Metal-rich stars inhibit chances of life on their planets

Scientists hoping to narrow down the hunt for life outside of our solar system have hit on an indicator that may guide the search: metal. Specifically, the number of elements heavier than hydrogen or helium in the planetary systems’ host star. Although relatively metal-rich stars emit comparatively less UV radiation, more is …

[KittenHuffer]

Ozzy has a lot to answer for!

If heavy metal is responsible for the lack of life in our galaxy, and why we haven't found any yet, then we need to get together and say some strong words to Ozzy about the results of his life!

Mines the one with the post-grunge in the pocket!

[Plest]

Re: Ozzy has a lot to answer for!

My observations are that when I crank up my Decapitated or Fear Factory CDs it certainly clears the room pretty damn quick. So I guess with just me there nodding my addled brain, my wife would certainly concur that the room is thus devoid of intelligent life!

[lvm]

How NOT to write

So the ignorant hack who wrote this piece copypasted the abstract several times repeating what happens again and again, but got brain-freeze before the part explaining WHY this happens. Let me amend that:

The UV flux drops substantially with increasing metallicity, creating seemingly more favourable conditions for life. However, metallicity affects radiation in the O3-producing Herzberg continuum much more strongly than in the O3-destroying Hartley band. Thus, the net photochemical effect leads to a decrease of O3 with metallicity.

Thanks for drawing attention to that, but otherwise it was utterly unprofessional.

[LybsterRoy]

Re: How NOT to write

Thank you for explaining that - I was wondering how lower levels of solar UV could lead to higher levels at the surface of a planet.

[Anonymous Coward]

Re: How NOT to write

Thanks, a useful explanation!

Haven't had chance to read the paper, but my query would be how this applies to the reducing (low O2) atmosphere that was supposed to be around when life evolved (the oxygen only comes into play when the cyanobacteria started with photosynthesis)?

[parlei]

Re: How NOT to write

IIRC the model is

1. Oceanic cyanobacteria (et al) start dumping nasty reactive oxygen into the atmosphere

2. UV (of the correct type) start producing ozone from the atmospheric oxygen

3. Eventually enough of ozone has formed for there to be a "useful" ozone layer

4. Life invades land

5. Life evolves enough to develop AC, refrigeration and spray cans

6. Ozone layer starts to deplete

7. All die. O the embarrassment!

Steps 5-7 may be optional: the jury is still out on that part

[hplasm]

However...

Would a lifeform that sprang up on such a planet not develop to relish the high UV sunlight; adapt and thrive - the crux of Darwinism to local conditions?

"It's life, Jim - but not as we know it..."

[Charlie Clark]

Re: However...

More than an interesting thought experiment. Life of earth started in conditions that are antithetical to most of life on earth now: no oxygen, no photosynthesis, not much of an atmosphere.

I can understand the research in the context of whittling down the number of stars with potential earth-like planets, but, given what we've learned and then had to unlearn about exo-planets in the last twenty years alone, I wouldn't give it much shelf-life! But same goes for most of this stuff. And, until we can develop faster spaceships and means of communication over the distances, it's all a bit academic®. But, I guess that's the point!

[parlei]

Re: However...

History of earth indicates that life on land only really got started once there was an ozone layer. But n=1, so...

[Potemkine!]

There are a lot of assumptions in this study, for instance UV makes genomic damage in life forms as we know it. This study is about probably to find "evolved" life forms as it exists on Earth, more precisely on Earth and on land, excluding seas. This is very restrictive.

[Combat Epistomologist]

Wait a minute ...

One has to read the referenced paper with a grain of salt. A VERY LARGE grain of salt, upon which are written the following words:

"Keep in mind that a star having *no* 'metals' has no possibility of life on its planets at all, because in astronomer-speak, 'metal' means 'any element heavier than hydrogen and helium', and nobody has ever come up with an even remotely possible mechanism for life to evolve in a planetary environment where ONLY hydrogen and helium are available."

The authors of the research appear to have neglected the question of whether life on planets around their "metal"-poor stars is even possible at all. We don't have enough data points yet to establish what alternate biochemistries to our own are possible, but it is a pretty safe bet to make the general statement that a certain threshold level of chemical complexity is *required* for the development of life. ANY form of life is going to need to be able to build at least somewhat complex molecules. And that means "metals" need to be available. We don't know for sure what that minimum required chemical complexity *is* ... but I can flatly, iron-bound, copper-bottomed guarantee you it's more than 'hydrogen and helium'. And they need to be present in sufficient quantities to, y'know, get together and react. Or there won't be any life, or even any complex chemistry, happening at all.

[Claptrap314]

Huh?

Okay, I'm certainly no astronomer or physicist, but it sounds to me like they are saying not to look for intelligent life around Population I stars. If that's the case, I have one data point that... Nope. Never mind. Carry on.

Bring back the Paris icon!

[Claptrap314]

In the opposite direction

I've been thinking about this for the last few weeks, and would REALLY appreciate it if some could answer or point me in the right direction for my hypothesis.

It seems that in our case, it took 2GY for complex life to form. If we take 1GY as the minimum, this appears to put some hard geological limits in place. Specifically, if you want civilization, you need sizable oceans & sizable continents both. This requires an active core, which in turn requires the presence long-lived isotopes. Looking at https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_by_half-life#1015_seconds_(petaseconds), I don't see a lot of candidates. In particular, K-40 is lighter than iron, and so unlikely to be a major factor in the core of a rocky planet. So we are left with U-238, U-235 & maybe Th-232 to keep the core active.

But the only known way to produce U is for two neutron stars to shear each other & send out jets of the stuff. This seems to me to be an incredibly rare event. Enough to substantially affect the Drake Equation.

I know I'm uneducated here. Anyone with the appropriate background to help me out?

[ThatOne]

Re: In the opposite direction

> This seems to me to be an incredibly rare event.

Astronomy: Very different scales along both space and time: It is an incredible rare event, but which happens every second somewhere...

To illustrate, just take the amounts of heavy elements you find in our own solar system: How many massive stars must have died for all that waste to accumulate in this specific area, given local planets and assorted boulders only captured a fraction of it, and most has been blown away over time by solar radiation and gravity interactions?

On the other hand one needs to keep in mind the very first generation of stars was mostly pretty huge, very short-lived super-super-giants, and thus created pretty quickly a lot of the heavier elements. "Quickly" in astronomical sense, of course.

[Claptrap314]

Re: In the opposite direction

"Heavier", yes. But not U or it's neighbors, by my understanding.

And yes, space is much bigger than a trip to the chemist. But just how many neutron star pairs are there in this galaxy? And almost none will ever have this class of interaction. When I say "incredibly rare", I mean rare enough to matter in terms of astronomy.

[ThatOne]

Re: In the opposite direction

> When I say "incredibly rare", I mean rare enough to matter in terms of astronomy.

No, in terms of astronomy they are quite common. Star pairs are quite common, all stars eventually collapse, and depending on their mass, some of them go supernova and will become neutron stars. There must be at least a billion neutron stars in our Galaxy right now, we have actually detected many thousands of neutron stars "nearby" (and we can only detect the very young, exuberant ones, the older ones are difficult to spot). Now 5% of those we've spotted are binaries, so binary neutron stars aren't that rare. Given the distance of binaries tends to shrink because of the gravitational waves they emit, all of them are bound to merge, eventually.

Anyway, just consider how much uranium there is, just on our planet (not to mention all other elements heavier than iron!). It took a number of supernovae and neutron star mergers to create all that stuff, but one thing is sure, it has been created, so one has to assume enough supernovae and mergers have happened in our neck of the woods...

[Claptrap314]

Re: In the opposite direction

5%. WOW. That's a lot higher than I would have expected. Babe in the woods, I guess.

My question was about just how special is our particular neck of the woods is. With neutron star pairs that common, I guess we have to move to my (previously only implied): how long does it take for them to merge, and how "messy" is the merge? If the average time to merge is a trillion years, then we likely still have a paucity of source material. If a million year, then not so much.

<sigh> Lots of learning to make sense of this, I guess.

[ThatOne]

Re: In the opposite direction

> That's a lot higher than I would have expected.

Many seemingly unusual features are a lot more common than expected. Neutron stars are a normal feature of a star's evolution, so they are very common. Binaries are also more common than one would expect, heck, there are even monsters like the sextuple Alpha Geminorum ("Castor")!...

.

> how special is our particular neck of the woods

Scientifically speaking, there is no reason to think our area is special in any way.

.

> how long does it take for them to merge

It depends on so many different factors (initial distance, individual mass, relative mass, individual spin, individual magnetic fields) that you can't give a figure. The thing to keep in mind is that supernovae and neutron star mergers happen constantly somewhere in our galaxy, and both create those heavy elements. While their distribution across the galaxy isn't uniform (some star systems have less, some more), there is no indication that our system is outside the norm -- the norm for the intermediate suburbs of our galaxy. Further out, and especially further in, things change somewhat. Downtown, in the central bulge, stars are very dense, new stars are created constantly, there is a lot of dust and radiation, and the environment is generally unhealthy. Life would have a hard time appearing there I guess, but I'm no specialist.

[Claptrap314]

Re: In the opposite direction

Okay, not "scientifically special", "statistically special". Apparently, not so much.

[Claptrap314]

Looking for love in all the wrong places

I've been thinking. We're really looking for life in an incredibly small corner of even just this galaxy. It seems to me, however, that Type II.5 civilizations would have pretty clear signatures on the spectrum of their parent galaxies. And we can look at a LOT of galaxies for such a signature.

Again, not an astronomer nor a physicist.

[_Elvi_]

.. More Heavy Metals ..

More radioactive core, more metal in the planet core, stronger Van Allen radiation belt protecting the planet.. less UV at the planet surface..