Supporting Evidence 4

Are there extra-solar planets?

Planets concentrate the molecules needed for creating life

Life either began here on Earth after the development of a unique DNA, or was seeded by some kind of alien DNA carried in a comet or some other object (assuming ETs are unable to travel between the stars). Whichever way life began on Earth, creating life from the genetic code in DNA is easier should enough of the raw materials and molecules are concentrated in a particular region of space. While certain types of clays can do this (from a more electromagnetic perspective), so too can a rock the size of a planet because of its strong gravitational attraction (probably also electromagnetic in nature according to Einstein's Unified Field Theory). If scientists are to easily find and identify life as truly alien, we need to find planets as this is where we will find complex alien life.

Evidence for planets can certainly be found in our solar system, of which Earth definitely does harbour living things on its surface. However, for the most part, the more rational scientists among us often need a little more convincing. Thus the aim for many scientists today is to find evidence of a planet beyond our solar system at the right distance from the parent star and of the right size if they are to give any serious credence to the idea that advanced lifeforms may exist elsewhere in the universe.

Finding the world's first planet outside our solar system

In 2017, the most powerful optical, infra-red and radio telescopes on Earth could not directly observe extrasolar planets, even of the size of Jupiter (the largest planet in our solar system). The intense glare of their parent-star and the great distance of the star from the Earth puts an unfortunate dampener on the scientists' "planet hunting" party. In other words, the stars are usually too bright and the planets too close and/or small to detect. We are at a distinct disadvantage. Astronomers would need a planet several times the size of Jupiter orbiting at a reasonable distance from a dimly glowing and nearby star if it is to be directly observed.

In the days of Giordano Bruno, he already knew how difficult it would be to detect extrasolar planets when he said in his 1584 book On the Infinite Universe and Worlds:

"...we discern only the largest suns, immense bodies. But we do not discern the earths because, being much smaller, they are invisible to us."

Things haven't changed a lot since those days. Technology has improved in leaps and bounds, and there is certainly no shortage of ingenious methods from the scientists to find different ways to detect these distant worlds beyond our solar system. However, as of 2019, practically all of the extrasolar planets detected so far have required a more indirect approach. In other words, none have involved a direct observation of an exoplanet. All this is expected to change in the 2020s.

For example, in January 1983, the Infra-Red Astronomical Satellite (IRAS) provided scientists with intriguing evidence of what appears to be the presence of clouds of cool material forming a disc around stars. Such discs are thought to be conducive to planetary formation. There was even a strong possibility that some of the debris detected in the clouds might be of planetary size. However it wasn't enough to prove conclusively planets exist beyond our solar system.

Then on 9 January 1992, the world's first undisputed evidence for a "solar system beyond our own" came in the most unexpected way. A group of astronomers from the Arecibo radio telescope in Puerto Rico announced in the British journal Nature the discovery of planets around a distant star called PSR1257+12, located at a mere 1400 light years away in the Virgo constellation.

PSR1257+12 is termed a pulsar by astronomers because of the pulses of electromagnetic energy it emits. This discrete emission of energy is due to its rapid gyroscopic motion that was created at some time in its history after undergoing a massive supernova explosion. In the case of PSR1257+12, the star spins on its primary axis at 161 times a second, which causes its accelerating mass around the equator to produce a powerful gravitational field. So powerful is this field that most of the light emanating from the equator is bent back on itself. Only the polar regions of the star, where the mass of the star accelerates the least, is the gravitational field at its weakest and thus light can escape into space like the beams of a lighthouse. The star then rotates about a second axis, which causes the cones of energy emitted around the poles to sweep across space and so giving the pulsar its characteristic on-and-off effect.

Early observations of these cosmic lighthouses have suggested that the timing for each pulse received was more accurate than a Swiss-made pocket watch. However, the astronomers noticed that the pulses of electromagnetic radiation emitted by PSR1257+12 were not exactly precise, but were arriving too early or too late by 1.5 milliseconds over a period of several months.

Dr Alexander Wolszczan, an astronomer from Pennsylvania State University, USA, has spent three years examining the pulsar's puzzling pulse rate. He attributes it to the Doppler effect whereby a slowing down of the pulse rate is due to the pulsar moving away from us, and a speeding up of the pulse rate is due to the pulsar approaching us. It is as if something was pulling the star into tiny circular orbits. That something was later calculated to be of planetary size.

Astronomer, Dr George Gatewood of Allegheny Observatory in Pittsburgh, USA, explains it as follows:

"Imagine two people dancing a polka. As they whirl about to the music, each person - pulled by the other - moves in a series of circles across the floor. Now imagine that one of the dancers is invisible; we can still tell he is there by the motion of his partner."

A total of three planets have been detected so far around PSR1257+12. Two of the planets are estimated to have masses of 3.4 and 2.8 times that of Earth, orbiting the pulsar at distances corresponding to about where Mercury is in our solar system. The third one is much smaller. Calculations suggest this third planet is about 0.01 times the mass of the Earth and orbits the pulsar at a distance approximately half that of the other two planets.

Planets around pulsars

In 2006, scientists succeeded in discovering another phenomenon associated with pulsars. The accretion disc surrounding a pulsar can form new planets. As Deepto Chakrabarty of the Massachusetts Institute of Technology said:

"What's remarkable here is this process of planet formation — which we associate with the birth of stars — seems to also be able to occur at the end of the stellar lifetime, sort of a renaissance of the system, in some sense.

It says that this planet formation process seems to be a much more robust process than we initially realised."

He supports this with observations of another pulsar in the Milky Way containing planets located 13,000 light years from Earth in the constellation Cassiopeia using NASA's Spitzer Space Telescope capable of tracking infrared light.

But despite the high probability of finding planets around this star, don't expect life to suddenly arise on the surface of one of these planet around this or any other pulsar in the universe. The incredibly deadly levels of high frequency x-ray and gamma radiation and the constant collisions on the surface of a planet from matter in the accretion disc would make it virtually impossible for life to take hold let alone reach any form of intelligence.

While all these observations of extra-solar planets might give greater confidence to the scientists that ETs probably exist, we have still to detect the existence of Earth-sized planets.

Gravitational microlensing

In 2004, a new technique showed greater promise in detecting extrasolar planets approaching the size of the Earth. Known as gravitational microlensing, this new method involves a phenomenon predicted by Albert Einstein's General Theory of Relativity whereby the gravitational field of one object in a solar system can bend and focus the light from another object lying directly behind it. When light is focused, there is a brightening of the object, detectable by Earth-based telescopes. This technique works best when the ecliptic plane of the extrasolar system in question is almost edge on to an observer on Earth and the star showing a brightening effect is small relative to the size of the other object.

As Dr Ian A. Bond of the Institute for Astronomy in Edinburgh, Scotland, and lead author of the paper discussing the results, explained: "The real strength of micro-lensing is its ability to detect low-mass planets."

The idea to use gravitational microlensing to detect planets was first proposed in 1991 by Bohdan Paczynski of Princeton University. Paczynski says the technique is potentially effective at finding plants the size of the Earth. All it requires are enough stars lying edge on to us to increase the number of Earth-like planets to be detected: As he said:

"In principle, if you have observations of enough stars, you can detect Earth-like planets," says Paczynski. "It’s not so difficult to see it when it happens, the difficulty comes from monitoring enough stars."

As a result of this technique thanks to co-operation between two international research teams —Microlensing Observations in Astrophysics (MOA) in New Zealand and Optical Gravitational Lensing Experiment (OGLE) in Chile — a planet was detected around a star lying 17,000 light years in the constellation Sagittarius. The planet is larger than Jupiter and lies three times farther from its star than the Earth is from the Sun. At the time of the discovery, the team was still searching for smaller planets. More details about this discovery and the "cosmic magnifying glass" technique is available in the 10th May 2004 edition of Astrophysical Journal Letters.

The raw data image used by scientists at MOA and OGLE to detect the planet.

Still not quite Earth-sized?

All it takes is a little time, and some patience.

Well, on 26 January 2006, scientists officially announced the discovery of a planet approximately 5.5 times the mass of the Earth (but still considered much less massive than all the Jupiter-sized objects detected so far around other stars). This cool, rocky planet called OGLE-2005-BLG-390Lb (scientists must be running out of memorable names to give to so many astronomical objects) is orbiting a small red dwarf approximately one-fifth the mass of our Sun, taking 10 Earth years to complete a revolution around the star. The planet lies at a distance equivalent to between Mars and Jupiter in our solar system, suggesting this is more than a cool rocky planet. More likely we are facing a very cold world. If any life could be found here, it will have to be highly primitive and living underground near geothermal vents. Scientists made the interesting discovery in the constellation Sagittarius, not far from the central bulge of our galaxy. It is approximately 22,000 light years away.

What about a planet at the right orbit?

You have asked, and the scientists have listened. Already the search for Earth-like worlds is on.

The Kepler Mission — Searching for Earth-sized planets

The search for Earth-like planets around single Sun-like stars has reached such a high fever pitch that one can see the confidence oozing out of a number of scientists as we speak. Such confidence can only mean one thing: it is just a question of time before the evidence to support this next step is found as our technology gets pushed to unprecedented levels of power and sophistication.

For example, NASA has developed a new technology to enable the detection of such planets to be made a little easier. Sent into space on 9 March 2009, the Kepler space telescope is designed to detect planets as small as 0.5 times the mass of the Earth around other stars (although with a bit of imagination from the NASA scientists we hope the stars will be more Sun-like for the sake of determining the likelihood of finding advanced alie life in our universe). If exoplanets between 0.5 and 2 times the mass of the Earth exists in what scientists call the habitable zone, it will mean the chances of finding ETs will be bumped up by a few orders of magnitude thank you very much.

The Kepler probe carries a 0.95-metre diameter Schmidt telescope with an array of highly sensitive charge coupled devices (CCDs) for measuring the light from the stars called a photometer or light meter. It is designed to take in up to 100,000 stars in one area of the sky along our Milky Way arm where we are situated (in the constellations Cygnus and Lyra). Actually, it needs to be able to gather this many stars in a single hit. Apart from collecting enough information for statistical purposes, it should be remembered that the technique does require enough stars in the field of view of the telescope's eye to pick up planets so long as the solar systems are edge-on to our field of view (these distant planets have to pass in front of the stars to help dim down the light ever so slightly for the probe to do its job). If the exoplanetary solar systems are not aligned edge-on, the technique will not work.

Also the technique works best when the telescope is orbiting in space because we know on Earth how stars can change their brightness very quickly, especially near the Earth's horizon when we look up at the night sky. This flickering effect is caused by the Earth's atmosphere as the air flows and there is a variation in temperature at different altitudes. But in space, there is no air. Stars will shine constantly in space unless they undergo a supernova explosion or some other reason for varying the brightness (e.g., a planet moving in front of a star). As NASA said:

"The photometer must be space-based to obtain the photometric precision needed to reliably see an Earth-like transit and to avoid interruptions caused by day-night cycles, seasonal cycles and atmospheric perturbations..." (1)

With the telescope already placed in an Earth-trailing heliocentric orbit, it will maintain its view of a large number of stars throughout the mission, observing any variation in the brightness of stars. Should there be a consistent cyclic reduction in brightness over time before returning to normal, it is likely an exoplanet has moved across the face of the star. Once this information is obtained, it is possible for scientists to use Kepler's Third Law of planetary motion to calculate the size of the planet's orbit (i.e. the time it takes to go around the star) as well as the mass of the star itself. Finally the size of the planet is determined simply by how much of a reduction in the brightness of the star has occurred with respect to the size of the star. Then scientists will know whether the orbit of the planet is within the habitable zone and is of the right size to potentially harbour life.

Time will be a crucial factor in this experiment as any potential exoplanet detected could involve more than one planet, or the star could show evidence of serious sunspots moving over its surface. However, given enough time, the larger exoplanets lying further out from the star will have moved out of the way and the sunspots would disappear leaving behind the smaller rocky planets nearer the star. Then we will know what we have got. The first results won't come for at least a year and probably up to 5 years for the results to be reliable and consistent. (2)

19 June 2017

NASA has released the complete set of data gathered over four years of the Kepler probe looking at 100,000 visible stars in our Milky Way arm. In total, there have been 4,034 planets detected around other stars (the ones where the solar systems were facing edge on to us). At the present time, scientists have confirmed 2,335 of those are definitely planets with more being analysed as we speak. Since the last unveiling of data, Kepler has discovered an additional 219 new planets. Give it more time and we can expect more planets to be detected.

In terms of the number of Earth-sized worlds out there, Kepler has found up to 50 of this type. NASA officials have checked this data more closely and at present can confirm more than 30 of those as being correct in the size indicated by the Kepler probe. Actually, if you do not want a precisely Earth-sized world, the latest observations as of August 2017 have it that there are many more planets that are about twice the size of the Earth than there are of Earth size. With a potentially thicker atmosphere and the right greenhouse gas levels, such a planet harbouring life can survive in a wider habitable zone than the Earth is currently in within our solar system. It means the chances of finding life can only increase. As Professor David Charbonneau, astronomer at Harvard University, said:

"One of the most amazing discoveries to me really from the data from the NASA Kepler mission has been that the most common kind of planet in the galaxy is a planet that is about twice the size of the Earth, which is amazing because there is no planet like that in the solar system." (3)

Professor David Charbonneau

Even if life can exist on larger or smaller planetary worlds, there is one fact all scientists can agree on. It can be best summed up by theoretical physicist Professor Lawrence Krauss:

"We've discovered that planets are more ubiquitous and more varied than we ever imagined." (4)

Professor Lawrence Krauss

A very promising result to say the least.

First Earth-like exo-planet in a habitable zone found

Yay! It has taken a little while, but at last scientists have confirmed the existence of the first Earth-sized planet within the habitable zone of a star. And no, it isn't our own planet (a welcome change). The Kepler space telescope has detected a planet of the right size as our own lying at a distance of 490 light years away. And more amazing, it actually sits at the right distance from its parent star known as Kepler-186 (it is the fifth and outermost planet in this system) to allow water to exist in liquid form for a very long time. Elisa V. Quin­tana of the SETI In­sti­tute at NASA Ames Re­search Center in Moun­tain View, Ca­lifornia, USA, gave her backing to this claim when she said:

"This is the first de­fin­i­tive Earth-sized plan­et found in the 'hab­it­a­ble zone' around an­oth­er star. Find­ing such plan­ets is a pri­ma­ry goal of the Kep­ler space tele­scope. The star is a main-sequence M-dwarf, a very com­mon type. More than 70 per­cent of the hun­dreds of bil­lions of stars in our gal­axy are M-dwarfs."

Not exactly a sun-like star like our own. But then as they say, beggars can't be choosers. At any rate, there is still a high probability that primitive alien life does exist on the surface of this distant world even if the star is just a mere fraction of the mass and luminosity of our Sun (because it is a typical red dwarf commonly found throughout the Milky Way). This is especially true since the distance from the star is enough to prevent a "tidal locking" situation where the planet stops rotating leaving one side very warm or hot and the other side very cold. Another problem is that red dwarfs tend to be of the flare-up variety and there is a risk this star might just be one of those types. At the moment there is no evidence to suggest this, making it one of the more stable red dwarfs around.

Of course, all this assumes the planet is not depleted of important greenhouse gases in the atmosphere that might lead to an irreversible Ice Age. Oops, we shouldn't let that one get out of the bag. Otherwise we will need yet another piece of technology to observe the atmosphere of this planet and use spectroscopic analysis to determine the atmospheric composition to see if it contains the right chemical elements, including oxygen if alien plants are thriving there.

Probably another NASA project to come in the next 25 years.


Still, if you need something to keep you awake, you can read the latest results from the Science journal, Volume 344, Number 6181, pp.277-280, published on 18 April 2014, under the title, "An Earth-Sized Planet in the Habitable Zone of a Cool Star". An online version can be found here.

Multiple Earth-sized planets in the habitable zone around one star

The TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST) has discovered an interesting star system. Independent observations from the Spitzer space telescope, the Very Large Telescope, UKIRT, the Liverpool Telescope and the William Herschel Telescope, has confirmed the star system contains at least seven planets in orbit.

Before we reveal more about the planets, we know the star is less massive than our Sun by a factor of 12 and only slightly larger than Jupiter, making this effectively a red dwarf, but only just. Any less massive and this could have been a brown dwarf emitting lots of heat and almost no light. However, despite its modest size, don't let this object deter you in any way. Apparently it is generating a good amount of heat and light even if in the scheme of things such a star is described as "ultra cool" compared to other red dwarfs. More importantly, the scientists are claiming three planets are close enough to the star and within the life zone to permit water to exist in its three physical phases. That is a lot for one star system. In fact, all of the planets are remarkably close together to each other and the parent star. To give an indication of just how close, should the red dwarf be replaced with our Sun, the outermost planet would be six times closer to the star than Mercury is to our Sun. Essentially all the planets in this red dwarf system lie within 6 million miles of the star. Now that is really close together. This is unusual in itself (perhaps because we have not visited enough red dwarfs to get an idea of whether this kind of solar system is common or not) because Burgasser and Mamajer has stated that the star is a little older than our Sun. For such stability in the planetary system to occur, the orbits must be almost perfectly circular, the planets are small enough not to influence the others, and the position of the orbits are such that they are in harmonious resonance with each other to the extent that when one planet orbits, the next planet further out will orbit a fixed number of times precisely. As Kenneth Chang, a reporter for the New York Times, said:

"The original discoverers noted that those orbits were almost exactly in what scientists call "resonance". That is, the second planet completes five orbits in almost exactly the time the first planet makes eight. The third planet completes three orbits for every five orbits of the second planet, and the fourth planet makes two orbits for every three orbits of the third." (5)

Speaking of planetary sizes, all are rocky worlds ranging in size from something smaller than our Moon for the innermost planet, three are virtually Earth-sized, one is slightly larger than the Earth by about 20 per cent, and the other two planets are slightly smaller than the Earth by about 30 per cent. No giant gaseous planets have been detected, nor do the scientists expect to find any.

As a result of the closeness of the planets to its parent star and the way they orbit in resonance, all of them would not have moons of their own. Furthermore, they have rapid orbital periods. To get an idea of just how fast, the innermost planet has been calculated to orbit the star in 1.5 days. The outermost planet orbits the star in 19 days.

The star and its unusual number of planets is aptly named TRAPPIST-1. This is in recognition for being the first object to be discovered by the new telescope. Officially it is catalogued as 2MASS J23062928-0502285.

The chances of finding Earth-sized planets in the habitable zone around other stars is looking very good indeed.

A water-world Earth-sized planet?

On 25 May 2007, a team of European researchers led by Stephane Udry from the Geneva Observatory in Switzerland announced in the journal Astronomy and Astrophysics they had discovered using the HARPS instrument on the European Southern Observatory 3.6 metre telescope in La Silla, Chile, on 24 April 2007 the lightest exoplanet detected so far.

Orbiting the seemingly unremarkable red dwarf (located 20.3 light years away in the constellation Libra), scientists initially claimed Gliese 581C is more Earth-like than any other extrasolar planet detected to date. This is partly because of its mass (being the lightest of all exoplanets), but also it was thought the planet was situated just far enough away from its parent star to allow the right Earth-like temperatures (estimated in the range between 0 and 40°C) to permit water to exist in the liquid phase and hence most likely to support life. More refined calculations in April 2009, however, have now made Gliese 581D, another exoplanet lying slightly further out from the red dwarf, to be more Earth-like in temperature.

A total of four exoplanets have been detected.

Gliese 581C is roughly 5 times as massive as Earth with about 1.5 times Earth's diameter. It briskly orbits the red dwarf once every 13 days. Computer models created by Werner von Bloh of the Institute for Climate Impact Research in Germany and his team suggest this planet would be too hot to support liquid water (an important requirement for life to exist). While not as hot as Venus in our solar system, the planet is likely to have a runaway greenhouse effect exceeding 100°C forcing water to boil away and leaving behind a choking atmosphere of carbon dioxide and methane.

On the other hand, Gliese 581D is 8 times as massive as the Earth. So it should have no trouble retaining adequate quantities of water and other materials. Furthermore, the water can potentially exist in liquid form assuming a mild greenhouse effect is present in the atmosphere, making it one of the best candidates for finding alien life, possibly the size of bacteria or some larger creatures swimming in the oceans (anything more complex for land-based animals would have to be very flat or short in stature and walking on very thick and stumpy legs given its high gravity). As Manfred Cuntz, an astronomer at the University of Texas at Arlington, USA, and a member of von Bloh's team said:

"This planet is actually outside the habitable zone. It appears at first sight too cold. However, based on the greenhouse effect, physical processes can occur which are heating up the planet to a temperature that allows for fluid water."

Sounds like the smoking gun to support alien lifeforms.

To further fuel the fire of finding alien life on this veritable planet, Jaymie Matthews, an astronomer at the University of British Columbia in Canada, has studied the red dwarf in question in greater detail using the Canadian space telescope. He has realised how remarkably stable the red dwarf is. There were very few solar flares during the time he observed it over a period of 6 weeks and even in those instances the extra energy emissions from the star would quickly be dampened down by a thick atmosphere and deep ocean around Gliese 581D.

If that's not exciting enough, scientists have noticed the star is at least as old as our Sun. As Matthews said:

"We know it took about three and a half billion years for life on Earth to reach the level of complexity that we call human, so it's more encouraging for the prospects of complex life on any planet around Gliese 581 if it's been around for at least as long."

While scientists are not expecting life around Gliese 581D to be terribly advanced (and without land on this watery world to allow for legs to evolve and support a body and any remaining limbs to manipulate the environment, it is unlikely we will find technological-advanced aliens either), the search is definitely on for another planet that looks almost exactly like the Earth (in terms of mass) and at the right distance around a more Sun-like star.

More of these near Earth-sized planets are coming out of the universal woodworks

In 2019, scientists have upped the ante with the discovery of the closest thing to an Earth-like planet with only twice the size of our Earth (but still has 6 times the mass) and is within the necessary "Goldilocks" range around a stable star to allow liquid water to exist. An international group of astronomers discovered the planet — named GJ 357d (so yes there are at least another three other planets in this distant solar system) — using NASA’s Transiting Exoplanet Survey Satellite (TESS). The planet was detected early in the year in the constellation Hydra, about 31 light-years from Earth, according to a statement by NASA.

Further details about this discovery can be found in the Journal of Astronomy and Astrophysics.

Going further...

We think readers are probably getting the picture pretty clear by now: Earth-sized planets are looking to be common, and a number of them are being located within the habitable zone around a stable parent star as required to support life of some type (and probably more than just some bacteria or a bunch of worms). It seems like it is reasonable to consider going to the next level, which, as some scientists have decided to do, is to see if life might actually exist by directly observing evidence of their activities on a distant exoplanet. Impossible you might think? Think again!

In yet another effort to find evidence to support alien life, the successor to the Hubble Space Telescope known as the James Webb Space Telescope is expected to have enough viewing power to directly observe Earth-like planets in nearby stars. It will be so powerful that scientists believe they can make an analysis of the atmospheres of these distant planets to help determine the likelihood of finding life beyond our solar system. Unfortunately, it won't have the resolving power to observe a planet like Kepler-186f discussed above — a distance of 490 light years away is just a bit too much. A star within 12 light years? Now that's a more realistic achievement.

Not to be outdone in this field, we have NASA considering the idea of combining a suite of the latest and most sensitive space telescopes with revolutionary new imaging technologies to allow NASA to study all aspects of planetary formation outside our solar system. The system will be so sensitive, NASA claims it will be able to photograph planets as small as the Earth in the habitable zones of distant solar systems. And, using spectroscopic analysis, scientists should be able to analyse the atmospheres of exoplanets by measuring the amount of gases like carbon dioxide, water vapour, ozone and methane. Then atmospheric chemists can give a probability of just how likely extraterrestrial life exists. The system is known as the Terrestrial Planet Finder (TPF).

It has been speculated that this technique of analysing alien atmospheres could help to detect whether a technological civilisation exists. The reason being that a technology would probably be emitting pollution into the atmosphere like we do by way of soot, fluro carbons, and other artificial chemicals. Of course, all this naturally assumes that the civilisation is at the same level of technical capabilities as us. As Professor Brian Cox said:

"It does raise this wonderful possibility that you can search for the signs of an industrial civilisation in the atmosphere as well, and that might be the way that we detect a civilisation, rather than detecting radio signals." (6)

Professor Brian Cox

In reality, a truly advanced technical society may well have solved their waste problems by ensuring 100 per cent recycling of everything they produce. Whether this means technology has advanced to solve many of the problems for the aliens, or a new world order has started to ensure sustainability and recycling occurs, pollution would most likely drop and eventually the planet will return to a pristine condition. The technique will not necessary help to detect those truly advanced civilisations. Only that life exists on the planets and nothing else.

Until the technology is built, it is clear from the evidence we have so far that there are plenty of planets beyond our solar system. Between 1995 and 2005 over 170 exoplanets have been discovered, as of 2009 the figure has reached 300, and by April 2010, the figure has shot up to 443 orbiting around 350 or so stars. And not all are the massive Jupiter-sized bodies scientists had first come to observe. It is looking pretty clear at this stage that extrasolar planets of various sizes are common throughout the Universe, including Earth-sized ones. And already the first has been found in the habitable zone. It won't be long before these sorts of rocky planets will become routinely detected around more and more stars and soon we will be counting them like they were confetti.

What will alien solar systems look like?

With the prospects of finding extrasolar planets and of the Earth-sized variety looking good with each passing year, including direct observations of protoplanetary systems in the Orion Nebula with the help of the Hubble Space Telescope, there are two other conditions that must be met if we are to have an excellent chance of finding sufficiently complex and intelligent life on another planet. The first condition is that the planet must have a cool solid rocky surface not only to protect life from the heating effects of hot molten iron inside the planet but also for intelligent life to emerge from the oceans and eventually develop a technology. And the second condition is that there is an optimum planetary size to ensure essential raw materials to support life are retained on the surface.

Are there planets in the universe satisfying these two conditions? Steven Dole believes the conditions will be common throughout the universe.

In an attempt to simulate solar system formulation, Dole fed all the available astronomical theories on planetary formation into his computer and let the machine create models of solar systems that could exist in the universe. Assuming the star is sun-like, the result was this: All the planetary systems looked remarkably similar to our own (shown below). Furthermore, there will be rocky planets located close to a star.

Below is typical of the results obtained by Dole:

Will alien Earth-like planets have similar mineral contents to our own planet?

While the chances of finding ETs are looking mightily better the further scientists look into this issue, not every scientist in the world is completely convinced. Maybe all the observations and computer simulations are just lucky results or a pure coincidence in the minds of some of these hard-headed rational people? Okay. So what about having the right mineral content to Earth? Are there Earth-like planets out there that could look very similar to Earth with the right minerals, and how common could they be? The importance of the right minerals and ratio of those elements cannot be underestimated in the search for ETs. As astronomer Professor Brad Gibson of the University of Hull in the U.K. realised:

"The ratio of elements on Earth has led to the chemical conditions 'just right' for life. Too much magnesium or too little silicon and your plan­et ends up having the wrong balance between minerals to form the type of rocks that make up the Earth's crust. [More­over,] too much car­bon, and your rocky plan­et might turn out to be more like the graphite in your pen­cil than the surface of a plan­et like the Earth."

Can science provide the answer?

Well, ask and you shall receive!

Apparently a new computer simulation with more detailed and up to date data on planetary formation and the typical composition of nebulas has surprised astronomers involved in the study after observing the results on the computer screen. It would appear that nearly all rocky planets, including Earth-like planets with similar planetary sizes as our own planet, will have remarkably similar mineral content and ratios. Earlier calculations had previously indicated that only one in three Earth-like planets will be a close match. Now the prospects of Earth-like planets looking very similar to ours has dramatically increased in favour of finding ETs.

The astronomers were not expecting the results to be what they were. As Gibson, a member of the study group who conducted the simulation at the E.A. Milne Centre for Astrophysics located in the University of Hull, said:

"At first, I thought we'd got the mod­el wrong! As an over­all rep­resentation of the Milky Way, everything was pretty much perfect. Everything was in the right place… But when we looked at planetary forma­t­ion, every solar system we looked at had the same elemental building blocks as Earth, and not just one in three. We couldn't find a fault with the mod­el, so we went back and checked the observations. There we found some uncertainties that were causing the one-in-three result. Removing these, observations agreed with our predictions that the same elemental building blocks are found in every exoplanet system, wherever it is in the galaxy."

However, as Gibson added, "even with the right chemical building blocks, not every planet will be just like Earth."

Gibson clarified what he meant by this when he said:

"Conditions allowing for liquid water to exist on the surface are needed for habitability," he said. "We only need to look to Mars and Venus to see how differently terrestrial planets can evolve. However, if the building blocks are there, then it's more likely that you will get Earth-like planets — and three times more likely than we'd previously thought."

The fascinating findings were presented on 8 July 2015 at the U.K.'s National Astronomy Meeting in Llandudno, Wales.

If, after all of this, there are some scientists still not totally convinced that ETs probably exist in the universe (sounds like they are also among the one percent of scientists who still continue to deny the reality of climate change, so we might as well call them the alien deniers too), you can be sure more computers simulations and observations of the universe will keep them busy over the coming years.

Or maybe the question we should be asking is, is the evidence already here to prove ETs existence? Now that might be a more interesting angle to consider.