 91% of that of the Earth which would be sufficient.
  • More solar energy. Any colony would be likely to use solar energy as its main energy source. Venus is closer to the sun than the Earth and receives roughly twice as much solar energy as the Earth. See Notes at the end of this post.


As readers of my previous post will know, Venus is a very inhospitable world. Its surface temperature is on average nearly 500 degrees Celsius and its air pressure is a crushing 92 times that of the Earth. No spacecraft has been able to survive for longer than about an hour on its surface without being destroyed by the intense heat and pressure. The thick atmosphere forms a thermal blanket around the planet. So even at the poles the temperature is not any cooler and, although the temperature drops with altitude, there is nowhere on the planet’s surface which is less than than 380 degrees Celsius. In addition, there is almost no water or oxygen in the atmosphere – both of which are essential for life and Venus does not have a magnetic field to protect the planet from the harmful effects of the solar wind.

Floating cities?

Because the temperature and pressure both fall with altitude there is a region around 50 km above the planet’s surface where both the atmospheric pressure and temperature are similar to that on the Earth.


The graph above shows how the temperature and pressure of Venus’s atmosphere varies with altitude (from Wikimedia Common). 1 Bar is air pressure at sea level on Earth

At this 50 km point, the atmosphere of Venus is the most Earth-like environment, other than Earth itself, in the Solar System. In a paper written in 2008, the NASA scientist Geoffrey Landis suggested building floating cities in the Venusian atmosphere (Atkinson 2008) .  The atmosphere of Venus consists of 97% carbon dioxide, which is denser than the Earth’s atmosphere, which is mainly composed of nitrogen and oxygen. Landis suggested that a large space filled with with breathable air could float high above the Venusian surface in the same way that a helium balloon floats in the Earth’s atmosphere.

Venus Floating City

It would be possible to build large enough spaces for humans to live and work in, although there is the obvious risk that if there were a major leak the entire structure would fall down to the surface to its destruction.

Terraforming Venus

I think that humans will only be able to live on Venus after the entire planet has been transformed to make it more Earth like. This is called terraforming. This process, which is well beyond our current technology, and is at the moment more in the realm of science fiction writers, will involve removing nearly all the carbon dioxide from the atmosphere, adding oxygen, reducing the surface temperature and pressure to similar values to those on Earth, and adding water. It will also be necessary to do something about the long day/night cycles.  A day on Venus lasts 116.8 Earth day which is too long for Earth life to adapt to. (Incidentally, Mrs Geek recently read and enjoyed Karen Thompson Walker’s novel “The Age of Miracles” which describes how humanity struggles to adapt to a world in which the length of a day is much longer than 24 hours.)

In my next post I will discuss how, if humanity doesn’t destroy itself and we become a very advanced civilisation, we could terraform Venus.

The Science Geek





Interestingly, the amount of solar energy reaching the surface of Venus is, on average, far less than that reaching the surface of the Earth. This is because, although Venus gets more sunlight, most of the solar energy which hits Venus is reflected back into space by the thick cloud layer high above the planet’s surface. Most of the remaining sunlight is absorbed by the thick atmosphere before it reaches Venus’s surface.  Howver,If Venus is terraformed its surface will get more sunlight than the Earth, because its clouds and atmosphere will be much thinner.


Atkinson N. (2008) Colonizing Venus with floating cities, Available at:http://www.universetoday.com/15570/colonizing-venus-with-floating-cities/ (Accessed: 23 Jan 2016).

Williams D R (2015a) Mars fact sheet, Available at:http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html (Accessed: 23 Jan 2016).

Williams D R (2015b) Venus fact sheet, Available at:http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html (Accessed: 23 Jan 2016).

The Future of humanity

As described in my previous post (The Future of the Sun), in about 5 billion years time the Sun will swell up to at least 100 times its current diameter and this will make the surface of the Earth far too hot to sustain life.

Future Sunrisev2

What Sunrise might look like when the Sun is a red giant.

This post discusses other natural events which could spell the end of life on Earth, long before the Sun becomes a red giant.

Gradual increase in the Sun’s brightness

Astrophysicists predict that the Sun is gradually increasing in brightness by 1% every hundred million years. This increase in solar output will, over the long term, cause a gradual warming of the Earth’s surface.

This is what will happen:

  1. The increased energy from the Sun will cause a warming of the Earth’s surface.
  2. Because water evaporates more rapidly at higher temperatures, there will be an increased rate of evaporation from the Earth’s seas and oceans.
  3. This will in turn lead to an increased concentration of water vapour in the Earth’s atmosphere.
  4. Water vapour is a very efficient greenhouse gas and will act to trap heat escaping from the Earth’s surface, making it even warmer.
  5. The temperature rise caused by the greenhouse effect will add to the temperature rise caused by the increased output from the Sun. This will lead to a higher surface temperature, which will lead to a greater rate of evaporation of water.

The process is actually called a runaway moist greenhouse, and is illustrated in the diagram below.

Runaway Moist Greenhouse


It has been calculated that, in roughly 1 billion years, which is long before it becomes a red giant, the combination of the Sun’s gradual increase in output and the moist greenhouse effect will make the Earth’s surface too hot for liquid water to exist (ref 1).


Comet or Asteriod impacts

About 65 million years ago a comet or asteroid approximately 10 km in diameter and weighing over 1 trillion tons hit the Earth (ref 2).  You may recall from your high school science lessons that the energy that a moving object has varies with not its speed but its speed squared. What this means is that an object moving at  10 km per hour has 100 times the energy of an object of the same size moving at 1 km per hour and an object moving at 100 km per hour would have 10,000 times the energy. The comet or asteroid which collided with the Earth 65 million years ago may have hit the Earth with a speed of up 50,000 km per hour. This high speed coupled with its huge mass meant that it smashed into the Earth with an absolutely enormous energy. In fact the energy of the impact was equivalent to that released by 100 trillion tons of a high explosive called TNT (ref 2). This is 6 billion times greater than the atomic bomb dropped on Hiroshima at the end of the Second World War.

KT extinction asteroid

The impact melted much of the local crust and blasted molten material outwards. Any object near to the impact site would have been instantly vapourised. Such was the energy of the impact that some of the Earth’s crust was thrown upwards with so much force that it went out into space. Much of the remainder eventually came back to Earth over the next few hours which caused molten rock, dust and ash to rain down on an area millions of square kilometres in area. This hot material would have ignited fires, destroying plant and animal life within a large area.

Kt ejecta map


The impact 65 million years ago occurred in what is now the Yucatan peninsula in Mexico.  The outer ring shows the area which become covered in debris.

A fine cloud of dust from the impact circled the entire Earth. This blocked out sunlight, causing the Earth’s temperature to fall by about 15 degrees Celsius. The sudden drop in temperatures and lack of  sunlight getting through meant that plant growth stopped for several months.  As a result, many species of animals which fed on plants became extinct and the carnivores which fed on them became extinct too. Those species which did survive  had their numbers reduced. In fact, nearly 75% per cent of the species of animal alive before the impact became extinct, including every species of dinosaur.

There has been many such large impacts throughout the history of the Earth and it is extremely likely than one will occur within the next 50 million years or so, although we can of course not predict when.  The extremely rare possibility of this has nonetheless inspired a number of science fiction books and films!

Other events

Although a large comet or asteroid impact poses probably the greatest threat to life within the next 50 million years or so, there are other natural events which could effect the existence life on our planet and I have highlighted a few below.

Smaller Asteroid or Comet impacts.

Although large impacts, such as that which wiped out the dinosaurs, occur only once every 100 million years or so, smaller impact are much more common. The chances of an asteroid 1 km in diameter hitting the Earth are such that it will occur once every 500,000 years. Although the effects are less drastic than a more massive impact they are still substantial. An object 1 km in diameter smashing into the Earth, at a speed of 50,000 km per hour would have the explosive energy of around 100 billion tons of TNT and would devastate anything within 100 km of the impact site. It would throw up a thick cloud of dust into the upper atmosphere, which would cause global temperatures to drop by a few degrees for a year or so. This fall in temperature would have a massive effect on plant and animal life.

Supernovae. Massive stars end their lives in huge explosions called supernovae in which the star is totally destroyed and a massive amount of energy is released. When a star becomes a supernova it can briefly reach a peak brightness 5 billion times brighter than the Sun.


If a supernova were to occur within 30 light years of the Earth then the radiation emitted would severely damage the Earth’s upper atmosphere, letting harmful radiation hit the Earth’s surface. At the moment it is unclear how likely this is to happen. Only a very small percentage of stars end their life in supernova explosion but a recent scientific paper suggests that a  supernova will occur within 30 light years of Earth every 300 million years (ref 3).

Large Volcanic Eruptions

Roughly 70,000 years ago, an enormous eruption occurred in what is now Sumatra, leaving behind Lake Toba. The huge eruption sent a cloud of dust and ash into the air which  triggered a major environmental change which caused the near extinction of the human race. At one stage there were only 2000 individual humans alive on the planet.


Lake Toba, site of a supervolcano eruption 70,000 years ago

Such super volcanoes tend to occur a few times every million years.

For more information on the Toba eruption and its possible effect on humans, see http://toba.arch.ox.ac.uk/project.htm

What can humans do to survive these catastrophes?

Of all the natural threats, the most deadly to humanity would be if an asteroid or comet 10 km in diameter or larger were to strike the Earth. If this were to happen, all life within hundreds of kilometres of the impact would perish instantly. The sudden drop in temperatures of 15 degrees caused by the Sun being blocked out would cause crop failure and mass starvation. Conditions would be very harsh and many people living in currently hot countries might have trouble adapting without warning to colder temperatures. I don’t think humans would become extinct. We are too advanced for this and there would be sufficient food reserves for a proportion of the population to wait the few years or so before agriculture could be reestablished.  People would not be able able to survive by hunting and gathering because there would be nothing to hunt and very little to gather.

At the moment, our space technology isn’t advanced enough to allow us to prevent such an impact. However, asteroids’ and comets’ orbits are plotted well enough that we are pretty certain that won’t be any such impact within the next few hundred years. I believe that long before the Earth is due to be hit by such a object, humanity or whatever species we have evolved into will be able to remove the threat. We could,  for example, dispatch a spacecraft to explode a massive nuclear bomb to destroy the object, or deflect it into different orbit so it wouldn’t collide with the Earth.

What about man made disasters?

This post has described some possible natural scenarios which could spell the end of life on Earth. In addition to this there are other man made scenarios, such as a world wide nuclear war or a genetically engineered fatal disease.  There is even the remote possibility (probably only really taken serious by lovers of science fiction) that humanity might be destroyed by an advanced artificial intelligence that it had itself created – a sort of killer robot.

killer robots

Indeed what it is clear is that while humanity is confined to a single planet, the Earth, we are vulnerable to being wiped out by natural or man made disaster. In a recent article reported in the British newspaper The Independent  Stephen Hawking, the famous theoretical physicist, believes that we should colonise other planets to ensure the survival of the human race.

Stephen Hawking

“I believe that the long term future of the human race must be space and that it represents an important life insurance for our future survival, as it could prevent the disappearance of humanity by colonising other planets.”

Stephen Hawking 2015



1) http://www.redorbit.com/news/science/1113029594/earth-oceans-will-dry-up-in-a-billion-years-121713/

2) http://www.ucmp.berkeley.edu/education/events/cowen1b.html

3) Gehrels, Neil; Laird, Claude M. et al. (2003-03-10). “Ozone Depletion from Nearby Supernovae”. Astrophysical Journal 585 (2): 1169–1176

Artefacts From Earth

This is the final post in a series about human efforts to contact extraterrestrials.  Today I want to discuss the objects which have already been sent out into interstellar space in the hope that at some point in the distant future an alien civilisation will retrieve and decipher them.

The Pioneer Plaque

On 3 March 1972 Pioneer 10 was launched from Cape Canaveral on its mission to become the first spacecraft to fly past Jupiter, which it did in November 1973. After passing Jupiter it continued its journey to the edges of the solar system and beyond, becoming the first of only five spacecraft ever to pass beyond the orbit of the outermost planet Neptune – if you remember from a previous post, Pluto has been downgraded from a planet to a plutoid on the grounds of it being extremely small – its mass is only a tenth of that of our Moon.

pioneer10 Jupiter

Pioneer 10 passing the giant planet Jupiter in 1973- Image from NASA

When it leaves the Solar System, Pioneer 10 will drift through interstellar space getting further and further from the Sun. The spacecraft could last for millions, possibly even billions, of years and could in theory be recovered by an alien civilization.

In case that should happen, Pioneer 10 carries a simple plaque, shown below. This would tell intelligent beings from another planet where the spacecraft had come from and give them some basic information about humanity.


The Pioneer plaque- Image from NASA

The Pioneer plaque was designed by Carl Sagan (1934-96) and shows four relatively simple things, which he hoped an alien civilisation would understand.

  • On the top left is a diagram of a hydrogen atom. Hydrogen is the most common element in the Universe and emits radiation naturally at a wavelength of 21-cm, when it moves from one state to another. Sagan felt that any intelligent civilisation would know this and understand this diagram.
  • On the right is a figure of a man and woman. The man has his hand raised in a gesture of friendship, although there is no way of knowing whether an alien race would correctly interpret this.  The figures have caused some controversy – some have objected to the lack of clothing, whereas others, much more significantly, feel that the fact that both figures are clearly Caucasian does not fairly represent humankind.
  • Behind the figures is a diagram of the spacecraft. The man, woman and spacecraft are all drawn to the same scale. An alien race could therefore figure out how large we are.
  • At the bottom is a diagram of the Sun and nine planets. The arrow indicates which planet the spacecraft has come from. Pluto still features in the diagram, as its demotion only occurred in 2006!

The fifth item on the plaque is the diagram with 15 lines coming out of it and was devised by Frank Drake, who I have mentioned before regarding his interest in SETI. The centre of the diagram, from which the lines radiate, represents the sun.  The right-hand end of the longest line (at 3 o’clock) represents the centre of the galaxy.  The end of each of the remaining lines represents an object called a pulsar.  Pulsars are rapidly rotating objects which emit radio waves in regular pulses a few seconds or fractions of a second apart. You will notice that the lines to the pulsars are not smooth – you will see these more clearly if you use the zoom facility – and the marks drawn on the lines depict the length of the pulsar period in time units that an alien might understand.  The alien civilisation could then have sufficient information to identify the fourteen pulsars, and thus the location of our Sun and then the Earth.  If you are interested, there are additional notes at the bottom of this post explaining the technicalities of this.

An identical plaque was sent out in April 1973 on the spacecraft Pioneer 11.  This went past Saturn as well as Jupiter and, like Pioneer 10, is currently well beyond Neptune and on its way out of the Solar system and heading out into interstellar space.

The Voyager missions

The next spacecraft to leave the solar system will the two Voyagers.  Voyager 1 was launched on 5 September 1977 and, like Pioneer 11, flew past Jupiter and Saturn. Voyager 2 actually set off a couple of weeks earlier, on 20 August, on a mission to fly past all four outer planets – Jupiter, Saturn, Uranus and Neptune, Each Voyager contained a golden record, the cover of which is shown below.

Voyager Record Cover

Image from NASA

You will notice right away Drake’s pulsar map and the hydrogens, but perhaps less obvious are a picture of the record itself plus instructions for playing it.  These instructions use symbols which Sagan hoped aliens would understand.

Voyager Record

Image from NASA

The record itself, entitled ‘The sounds of Earth’ includes:

  • greetings in 55 different languages,
  • natural sounds and some music from Earth
  • 116 pictures of a variety of objects such as the planets in the solar system, human anatomy, groups of children, important landmarks, interesting places, and man-made structures such as airports, large telescopes, the Golden Gate Bridge in San Francisco, and an American highway in the rush-hour.
  • a printed message from the then United States president Jimmy Carter, part of which is given below:

“…This is a present from a small different world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings.  We are attempting to survive in our time so that we we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilisations. This record represents our hope and our determination and our goodwill in a vast and awesome universe.”

Where are the space probes now?

The table below shows where the four spacecraft are now. However, the location given for the Pioneer spacecraft is only an estimate, as they are no longer in contact with Earth.  There are two possible reasons for this.  Either their power supply has run out, or the radio transmitter is no longer lined up with the Earth and is beaming out signals in a completely different direction.  We can therefore only guess where they are, based on their last known location, as they are too small and faint to see with any telescope. The Voyager spacecraft are still in contact and should have enough power to continue transmitting messages back to the Earth until the mid 2020s, but after that we will have to rely on projections for them too.

Voyager and Pioneer distances

In the table, the distance of the probes on 1 Oct 2014 is given both in kilometers and astronomical units (AU). 1 AU is the average distance from the Earth to the Sun and is equal to just under 150,000,000 km. The outermost planet Neptune is about 30 AU from the Sun and the nearest star about 250,000 AU away. The speed column shows how the spacecraft s moving away from the Sun in AU per year.

New Horizons

The final spacecraft already launched which is due to leave the Solar System is New Horizons. This was launched in 2006 and will fly past Pluto and its moons in July 2015.

New Horizons

Artist’s Impression of New Horizons passing Pluto -Image from NASA

New Horizons doesn’t have any golden records, plaques or maps to tell an alien civilisation where it came from. Instead, it carries the following nine objects from Earth.

  • Some of the cremated ashes of the astronomer Clyde Tombaugh(1907-1998), who discovered Pluto
  • A CD with the names of 434,000 people who submitted their details to the project team – I would have loved to do this myself, had I only known about it in time!
  • A CD with the pictures of some of the staff who worked on the spacecraft
  • Two quarters (25 cent coins) from Florida and Maryland, where the spacecraft was built and launched
  • A small piece of SpaceShipOne, the first privately funded spacecraft to fly into space
  • Two US flags (I have no idea why there were two!)
  • A 1991 US postage stamp proclaiming, “Pluto: Not Yet Explored”

The reason for there being nine objects is that Pluto was still considered to be the ninth planet from the Sun at the time the mission was being planned.  It is ironic that the planet was demoted the very same year the mission was launched!

Will any of the objects ever reach their intended recipients?  

Even astronomers who think that alien life is widespread within our galaxy think that it is very unlikely, given the vastness of space, that any of these five spacecraft will ever reach an alien civilization able to recover the ojects sent for their perusal.  The spacecraft are small and their power sources will have long died, thus making them unable to transmit a signal which could be picked up.

I personally believe that we are alone in the galaxy.  If I am right,  there is no alien race in existence to find the objects, let alone one intelligent enough to decipher them.

More likely, but still incredibly unlikely in my opinion, is the possibility that in the far distant future, long after the Voyagers, the Pioneers and New Horizons have been forgotten, mankind itself may leave Earth and colonise planets around other stars, and in millions of years time our descendants could discover one of these craft and its contents. It is fascinating to think about what they would make of them.

In popular culture

The Pioneer plaque and the Voyager golden record have made numerous appearances in popular culture including science fiction series such as Star Trek, Buck Rogers and the X-files.

In an episode of the”The Simpsons”.  The Pioneer plaque is shown with an alien holding the plaque upside down struggling to make sense of it!



Next Post

This brings to a close my series on extraterrestrial life.  My next will be about the expanding universe.

Note about the pulsar diagram

Clearly Earth-based units of time such as seconds would be meaningless to an alien. Therefore Drake used the transition of a hydrogen atom, shown on the plaque, to create a time unit he hoped an extraterrestrial race would understand.

When a hydrogen atoms flips from one state to another it emits radio waves at a wavelength of 21.1 cm.  A wavelength of 21.1 cm corresponds to a frequency of 1,420,406,000 cycles per second. So each individual cycle corresponds to a time interval of 0.000 000 000 704 seconds. All the pulsar periods are expressed in multiples of this fundamental time interval.




As I discussed in my last post, the search for signs of extraterrestrial life has caught the interest of many people for a very long time, and the specific search for signals from other life forms has been a particular source of fascination over the last 50 years.

In the 1997 movie Contact Jodie Foster’s character detects an alien broadcast from a nearby star while listening to radio signals.  It was a huge box office hit.


Poster for the 1997 Warner Bros. film contact

In the poster above you can see that Jodie Foster is wearing a pair of headphones. However, I’m sorry to disappoint you, but astronomers do not actually sit around looking cute and wearing big headphones. All analysis is done by computers which monitor millions of channels simultaneously, but this wouldn’t make such a good movie!

What types of signals are we looking for ?

The search for extraterrestrial intelligence (SETI) is almost entirely carried out using the large radio telescopes which are used to identify and examine astronomical objects like galaxies, gas clouds or stars.  These astronomical entities transmit radio signals over a wide range of frequencies at the same time, and this can be clearly picked up and identified by the powerful telescopes.  Astronomers have, however, reached a consensus that an alien civilisation trying to make contact with other life forms would be likely to transmit radio signals at one particular frequency, rather like a radio station.  The other characteristic of a deliberate attempt at communication would be that the signals contained some identifiable patterns.  Signals from something like a gas cloud would not contain any such patterns or information.

seti source

Radio waves from a natural source such as a gas cloud (A) are spread over a much larger range of frequencies than an artificial broadcast such as a radio message (B).

Essentially there are two types of signal we could in theory receive from an extraterrestrial intelligence.

  1. A signal which has been sent out by an alien civilisation not intended to received by us. Radio and TV signals generated by humans on Earth escape into space and have been slowly spreading out in all directions into a larger and larger volume of space since the first radio transmissions over 100 years ago. If another civilisation elsewhere had developed similar technologies, we could in theory pick up these signals here on earth.  However, with our current technology these signals would just too weak to pick up on Earth even from the nearest stars. So sadly we cannot yet tune into alien TV broadcasts 😉 – but maybe we will be able to do so in the next ten years or so – if there is anyone out there sending them!
  2. A signal sent by an alien civilisation using a powerful transmitter, deliberately beamed at the Earth, with the intention of letting us know that they are there and probably revealing information about itself.  (Although we cannot possibly know for certain what another civilisation would choose to disclose, we could perhaps speculate that it would contain similar information to the message that we ourselves broadcast into space from the telescope in Arecibo in 1973, in the hope that extraterrestrial beings might hear and understand it.  I will talk about this at a later date.)   This second type of signal would be many millions of times stronger than the first type and could be picked up from stars up to one thousand light years away with our existing technology.  (See notes at the end for what is meant by a light year.) Deciphering such a message constructed by an alien intelligence might prove to be incredibly difficult, but there would be no shortage of people who would be happy to devote their entire life to carrying out this amazing task.


The second type of signal (B) is many millions of times stronger than the first type (A) because all the energy is concentrated in a  narrow beam.


Drake’s Experiment

As mentioned in my previous post he first search for radio signals from alien civilisations was performed by a team led by one of the pioneers of SETI, Frank Drake (1930-), in 1960.

Frank Drake 2

The Father of SETI- Frank Drake -Image from Wikimedia Commons (Flanker)

Drake’s team used a radio telescope with a diameter of 85 feet (26 metres) to examine two nearby Sun-like stars that he thought could have planets with intelligent life. He decided to search for signals at a wavelength of 21 cm, which is the wavelength of the radio waves emitted by hydrogen gas. Because hydrogen is the most common element in the universe and the 21 cm radio waves easily pass through the atmosphere of the Earth and any other Earth-like planets, Drake thought that this would be the wavelength that aliens would naturally use to transmit messages to us.

In total he scanned 4,000 narrow radio channel over a four month period. When the data was analysed no detectable alien signals were found.


The telescope in Greenbank West Virginia used by Drake in 1960 to look for extraterrestrial signals. – Image credit NRAO

Later Work

Since Drake’s project there have been a large number of searches for signals from extraterrestrial civilisation by astronomers from many countries in the world. Over the years the sensitivity of the searches has improved by using larger telescopes and cooling the receivers to very low temperatures, which cuts out some of the background noise generated by the telescope itself. This has meant that, when using the largest telescope such as the 305 metre dish in Arecibo, Puerto Rico, we can now look for signals out to the aforementioned distance of about 1,000 light years. Improvements to electronics have allowed more channels to be scanned at the same time.

Arecibo Observatory

The giant radio telescope in Arecibo, Puerto Rico- Image from US Government (The Science Geek took some of the observations for his PhD here in the 1980’s 🙂 )

For example, from 1995 to March 2004, a study known as Project Phoenix conducted observations in New South Wales in Australia, Green Bank in West Virginia, and Arecibo. The project observed around 800 sun-like stars over wavelengths between 10cm and 30cm.  Around 2 billion narrow channels were analysed for signals. When the project concluded in 2004, no extraterrestrial signals had been detected, leaving the project leader to conclude that the Earth must be in a quiet corner of the universe.


Funding for SETI has always been limited. Compared to activities such the space programme, the amount of public money made available has been very small. Until the Allen telescope (see below) was completed there was no radio telescope allocated for SETI. SETI researchers had to compete for time on telescopes used for conventional radio astronomy. In general conventional radio astronomy has always been given priority.

In 1994 Congress cancelled all public funding for SETI, believing it to be a waste of money. For this reason Project Phoenix, and many subsequent studies have been privately funded by the non-profit making SETI institute (www.seti.org).

The Allen Telescope

SETI finally got its own telescope when the Allen telescope (www.seti.org/ata) was built in California. It is named after Paul Allen, the co-founder of Microsoft, who has contributed more than $30 million to the project  It consists of 42 separate dishes, each 6.1 metres in diameter. The signals from the individual dishes are combined to give the same sensitivity as a large single dish telescope at a fraction of the cost. The Allen telescope, which started operation in 2009, will be used for both conventional radio astronomy and for SETI.  Unlike other telescopes, rather than having to look at an object multiple times to cover different wavelengths it allows a large number of channels to be searched at the same time over the 3-cm to 30-cm wavelength range.  This greatly speeds up the search. It will survey 1,000,000 stars for non-natural extraterrestrial signals with enough sensitivity to detect a strong signal out to 1000 light-years.

allen telescope

Some of the 42 individual telescopes which make up the Allen telescope- Image from SRI International

Will we find anything?

Despite over fifty years of searching, no extraterrestrial signal has ever been detected. It is becoming clear that the locality of our own galaxy is not full of advanced civilisations communicating with each other! My own feeling is that the large searches performed by the Allen telescope won’t find anything and that we will come to the realisation that intelligent life is rare.

It may well be the case that  the Earth is not just an ordinary planet orbiting an ordinary star in an ordinary galaxy, but rather a very special place indeed, for it is the only place for tens of millions of light years where intelligent life exists.

Next Post

I hope you have enjoyed reading this (and there is much more chance of this now that Mrs Geek has corrected my terrible English), and for my next post I’ll been talking about that Arecibo message from Earth to extraterrestrial civilizations.


When measuring the vast distances to stars, astronomers sometimes use a unit called a light year (ly). One light year is the distance light travels in a year and is equal to 9.46 trillion (9,460,000,000,000) km. To give some idea of scale:

  • The distance from the Earth to the Sun is 0.000016 light years.
  • The nearest star other than the Sun is 4.2 light years away.
  • The centre of our galaxy is 26,000 light years away.
  • The gap between my English and Mrs Geek’s is 4.2 billion light years (she wrote this bit).



Space Tourism

This post is about  space tourism, which means ordinary people travelling into space for leisure purposes and paying to do so.  This is a subject which has always been of great interest to me and although the market is very small at the moment I think it will grow over the coming decades. With the proposed launch of Virgin Galactic’s SpaceShip Two later this year, it is a topic which is likely to be in the headlines.

The stuff of science fiction

Even since as a child I read the the novels of British author Arthur C Clarke (1917-2008)  I have been fascinated by the idea of space tourism.

As I mentioned in my post on 27 June, “Living on the Moon”, I am particularly fond of  “A Fall of Moondust” . It was written in 1961, but set in the 2050s. In the novel the Moon has been already been colonised, and it is visited by tourists from Earth. One of its attractions is a cruise, in a specially designed boat, across one of the maria, or lunar seas, which is filled with an extremely fine and very dry dust which flows like water.

Arthur C Clarke

Arthur C Clarke author of “A  Fall of Moondust”

Sadly, I think that the chances of frequent tourist visits to the Moon by the 2050s are zero. However,  I think that in the future there will be a large growth in space tourism and in the next few decades more ordinary people will be venturing into space.

What do we mean by ‘going into space’ ?

One question we need to think about what talking about space tourism is: what do we actually mean by ‘going into space’? Where does the Earth’s atmosphere end and space begin? This is a question to which there are no hard and fast answers. As we get higher up, the atmosphere gets gradually thinner and thinner and very gradually merges into interplanetary space, but there is no clear line where the Earth’s atmosphere ends and space begins. Most people would agree that:

  • a jet airliner flying at 35,000 feet in altitude (10.6 km) is not in space, even though a human would be dead at that altitude without supplemental oxygen, and
  • the International Space Station (ISS) which orbits around 400 km above the Earth’s surface is in space.

The diagram below shows a number of key altitudes above the surface of the Earth.




Various Key Altitudes

  • The summit of Mount Everest -8.8 km. At this point the air pressure is only one third of that at sea level and even a fit young person acclimatised to altitude could not survive for more than 30 minutes without extra oxygen.
  • A jet airliner -10.6 km. This is the height at which a jet airliner flies on a long journey. The air pressure at this height is around 27% of that at sea level and a human would be dead within minutes from lack of oxygen.
  • Concorde -18.3 km. This is maximum altitude at which the supersonic aeroplane Concorde could travel. Indeed Concorde, which is sadly is no longer in service, could travel at twice the speed of sound and was advertised as travelling ‘on the edge of space’. At this altitude the air pressure is around 6% that of sea level and the air is so thin the the sky is dark blue in daytime. At this pressure the boiling point of water is around body temperature so that any exposed liquids in the eyes, mouth throat and the lining of the lungs will literally boil away. To prevent this happening, a human would need to be enclosed in a pressurised space suit  to survive.
  • The manned balloon flight record -39 km. This the altitude record set by the Austrian skydiver Felix Baumgartner in August 2012.  When the balloon reached this altitude, he jumped out wearing a space suit. On his descent he reached a speed faster than the speed of sound in free fall before his parachutes opened to slow him down – hence his nickname name Fearless Felix.
  • Aurora 100 km to 200 km. Aurora are caused by high speed electrically charged particles from the Sun hitting the Earth’s upper atmosphere, at altitudes of 100 km upwards, causing it to glow.  Incidentally, Mrs Geek and I are hoping for a sight of the Aurora Borealis, more commonly known as the Northern Lights, when we visit Finland in September, as they are rarely visible in England.  The chance of this is actually pretty low, as we will be in Helsinki and they are seen more often further north, but we live in hope.
  • Low Earth orbit -160 km to 2000 km. 160 km is the lowest altitude at which a satellite can remain in orbit. At this altitude, a satellite would be slowed by air resistance, caused by traces of the Earth’s atmosphere, which means it would lose energy and spiral down to Earth within a day. As we get higher than this the atmosphere continues to get thinner and thinner and satellites are slowed less and less by air resistance, enabling them to stay in orbit longer. The International Space Station, which orbits at an altitude of 400 km, loses altitude at the rate of around 2 km per month and rocket motors attached to the station or on visiting spacecraft need to be used a few times a year to lift it higher up, thus maintaining its orbit and preventing it from crashing down to Earth.
  • Medium Earth orbit -above 2000 km. Above 2000 km the traces of the Earth’s atmosphere are negligible and a satellite will remain in orbit indefinitely.

So where exactly does space begin?

The Fédération Aéronautique Internationale (FAI), the international body setting standards and keeping records in the field of aeronautics and astronautics defines space as starting 100 km above the surface of the Earth.  As you can see, this is a very conveniently rounded number, which strongly suggests that it is somewhat arbitrary.  At this altitude the air pressure is around 0.00003% of that at sea level, which is too low for a conventional aeroplane to fly.  Although this pressure is very low, it is still high enough to cause so much air resistance that a satellite could not orbit. The thin air would cause it to burn up like a meteorite.

Space Tourists

So, space travel means travel to beyond 100 km above the earth.  So far, the only space tourists are the few who have been carried into space in the Russian Soyuz spacecraft. The first of these was the American investment manager Dennis Tito who in 2001 traveled on a Soyuz to the ISS and returned 7 days later.

dennis tito

Dennis Tito (left) with his fellow crewmates in his Soyuz capsule- Image in public domain

He paid $20 million for his trip and had to undergo months of tough cosmonaut training in Russia. He was followed by six other space tourists. The last of them, Guy Laliberté, the Canadian founder of Cirque du Soleil,  paid $40 million for a 11 day stay in space in 2009.

At the moment, because of the high cost and physical demands of getting into orbit, space tourism is only open to those who are super-rich and able to undergo the necessary training and preparation.  Not only is true demand therefore very small, but supply is also very limited indeed. The Russian space agency is – so far – the only organisation with the capacity and willingness to put space tourists into orbit.

NASA never allowed paying space tourists on the space shuttle and, following the retirement of the space shuttle in 2011, America has no capability of putting a human into space. Rather than NASA developing their own spacecraft to do so, the contract to ferry astronauts to and from the ISS will be put out to private corporations. The Dragon 2 spacecraft developed by the SpaceX company is the leading contender to win the contact.

Although initially its primary purpose will be to ferry astronauts to and from the space station, removing the reliance on Russia, it is likely that SpaceX will eventually sell seats on a Dragon 2 orbital flight to space tourists.  SpaceX plan to charge NASA  $140,000,000, or $20,000,000 per seat if the maximum crew of 7 is aboard.

Virgin Galactic

For a number of years the Virgin Galactic group have been developing the suborbital space plane called SpaceShip Two. This is planned to offers space tourists a much cheaper “taster” of space tourism. Launched from an aeroplane, it is a small plane with a rocket motor rather than a jet engine, which will take eight people up to just beyond the 100 km line thus – just about – qualifying as travel into space. During the flight the passengers will experience weightlessness for around 5 minutes and will be above the 100 km boundary for a couple of minutes.  Virgin Galactic eventually plan to have a fleet of five SpaceShip Twos, each seating six passengers, which will fly multiple times a day. Although a definite date for the first flight has not yet been released, it is likely to be later this year or early next year. There is a waiting list of over 500 people for SpaceShip Two flights, each of whom has already paid a $20,000 deposit.  At $250,000 for a seat it is hardly cheap, and is well beyond the budget of most ordinary people -including Mr and Mrs Geek. This works out at around $ 7.5 million for for each hour spent in in space!  Nevertheless, as competitors emerge and Virgin Galactic build more spacecraft the price may come down – but I doubt it will be within the reach of ordinary people.

space ship two

Virgin Galactic Space Ship Two in testing -Image provided by Jeff Foust


Next Post

In my next post I will say more about SpaceShip Two and discuss what being a space tourist would really be like.


Living on the Moon



Welcome to the latest post from the Science Geek. This post, which is the final one in a series about the Moon, looks forward to the future and discusses colonising the Moon. Will any future descendants of Mr and Mrs Geek ever live on the Moon? And what are the obstacles to them doing so ?

I hope you enjoy reading it and, as always, please let me know if you have any comments. I would also like to thank Mrs Geek for greatly improving the presentation of my earlier drafts of this post.

Colonising the Moon in science fiction

For centuries novelists have written about humans living and working on the moon. One of my favourite science fiction novels is “A Fall of Moondust”  by the British author Arthur C Clarke (1917-2008). It was written in 1961, before man had ventured  into space and when we knew very little about the Moon’s surface, but set in the 2050s. In the novel the Moon has been colonised, and it is visited by tourists from Earth. One of its attractions is a cruise, in a specially designed boat, across one of the maria, or lunar seas, filled with an extremely fine and very dry dust which flows like water.

Arthur C Clarke

Arthur C Clarke -the author of “A Fall of Moondust” Image provided by Amy Marash

Why would we want to colonise the Moon ?

There are many reasons for building permanent colonies on the Moon.  I have listed a few below which I think are the most important.

  • To ensure the continuation of humanity. One reason, which applies to colonising space generally not just the Moon,  is that while the human species is restricted to life on a single planet it is vulnerable to extinction caused by natural or man made disasters.  If humans could live in a self supporting colony on the Moon, then this would provide a Plan B to allow the continuation of our species.
  • To spread civilisation to other places.  Since humans first evolved, they have constantly sought new territories. It seems to be almost a biological imperative to find other places to live.  There are not many uninhabited places on Earth, so humans may one day extend their civilisation not only to the Moon but also to other places in the solar system such as Mars and the moons of Jupiter and Saturn.
  • It is relatively easy to get to. Compared to Mars, the next most likely candidate, the Moon is much closer to the Earth. The Moon is on average 384,000 km away from Earth, whereas Mars at its closest approach is still around 60,000,000 km away. It is therefore easier, and therefore cheaper, to reach.
  • To stimulate the economy. Despite the enormous cost, building bases on the Moon will give a huge stimulus to the Earth’s economy and there will be many jobs created in high technology industries. There may well be spin-offs that we are not yet aware of, in the same way that the Apollo programme in the sixties and early seventies led to huge technological developments unconnected to space travel such as improved kidney dialysis equipment.
  • There would be no biological impact. The Moon has no indigenous lifeforms which could be damaged by contact with humans.  This is not true of the few uninhabited areas of the Earth, like Antarctica.
  • To exploit resources. In the longer term it may be possible to exploit the minerals found on the Moon, including a rare form of helium called helium-3.  This is more common on the Moon than the Earth and could be used to generate nuclear power, without the radioactive waste produces by conventional uranium-based reactors. (See Notes)

Challenges Faced

Even compared to the most extreme places on Earth, the Moon is a very harsh environment and there are huge challenges to be faced in building a lunar colony.

  • No atmosphere. The Moon has no atmosphere so a human  would need to wear a space suit or they would be dead within minutes.  Death would come not only from a lack of oxygen but also from the fact that any exposed fluids in their tears, saliva and even inside their lungs would quite literally boil away!
  • Deadly radiation. The Moon has almost no magnetic field to shield the surface from cosmic rays from space. There is also no atmosphere, so other deadly radiation such as X-rays can get to the surface and cause damage to human health.  When they left the protection of the Earth’s magnetic field, the Apollo astronauts kept seeing flashes of light even when they were inside their spacecraft with their eyes closed. This was due to cosmic rays passing through the wall of their spacecraft, and into their bodies, including their eyes.  When the rays hit their their retinas, the light sensitive area at the back of their eyes, flashes of light were visible. Exposure to cosmic rays and other forms of harmful radiation greatly increases the risk of developing cancer.
  • Extreme variations in temperature. The Moon rotates much more slowly than the Earth. On the Moon there are 15 days of daylight followed by 15 days of darkness. This, coupled with the lack of an atmosphere which would help to hold heat at night, means that the surface of the Moon is exposed to extreme variations in temperature. At the Moon’s equator over a 30 day period, the temperature ranges from +130 degrees to -140 degrees Celsius.
  • Risk of meteor strikes. On the Earth, meteorites with a mass of around a ton or less burn up in the Earth’s atmosphere before they hit the ground. On the Moon there is no atmosphere in which this can occur, so anything which is attracted by the Moon’s gravity will hit the surface.  Because meteorites move so fast they have a large amount of energy and can therefore do great deal of damage. A  tiny pebble-sized lump of rock weighing  only 10 grammes but travelling at 100,000 km an hour would have the same energy as a huge 10 tonne boulder travelling at 100 km/h (63 mph), and if this were to hit a moon base the results would be catastrophic.

For these reasons, I believe that a moon base would be better built underground where it would be shielded from the aforementioned radiation, meteorite strikes and extreme swings in temperature.

undergound moonbase

An Underground Moon-base


Another factor to consider is the long term impact of low gravity on the human body. This has never been studied before, although studies have been carried out in zero, rather than low, gravity conditions, primarily on astronauts who have spent time on the International Space Station (ISS).

Zero gravity

Astronauts in zero gravity aboard the International Space Station -Image from NASA

When astronauts spend time in zero gravity their muscles weaken because they no longer have to support their weight. For this reason, astronauts in the ISS spend a great deal of time exercising to try and minimise the loss of muscle strength. Also, in zero gravity the body does not need to have strong bones for support. Astronauts’ bodies lose bone matter at the rate of 1.5% per month. After a year in space an astronaut would have lost roughly 20% of their initial bone mass, greatly weakening their skeleton. The minerals lost from their bones are excreted in their urine, which can give rise to kidney stones. After returning to Earth from a long space mission, it can take several years for bones density to return to normal, and astronauts may run the risk of osteoporosis in later life.

Although there is some gravity on the Moon, many of the negative impacts of zero gravity would surely occur, albeit to a lesser degree.  I think it is highly likely that there would be  loss of muscle and bone density if people spent long period of time there.  One solution to prevent long-term damage might be for people to be attached to heavy weights so that they would weigh the same as on Earth. What is also unclear is how the development of young children would proceed. Would a child born and brought up on the Moon have weak muscles and thin bones, which would mean that they would never be able to live on Earth?


The International Space Station – Image from NASA



The International Space Station, pictured above, orbits the Earth less than 500 km above the surface. It  normally holds only six astronauts and is the most expensive single object ever constructed, costing around $150 billion in today’s money. It costs around $5 billion a year to run.  All consumables such as food and water have to be brought up from Earth at great cost.

Building a large moon-base in which hundreds of people could live and work would undoubtedly cost far, far more. I would expect that the costs would be in the trillions of dollars. It would be too expensive for any single nation to afford and its costs- and benefits – would need be shared among all the countries of the world.

The moon-base would have to be as self sufficient as possible, because getting supplies from Earth would be so expensive. It might use the energy from sunlight to grow plants to produce food and oxygen, so that food would not need to imported from Earth. Water is also in very limited supply on the Moon.  Although there are small deposits of ice in areas which are in perpetual shadow, such as the bottoms of craters, this would have to be strictly rationed and recycled.

Given the costs and complexities involved, I would predict that a large moon-base will not be built for at least one hundred years.

Next post

I hope you have enjoyed reading these posts. My next post will be about something more down to Earth.


Many articles have been written about helium-3 mining on the Moon, suggesting that it could be a source of cheap and pollution-free energy.

For example, the Sci Fi  film “Moon” which Mrs Geek and I enjoyed watching a few years ago (although Mrs Geek seems to remember sleeping all the way through it) is set in the year 2035. In the film a large corporation called Lunar Industries have made a great deal of money constructing a large, automated lunar mining base and sending the helium-3 back to  Earth.

Moon 2009 filmjpg

Poster for the 2009 Film “Moon”

In reality, there are still huge obstacles to doing this.  The concentration of Helium-3 found in moonrocks is still very low and it may never be economically viable to extract it . Another point is that although Helium 3 could, in theory, be used to generate clean energy in a nuclear fusion reactor, no one has yet found a way of doing this.