Wednesday, April 25, 2007


New Planet Discovered - just how 'earth-like' is it?

Steve Reuland over at The Panda's Thumb blog makes a big deal of the discovery, announced in multiple news media on Wed April 25th, that scientists think they have discovered: 'a planet outside our solar system that is potentially habitable, with Earth-like temperatures, a find researchers described Tuesday as a big step in the search for “life in the universe.”'

However, a big step does not a completed journey make.

The above quote is actually Reuland quoting, with cautious approval, an Associated Press article by Seth Bornenstein entitled 'Potentially habitable planet found'. Rueland touts this discovery as undermining the 'designed for discovery' hypothesis put forward by the authors of The Privilaged Planet (who simultaneously advocate the 'designed for life' interpretation of the Rare Earth hypothesis). The discovery might equally be thought to undermine the Rare Earth hypothesis, and thereby and ID interpretation of it.

However, just how 'Earth-like' is 'Earth-like'? Well, as Rueland notes, quoting Bornenstein: 'There's still a lot that is unknown about the new planet, which could be deemed inhospitable to life once more is known about it...'

Borenstein also observes: 'it's worth noting that scientists' requirements for habitability count Mars in that category: a size relatively similar to Earth's with temperatures that would permit liquid water. However, this is the first outside our solar system that meets those standards.'

Mars is lifeless. Moreover:

'The new planet is about five times heavier than Earth. Its discoverers aren't certain if it is rocky like Earth or if its a frozen ice ball with liquid water on the surface. If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball... it would be even bigger. Based on theory, 581 c should have an atmosphere, but what's in that atmosphere is still a mystery and if it's too thick that could make the planet's surface temperature too hot... "You need more work to say it's got water or it doesn't have water," said retired NASA astronomer Steve Maran, press officer for the American Astronomical Society... [and] Gravity is 1.6 times as strong as Earth's...' (my italics)

Wednesday's Daily Mail Newspaper made the discovery front page news, proclaiming:

'The New Earth - does the discovery of a planet just like ours means there IS life out there?'

This is tabloid sensationalism pure and simple. The new planet orbiting Gliese 581 is not 'just like ours' and does not qualify as a 'new earth'. The article (p12-13) by science editor Michael Hanlon is a little more down to earth (if you'll excuse the pun), because it does put in the qualifications that this is 'what is possibly the most extraordinary world to have been discovered by astronomers... The Earth-like planet that could be covered in oceans and may support life... It probably has a substantial atmosphere and may be covered with large amounts of water - necessary for life.' Nevertheless, the general tone of the article is so upbeat that only careful readers are likely to spot the import of the occasional 'could' and 'may'. Large print talks of 'evidence that life - just like us - might be out there.'

The simplistic leap from 'there may be water' to 'there may be life' flies in the face of all the evidence. Water is necessary for life, but there's a lot more to life than water! Hanlon does admit that: 'If there is life there it would have to cope with the higher gravity and solar radiation from its sun', and that 'Just because Gliese 581c is habitable [and remember 'habitable' can mean being like Mars!] does not mean that it is inhabited.'

Indeed, while the general pop-culture may be thinking in terms of intelligent life, even those scientists who think there may be life on 581c are mainly thinking in terms of microbial life. Indeed, there is currently a lack of the evidence we'd expect if 581c was inhabited by an advanced alien civilization: 'According to Seth Shostak, of the Search for Extraterrestrial Intelligence Institute in California, the Gliese system is now a prime target for a radio search. 'We had actually looked at this system before but only for a few minutes. We heared nothing, but now we must look again.' Seems to me that if radio signals were coming from that direction we'd have noticed the first time we tuned in. So what if we look again and find nothing? Will this count as evidence against the assumptions about easy evolution etc. undergirding SETI? After all, this is the best candidate for ET's home so-far discovered, 'its sun is an ancient star - in fact, it is one of the oldest stars in the galaxy, and extremely stable. If there is life, it has had many billions of years to evolve'!

It is also interesting to note Hanlon admitting (p13) that: 'We don't understand how life began on our world, let alone how it could arise anywhere else. There may be an awful lot of bugs and bacteria out there, and only a few worlds with what we would recognize as plants and animals. Or, of course, there may be nothing.' If we don't understand how life began (within a non-teleological framework!), then it is surely a little premature to be making statements about the possibility of life on 581c supported by nothing besides the possibility that there may be liquid water there, if it doesn't have the wrong sort of atmosphere!

Here's some quotes from other sources:

'Nature says the new planet would be a so-called "super-Earth" - a very exciting prospect, says exoplanet expert David Charbonneau at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "If the planet is a rocky super-Earth, then perhaps it has a surface with liquid water and life," Charbonneau suggests. There is another, less exciting option, however, which would make the planet slightly less homely, he adds: "If instead the planet is a 'sub-Neptune', then it would have a large gas envelope that buries the surface below, making it inhospitable for life."... Sara Seager, a planet expert at the Massachusetts Institute of Technology, said, "For example, if the planet had an atmosphere more massive than Venus', then the surface would likely be too hot for liquid water."' ('New Planet Might Support Life', rediff news @, my italics)

The Panda's Thumb's Nick Matzke comments: 'A planet that massive might have the problem of being so smooth it has a global ocean, which probably would make it tough to produce the concentration mechanisms (evaporation in pools etc.) that might be required for the origin of life. But you never know…'

In short: Gliese 581c is the first non-Gas giant discovered within the so-called 'goldilocks' zone of potential orbits around its star - so it fulfills one of the necessary conditions for a life-sustaining body. In addition, it might or might not have a temperature in the right 'goldilocks' zone as well, depending on what the atmosphere is like. If it does have the right temperature, then it might or might not have liquid water, which is another necessary condition for life. However, a) there are other necessary conditions for life and b) necessary conditions are not necessarily sufficient conditions. Life needs a lot more to get going and to thrive than a big rock plus liquid water and a star!

For a run down of the many parameters required by a life-supporting body, cf. Hugh Ross, 'Probability for Life on Earth'

David H. Rogstad of Reasons to Believe has written a short article on this topic Earth-Like Planet Discovered

Astronomer Guillermo Gonzalez comments:

'You are right about the host star being an M dwarf posing problems for habitability. The smallest planet's eccentricity is comparable to that of Mercury, so it is probably locked into a 3:2 spin-orbit resonance. So, the planet will experience large temperature variations over the course of its orbit. What's more, because its rotation is slower, it should have a weaker magnetic field and be subject to enhanced solar wind stripping of its atmosphere. Finally, the fact that it has a mass at least 5x Earth's means that it will have a high surface gravity and less surface relief than the Earth -- meaning no dry land.'

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