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

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.

Notes

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.

Reference

BBC (2010) Toba super-volcano catastrophe idea ‘dismissed’, Available at:http://www.bbc.co.uk/news/science-environment-22355515 (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.

https://www.nasa.gov/press-release/nasa-missions-provide-new-insights-into-ocean-worlds-in-our-solar-system

The Science Geek

The Science Geek

Welcome

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…

View original post 492 more words

Enceladus Flyby 28 Oct 2015

On 28 October 2015 the space probe Cassini, which has been orbiting Saturn for the last 10 years, will pass within 50 km of the surface of Saturn’s moon Enceladus. This is an extremely close approach by an interplanetary spacecraft (by comparison the New Horizons mission only got as close as 12,500 km above the surface of Pluto) and will help us understand more about this icy moon.

Cassini spacecraft

Image from NASA

This post discusses this flyby and explains why, in many ways, Enceladus might be a better bet than Mars for finding life in our solar system.

Early views of extraterrestrial life

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 Canals

Mars Canals

A Cold Dry Mars

Hopes of life on Mars were dealt a big blow in the 1960s when the American and Soviet space probes showed that it is a very dry, cold, hostile world.

Most biologists believe that liquid water is needed for life to emerge and prosper. The atmospheric pressure on Mars was discovered to be less than 1% of the pressure of the Earth’s atmosphere, which is far too low to allow liquid water to exist and the lack of an atmospheric “blanket” means  the night temperatures are very low. Even in summer at the equator it drops to -70 degrees C (ref1). Unlike the Earth, Mars does not have a significant magnetic field to protect the surface of the planet from deadly radiation. Therefore it is very unlikely that life could exist on the surface of Mars, although it is possible that primitive life forms could exist within rocks.

Another Candidate for Life

However in the last ten years another place where life could exist has emerged,   Enceladus. It might at first sight appear to be an odd candidate. It is nearly ten times further away from the Sun than the Earth. At this distance the Sun’s energy is so weak that the surface temperature is on average -200 degrees Celsius. In addition it is very small, only 500 km in diameter, which is only 14% of the diameter of the Earth’s own moon.  Because it is so small, the mass of Enceladus is so low that the surface gravity is only 1.1 per cent of the Earth’s gravity. So, on the surface of  Enceladus a 12 stone (168 pound) astronaut would weigh only two pounds.

The weak gravity means that Enceladus should be unable to hold onto any form of atmosphere. Any gases should escape into space. It also has no magnetic field to shield its surface from lethal radiation. So it is safe to assume that it is impossible for life to exist on the surface of Enceladus.

Enceladus

enceladus_comparison

Images courtesy of NASA

However, previous flybys by the NASA Cassini space probe yielded  surprising results. They detected a thin atmosphere containing over 90 per cent water vapour together with trace amounts of nitrogen, carbon dioxide and methane. This atmosphere is thought to emanate from the volcanoes spotted by Cassini which pump large amounts of water vapour and other gases onto the surface of Enceladus, replenishing the gases which continually escape to space. In the same way, as the volcanoes on Earth sit over pockets of molten magma deep underground, the volcanoes on Enceladus, known as cryovolcanoes because they are so cold, form over pockets of water.

ice volcanos

 Image courtesy of Gordon P. Hemsley

Indeed many scientists strongly believe that for billions of years there have been warm underground oceans under the surface of Enceladus which contain the basic chemicals such as methane, formaldehyde, ammonia and carbon dioxide which are needed to form the more complex chemicals which are building blocks for the evolution of life.

However this does not mean that we expect to see fish swimming in these underground oceans! What is more likely is that, given water, an underground heat source and  the raw chemicals, something more akin to single celled creatures and bacteria may have evolved on Enceladus.

What will the October 28 Flyby tell us?

The flyby will bring the spacecraft within 50 km of Enceladus’s  surface near its South pole. It will pass through one of the icy volcanic plumes and its instruments will sniff the gases in the plume which will give a measure of the amount of hydrothermal activity going on.  If there is a lot of hydrothermal activity then this could provide an energy source for life. It has a dust detector which will enable it to study the complex organic molecules found in the plume.

Unfortunately Cassini doesn’t have the instruments to detect life. That will have to wait until a future mission which may land on the surface and drill through the ice.

For information on the Enceladus flyby see the following link

http://saturn.jpl.nasa.gov/mission/flybys/enceladus20151028/

 

References

  1. http://www.space.com/16907-what-is-the-temperature-of-mars.html

 

 

 

Is There Anyone Out There ?

As a child I was fascinated by the idea of people from Earth encountering alien lifeforms. I was an avid watcher of Star Trek and the British science fiction TV shows Dr Who and Blake’s 7.  I am not alone in my fascination – the idea of humans making contact with intelligent aliens from other planets has intrigued people for hundred of years and has been taken up by huge numbers of writers and film-makers. Films such as the Star Trek series, Star Wars, Close Encounters of the Third Kind, Alien and E.T. have been great successes at the box office.

Blakes7

An alien from the 1970s BBC TV science fiction series Blake’s 7

The Earth is one of eight planets which orbit the Sun. The Sun is an ordinary star among the 100 billion or so stars in our Milky Way galaxy.  The Milky Way itself is an average-size galaxy. To me one of the most fascinating questions is this: how likely is it that there are other intelligent civilizations within our galaxy ?

Milky Way from outside

The Milky Way- Image from ESO

Our galaxy the Milky Way. The picture above shows what our galaxy would look like if we were to look at it face on from  a distance of hundreds of thousands of light years away. See notes at the end of the post for what is meant by a light year.

Drake’s Equation and the seven numbers

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

.  FrankDrake

Frank Drake- Image from Wikimedia Common (Raphael Perrino)

In 1961 he invented an equation to estimate the number of intelligent civilizations within our galaxy that we could communicate with, which he gave the symbol N.  To arrive at N,  Drake multiplied together seven other numbers.

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

Drake’s seven numbers are follows:

  • R* is the number of average number of stars formed per year in our galaxy. This has a value of about 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 means that no stars have planets. Current estimates are around 0.2 to 0.5.
  • NE is the average number of bodies, either planets or moons of planets, with the right conditions to support life. Current estimates for this vary widely, but it is sometimes considered to have a value of 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. If, in the future, life is found in 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.

 

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= 0.5, NE=0.4, FL=1, FI=1, FC=0.2, L= 100 million) then we get the following:

N= 10 x 0.5 x 0.4 x 1 x 1 x 0.2 x 100,000,000

which works out as 40 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.

Indeed for over fifty 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 planets where there is life, it never gets beyond this point.

Another point is that mammals only become became the dominant lifeform 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. At one stage there were only 2000 individual humans alive on the planet.

Lake_Toba

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.

Next Post

I hope you have enjoyed reading this.  In my next post, I’ll be talking about the work which has been done so far to search for extraterrestrial intelligence.

Notes

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. The distance from the Earth to the Sun is 0.000016 light years and the nearest star other than the Sun is 4.2 light years away. The centre of our galaxy is 26,000 light years away and the galaxy itself is 100,000 light years in diameter.

How Would We Get to Enceladus ?

 

Introduction

Welcome to the third post  from the Science Geek. This post continues my previous two posts and discusses how we might get to Saturn’s moon Enceladus, which many scientists now believe is the most likely place in the solar system, other than the Earth, to harbour life.

Enceladus

 

Image from NASA

Types of mission 

There are two types of mission to Enceladus: a one way trip and a return trip.

(a) the one way trip

As said in my previous post, NASA’s Cassini mission (http://saturn.jpl.nasa.gov/mission/introduction/) was launched in 1997 and arrived at Saturn in 2004 to study the planet and its moons.  It has already flown past Enceladus a number of times. A few more flybys are planned before the mission ends in 2017 and one in particular, in October 2015, is scheduled fly only 50 km above its surface.

A new mission could fly much closer to the “water volcanoes” than the current Cassini mission, and might even fly through one while it was erupting. It could have specific experiments to look for life, and more up to date instruments to analyse the chemical contents of the volcanic plumes in more detail. The mission could land on the surface, perhaps near one of the water volcanoes and analyse material which had gathered nearby.

(b) the return trip

Another more exciting possibility would be to have a return mission which would land on Enceladus, capture some material, and then return it back to Earth. At the moment such a mission is sadly beyond the technical capabilities of any nation – a sample return mission has still not been attempted for the planet Mars which is much closer and thus far easier to get to than Enceladus. However, technology is continually evolving and such a mission might be feasible in 80 to 100 years time. The Science Geek is very unlikely to be around to see it!

How Long Would the Mission take?

The mission would probably take a similar amount of time to reach Saturn as did the Cassini space probe which is currently in the area. This was launched in October 1997 and arrived at Saturn in July 2004, nearly seven years later. Cassini’s trajectory is shown in the diagram below:

Cassini TrajectoryC

Cassini Trajectory (from the NASA website)

As you can see from the picture above, the mission used the gravity of the planet Jupiter (see Notes below) to attract the probe, speed it up and ‘slingshot’ it onto Saturn. Using the slingshot, or to be more precise, ‘gravitational assist’, means that the gravitational field of Jupiter does much of the work. This has cost implications for the mission: because the spacecraft needs to contain less fuel, it is much lighter, so the rocket required to launch it into space is smaller – and therefore cheaper.

There have been four missions so far to Saturn and all four spacecraft have used the gravitational assist.  Indeed I would go so far as to say that, using today’s rocket technology, it would not be possible to launch a complex spacecraft to Saturn without using a Jupiter gravitational assist. The costs would be astronomical.

Limitations of the Gravitational Assist

The limitation of the gravitational assist is that Jupiter and Saturn need to be in the correct alignment for it work and this only happens every 20 years. The last time was in 2000, the next opportunity will be in the year 2020, and the one after will be in 2040.

Because it always  takes at least five years to get from the financial approval of a mission to the actual launch date, plus up to three years to get to from Earth to Jupiter, we have missed the opportunity of using Jupiter to perform the gravitational assist in 2020. So any mission to Enceladus will have to wait until Jupiter is correctly aligned with Saturn in 2040, meaning that the spacecraft could leave Earth around 2037 in order to reach Jupiter in time.  It would then arrive at Saturn around 2044.

In Summary

At the moment although the Cassini spacecraft is performing a few more flybys of Enceladus, there are no further mission there planned by any nation. I think this is great pity since it is such a promising place where there could well be life.  I hope that a mission to go there is given approval and that a space probe arrives at Enceladus in the mid 2040s, with all the instruments on board to see what kind of life exists.

Notes

* Cassini actually performed two flybys of Venus and one of Earth, bfore heading to Jupiter. Although this meant that the spacecraft took longer to reach Jupiter than if it had flown there directly, it meant that the amount of fuel needed was kept to a minimum, thus reducing the overall costs of the mission.

 

Enceladus what kind of life ?

As stated in my previous post NASA’s Cassini probe  has shown that Saturn’s moon Enceladus not only has an thin atmosphere, but that volcanoes of water are erupting from its surface into space. Even more remarkable  has been its  discovery, that these volcanoes  contain the raw chemicals which are the building blocks for life.

Enceladus Ice Volcano

Image from NASA

The question which really fascinates me is  – What sort of life could have evolved on Enceladus ?

Before we answer this it is worth thinking about the Earth,which  is the only place in the Universe where we know 100% for definite life has evolved !

What stages did life go through while evolving on Earth ?

The Earth formed around 4.6 billion years ago.  It is generally accepted that life originated  in the sea and later moved onto land. Some rough timescales of the evolution of life on Earth are given below.

      • 3.7 billion years ago simple cells
      • 1.0 billion years ago multicellular life
      • 600 million years ago simple animals
      • 200 million years ago mammals
      • 60 million years ago the primates (monkeys and apes)
      • 20 million years ago the great apes
      • 2.5 million years ago the genus Homo (human predecessors)
      • 200 thousand years ago anatomically modern humans.

As you can see, although life evolved on Earth fairly rapidly  for most of  its existence the Earth had only very simple life forms.

What sort of life could exist on Enceladus ?

I think that given that

  • the age of Enceladus (which is similar to the age of the Earth)
  • all the key ingredients are there: namely water, the chemical builiding   blocks for life and an internal energy source

it is highly likely that life has evolved there.

One possibility is that the most advanced form of life is akin to single celled creatures found on Earth, which for most of the Earth’s history was the most advanced form of life.

However, a more exciting possibility is that much more sophisticated life form have evolved in the dark underground oceans. Given the length of time over which evolution could have worked, complex life forms could exist, perhaps preying on simpler life forms.  There  could be very strange creatures indeed!

 

 

 

Enceladus Life

Image provided by Sanjay Acharya

Hopefully within the not too distant future we will be able to visit this strange little world and find out more. I will talk more in my next post about possible missions to Enceladus.

Enceladus -Could there be life?

Welcome

Hello and welcome to the first post from the Science Geek. 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 scientific 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 Canals

Mars Canals

A Cold Dry Mars

Hopes of life were dealt a big blow in the 1960s when the American and Soviet space probes showed that Mars is a very dry, cold, hostile world.

Most biologists believe that liquid water is needed for life to emerge and prosper. The atmospheric pressure on Mars was discovered to be less than 1% of the pressure of the Earth’s atmosphere, which is far too low to allow liquid water to exist. Unlike the Earth, Mars does not have a significant magnetic field to protect the surface of the planet from deadly radiation. Therefore it is very unlikely that life could exist on the surface of Mars although primitive life forms could exist within rocks.

Another Candidate for Life

However in the last ten years another place where life could exist has emerged. It is one of Saturn’s moons called Enceladus. It might at first sight to be an odd candidate. It is nearly ten times further away from the sun than the Earth. At this distance the Sun’s energy is so weak that the surface temperature is on average -200 degrees celsius. In addition it is very small, only 500 km in diameter, which is only 14% of the diameter of the Earth’s own moon.  Because it is so small, the mass of Enceladus is so low that the surface gravity is only 1.1 per cent of the Earth’s gravity. So, on the surface of  Enceladus a 12 stone (168 pound) astronaut would weigh only two pounds.

The weak gravity means that Enceladus should be unable to hold onto any form of atmosphere. Any gases should escape into space. It also has no magnetic field to shield its surface from lethal radiation. So it safe to assume that it is impossible for life to exist on the surface of Enceladus.

Enceladus

enceladus_comparison

Images courtesy of NASA

However, recent flybys of the NASA Cassini space probe yielded  surprising results. It found a thin atmosphere containing over 90 per cent water vapour together with trace amounts of nitrogen, carbon dioxide and methane. This atmosphere is thought to emanate from the volcanoes spotted by Cassini which pump large amounts of water vapour and other gases onto the surface of Enceladus, replenishing the gases which continually escape to space. In the same way, volcanoes on Earth sit over pockets of molten magma deep underground. The volcanoes on Enceladus, known as cryovolcanoes because they are so cold, form over pockets of water.

ice volcanos

 Image courtesy of Gordon P. Hemsley

Indeed many scientists strongly believe that for billions of years there have been warm underground oceans under the surface of Enceladus which contain the basic chemicals such as methane, formaldehyde, ammonia and carbon dioxide which are needed to form the more complex chemicals which are building blocks for the evolution of life.

However this does not mean that we expect to see fish swimming in these underground oceans! What is more likely is that, given water, an underground heat source and  the raw chemicals, something more akin to single celled creatures and bacteria have evolved on Enceladus. Why I think this is case, I shall say in my next post.