Visions of the Cosmos

Life Among the Stars

Extra-solar Planets

We live in a stupendous Universe of billions upon billions of stars and planets.  

Many scientists now believe that a few of these planets may be teeming with organic life.
We only know of one for certain and that is Earth.
We call it a Goldilocks Planet.
They are indeed rare and wonderful places
These life-abundant worlds - Oases in the Deserts of the Cosmos
What conditions are needed for life to exist and evolve?
Why do we think that in the vast immensity of space there are other life-bearing worlds?

Water - The Elixir of Life

Most scientists now believe that water is necessary for the majority of biochemical reactions to occur.   It is postulated that for life, certainly advanced life, to occur water in the liquid state must be present.   This has led to the concept of the HABITABLE ZONE.  It is believed that life is likely to arise when a planet is at the right distance from its star for liquid water to exist.  For the long periods of time necessary for life to evolve liquid water must continue to exist for tremendous periods of time.  The Earth formed about 4,500 million years ago.   It is believed that although life began in a very primitive form around 3,800 million years ago, it was not until the Cambrian Explosion 544 million years ago the advanced life began to evolve.

The Habitable Zone

Most of the material in the proto-solar disc consisted of hydrogen and helium but significant amounts of other elements were present such as oxygen, carbon, nitrogen, silicon and sulphur.   Most of the elements were in the form of their compounds such as water, ammonia, carbon dioxide etcetera.   The inner terrestrial planets formed from the dust closest to the sun .  It is now thought that significant amounts of water was bound in the minerals of the dust and that this together with water from colliding comets formed the oceans of Earth  At the moment we can only speculate on how long if at all oceans of liquid water existed on Mars and Venus. It was only on Earth that the oceans lasted long enough for advanced life to evolve.  Mars is now too cold and Venus too hot for liquid water to exist.   Earth alone remains in what is called the habitable zone as illustrated in the diagram.

Diagram Credit to NASA

Earth - The Goldilocks Planet

          Kyoto Gardens Holland Park London                                                 Keukenhof Gardens in the Netherlands                                        The Waterfall in the Kyoto Gardens

Our planet is teeming with life.  Everywhere except in the most arid deserts there is abundant water.    It is neither too near the Sun nor is it too far away. For this reason it is called the Goldilocks Planet - neither too hot nor too cold. For hundreds of millions of years it has maintained an equable climate relying not only on the heat of the Sun but also on the gases of its atmosphere and on the balance of the biosphere.  I recommend the works of James Lovelock and Lynn Marguilis who have worked on the Gaia Hypothesis to explain how the Earth maintains a balanced temperature.

Mars - The Planet of Cold Deserts

The European Space Agency's Cameras on the ESA Mars Express have taken many of the best photographs ever taken of the surface of the planet.   The first photograph on the  left shows a picture of the Candor Chasm whilst the second on the left shows The Tithonium Chasm.  The third picture is an artist's impression of the Mars Express space vessel orbiting Mars.  The picture on the far right shows the covering of water and carbon dioxide ice at the north pole during the northern winter.

 In contrast to Earth Mars is a cold red desert where the temperature is nearly always below zero.  The air is very thin and consists mostly of carbon dioxide with small amounts of nitrogen and water vapour.  The pressure is so low that H2O cannot exist as a liquid but sublimes directly from ice to vapour.  In the far distant past the planet may have had a thicker atmosphere and the planet may have been bathed in liquid water.   Seas, lakes and rivers may have existed.  Primitive life may have started and may even now exist beneath the surface.   However in its present state it is a cold environment, hostile to life.  The men and women who may one day visit Mars will have to wear warm space suits and be protected from the fierce ultra-violet radiation from the Sun.  Although Mars is further out from the Sun there is no protection afforded by a magnetosphere or from an ozone layer.

Venus - The Blazing Inferno

   The highly romanticised painting by Sandro Botticelli of the Birth of Venus bears no resemblance to the truth.  Instead of a planet full of tropical islands peopled by beautiful women and luxuriant flowers, Venus is the nearest thing in the Solar System to Dantes Inferno.   The picture of 'The Birth of Venus' is reproduced from the Free Dictionary by Farlex.  The second picture is an artist's impression of the European Space Agency's Venus Express Spacecraft orbiting the blazing rocks of Venus.  Acknowledgement ESA.   The third picture of the Ushas Mons Volcano was obtained from the NASA Magellan Spacecraft by radar.  Acknowledgement NASA.

The conditions on Venus are extremely hostile with  surface pressures of over ninety atmospheres due mainly to carbon dioxide which creates a suffocating temperature of around 450 degrees Celsius due to the greenhouse effect.  In the upper atmosphere it rains concentrated sulphuric acid which evaporates long before it gets near the surface.  It is only about 50 kilometres above the surface of the planet that the temperature drops to around 15 degrees.

Extra-solar Planets

We might rise from this limited Earth and,
looking from above, thinking, whether nature all its
splendour and glory had wasted to this heaply of dirt.
So we will, like traveller in other far away lands,
get a better judgement about the things at home and
form judgement of any thing by its worthiness.
What the world calls great we will admire less and
all the nullities most of the people set their heart on
we despise noble, because we will know, that myriads of
settled and equally good fitted worlds like ours exist.
(Christiaan Huygens in "The Discovery of Celestial Worlds", ca. 1690,
cited from Carl Sagan: "Unser Kosmos", Droemer-Knaur 1982, retranslated)

To find worlds similar to Earth we must cross the immense distances of interstellar space that separate the 'Empire of the Sun' from other solar systems and investigate the planets of  other stars.

Over the last 10 years a larger number of gas giant planets have been detected orbiting  nearby stars.  So far it has not yet been possible to see them directly.   However indirect methods using  a 'wobble' in the position of the star, caused by the gravitational forces between the star and its large planet, has not only proved the existence of extra-solar planets but has allowed scientists to calculate the approximate masses of the planets and the trajectories of their orbits round the parent star.  So far the smallest planet discovered has a mass approximately equivalent to that of  Neptune. 

The European Space Agency are planning the Darwin Project in which they will launch a system of interferometers into space to hunt for direct evidence of Earth-like planets orbiting other stars.  In about ten years time (2015), it is intended to place six linked telescopes in space to look for evidence of life. Using advanced spectroscopy they will probe the atmosphere of any Earth sized planet for ozone, water vapour, carbon dioxide and methane.   NASA are planning a similar mission called the Terrestrial Planet Finder to be launched about the same time.


Each telescope will be focussed on the same star system using a technique called interferometry.  The light of the star will be blacked out so that the light of the planets in the system (infra-red or visible) can be seen.  The first two illustrations (courtesy ESA macromedia) show the arrangements of the components of the project in interplanetary space.  The picture on the extreme right shows how using the spectrometer can be used to determine the composition of the atmosphere of the Earth and similar Earth-like planets.   This will enable scientists to detect the possible presence of life.  Courtesy ESA.

Selected Star Systems

Quite a lot of information is now available concerning a number of nearby stars.   Just over 200 extra-solar planets had been detected by September 2006.  A few stars have been found with more than one companion planet.   It is intended to describe some well known systems


55 Cancri is a double star system.  55 Cancri A, the larger of the two stars is 0.95 times the mass of the Sun and 1.1 times its diameter.  The smaller star Cancri B is  a red dwarf of only about 0.13 solar masses.   It is separated from the larger Sun-like star by 1,100 astronomical units that is to say 1,100 times further than the distance of the Earth from the Sun.  This means that the larger star can almost be regarded as a single star similar to the Sun with the possibility of the possession of a life bearing planet similar to the Earth.  It is far richer than the Sun in 'metals' - this needs some explaining.  In astronomy the term metals has a different meaning than it does in chemistry.  It means all elements except hydrogen and helium.  Stars vary in the percentage of metals they contain.  Astronomers talk about the 'metallicity ' of a star.  If the metallicity of the Sun is taken as 100, Cancri A is about 186.  The proto-planetary disc from which any planets may have been formed would have contained a lot more silicate dust than our Sun's disc and would have a larger content of material that may have led to the formation of rocky planets.  

Cancri  A is known to possess 4 planets one of which is only 18 times as massive as the Earth. (Neptune size) as shown in the diagram.

The star map in the left hand illustration shows the position of the 55 Cancri system in the sky.  The middle illustration compares the details of the Cancri A system as far as is known compared to our solar system.  Two of the gas giants and the Neptune-sized planet are  close to the star whilst the other gas giant is about as far out as Jupiter is from the Sun.  This leaves room for rocky planets and an asteroid belt.  A rocky planet could well exist within the habitable zone.  The third illustration compares the size of Jupiter and the Earth with the Neptune sized planet.  This could well be a very large rocky planet surrounded by a thick atmosphere of hydrogen, helium and other gases,  Because of their close proximity to the star the two gas giants and the Neptune-sized planet would all be very hot.  Acknowledgment for illustrations -central illustration to NASA JPL and Caltech - illustration on right to NASA JPL.

NASA / JPL-Caltech

This artist's conception shows four of the five planets that orbit 55 Cancri, a star
much like our own. The most recently discovered planet looms large in the
foreground. The colours of the planets were chosen to resemble those of our own
solar system.

The discovery of a fifth planet orbiting 55 Cancri was reported in the New Scientist dated 6 November 2007.  The discovery was made by researchers led by Debra Fischer of San Francisco State University in California and Geoff Marcy of the University of California in Berkeley, both in the US.

The new planet, called 55 Cancri f, orbits the star at a distance of 117 million kilometres, about 8% farther than Venus is from our Sun, putting it in the right zone for liquid water to exist (the habitable zone). The planet itself is unlikely to be the abode of life since because its mass is between that of Neptune and Saturn (or 45 times that of Earth), suggesting it has a gas-rich composition that is unfavourable for life as we know it.

However, there is still a chance for life-friendly conditions on any moons that might exist around the planet, she says. "The gas-giant planets in our solar system all have large moons," she says. "If there is a moon orbiting this new, massive planet, it might have pools of liquid water on a rocky surface." Such a moon would need to be at least as massive as Mars in order to have enough gravity to hang onto its water over the long term -  none of the moons in our solar system are that massive not even Ganymede or Titan.  Titan dose have an atmosphere but is extremely cold.

As well as the possibility of a large moon of the newly discovered gas giant planet, planetary scientist Jonathan Lunine of the University of Arizona in Tucson, US, who is not a member of the discovery team, notes that there is a large 'gap' – apparently devoid of planets – between the newly discovered planet and the much more distant one in that system."Is there perhaps a much smaller, terrestrial-sized planet lurking in that gap – one that might be habitable?" he wonders. Future calculations may indicate whether any stable orbits can exist in the gap, he says, or whether the giant planets on either side of it would keep it clear of potentially habitable planets.

55Cancri A is about 5 billion years old, which compares to our own Sun (4.6 billion)

Epsilon Eridani

Epsilon  Eridani is one of the closest Sun-like stars.  It is only 10.8 light years away and is 0.7 times the mass of the Sun.  Therefore its habitable zone is somewhat nearer and less wide than that of the Solar System.  It could however give rise to a planet within this region which could be habitable.  It is now known to have a large Jupiter sized planet with an elliptical orbit which goes out nearly as far as Jupiter and almost as near as Mars.  It was selected as a star which might have played host to a life bearing planet when Frank Drake began a project designed to look for radio signals from other nearby civilisations.
Even though the science fiction character Mister Spock of Star Trek fame was reputed to come from the planet Vulcan which was said to orbit Epsilon Eridani, it is unlikely that there can be advanced life on any planet in the system yet since the star is only about a billion years old. It took about 4 billion years for advanced life to evolve on Earth.  Being somewhat less massive than the Sun, Epsilon Eridani will have a longer main sequence life -around 15 billion as against 10.5 billion years giving a longer period for life to evolve and flourish.
Diagram shown below is from website 'exoplaneten' published on the web in English and German websites  

Beta Pectoris


Protopanetary Disc round Beta Pictoris photo by European Southern Observatory

Beta Pictoris is located about 62.9 light-years from the Solar System.  In 1983, astronomers using the Infrared Astronomical Satellite (IRAS) discovered a circumstellar dust disk around this star which was photographed from the ground by the following year  Subsequent observations suggested the presence of at least two giant planets in outer orbits.

Beta Pictoris is a bluish white main sequence dwarf star of spectral and luminosity type A5 V,  The star may have about 1.75 times Sol's mass, 1.4 times its diameter, and 8.7 times its luminosity.  Beta pictoris is thought to be a very young star perhaps only 20-200 million years old

The Search for Other Earths

Roger Bracewell has proposed using an instrument called an interferometer to pick out infrared images of Jupiter-sized planets from a pair of space-based telescopes.  It has been realised that there would still be sufficient of the 'glare' of the parent star to make it difficult to visualize Earth-sized planets even in the infrared.   Roger Angel, Director of the Stewart Observatory Mirror Laboratory proposed the use of more than two telescopes to eliminate this problem.   Another difficulty presented itself when it was realised that, even if all the starlight were cancelled out, there would still be the problem of our own Solar System's cloud of dust particles which cause the ZODIACAL LIGHT.   This would create such background of heat radiation (noise) that the signal from a distant extra-solar planet would be overwhelmed.   Alain Léger and Jean-Marie Mariotti of the University of Paris Observatory and their collaborators proposed a solution to this problem.  They suggested placing an interferometer system in orbit round the Sun at a distance of 5 astronomical units (about as far out as the orbit of Jupiter), where the dust is so cold that the background thermal radiation is negligible.    They showed that an orbiting interferometer at that distance using telescopes  as small as one metre in diameter would be sensitive enough to detect an extra-solar planet the size of the Earth. An international group of scientists is now actively engaged in the momentous task of building interferometers in space which will be able to analyse, not only the atmospheres of gas giants such as Jupiter and Saturn but, planets as small as the Earth and Venus or even Mars.  

There is no doubt that a vast international effort is now in operation to look for the possible existence of life bearing planets orbiting other stars. Within 30 Years, we may be actively investigating a large number of nearby 'solar systems'

  The table shown below lists some of the major undertakings that are currently being planned.

Name of Project



Astrometric  observations

Searching for 'wobbles' in nearby stars-also Doppler.


Detection of Planets between 0.44 - 11 times the Mass of Jupiter.  Many of them are very near their star and are called hot Jupiters.  A few are further out and have elliptical orbits

European Very Large Telescope (VLT)


Search for Uranus size planets orbiting 1000 nearby stars.

Keck Interferometer

Mauna Kea, Hawaii


Search for Uranus size planets orbiting 1000 nearby stars.

Large Millimetre Array in Chile ALMA project Europe, USA, Canada and, Japan


Planned for 2010 64 units placed on high mountain 5000 metres above sea level above the Atacama Desert in Chile

Upgrade of Merlin at

Jodrell Bank



French COROT Space



Search thousands of stars.  Near ones

Planets twice size of Earth

NASA Space SIM Project


Detection Earth sized planets orbiting

Near stars. Jupiter size up to 490 Lys

European 3.5 meter infra-Red Space Telescope



Next Generation Space Telescope NASA/ ESA


Directly image and + spectroscopic

Study of nearby 'Jupiters'

European GAIA Satellite



European IRSI or Darwin IR Interferometer


Images of 'Solar Systems' out to 65 Light years.  Study of spectra for ozone, co2, methane and water vapour

NASA Terrestrial Planet Finder (TPF)


Images of 'Solar Systems' out to 65 Light years.  Study of spectra

OWL Telescope European Southern Laboratory Atacama Desert Overwhelmingly Large Telescope


100 metre telescope – resolution 40 times and a sensitivity several thousand times higher than Hubble Space Telescope

Space Vehicle/larger than



Study of visible images of nearby

Earth sized planets.  Analysis of spectra

Planet Image Satellite. An Interferometer of 5 space- craft 6000 km apart. Possibly beyond Jupiter to avoid interplanetary which causes zodiacal light


At 30 light years distance  Resolution of 500km objects on Earth-sized

Planets.  Visual observation for land masses, oceans, forests, deserts, ice caps. Spectroscopic analysis in visual and infrared or atmospheres

O3, H2O, CO2, CH4 and other gases

The COROT Mission*

 Artists impression of COROT Satellite Courtesy CNES ESA

On the night of 27 December 2006 the COROT spacecraft was launched from Kazakstan.  It was first proposed by CNES, the French National Space Agency  in 1996.    The mission is led by the French national space agency.   ESA has joined the mission by providing the optics for the telescope and testing of the payload.  The payload of the COROT satellite consists of a telescope, two cameras - one for each of the two mission objectives (exoplanet search and asteroseismology), and the on-board computer processors. The latter were manufactured in ESA's European Space Research and Technology Centre (ESTEC) at Noordwyk in the Research and Scientific Support Department as one contribution of ESA to the COROT mission. COROT is the first mission capable of detecting rocky planets around nearby stars. It consists of a 30-centimetre space telescope. COROT will use its telescope to monitor closely the changes in a star’s brightness that comes from a planet crossing in front of it.

From the ground, the only planets detected around other stars have been giant gaseous worlds (Jupiter-like planets), over 10 times the diameter of the Earth. Not affected by the distorting effects of the atmosphere, COROT will be the first spacecraft capable of finding worlds made of rocks.  It will monitor closely the changes in a star’s brightness that comes from a planet crossing in front of it. Although luck may result in the detection of nearby worlds about the mass of the Earth,, the mission is designed to detect rocky planets more  massive than the Earth.   Such rocky worlds will be smaller than the gas giants but several times larger than the Earth, itself the biggest rocky planet in the Solar System. Such planets would represent a new, as yet undiscovered, class of world that astronomers believe exists. With COROT, astronomers expect to find between 10-40 of them, together with tens of new gas giants, in each star field that COROT will observe. Every 150 days COROT will move to a new star and begin observing again.  ESA then plans to continue its search for Earth-like worlds into the second decade of the century with the launch of the Darwin mission. This flotilla of 4 or 5 spacecraft will take pictures of Earth-like worlds, allowing scientists to search for signs of life.

COROT will also use its telescope to fulfil the other important objective of the mission which is the detection of 'starquakes’, acoustical waves generated deep inside a star that send ripples across a star’s surface, altering its brightness. The exact nature of the ripples allows astronomers to calculate the star's precise mass, age and chemical composition.

This technique is known as asteroseismology and ESA’s Solar and Heliospheric Observatory (SOHO) has been taking similar observations of the Sun for years. The COROT data is therefore essential to compare the Sun with other stars.

Extensive details of the mission can be found in the ESA website.  A direct hyperlink for the ESA page relating to COROT is provided in the section of this website relating to External Links.

Details of the results of the observations from the COROT Mission will be reported on this website as they become available.

Breaking News Report of solar-type system, 14  February 2008 Warsaw University Poland

Polacy zaobserwowali kopię naszego układu planetarnego
An artist concept of the newly discovered system. Credit: OGLE/OA UW/KASI/CBNU/ARCSEC.

An international team of scientists led by astronomers based in Warsaw and working within OGLE project has announced a discovery of an extra-solar planetary system, which - after rescaling - resembles our own Solar System. An article on the discovery will appear in tomorrow's issue of Science magazine.

The system, designated OGLE-2006-BLG-109, is situated 4,500 light years away from Earth. It is composed of two massive planets which resemble Jupiter and Saturn, and which revolve around a star similar to our own Sun.

The planets were discovered with the use of gravitational microlensing method. Gravitational microlensing happens when a mass-endowed celestial body (for example a planet or a black hole) transits close to the line-of-sight between a star and the Earth (observer), resulting in a noticeable brightening of the light from the star.

The models put forward by the scientists assume the existence of two planets. The first of the planets has a mass equal to 0.71 that of the Jupiter and revolves around the parent star in the distance equal to 2.3 Astronomical Units (AU), while its second sibling has a mass of 0.27 Jupiter mass and orbits the star in the distance of 4.6 AU. After rescaling, the planets correspond to Jupiter and Saturn respectively, while the star is half as massive as our Sun. It is also cooler than our nearest stellar object.

Scientists discover around 600 gravitational lensing events every year within the OGLE project, which positions them as world leaders in this field. The project, based at Warsaw University, uses a dedicated 1.3-metre telescope mounted in Las Campanas in Chile. The undertaking is partially financed by the Ministry of Science and Higher Education, the Foundation for Polish Science, and the Foundation for Polish Astronomy. The OGLE Web Site is available at

The OGLE team includes: Professor Andrzej Udalski, Professor Marcin Kubiak, Professor Michał Szymanski, Professor Grzegorz Pietrzynski, Dr Igor Soszynski, Dr Lukasz Wyrzykowski, Dr Olaf Szewczyk and Krzysztof Ulaczyk from Warsaw University Astronomical Observatory.

Almost 300 extrasolar planets have been discovered so far, with as many as 13 objects by the OGLE team. Also other Polish astronomers made notable planetary discoveries, namely Aleksander Wolszczan (the first ever extrasolar planets), Maciej Konacki (a planet in a triple star system), Andrzej Niedzielski (a planet around a red giant) or Krzysztof Gozdziewski (who, by means of theoretical calculations, found a fourth planet in a system where other observers had seen only three objects).

Breaking News  Detection of Water and Methane in Atmosphere of Extra-solar Planet

A joint international effort between Mark Swain and Gautam Vasisht the Jet Propulsion Laboratory in Pasadena and Giovanna Tinetti of University College London detected both water and methane in the atmosphere of a 'hot Jupiter'.   The astronomers reported on Wednesday 20 March 2008 that they had made the first detection of an organic molecule, methane, in the atmosphere of a planet outside our solar system and had confirmed the presence of water there, clearing the way for a bright future of inspecting the galaxy for life bearing planets, for the chemical stuff of life, or even for life itself.  The presence of these two compounds was detected spectroscopically using the Hubble Space Telescope.   Sara Seager, a planetary theorist at Massachusetts Institute of Technology, called it “another great day for exo-planets,” and a “tipping point” for the study of their detailed properties, though she cautioned that the findings still needed to be duplicated. “Hubble was never been designed to make measurements like this,” she said. “This is pushing the telescope to its limits.”  The detection was carried out using the transit method as the large planet moved across the face of the star

She said she was looking forward to the day when the experiment would be repeated on Earth-like planets with the much more powerful James Webb Space Telescope, set to be launched in 2013. In that case, she said, the existence of methane and water would be indicative that the planet was habitable.

The planet in question, known as HD 189733b, is definitely not a candidate abode for life. It is a hot ball about the mass of Jupiter orbiting only about 3 million miles from a star slightly smaller than the Sun. The temperature is a toasty 950 degrees Celsius.

ESA, NASA and G. Tinetti (University College London, UK & ESA)

Illustration - An artist's impression of the extra-solar planet HD 189733b

Breaking News 20 November 2008

Recent reports of the actual photographs of tow sets of extrasolar planets.  The first report was of the photograph of a planet about eight times the size of Jupier in arbit around the well known star Formalhaut.  The second report of three gas giants orbiting a star over a hundred light years away.  Many thanks for the blog by Seema Singh

Seema Singh - Friday, November 14, 2008 7:55 PM

More than 375 extrasolar planets have been detected so far but all through indirect methods, not by imaging. Using Keck and Gemini telescopes in Mauna Kea, Hawaii, a group of scientists from the US, UK and Canada have produced the first-ever (direct) image of three planets orbiting a star other than our own. The star, HR 8799, is a "main sequence star," in the prime of its life, fuelled by nuclear reactions within its core, and it occurs 128 light years from Earth, researchers say in today's issue of Science. Pics courtesy Science



  image of HR8799 system

The Next Momentous Decade

The next decade may well prove to be the most momentous yet for the discovery of extra-solar planets.  This may be largely due to the progress made in the construction of new super-telescopes.  Even a year or two ago when this web-site was first began the only hope of detecting Earth type planets seemed to lie in the construction of special space telescopes of the Darwin  and  Terrestrial Planet Finder missions planned by the European Space Agency and NASA.  Since then considerable progress has been made in actually producing direct images of Jupiter type gas giants orbiting the stars Formalhaut and HR 8799 referred to above.  Advances in ground based telescope design promises to bring about the construction  of gigantic ground based super-telescopes.  This is discussed in the article by Anil Ananthaswamy entitled 'New Earths and the Edge of the Universe' in the 6 December edition of the New Scientist.

Three huge telescopes are discussed

The Giant Magellan Telescope (GMT) 24.5 meters to be built in Chile

The Thirty Meter Telescope (TMC) to be built under the auspices of the University of California at a site in Mauna Kea. Hawaii or in Chile.

The largest of all will be the 42 meter European Extremely Large Telescope (E-ELT) to be constructed in the Canary Islands or in Chile.

These immense telescopes will be able to collect enough light to allow astronomers to study the compositions of the atmospheres of Earth-type planets orbiting other stars.

On 5 January 2009 the Sky at Night on BBC 1 TV dealt with the evolution of the telescope over the last 400 years.  It finally showed the way in which the immense mirrors of very large telescopes are built.

Extra-solar Moons

Much has been written and discussed about extra-solar planets.  Of almost equal interest is the possible presence of moons orbiting these extra-solar planets.  This considerably extends our field of investigation, since it would seem highly possible that life may well exist on large moons of gas giant planets.  If these are within the habitable zone and are sufficiently massif to maintain an atmosphere then they could possibly support life.   One interesting way in which such moons may be found is by detecting a wobble in the path of the gas giant planet in the same way as large planets have already been discovered by the wobble in the star.   Even though the sizes (volumes) of Ganymede and Titan are larger than Mercury and approaching the size of Mars their masses are considerably smaller since their bulk densities are much lower.  Whereas they consist of silicate rock and large amounts of water ice, both Mercury and Mars have iron cores and much higher amounts of silicate rock material.  However planets closer to the star may well be similar to the Earth and have iron cores and a far higher proportion of silicate rock than water.   Such moons would be Earth-like planets in their own right.   It would be interesting to know what the effect of the magnetosphere of the gas giant would be on the development of life on such a large rocky moon.

The Kepler Mission

NASA is planning to launch the Kepler Discovery mission in March 2009.  The aim of the mission is to detect for the first time Earth-like extra-solar planets. 

In the words of the principal Investigator, William Borucki of

 NASA's Ames Research Center in California "The Kepler Mission will, for the first time, enable humans to search our galaxy for Earth-size or even smaller planets," With this cutting-edge capability, Kepler may help us answer one of the most enduring questions humans have asked throughout history: Are there others like us in the Universe?" s a space telescope designed to survey distant stars to determine the prevalence of Earth type planets.

Kepler will detect planets indirectly, using the "transit" method. A transit occurs each time a planet crosses the line-of-sight between the planet's parent star that it is orbiting and the observer. When this happens, the planet blocks some of the light from its star, resulting in a periodic dimming. This periodic signature is used to detect the planet and to determine its size and its orbit.

We are reminded here of the transits of Venus and Mercury.  From Mars the Earth would also transit across the face of the Sun from time to time.  Even though the dimming of a star is very small, Kepler will be able sensitive enough to detect it.












Illustrations Courtesy NASA

Seth Shostak, a senior astronomer at the SETI Institute published in SETI's web-site puts it very dramatically:-

"Take a bare 100 watt light bulb and switch it on.  Now step back about 300 miles. Once you're in position, arrange for a friend to slowly pass a pinhead 30 feet in front of the bulb without notice or warning. Your job?  Detect the decrease in light when the pinhead gets between you and the bulb.

I suspect that's not something you do every day.  But NASA's Kepler telescope will be doing it every half-hour for the next three years and more.

Actually, not quite. Kepler will be measuring the brightness of more than 100,000 "light bulbs."

This new NASA space-borne instrument, which is now completing its shakedown cruise, is engaged in the ultimate staring contest.  Kepler will continuously monitor the luminosity of 145,000 stars in the region of constellations Cygnus and Lyra, looking for dimming of as little as 0.006 percent of a star's brightness. Unlike other schemes for finding planets around distant stars (so-called "exoplanets"), Kepler can unearth Earths. That is, it can detect worlds hundreds of light years away that are comparable in both size and orbital position to our home planet. Cousins of the Earth – and obvious candidates for life."


Artist's Rendering of Kepler's Target Region in the Milky Way

An artist's rendering of what our Galaxy might look as viewed from outside

our Galaxy.  Our sun is about 25,000 light years from the center of the Milky Way.

The cone illustrates the neighbourhood of our galaxy that the Kepler Mission

will search to find habitable terrestrial type planets.

Credit: Jon Lomberg NASA

The key technology at the heart of the photometer is a set of charged coupled devices (CCDs) that measures the brightness of hundreds of thousands of stars at the same time. CCDs are the silicon light-sensitive chips that are used in today's TV cameras, camcorders and digital cameras. Kepler must monitor many thousands of stars simultaneously, since the chance of any one planet being aligned along the line-of-sight is only about 1/2 of a percent.


From 1995-1997 Jon Lomberg worked on the Warner Brothers film CONTACT, as Astronomical Visual Consultant. In this capacity Lomberg designed and storyboarded many of the film's astronomical animation sequences, including the three minute zoom out from Earth that opens the movie.

Jon Lomberg was the principal artistic collaborator of astronomer Carl Sagan. From 1972 until Sagan's death in 1996, Lomberg illustrated most of Sagan's books and magazine articles, and he was Chief Artist for Sagan's classic television series. For his work on COSMOS Lomberg received in 1981 a Prime Time EMMY Award for "Outstanding Individual Achievement in Creative Technical Crafts." Lomberg has art directed many other science programs for television and videotape.

In 1983, Lomberg's videotape with Carl Sagan about nuclear winter was broadcast worldwide and won first prize at the Vermont World Peace Film Festival in 1984.



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*Corot article added 28 December 2006