Milky Way Inhospitable?

tdfunk writes "Space.com reports that life in the universe may be more rare than previously thought. In an article published today, Space.com quotes Guillermo Gonzalez, an Iowa State University researcher, who has studied the structure of our galaxy and has concluded that life may not be as common as we may have believed. Apparently, conditions around the Milky Way Galaxy are generally less hospitable than once thought.

Comments

Old news...

[Boulder Geek]

Guillermo is well known for the "Rare Earth" hypothesis, which boils down to the thesis that planets identical to Earth are extremely uncommon. This has even been covered on Slashdot before.

I don't entirely disagree with Guillermo, but he does make one major blunder, IMHO: He assumes that complex life can only develop on planets with all of the same characteristics as Earth. That sub-hypothesis is not proven.

Regardless, lets say that a exact Earth analogs occur around one out of a billion stars. That still leaves 100 Earth analogs in the Milky Way alone.

The real issue for finding ET, IMHO (that sure gets tossed out a lot when discussing life in the Universe ;-) is that time is so much longer than we humans can perceive. Humans have been around in our present form for only a few thousand years, with only a couple of decades when we could be detected by extra terrestrial civilisations. In terms of the age of the Earth that is nothing, and compared to the age of the galaxy it is smaller than nothing. Our window in time is so narrow that it seems unlikely that it actually overlaps with other civilizations.

less hospitable to HUMANS

[jimmcq]

Why does everybody always assume that life can only form in conditions that are hospitable to humans?

Who's to say that there aren't other strange forms of life that have evolved to survive in conditions that would be downright hostile to humans?

Re:less hospitable to HUMANS

[barawn]

Because if you think about it, the life that we have (as humans) is, in many ways, analagous to a "minimum-energy solution" to a problem.

Think about it. Life on Earth begins, fundamentally, with long carbon chains and water cycles. Why carbon? Carbon is the only element that can form arbitrarily long, stable chains. Silicon can form chains - but only short ones. Longer silicon chains break down. There are additional reasons for carbon later, too. Why water? Take a list of molecules, starting from the simplest you can make. That is, H2, LiH, etc. Many of these compounds won't exist, though. Keep going. Water will stick out like a sore thumb when you get to it - because it's the first strong dipole you'll come across that's covalently bonded. The covalence is important because in a liquid form, the molecules are still there, rather than just ions. Ammonia (NH3) is a dipole, but not of the same level as water is. So, a water solution provides literally TONS of bonding possibilities. Hydrogen bonds form all over the place, and you get extremely complex chemicals popping up everywhere.

The basic requirements for life, in my opinion, would have to be the possibility for many, many combinations of molecules. That's what allows life to exist, really. So carbon/water based life suddenly becomes your 'minimum-energy' solution to generating life.

The other reasoning here is that if you look at the basic life on Earth, the elements it uses are, well, a little bit "unique" on a stellar scale. The most important elements for life on Earth are undeniably carbon, hydrogen, nitrogen, and oxygen. Without a doubt, you could probably make living objects from just these few elements (probably really basic, but still life). Here's the kicker: hydrogen is the most abundant element in the Universe, and carbon, nitrogen, and oxygen are the elements produced in the second most common stellar nucleosynthesis event, the triple-alpha process (the pp chain is the most common: it turns 4 protons into 1 alpha particle). So flat out, you are NOT going to have carbon somewhere and NOT have water, not for stellar abundance reasons. Temperature-wise, it's possible, so in very bizarre temperature regions, you might get life - I will admit that - but I do consider it unlikely, since high temperature regions don't really allow for molecules to form easily. :)

That being said, I want to note that I don't agree with the author here: I think he's being exceptionally restrictive. My opinion is all you really need for life is carbon and water. You probably also need nitrogen for variety, but as I've said, where there's carbon and water, you'll have nitrogen as well. Now, the 'livable for humans' bit: I honestly think that anyplace that has carbon, liquid water, and nitrogen could be made livable for humans. You need trace elements (iron, for instance, for hemoglobin), but in general humans recycle them - they don't get 'consumed' - so a well designed colony could probably survive by taking some small amount of trace elements along with them. But as for life developing THERE? I think with the above ingredients, they would find a solution that doesn't use a trace element that they don't have.

It doesn't matter, really. We have one data point to play with, and we can do whatever we want with it. His instinct says "no life anywhere, it's really complex" my instinct says "life everywhere there's water and carbon: it has this 'knack' for showing up everywhere."

a galaxy full of germs

[bcrowell]

Unfortunately, popular articles, including this one, don't usually do a good job of making the distinction between unicellular and multicellular life. There's every reason to believe that unicellular life is common in our galaxy. Microbes are tough. They can survive and/or permanently adapt to extremes of temperature and chemistry. It's quite possible that even within our solar system, there is unicellular on three different bodies: Earth, Mars, and Europa. When the "rare earth" folks talk about the dangers to life, such as ionizing radiation and comet strikes, those are really more like hazards to multicellular life. An unknown, but probably very big, percentage of the earth's biomass consists of microbes living deep underground or underwater, where they're relatively invulnerable to these things.

Multicellular life is a whole different story. It's a lot more delicate, and in our planet's geological history, it appears as an afterthought. Germs are and always have been the dominant form of life here.

Sorry if you're in love with the Star Trek/Star Wars picture, but most likely if our species ever manages to send probes to the nearest 10,000 solar systems, all we'll find is unicellular life. I'll bet your great-great-great-great-great grandkids a six-pack on it!