ALIENS are surely AMONG US: Average star has TWO potentially Earth-like worlds

Two earth-like worlds? Not sure how they define that... my prediction is that evolved life in the universe will be far rarer than a lot of people are suggesting for two reasons that make life in THIS solar system a lot more likely.

All the goldilocks zone does is give you liquid water. That's a start but it's only a start. You also need a magnetosphere that's sufficiently powerful enough to prevent your host star from frying the planet. You need a large moon for several functions. It acts as a galactic vacuum cleaner, protecting the biosphere for 4.5bn years.

Firstly in this solar system we have large gas giants in long orbits. That's pretty rare. In most of the extrasolar systems we've observed so far, big gas giants tend to be pretty close in - and they're very obvious when they transit. With this solar system they're a long way out. This means that rocky planets inside the system are able to survive without being swept up by a gas giant AND it means that anything coming in from the edge or outside the solar system (comets, asteroids) along the plane of the system, is likely to hit the gravitational field of one of the gas giants first or at least at some point during its orbit of the sun. Over the space of billions of years, this gives Jupiter, Saturn, Uranus and Neptune the chance to swallow up most of the big stuff that gets in and doesn't go straight into the sun.

Secondly right at the beginning of the solar system, before the current orbits had settled and before the gas giants had much chance to clean up, a Mars-sized planet collided with the proto-earth. In doing so it will have vaporised and caused most of the earth to melt (again). Most of the combined material that WASN'T ejected into space became the earth but a substantial blob of the combined combined material became the moon. The moon is ENORMOUS - for the earth. Satellites THAT big around a planet this small are impossible under normal planet-forming conditions. The ONLY way to form a satellite that big is to have the collision we had.

The moon plays a number of interesting roles, not just in the mixing of surface liquids on earth. As it swings round the earth every 28 days or so, over the space of millions and millions of years, it creates tidal movement within the fluids of the earth's mantle which are thought to have been part of the process which triggered the start of plate tectonics - the other part of the process is the role of water which at high temperatures and pressures acts as a lubricant. It is this water coming to the surface that has allowed life on earth to begin - in waters that were mixed by the movement of the moon, acting like a cosmic wooden spoon, mixing the ingredients back and forth - the simple carbon, nitrogen, sulphur, oxygen, hydrogen, iron molecules, heating them up, cooling them down, mixing them around.

Without the gravitational tidal action of the moon, none of that can happen. It's also quite possible that the gravitational action of the moon plays a role in helping to establish the stability of the earth's electromagnetic field. Remember that without the EM field, we all fry. So what we need to be looking for, to find evolved life outside the solar system, is a very stable main-sequence star with the capacity to last for 10 bn years, a rocky planet in the goldilocks zone, with an abnormally large moon due to some random process early in its lifespan, a strong and stable electromagnetic field and large (but not too large) gas giants on the outer edges of that solar system. Simples.

Alternatively viable conditions might exist on satellites around a gas giant in orbit around a main sequence star but the planet would get bathed with regular sweeps of EM blasts from the gas giant so that might effectively sterilize the planet.

Python

So remember, when you're feeling very small and insecure

How amazingly unlikely is your birth

And pray that there's intelligent life somewhere up in space

'Cause there's bugger all down here on Earth

Understanding principles of the drive behind molecular complexity

In order to get a better picture of the probability and scale of other life forms in the Universe we need to get a better understanding the factors creating life. Given the ideal mixture of chemicals on our planet, simple molecules became more complex and created the living things we see. Which law of physics, if any, is driving this build up from a simple soup of algae to highly complex and specialized creatures like sharks, whales, birds and even humans ?.

Being goldilocks is one thing, a given planet also needs to have the elements allowing an endless cycle of chemical reactions in the temperature range present, using the energy of their star to create the perfect cycle of life like we have here, from dust to dust. Also the life needs to be distributed over creatures made of complex molecules, and creatures turning complex molecules into basic elements like bacteria... Life = Tossing a dice 10^X times with 6 on top, Science: Find X and the reasons why 6 came of top often enough to create life.

Space-life enthusiasts like to say that “absence of evidence is not evidence of absence”. Perhaps, but they have never been able to answer the famous question posed by Nobel-Prize-winning physicist Enrico Fermi half a century ago concerning all the other alleged civilizations in the universe: “Well then, where is everybody?” SETI, the Search for Extraterrestrial Intelligence, which now uses equipment that scans 28 million radio frequencies per second, has failed to obtain a single “intelligent” signal from outer space in over 50 years.

In April 2000, 600 astronomers, biologists, chemists, geologists, and other researchers met at the First Astrobiology Science Conference, held at NASA’s Ames Research Centre, California, to evaluate the evidence on whether, biologically speaking, we are alone in the universe. The predominant mood of pessimism was encapsulated by British palenontologist Simon Conway Morris’s comment: “I don’t think there is anything out there at all except ourselves,” and Dan Cleese, a Mars program scientist at NASA’s Pasadena Jet Propulsion Laboratory, who said that it is time to “tone down expectations”.

Conventional wisdom about interstellar comms gets well thumped when a civilisation starts using Claudio Maccone's gravity lens system. The idea is to use one's own star as a giant focuser of radio and light waves. Great telescope, great radio antenna. With about 10 watts we could establish comms with the Alpha Centauri system and get 5 by 9 clarity and good bandwidth. Hard to believe, but that's what the maths says. Of course, there is a bit of a lag.

Our own grav focus begins at about 550 AU out. We'd place a transceiver (nuclear thermal powered I assume) on the opposite side of Sol to the target star system. At the target system we'd do the same. So we end up with a straight line that links remote Tx/Rx - remote star - Sol - local Tx/Rx.

The chief impediment we ourselves currently face is the ability to make such long trips quickly. Once we have that, we could set up radio comms all over the place.

But to the question about aliens. If they are using this mode of communication, there's not a chance in hell that we could detect it.

There's a heavy piece of irony here, as Maccone is chief of SETI.

Re. gravitational lens

Interesting idea.