Methane on Mars

I was very excited to read about the discovery published last week by NASA’s Curiosity rover of the seasonal variation in the amount of methane in Mars’ atmosphere. Curiosity found that the average methane concentration varied from 0.24 parts per billion (ppb) in the northern hemisphere winter to around 0.65 ppb in the summer.

This was widely reported in the world’s media e.g.the New York Times.The interesting fact is that, on Mars, methane should have a very short lifetime because it is destroyed by ultraviolet light from the Sun. The presence of any methane in Mars’ atmosphere means that there must be some process, as yet unknown, continually producing it.  On Earth nearly all methane is biological in origin and is generated by microorganisms as a waste product. The seasonal variation in methane in Mars’s atmosphere is certainly consistent with life, but there may be other non-biological processes making this methane.

A joint mission between the European Space Agency (ESA) and the Russian space agency, called the TGO has just started scientific operations and may shed more light on the origin of this methane. I’ve therefore attached an updated version of my earlier post about this spacecraft.


Two years ago on 14 March 2016 the ExoMars Trace Gas Orbiter (TGO) spacecraft was launched from Baikonur, Kazakhstan on a journey to Mars. The purpose of its mission is to study how the distribution of the gas methane varies with location on the planet’s surface and over the course of time.

Trace Gas orbiter

Image from ESA

What is the significance of methane on Mars?

Compared to the Earth, Mars has a very thin atmosphere. Its surface pressure is only 0.6% of that of the Earth. The atmosphere mainly consists of carbon dioxide. However, it also contains a small amount of methane, around 0.5 parts per billion. This is a puzzle to scientists because the ultraviolet light from the Sun should break up any methane within 600 years, and Mars is 4.5 billions old. Therefore there must be some process occurring which is constantly replenishing the methane.


Mars- Image from NASA

There are various possibilities for the origin of this methane. One is that it is released by geological processes such as volcanoes or a chemical process occurring within rocks called serpentinisation. This is not as exciting as it sounds (no snakes, I’m afraid) – it is simply a slow chemical reaction between olivine (a mineral found on Mars) carbon dioxide and water which can produce methane.  Another is that there is a large reservoir of methane locked away in the ice below the Martian surface and as the temperature varies some of the ice may melt, thus releasing the methane into the atmosphere.

A fascinating possibility is that the methane is created by microorganisms below the planet’s surface.  On Earth more than 90% of methane in the atmosphere is produced by living organisms (ESA 2014). There are over 50 species of microorganisms known as methanogens that live off organic matter and produce methane as a waste product.  These microorganisms are found not only in wetlands (producing what is known as marsh gas) and in the soil but also in the guts of many animals such as cows and humans.  At the risk of sounding somewhat vulgar, the methane gas escapes from both cattle and ourselves in the form of flatulence.



What will the TGO measure?

The TGO will measure how the methane content of Mars’s atmosphere varies with space and time. It will also be able to measure the concentration of other gases such as sulphur dioxide (which on Earth is normally associated with volcanic activity) and organic compounds such as ethane, methanol and formaldehyde (which on Earth are produced by living organisms).  Although the TGO won’t be able to say for definite what the sources of the methane found on Mars are, if the concentration of methane were found to vary with the seasons and also if methane were found in conjunction with other organic chemicals it would point towards a biological origin.

How long with the mission be?

The TGO is a joint mission between the European Space Agency (ESA) and the Russian Space Agency (Roscosmos).  The mission is described in more detail on the ESA website  (2018).  It arrived at Mars in October 2016 and was initially placed in a high elliptical orbit around the planet. It took until March 2018 to gradually manoeuvre into the intended orbit and, now it is in the correct position, will spend the next five years mapping the methane distribution. This is a low circular orbit only 400 km from the planet’s surface. The orbit is inclined at an angle of 74 degrees to Mars’s equator. This high inclination enables the spacecraft to see most of the planet’s surface.

The high inclination of the TGO’s orbit means that, as the planet rotates, all area of Mars between latitudes -74 degrees South and 74 degrees North will at some stage be directly below the TGO.

Footnote- Schiaparelli

When the TGO arrived at Mars, it it deployed a small lander called Schiaparelli. This was an ‘add on’ to the main mission and was only designed to operate for a week on the Martian surface. Schiaparelli was intended to measure the wind speed and direction, humidity, pressure and surface temperature, and determine the transparency of the atmosphere. Sadly, when Schiaparelli arrived in the upper regions of the Martian atmosphere, a parachute to slow it down failed to open properly and it crashed into the surface at thousands of km/h and will was destroyed by the impact.


ESA (2014) The enigma of methane on Mars, Available at: (Accessed: 20 March 2016).

ESA (2018) Robotic exploration of Mars, Available at: (Accessed: 12 June 2018)

The Rare Earth hypothesis

Ever since the pioneering work of Frank Drake (1930-) in 1960, astronomers have been looking for radio signals from extraterrestrial civilisations and have failed to find anything. This could be because Earth-like planets containing complex life forms (such as ourselves) are rare in the Universe and only a series of highly improbable events led to the evolution of intelligent life on Earth. In 2000 geologist and palaeontologist Peter Ward and astronomer Donald Brownlee published a book in which they explained the term ‘Rare Earth Hypothesis’ which they had coined to describe this viewpoint.

However, they were not the first people to arrive at this conclusion. These ideas had been circulating for decades before the publication of their book. For example, the astronomers John Barrow and Frank Tipler discussed them in detail in their 1987 book ‘The Anthropic Cosmological Principle’.

A little background – the Drake Equation

Back in 1961, Frank Drake invented an equation to estimate the number of intelligent civilizations within our galaxy with whom we could potentially communicate, to which he gave the symbol N.  His equation, known as the Drake equation, consists of seven numbers multiplied together:

N=  R* x FP x NE x FL x FI x FC x L

in which

  • R* is the average number of stars formed per year in our galaxy. Current estimates are that this has a value of around 10.
  • FP is the fraction of the stars within our galaxy which have a planetary system with one or more planets, expressed on a scale of 0 to 1. A value of 1 means that all stars have planets. 0 would mean that no stars have planets. Current estimates are that FP is very close to 1.
  • NE is for the average number of bodies, either planets or moons of planets, with the right conditions to support life. For this to happen liquid water must exist somewhere on the planet.  A reasonable value which many astronomers would agree with is 0.4, meaning that out of every 10 stars which have planets, 4 have bodies which could support life.
  • FL is the fraction of bodies with the right conditions to support life, on which life actually evolves, expressed on a scale of 0 to 1.  A value of 1 means that on all  planets with the right conditions life will evolve. There is no consensus among astronomers about the value of FL.
  • FI is the fraction of bodies having life, on which life has evolved into intelligent civilisations, again expressed on a scale of 0 to 1. Again, there is no consensus among astronomers about what this value is.
  • FC is the fraction of bodies with intelligent life which develop a technology that releases signs of their existence into space. For example, on Earth TV and radio signals escape into space and could be picked up by a nearby alien intelligence with a sensitive enough receiver tuned to the right frequency. No one knows what the value of FC is.
  • L is the average lifetime of a civilisation in years.  Again, there is no consensus on this point.

As the values of many of the terms in the Drake Equation are not known to any degree of accuracy, it cannot be used to provide a meaningful estimate of N.  However, it is still very useful to illustrate the factors involved

Could we be alone? Could FI could be very very low?

Perhaps the term with the biggest degree of uncertainty in the Drake equation is FI, the fraction of bodies having life on which life has evolved into intelligent civilisations. I will outline the arguments for believing that this number is very low indeed.

The Earth is roughly 4.6 billion years old. Simple single-celled lifeforms emerged 300 million years later, a relatively short time after the Earth had cooled enough for liquid water to exist. These simple cells, called prokaryotes, cannot form complex organisms where different types of cells perform different functions. However, individual prokaryotes  can group together in colonies, forming a kind of slime.

Colonies of prokaryotes

All complex life on Earth is based upon cells called eukaryotes. These cells have a nucleus (containing the genetic material of the cell), structures called mitochondria, which regulate the cell’s energy and other specialised units known as organelles.

The first eukaryotes didn’t emerge until 2 billion years after prokaryotes, indicating that it was a much bigger step in evolution than the emergence of the first simple cells. It could well be the case that the large number of sub-steps needed in the evolution from prokaryotes to eukaryotes means that even where simple lifeforms have emerged,  in the vast majority of cases there has been no further evolution beyond this stage.

Even after the emergence of these complex eukaryotes, it would take over one billion years before multi-cellular life forms such as the first plants and animals appeared. In these organisms cells are specialised, so different types of cells perform different functions within the organism. Given the large amount of time taken to move from eukaryotes to complex organisms, it might well be the case that even if something akin to eukaryotes emerge on a planet, which have the potential to eventually evolve into multi-celled organisms, evolution proceeds no further. The average time taken to evolve from complex cells to multi-celled organisms given favourable conditions might be 2, 5 or even 10 billions years.

The role of mass extinction events

It has taken 600 million years from the appearance of the first animals to the emergence of Homo sapiens in Africa, around 200,000 years ago. Over this vast amount of time the vast majority of species have disappeared and have been replaced by other species which are better suited to the changing environment. However, the disappearance of species and emergence of new ones doesn’t occur at an even rate. Every 50-100 million years there have been catastrophic events which have caused periodic mass extinctions when a large number of species failed to survive. The most dramatic of these was at the end of the Permian period, around 230 million years ago, when 95% of land and 70% of sea species became extinct.

Fossil of a Trilobite – one of many species to disappear in the mass extinction at the end of the Permian Period

Perhaps the best known mass extinction occurred 65 million years ago when a massive comet or asteroid 10 km in diameter hit the Earth at a speed of up 50,000 km per hour. Its high speed coupled with its huge mass meant that it smashed into the Earth in the area now known as the Yucatan peninsula with an energy 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 velocity that it went out into space. Over the next few hours molten rock, dust and ash rained 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 herbivorous animals which fed on those plants became extinct and the carnivores which fed on the herbivores became extinct too. Those species which did survive had their numbers drastically reduced.  Nearly 75% per cent of the species of animals alive before the impact became extinct, including every species of dinosaur. After the disappearance of the large reptiles, mammals became the dominant land animals.

Although we as a species are now probably sufficiently advanced as to be able to survive a mass extinction event, even if only in small numbers, this would not have been the case if one had occurred earlier in our development. If one had happened 150,000 years ago, when Homo sapiens were few in number and less equipped to withstand a major famine – those hunter gatherers would have had nothing to hunt and nothing to gather for many months – we would have become extinct long before we could develop civilisation.

Indeed,  if mass extinctions were to occur every million years, rather than every 50 million years, it is difficult to see how any intelligent species could ever evolve. It would be wiped out before it became fully established. The reason why mass extinctions occur infrequently is due to the unusual layout of the Solar System, and I’ll talk about this next.

Our special Solar System

The Sun is a single star in an uncrowded region of space, in the outer regions of the Milky Way galaxy. The nearest star to the Sun is over 4 light years (40 trillion km) away, more than ten thousand times further than the outermost planet Neptune. If the Sun were in a more crowded region of the galaxy, a passing star’s gravity could easily disrupt the Earth into a different orbit, which might be closer to Sun, making it too hot to support life, or further away, making it too cold to support life.

The giant planet Jupiter is more than 300 times the mass of the Earth. As comets enter the inner Solar System from its outer reaches, Jupiter’s gravity slings most of these fast-moving ice balls out of the Solar System before they can get close to Earth.  Without Jupiter, comets like the one which hit the Earth 65 million years ago would collide with our planet much more frequently.

Image from NASA

Observations of planets detected around other stars have shown that arrangements of planets similar to our Solar System, with small inner rocky planets surrounded by massive giants in the outer reaches, are relatively rare.

Another factor which may be essential to the emergence of complex lifeforms is the presence of a large moon close to the planet. The Moon is 25% of the Earth’s diameter and is only 400 000 km away, a very short distance in astronomical terms.

Relative sizes of the Earth and the Moon

The Moon  is much larger in comparison to its parent planet than any other moon in the Solar System. This means that the Moon’s gravity stabilises the Earth’s tilt so that it doesn’t vary too much from its current value. Without the Moon there would be massive swings in the tilt between 0 degrees, when there would be no seasons, and 50 degrees, where there would be extreme seasons where much of the planet would be in darkness or full daylight for months at a time.

The Earth’s magnetic field

The Earth’s magnetic field is generated by convection currents stirred up by rotation in its liquid outer core, which is made out of iron. In fact for any planet to have a strong magnetic field, part of its interior must consist of a liquid which conducts electricity and it must be rotating rapidly enough to generate convection currents.

Earth Interior

Without a magnetic field the planet would not have a protective ozone layer shielding its surface from deadly ultraviolet radiation. It would be very difficult for advanced lifeforms to exist on the surface.  It is not known how many planets around other stars satisfy the criteria to have a magnetic field. However, the Earth is the only one of the inner planets in our Solar System (Mercury, Venus, Earth and Mars) to have a strong magnetic field.

Planetary size

In order for life to evolve, the planet must be large enough to retain a significant  atmosphere, without which liquid water cannot exist. Mars is roughly one tenth the mass of the Earth and its gravity is so low that its atmospheric pressure is only 0.6% of that of Earth – too low for liquid water to exist.

Man has been lucky to survive

In addition to periodic mass extinctions which wipe out most species, all populations come under pressure due to sudden changes in climate, such as ice ages, major volcanic eruptions, loss of habitat, disease and competition from other species for food and shelter. The first Homo sapiens were confined to a single region of Africa and were few in number, and thus vulnerable to becoming extinct. 70,000 years ago a super-volcano erupted in Indonesia causing the Sun to be partially blocked out and resulting in a fall in global temperatures. Only an estimated 15,000 humans are thought to have survived (Edwards 2010).


If we take all the factors I’ve talked about into account, for single-cell organisms to evolve into intelligent lifeforms capable of building civilisations, all of the following must happen.

  • Single cell creatures must have evolved in into complex cells, something akin to eukaryotes.
  • To reduce the frequency of mass extinctions, the planetary system must have a large giant planet in its outer reaches.
  • To ensure the planet remains at a habitable temperature, the parent star must be a single star in a less crowded region of the galaxy.
  • To ensure the planet remains at a habitable temperature over a long period of time, the parent star’s energy output must not vary too much.  This constraint rules out advanced life around the most common type of star in the galaxy, red dwarfs .
  • To reduce the frequency of dramatic changes in climate leading to mass extinctions, the planet must have a large satellite.
  • The planet must rotate rapidly enough to generate a magnetic field, as without this complex life would not be possible on its surface.
  • The planet must be large enough to hold an atmosphere.
  • Multi cellular organisms must have evolved.
  • The planet must have a significant fraction of its surface as dry land. The assumption is that although aquatic creature such as dolphins are undoubtedly intelligent, only land based creatures could build civilisations.
  • A land-based intelligent species has emerged during a survival of the fittest.
  • The intelligent species has managed to survive major environmental changes such as ice ages and has built a civilisation.

Putting all these together, followers of the Rare Earth hypothesis believe that the probability of all the above happening on a planet on which simple life has evolved could be as low as a billion to one.

If it were this low, then the expected number of intelligent communicating civilisations in a galaxy such as ours would be very low.  If the disputed figures within the Drake equation were guessed to be on the low side, N could be as low as 0.000016.  This would mean that not only are we the only intelligent communicating civilisation in our own Milky Way galaxy, but also that there are none in any galaxies within tens of millions of light years of us.

If this is the case then the Earth would not be just be an ordinary planet orbiting an ordinary star in an ordinary galaxy.  It would be a very special place indeed!

I hope you have enjoyed this post. To find out more about the Science Geek’s blog, click here or at the Science Geek Home link at the top of this page.


Edwards, L. (2010) Human were once an endangered species, Available at: (Accessed: 7 April 2018).



A Christmas gift from The Science Geek 2017


Christmas is almost upon us. Once again I’m offering my e-books for free during the first five days of December!  Just call me Father Christmas :-).

Is Anyone Out There?” is about the likelihood of there being extraterrestrial intelligent life.  It is based on a number of posts from my blog.  For readers based in the UK the book is available to download from Amazon in Kindle format by clicking here and for readers in the US by clicking here. If you’re based outside the UK or US , see the notes at the end of the post.

Is Anyone Out There Cover

The Moon” is also based on a series of posts from my blog and you can guess what it is about.  UK readers download here, US readers here and anyone else please see the notes below.

Moon Cover

How to download the books if you’re based outside the UK or US.

There are threeways of doing this.

Option 1 if you go into the Amazon Kindle store and search for “The Science Geek” as the author you should find my books.

Option 2  I have created a page on my website where you will be able to download either of books for free.

I’ll put them there until at least the end of the year.

Option 3  If your country is listed below, I have added some links  to allow you to download the books by just clicking on the link for your country.

Is There Anyone Out There?













The Moon













Voyager 40th anniversary

Nearly 40 years ago, on 20 August 1977, the Voyager 2 space probe was launched from Cape Canaveral, Florida, on a mission to study the Solar System’s four outermost planets. It was followed 15 days later by the launch of an identical spacecraft, Voyager 1.

The Voyager spacecraft -Image from NASA

Although Voyager 1 was launched after Voyager 2, it followed a different path which meant that it actually visited its first target, the planet Jupiter, four months earlier.

Image from Wikimedia Commons

The diagram above shows the trajectory of the Voyager spacecraft. The first targets, the giant planets Jupiter and Saturn, had previously been visited by NASA’s Pioneer 10 and 11 spacecraft, but the Voyagers had better instruments and were able to take more accurate observations. Among the discoveries made by Voyager was that Io, one of Jupiter’s moons, has a number of active volcanoes. This made Io the first place other than the Earth where volcanoes had been seen to erupt.

Jupiter’s moon Io – Image from NASA

Voyager 1 passed close to Saturn’s giant moon Titan. Titan is 5,150 km in diameter, nearly twice as large as the Moon, and is in fact slightly larger than the planet Mercury. It is the only moon in the Solar System with a thick atmosphere, which surrounds it with a dense haze hundreds of kilometres deep, making it impossible to see any surface details. At Titan’s surface the atmospheric density is roughly 5 times greater than the Earth’s at sea level.  Voyager 1 discovered that it consists mainly of nitrogen (98.4%) and methane (1.4%) with trace amounts of other gases such as ethane.

Saturn’s moon Titan – Image from NASA

These discoveries led to speculation that, like Earth, Titan has complex weather patterns. Being so far from the Sun, Titan’s surface is very cold, around minus 180 degrees.  This temperature is near the boiling point of hydrocarbons such as ethane and methane, which on Earth are found in natural gas. Voyager 1’s discoveries suggested that on Titan it rains liquid hydrocarbons in a similar way to how it rains water on Earth and that there were lakes of liquid hydrocarbons on Titan’s surface. A later mission by the spacecraft Cassini to Saturn and its moons did indeed detect many lakes of liquid methane on Titan (NASA 2016).

After passing Saturn, Voyager 2 visited the two outermost planets Uranus and Neptune (shown below).

Neptune – image from NASA

Uranus and Neptune are of similar size and are both much smaller than the gas giants Jupiter and Saturn. They are mainly composed of frozen water, ammonia and methane and are sometimes called the “ice giants”  So far Voyager 2 is the only mission to have visited the ice giants and most of what we know about Uranus and Neptune came from this spacecraft. No further missions to Uranus or Neptune are planned. Although it is possible that a mission to the ice giants could be launched by NASA in the the 2030s (Clark 2015), this is very much at the proposal stage. I think that this won’t happen, given the high cost of space missions and other higher priority targets such as exploring Mars.

After completing their primary mission to study the outer planets, the Voyagers left the Solar System. They are still in contact with Earth and are now sending back data about interstellar space. For more details on this part of the Voyagers’ mission click here.

The golden record

Each Voyager contained a golden record, the cover of which is shown below.

Voyager Record Cover

Image from NASA

The purpose of the golden record was twofold. If either of the Voyager spacecraft were ever found by an alien intelligence in the far future then, as I’ll explain later, from the golden record cover they would be able to work out the location of the Sun within the galaxy and, by playing the record, get some information about the sounds and sights of Earth in the 1970s.

If you look at the bottom left hand corner of the golden record cover there is a small circle with 15 lines coming out of it. This is shown in more detail in the diagram below.

This diagram was also put on a plaque on the earlier Pioneer probes and was devised by Frank Drake (1930-), who has been heavily involved in the search for extraterrestrial intelligence (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 and the length of the line between the Sun and the pulsar represents the distance to the pulsar.

Pulsars are rapidly rotating objects which emit radio waves in regular pulses a few seconds or fractions of a second apart. Each pulsar has its own distinct interval or period between pulses and the marks drawn on the lines depict the length of the pulsar period not in seconds but in multiples of a fundamental time unit that an alien might understand (see note below).  The alien civilisation could then have sufficient information to identify the fourteen pulsars and the distance of the Sun from each pulsar, and thus work out the location of our Solar system.

On the upper part of the golden record cover is a picture of the record itself plus instructions for playing it.

Voyager Record

Image from NASA

The content of the record was agreed by a committee chaired by Carl Sagan (1934-1996) itself, and 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?

As well as the two Voyagers, three other spacecraft have been launched on a trajectory to take them out of the Solar System. They are New Horizons, which passed the dwarf planet Pluto in 2015 and Pioneer 10 and 11, which were the first spacecraft launched to leave the solar system. As you can see from the table, the Pioneer spacecraft  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. The Voyager spacecraft are still in contact and should have enough power to continue transmitting messages back to the Earth until the mid 2020s.


In the table, the distance of the probes 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 fast the spacecraft is moving away from the Sun in AU per year.

Will the Voyagers ever be found?

Even astronomers who think that alien life is widespread within our galaxy think that it is very unlikely, given the vastness of space, that the Voyager spacecraft will ever be found.  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. However if they were ever to be intercepted by an alien civilisation it is fascinating to think what they would make of them.

Note about the pulsar diagram

Clearly units of time such as hours, minutes and seconds, which have been invented by humans, would be meaningless to an alien. Atomic hydrogen is the most common element in the Universe and Drake used the transition of a hydrogen atom, shown on the bottom right hand corner of the record cover, to create a “fundamental time unit” which he hoped an extraterrestrial race would understand.  When a hydrogen atom flips from one state to another it emits radio waves at a frequency of 1,420,406,000 waves per second, a fact that any advanced civilisation would be well aware of. So each individual wave 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.


Clark, S (2015) Uranus, Neptune in NASA’s sights for new robotic mission, Available at: (Accessed: 15 June 2017).

NASA (2016) Cassini explores a methane sea on Titan, Available at: (Accessed: 15 June 2017).


Life in our galaxy?

With the recent discovery of three planets orbiting the red dwarf star Trappist-1 which have a similar size, mass and average surface temperature as the Earth, there has been considerable speculation as to whether one or more of these planets supports life.

What the surface of Trappist 1f, one of the planets orbiting Trappist 1, might look like – Image from NASA

Although there are challenges to complex lifetime forms  evolving on a planet around a red dwarf – which I discussed in a previous post – red dwarfs are the most common type of star in our galaxy. In this post I’ll discuss the likelihood that life has evolved in other places within our galaxy, including on planets around red dwarfs.

The Drake Equation

Frank Drake (1930-) is an American astronomer who is known as the ‘father of SETI’ – the Search for Extra Terrestrial Intelligence. Beginning in 1960, he was the first person to search for radio signals from aliens.

.  FrankDrake

Frank Drake- Image from Wikimedia Common 

In 1961 he invented an equation to estimate the number of intelligent civilizations within our galaxy with whom we could potentially communicate, to which he gave the symbol N.  This equation, which is known as the Drake equation, consists of seven numbers multiplied together:

N=  R*  x  FP  x  NE x FL x FI x FC x L

As I’ll explain below, some of these numbers are known to a reasonable accuracy, whereas others are not well known and astronomers differ widely their views of what the values should be.

  • R* is the average number of stars formed per year in our galaxy.  Current estimates are that this has a value of around 10.
  • FP is the fraction of the stars within our galaxy which have a planetary system with one or more planets, expressed on a scale of 0 to 1. A value of 1 means that all stars have planets. 0 would mean that no stars have planets. Planets are difficult to detect around other stars, because they are far too faint to be seen directly and have to be detected by other techniques. In 1961 Drake estimated that FP lay in the region of 0.2 to 0.5 (i.e between 20% and 50% of stars had planets). Current estimates are somewhat higher and that FP is very close to 1.
  • NE is for the average number of bodies, either planets or moons of planets, with the right conditions to support life. Current estimates for this vary considerably.  If most stars were like Trappist-1 then this value would be as high as 3. A reasonable value, which many astronomers would agree with, is 0.4, meaning that out of every 10 stars which have planets, 4 have bodies which could support life.

The Trappist-1 system – image from NASA

  • FL is the fraction of bodies, with the right conditions to support life, on which life actually evolves, expressed on a scale of 0 to 1.  A value of 1 means that on all  planets with the right conditions life will evolve. There is no consensus among astronomers about the value of FL. If, in the future, life is found in many other places in our solar system which have the right conditions  e.g. Mars, or in the warm underground oceans of Saturn’s moon Enceladus (see here for more information) then it would be reasonable to assume that, given the right conditions, in general life will evolve and FL is nearly 1 (see note 1).

Enceladus Ice Volcano

A geyser of warm water erupting from an underground ocean on Enceladus. Image from NASA

  • FI is the fraction of bodies having life, on which life has evolved into intelligent civilisations, expressed on a scale of 0 to 1. Again, there is no consensus among astronomers about what this value should be. Enthusiasts for extra terrestrial intelligence such as Drake believe that the value is close to 1, meaning that intelligent life will always evolve. Others, who believe that it was a highly improbable chain of events which led to the eventual evolution of man from single celled creatures, believe the value is very low.
  • FC is the fraction of bodies with intelligent life which develop a technology that releases signs of their existence into space. For example, on Earth TV and radio signals escape into space and could be picked up by a nearby alien intelligence with a sensitive enough receiver tuned to the right frequency. No one knows what the value of FC is, but current estimates are around 0.2.
  • L is the average lifetime of a civilisation in years. This could be very short if civilisations end up destroying themselves once they have discovered nuclear weapons – or it could be hundreds of millions of years.

The Optimists’ View.

As said previously, no one really knows what the values of most of the terms in the Drake equation are. If we go for values at the high end (FP= 1, NE=0.4, FL=1, FI=1, FC=0.2, L= 100 million) then we get the following:

N= 10 x 1 x 0.4 x 1 x 1 x 0.2 x 100,000,000

which works out as 80 million intelligent communicating civilisations in our galaxy!

One of the problems with such a large number is that we would expect a significant fraction of civilisations to be more advanced than us. Humans have only been civilised for a few thousand years and have already travelled into space.  If a civilisation had been around for more than 1 million years, for example, it is likely that they would have developed the ability to travel the vast distances to other planetary systems and would have already attempted to make contact with us. The fact that they haven’t may mean that civilisations much more advanced than us are rare.

It is also possible (although in my opinion extremely unlikely) that intelligent civilisations do exist and have been observing our planet for a long period of time. They deliberately do not contact us to avoid interfering with our development although they may decide to reveal themselves to us when we reach a certain level of development. This is known as the zoo hypothesis and has appeared in many science fiction stories.

What is clear is that for nearly 60 years, since the pioneering work of Drake in 1960, astronomers have been looking for radio signals from nearby civilisations over a wide range of radio frequencies and have failed to find anything.

Could we be alone ?

Other astronomers believe that some of the values in the Drake equation are very low. There are a large number of steps which occurred between the emergence of the first primitive single-celled life forms and the evolution of man. Each of the individual steps may have a very low probability. So FI the probability of life evolving into intelligent civilisations would be extremely small. For most of the Earth’s lifetime there were only single-celled organisms and, perhaps on most places where life emerges, it never gets beyond this point.

Another point is that mammals only become became the dominant life form after the extinction of the dinosaurs 65 millions years ago. Before that large small-brained reptiles were the dominant life form. Having greater intelligence does not always give an advantage over other traits such as size, speed and physical strength in the survival of the fittest.  There is therefore no guarantee that evolution will result in life forms with the intelligence necessary to develop civilisations.

In addition, dramatic events such as sudden changes in climate can cause any species to become extinct. Roughly 70,000 years ago, an enormous eruption occurred in what is now Sumatra, leaving behind Lake Toba. This triggered a major environmental change which caused the near extinction of the human race.  Humanity could have easily disappeared at this point. Although this has been recently disputed (BBC 2010).


Lake Toba, site of a supervolcano eruption 70,000 years ago – Image from Wikimedia Commons

For these reasons some scientists, such as the British theoretical physicist and popular science writer John Barrow, believe that FI could be around 0.000000001 or even lower. If it were this low, and we take the low end values for for the other parameters, then the expected number of intelligent communicating civilizations in the galaxy would be 0.000016. What this means that if we took 60,000 galaxies similar to our own Milky Way we would on average expect to find only one communicating civilisation. Ourselves!

If this is the case then the Earth would not be just be an ordinary planet orbiting an ordinary star in an ordinary galaxy.  It would be a very special place indeed, for it would be the only place for tens of millions of light years where intelligent life exists.


1 The Earth was formed about 4.6 billion year ago, and at first its temperature was thousands of degrees – far too hot for life to exist.  The first life forms appeared relatively early in the Earth’s history, when it was less than 1 billion years old when conditions became cool enough for life to exist.  This might seem to indicate that, if conditions are right, then life will evolve relatively quickly. Indicating that, perhaps, FL is close to 1.


BBC (2010) Toba super-volcano catastrophe idea ‘dismissed’, Available at: (Accessed: 15 Apr 2015).

Enceladus -Could there be life?

Three years ago my first ever post was about Saturn’s moon Enceladus. It is interesting that once again this small moon is in the headlines as a possible place on which there could be life.

The Science Geek

The Science Geek


Hello and welcome to the first post from the Science Geek 01. I intend to write  a weekly blog about various topics of interest, which will cover all aspects of science. The articles will be aimed at the non scientist and won’t require any previous detailed knowledge. I hope you enjoy reading them and please feel free to comment.

My first posts will deal with the subject of life within the solar system, which in astronomical terms is our own backyard.

Life on Mars

Throughout most of the twentieth century many scientists thought that there could be life on Mars. Indeed the famous American astronomer Percival Lowell (1855-1916) claimed to have seen through his telescope  a large network of canals built by an intelligent civilization  and even produced maps of the Martian canal network. These  canals certainly provided great material for science fiction writers but they were probably all due to Lowell’s imagination!

Percival Lowell’s Martian…

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The Trappist-1 system

I am sure that many of you will be aware of the discovery announced in February this year of seven Earth-sized planets orbiting a small cool star known as Trappist-1. (Gillon et al 2017). In this post I’ll talk about this exciting finding and the possibility that some of these planets might support life.

Trappist-1 and its planets were discovered and named by a team from the University of Liege in Belgium, using a telescope which is itself called TRAPPIST – the TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST) in Chile.

The team discovered the planets through their study of the way the light from Trappist-1 varies over time. Planets other than those in our solar system are known as exoplanets, and all exoplanets are much too faint to be seen directly from Earth.  However,  as shown in the diagram below, as a exoplanet passes in front of a star the brightness of the star dims because some of its light is blocked from reaching the Earth.


The interval between each time that the star is at its faintest is the same as the period of time it takes for the planet to orbit the star.

If the mass of the star is known then the distance of the planet from the star can be calculated by a relationship known as Kepler’s Law.  Clearly, the larger the planet the more of the star’s light is blocked out. The amount by which the star’s light is dimmed gives a measure of the diameter of the planet.  The mass of the planet can be determined by the strength of its gravitational pull on the star. This gravitational pull causes the star to wobble slightly.

The observations of the light from Trappist-1 are shown in the diagram below.  This shows that its brightness periodically falls due to its light being blocked by seven orbiting planets, which are labelled 1b to 1h.  The planet 1b is closest to the star and has the shortest period and 1h is the furthest away and has the longest period.  Mrs Geek, my talented proofreader and dearest companion, wonders what happened to planet 1a, but I’m afraid I have no idea.


Image from ESO

When the distances were estimated, three of the planets, 1e, 1f and 1g , turned out to be within the “habitable zone” meaning that they are at such a distance from the star that the temperatures are likely to be similar to those found on Earth. This exciting finding, coupled with the fact that all three of these planets are a similar size to the Earth, led to speculation that one or more of these planets might support life and perhaps even that intelligent life could have evolved.


The Trappist-1  system – Image from NASA.

The diagram above shows the Trappist-1 system. Underneath each planet  there are four numbers:

  • the length of time it takes to orbit the star, in days
  • the distance from the star, in astronomical units (1 AU is the mean distance from the Earth to the Sun).
  • the diameter of the planet, on a scale where Earth=1
  • the mass of the planet, on a scale where the Earth=1.


Life around a red dwarf?

Trappist-1 is a very different star to the Sun. It is a small compact star known as a red dwarf.  It is only 11% of the diameter and 8% of the mass of the Sun.  If Trappist-1 consumed its nuclear fuel at the same rate as the Sun, it would be  8% as bright as the Sun (because it is 8% of the mass of of the Sun). However it burns at a much lower rate and is only 0.05% as bright as the Sun. This slow burning means that it will shine for a long time. The predicted lifetime of Trappist-1 is around 10 trillion years, one thousand times longer than the Sun.

Because Trappist-1 is such a cool dim star compared to the Sun, the habitable zone is very close to the star. It lies in the region roughly 0.025 to 0.05 AU from it. For comparison,  Mercury, the innermost planet in our solar system, lies 0.4 AU from the Sun. When a planet orbits so close to a star it will become what astronomers call tidally locked. This means that one side of the planet always faces the star and the side other always faces away, in the same way that one side of the Moon faces the Earth and the other faces away.

The diagram above shows one of the planets orbiting Trappist-1. On the side of the planet facing Trappist-1 (marked with a ‘Y’) the sun would never set and it would always be daylight, and temperatures would be very high. At the point on the equator where the sun was directly overhead  the temperature might be well above the boiling point of water. On the other side of the planet (marked with an ‘X’)  the sun would never rise. It would always be dark and the temperatures would get very low, possibly hundreds of degrees below freezing (see notes).The region where the temperatures would be closest to those found on Earth would be on the edge of the daylight side or at high latitudes. Here, although the sun would always be above the horizon, it would be low in the sky, so it would not get too hot.

These huge temperature differentials across the planet would be likely to cause extreme weather conditions with very strong winds. Although this might not be a barrier to small simple lifeforms, like single celled organisms, it would be difficult for larger organisms to live on the planet’s surface.

What the surface of Trappist 1f might look like – Image from NASA

There are other factors which make the evolution of larger life forms more difficult. One is the star’s variability. Unlike the Sun, whose brightness is fairly constant,  the amount of energy emitted by red dwarfs rises or falls by as much as 50% over short timescales. This could cause huge swings in temperature which would obviously present challenges to larger and more complicated life forms.

Like all red dwarfs, Trappist 1 has a much lower surface temperature than the Sun. It is only 2,300 degrees C, compared to the Sun’s 5,500 degrees C. This lower temperature means that most of its energy is emitted as infrared radiation, rather than visible light.

This has practical effects to the evolution of life. As you may recall from high school biology, on Earth plants contain a pigment called chlorophyll.  This is used in photosynthesis, in which the energy in visible light is used to convert carbon dioxide and water into sugars and starches, at the same time releasing oxygen. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth’s atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth.

On Trappist-1 plant life would have to use a different chemical other than chlorophyll for photosynthesis. This chemical would be  sensitive to infrared rather than visible light. Similarly if any animal-like creatures existed they would have evolved eyes to see in infrared and might  be unable to see in visible light, in the same way that our eyes cannot see in ultraviolet.

Could there be intelligent civilisation around red dwarf stars?

There  are clearly significant challenges to advanced life evolving in planets around red dwarfs, even if the planets are Earth-like. However, there is one thing in their favour. Red dwarf are by far the most common type of stars, making up roughly 80% of the stars in the galaxy. Only 5% of stars in the galaxies are the same type as the Sun, which astronomers call a “spectral class G” star. In fact in 100 billion years time when all the larger stars have burnt their nuclear fuel, the slow burning red dwarfs will be the only type of stars left.

I will talk more about the possibilities of life around red dwarfs in my next post.


Strictly speaking, it is not true that one side of the planet is always dark and the other always in daylight. This is only correct if the planet moves in a perfectly circular orbit around Trappist 1.

If it orbits in an elliptical, or oval-shaped, orbit, then for a small region of the planet around the boundary between the always in daylight and always night sides,  the sun would drop just below the horizon and appear shortly afterwards, giving a day and night cycle.


Gillon M, Triaud A, Demory B, Jehin E, Agol E, Deck E, Lederer S, et al (2017) Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1,Available at: 9 Apr 2017).