Simulation Pinpoints the Most Likely Spots For Life In the Milky Way (sciencemag.org)

sciencehabit writes: Our home galaxy isn't as hospitable to life as you might think. Cosmic radiation, supernova explosions, and collisions with small galaxies make much of the Milky Way too hellish for biology. But a detailed new simulation locates quiet and fertile cosmic neighborhoods, including a surprising locale: wispy streams of stars flung far beyond the main body of the Milky Way.

Comments

Re:And when we finally discover life elsewhere.

[Velox_SwiftFox]

Outside the Slow Zone

Lots of assumptions

[surfdaddy]

Well, we are carbon life forms and we are looking at the situation from our perspective. I would say the chances of these simulations being accurate are vanishingly small. Do we REALLY understand how and where life forms? Being carbon-based, is it really realistic to assume any and all life is like us, formed like us (even if our other assumptions about our own formation are correct)? At one time we thought we were the center of the universe, right here on earth. We also thought that Mars has always been dry, and we thought that Pluto would be a featureless cold world. And THAT's only assumptions within our solar system!

You can be pretty confident that this "detailed new simulation" isn't very accurate at all.

Re:Lots of assumptions

[stevelinton]

The simulation is probably accurate, the summary article not so much. The simulation answers a rather more nuanced question -- something like "where in the galaxy could Earth;s history possibly have been replayed?" Some places there aren't enough heavy elements, others there are too many supernovae, or near-misses with other stars. Yes, life could evolve in other places, maybe -- on a neutron star, or in the complex magnetic structures in gas clouds near the central black hole or ..... but, although the article suggests it, that is not really the question being answered by the simulation here. Also note that elements much heavier than iron are pretty rare everywhere. Even if you could identify a feasible biochemistry based on iridium or something, there is very unlikely to be enough iridium anywhere for it to evolve.

Re:Lots of assumptions

[buchner.johannes]

Stars predominately form He (which is chemically inert), C, N, O (see CNO-cycle), a bit of Fe as well as a little bit of heavier elements from supernovae. Therefore life anywhere will most likely be formed of a combination these elements just because of their abundance.

Re:Lots of assumptions

[delt0r]

Well really bad scifi aside (Dr Who, star trek). A proper look at elemental abundance and chemical properties, something that we do know with a lot of accuracy, non carbon based life forms are a pipe dream. The only proposed element is silicon, and it is shit. Total shit. It simply does not form the range of compounds you need. Does not have any kind of useful solvent. doesn't naturally form anything interesting even in the slightest. And where you have silcon you have carbon. In fact silicon is far more prevalent on earth than carbon, yet life only uses it for shells of some diatoms.

Compare to carbon, where we have giant clouds of interesting organic molecules just floating around in space, that can bond to itself and other elements in an infinite range of ways with and equally diverse range of properties. Water is a *very* good and strong solvent and highly polar. But in a pinch i guess say methane may work as a solvent. But it wouldn't be as good as water.

In short there are very good reasons to believe all life in this universe will be carbon based. But lets not forget, that gives a huge scope for varation from what we see here on earth. With equal certainty all alien life will not be biocompatible with us. If we found anything with DNA, RNA etc, it would be very strong grounds to suspect common origin.

Some people i work with here, are astrobiologist. Honestly carbon is as impressive as a bable fish.

Re:Lots of assumptions

[delt0r]

So a solvent is important for moving things around. Mobility of compounds in other words. It turns out that some form of general mobility is always required, otherwise it would just sit there doing nothing. Without mobility nothing can spontaneously from. Water is again much like carbon, especially unique. However it is true that other solvents are possible. The most likely being liquid methane, because it can plausibly exist.

It should also be noted that *no one* has came even close to the most basic set of metabolism for anything other than carbon based life, in a water based solvent.

Re:Lots of assumptions

[amorsen]

If water were such a great solvent for organic compounds, then I'd be very afraid to drink any...

Selection bias. Water is an almost universal solvent. Everything we see is stuff that is left behind after water dissolves the rest, so to us, water does not seem very potent.

Supernovae as risk

[Framboise]

The research focuses on risks for life linked to cosmic radiation produced by supernovae (and massive stars in general).

This is only one of the risks. In dense regions of galaxies stars perturb the planetary orbits sufficiently frequently to destroy any climate stability. The solar system has been lucky not to have a star nearing the whole solar system in the last 4 billions years, such that even the outer planet orbits are near from circular.

On the other hand it is not difficult for life to screen strong cosmic radiation, such as
in the ocean and deep in the earth crust where most of the biomass exists. So the argument of cosmic radiation killing all life is probably wrong.

Re:Supernovae as risk

[wonkey_monkey]

On the other hand it is not difficult for life to screen strong cosmic radiation, such as in the ocean and deep in the earth crust where most of the biomass exists.

And that's why I'm staying in the basement.

Re:Supernovae as risk

[rgbatduke]

Building stargates aside, the problem with radiation is tied to the problem with magnetic moments. The radiation from the local sun alone is enough to make life anywhere from pretty unlikely at all to pretty unlikely to evolve into a rich ecology if the planet in question hasn't got enough of a magnetic field to provide a radiation shield from both cosmic rays and the solar wind. Without it, atmosphere is just blown away by the solar wind and cosmic rays reach the surface in abundance. The solar magnetic field may also be important, or rather the coupled geosolar field may be key. Oceans won't last without a stable atmosphere for the billions of years (apparently) necessary to get "interesting" life forms.

Another issue that I think is very much up in the air is how important the moon is to evolution. We have a very limited sample in our own solar system, but there are three planets that "should" be in a generically habitable zone. Earth and Venus are almost the same size, but Venus has no moon. As a consequence (?) it has an incredibly dense atmosphere (where I'm speculating that the collision that resulted in the moon blew off a substantial fraction of the Earth's early atmosphere and altered the composition of that which remains). Mars is perhaps too small to bind an atmosphere of the right composition, but in any event it lacks enough of a magnetic field to keep the solar wind from stripping off the atmosphere it has/had. It may have life. It may have HAD life. But it is very unlikely to be a place where life can develop into a complex ecology, let along intelligence.

It could well be that intelligent life requires several more "ands" of additional conditions: a planet with the "right" magnetic field in the habitable zone for the star in question, that has to have the "right" magnetic field as well, with at least one largish moon close enough to churn up its atmosphere (or worse, a moon that "has" to be formed by a collision between two proto-planets that strips the crust/atmosphere of the larger survivor), with the "right" mix of leftover heavy elements from the previous supernovae that created the stardust from which the whole system condensed to keep the core molten and magnetized, with the "right" mix of lighter crustal material to provide the needed carbon, oxygen, nitrogen, and hydrogen, especially oceans of water and at least eventually an atmosphere with a substantial proportion of oxygen.

But there are almost certainly more than Avogadro's number of planets out there, which is a lot of times to roll the dice for what is likely a fairly finite set of conditions. There are almost certainly billions of planets in just the visible part of the Universe alone, tens or hundreds or thousands per galaxy, that have all or most of the conditions needed for basic "life", and some fraction of them the conditions needed for the eventual evolution of intelligent life. However, we have no reliable way of computing the probability of life given those conditions, or intelligence given life. If either one requires the moon-forming collision, life could be quite rare as that probably doesn't happen (given all the other conditions) very often.

rgb

Re:Supernovae as risk

[delt0r]

You don't' really need a magnetic field. Earth for example has 10 metric tons per sq meter of atmosphere to protect you. And it does. Also even without a magnetic field an atmosphere can easily last billions of years, see venus. It is easy to imagine a set of parameters that would result in stable liquid water for billions of years, that requires no such magnetic field. As for moons... There is a big difference between alien life and multicellular alien life. It took a long time for that to get of the ground here, and many ways to get some form of cyclic thing going. Also there is nothing suggesting you need that either. It has been proposed with little evidence that it is required.

Re:Supernovae as risk

[rgbatduke]

I agree that this is controversial, but it is by no means a slam dunk that it isn't necessary. And if it isn't, it makes it more likely that a moon-forming atmosphere stripping collision is needed (or else bombardment by comets or whatever you think is needed for an ocean). And then there are the issues associated with radiation. The point is that there may be some subtleties associated with the requirements for life that mean that high radiation zones (sustained) are indeed inimical to life. Or (sure) not. It will likely be a decade or three before we even have a good enough theory (backed by at least SOME observations) to resolve these questions.

Re:Simulation is wrong.

[KGIII]

[citation needed] for the first sentence. No, I'll need actual proof, not speculation.

Re:Drake Equation

[buchner.johannes]

Most variables have become known to some degree in the last few years, namely the number of planets per star, the size distribution of planets, fraction of planets in the habitable zone, etc. see http://arxiv.org/abs/1508.0120... (it does not use the Drake equation).

The unknown in the Drake equation is the fraction of habitable planets in which life (or a intelligent civilisation) arises, which probably remains speculation until either >3 civilations have been found or civilations have been ruled out for a few hundred exoplanets.

Observer bias

[argStyopa]

If the premise of the study is to highlight the risks of near stellar neighbors and cluttered neighborhoods, of COURSE the conclusion will be that remote systems are 'safer'.

This is like asking a cancer doctor where it's safest to live, and getting the answer "in a sealed lead-lined vault"....yes, disregarding the need for air, water, and food, and only focusing on the cancer risk, that's probably great.

While we simply don't KNOW the primary drivers of life generation (or the Drake equation would be a lot less hand-waving), and while yes, there's a danger of nearby stellar events, one might also consider:
- our solar system didn't just appear ex nihilo: the heavier elements present suggest that our system formed from nova or supernova remnants. A more cluttered stellar neighborhood is going to have more of such events. While these events would be indeed dangerous (likely exterminatory) for nearby life, life might regrow with such staggering frequency that the stellar scales are outmatched
- radiation: dangerous, sure, but we exist because of mutations. LIFE is based on mutation. (And hell, there's persuasive evidence here on earth that living with higher level of background radioactivity actually increases life span; then again, that could also be a raised average due to selective weeding by same.) A higher-radiation environment is not necessarily inherently bad for life, and may actually accelerate the mutative processes.

These are just a couple of reasons that inner regions might be better. A lot of it is simply guesswork at this point.

Contradiction in terms

[tomxor]

Forget the summary or the article, the title makes no sense... "pinpoint" and "likely" are pretty close to antonyms of each other... that's like saying a weather simulation has pinpointed where it's going to rain next week.

Re:Drake Equation

[malditaenvidia]

This 'simulation' is no more realistic than a simulation in a video game.

I don't know about that: racing and flight simulators do take things like physics and weather into account. Farming sims have a firm basis on reality, by means of being boring, hard work.

Re:Drake Equation

[sycodon]

400 billion stars in our Galaxy, 100 billion galaxies in the Universe (that we can guess at). So even with ONE Planet for each star the odds of intelligent life out there is overwhelming.