Shortlist of Possible ET Addresses

An anonymous reader writes "Yahoo News is reporting that Astronomer Margaret Turnbull of the Carnegie Institution has released a 'top 10' list of potential inhabitable star systems. NASA is planning on using this top 10 list as the targets for their Terrestrial Planet Finder a 'system of two orbiting observatories scheduled for launch by 2020.'"

Comments

of particular concern is who is notified first

[wisebabo]

While the chances of hearing from alien worlds is depressing small ("Rare Earth"), still the thought that a few private individuals will know first should give us pause. If there is more information in the detected signal than "hello there", who knows what could be learned? Markets may move in a big way (here's how antigravity works, immortality, existence of god, a big black hole is headed your way, etc.).

Then again if that's the only way we're gonna get these projects funded, perhaps these philanthropists should be rewarded for their risk taking.

hmmm

[smash]

Apparently some systems were "tossed out" because they aren't stable enough (variable stars, strong gravity, etc).

Now, is it just me, or does the idea that life may well need some abnormal event to kick-start it in conflict with that very idea?

Perhaps include *some* of these systems?

smash.

Recent Articles on the Origin of Life

[Quirk]

The Royal Society is holding a symposium on the origins of life...

Life on Earth 'unlikely to have emerged in volcanic springs'

13 Feb 2006

"The latest findings of experiments to re-create the conditions under which life could emerge from chemical reactions suggest that volcanic springs and marine hydrothermal events are unlikely to have provided the right environment, a leading researcher from the United States will tell an international meeting tomorrow (14 February 2006) at the Royal Society, the UK national academy of science."

In the alternative Plos ran an interestin article titled Jump-Starting a Cellular World: Investigating the Origin of Life, from Soup to Networks which touches on the front running theories on the origin of life.

Re:Immigration?

[cruachan]

"Any biochemists out there feel free to disagree and/or expound."

I'll take that one. In a liquid water environment it's difficult to see how you'd end up with a biochemistry that wasn't nucleic acid, protein, carbohydrate and fatty acid based. By observation life on earth seems to have explored just about every type of possible molecular structure that carbon/hydrogen/oxygen + other minor elements can produce and if there were some other useful biological molecule then it's difficult to imagine why it's not been 'discovered' and exploited already. That's not to say that the details won't differ - I'd have thought it virtual certain that a mix of different nucleic acids and amino acids would be used in different combinations with a different genetics etc etc, but I'd expect life to be grossly similar on similar planets, just differing radically in the details.

Outside that I'm very unconvinced by non-water or carbon based life. Silicon just doesn't form complex enough molecules so that's out. The next best bet seems to me to me ammonia based.

Terrestrial planets maybe. Intelligent life not!

[bradbury]

It is unfortunate that Turnbull, the Carnegie Institution and NASA chose to affiliate themselves with the Search for Extraterrestrial *Intelligence*. TPF might be capable of locating "water worlds" but there is no experimental information with regard to what fraction of those might have no water or be entirely covered in water (water worlds). It seems obvious that planets like Venus and Mars do not support life or may have only supported it for a brief period (in large part because they are near the edges of the habitable zone). It is also difficult to envision how intelligent life, particularly intelligent life with robust technology (radio transmitters, integrated circuits, rockets, etc.) would evolve on planets entirely covered in water. So one needs to make careful distinctions between systems with dead planets, systems with only water covered planets (pure water worlds), systems with water worlds with primitive life (e.g. those before the Earth's current stage of development), systems with water worlds with intelligent life (our current stage) and those beyond our stage.

Lets do the math. Universe, ~13 billion years old. Earth, ~5 billion years old. Time to develop first sun-like stars perhaps 1 billion years. So there is a reasonable chance that there are (or were) Earth like planets up to 7 billion years older than Earth (at least around stars slightly smaller than the sun which age more slowly). There are some systems with younger Earths (*much* younger for those systems currently in the process of planetary formation). Lineweaver's group has worked on this and has concluded that ~70% of the Earth's in the galaxy are older than ours -- many of them by billions of years.

Based on this it is unlikely that either TPF or SETI (based on its current approaches) will discover "intelligent" life. The statistics dictate that you only have perhaps a 5000 (years) / 12,000,000,000 (years) chance (less than 1 in a million) of finding a planet which hosts "intelligent" life as we know it.

For those systems with terrestrial sized planets and those with water TPF is a reasonable effort -- it might manage to detect water and if lucky atmospheric composition that could hint at life. However pointing the SKA (or any other radiotelescopes) at the stars in the list provided are highly unlikely to be successful because they assume intelligent civilizations which are currently at (and remain at) our stage of development. (This changes the statistics to about 1 in a billion.)

The reasons for this are as follows... Whether you believe in steady state growth (Dyson's assumption in 1960), or exponential growth as "The Singularity" concept proposes the bottom line is that it seems very unlikely that a civilization would actively choose to remain at our state of development (i.e. zero growth for millions or billions of years). If you choose the steady state model the time to develop to a Dyson Shell is measured in a few hundred to a few thousand years. If you choose the singularity model then the time to develop a Matrioshka Brain (also here) is measured in decades. Once either of those states is reached the star goes "dark". So the star list is useless (to either the TPF mission or SETI) for identifying locations of intelligent civilizations with capabilities even slightly beyond our own.

Robert Bradbury

Notes:
For the above calculations I chose 5000 years as the longevity of humans with a reasonable level of technology development. One could limit it to smaller time frames (~100 years for radio or 40-50 years for lasers or rockets). TPF has a much greater chance of being successful than radio or optical SETI because it is working with a much larger time window. Water world longevities range from 100 million to many billion years if they restrict themselves to sun-like (

Correction -- Two "Top 5" Lists, and more...

[SirBruce]

The submitter got it slightly wrong. First off, Margaret Turnbull's team came up with a list of 17,129 potentially habitable star systems in 2003, and the work she has done since has been to refine that list.

What she announced yesterday were TWO "Top 5" lists. The first list includes the top 5 recommendations for a SETI search:

beta CVn
HD 10307
HD 211415
18 Sco
51 Pegasus

The second list includes the top 5 recommendations for the TPF to examine for Earth-like planets:

epsilon Indi A
epsilon Eridani
omicron2 Eridani
alpha Centauri B
tau Ceti

Why the difference? Well, the second list is of much closer stars, and much more likely to have planets that TPF can find and image. The first list has stars that are a bit farther away, but are, generally speaking, more like our Sun.

And here's a useful link:

http://www.aaas.org/news/releases/2006/0218habitab le.shtml

Bruce