
Planetary 'autopsies' indicate worlds like Earth common in the cosmos - weare138
https://www.reuters.com/article/us-space-planets/planetary-autopsies-indicate-worlds-like-earth-common-in-the-cosmos-idUSKBN1WW2M7
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vfc1
A possible explanation of why we haven't found anything is because intelligent
live once developed will quickly overload the ecosystem and start causing
things like climate change and quickly make the planet inhabitable, this could
all happen in less than 2 million years which is nothing on the cosmological
scale.

There was running water on Mars and it's within the goldilocks zone. Probably
Venus too, both those planets had stable conditions for the emergence of life
for billions of years.

Once a species like humans starts spreading like a virus and taking over the
ecosystem, it can easily go downhill very fast (cosmologically speaking).

~~~
vanderZwan
I suspect it's the other way around, really: it might be really hard to
develop out of the early stages without hitting a reset button. Yes, we're
destroying the planet at the moment and it remains to be seen if we learn
quickly enough. However, the first cyanobacteria repeatedly caused global mass
extinction events by poisoning the atmosphere with oxygen _for over 800
million years_ until something evolved that could breathe that poisonous
molecule[0]. That is almost one fifth of the entire age of Earth.

What if the odds that most planets are trapped in early development of life
for the entire time that it can support life are just really really big?

[0]
[https://www.patheos.com/blogs/daylightatheism/2009/02/bands-...](https://www.patheos.com/blogs/daylightatheism/2009/02/bands-
of-iron/)

~~~
vfc1
I think this is also a likely cause, the odds that life even develops beyond
the microscopic level, plus the fact that civilizations probably don't last
that long combined with the scale of the cosmos and the light speed limitation
means that it's unlikely that two civilizations even become aware of each
other.

Still, I think it's a bit surprising that no signs of former life have been
found so far in both Mars and Venus especially, and even elsewhere in our
solar system like on certain moons.

~~~
atupis
There are definitely lots of hints that there is live in Mars, but not a
smoking gun yet.
[https://en.wikipedia.org/wiki/Life_on_Mars#Possible_biosigna...](https://en.wikipedia.org/wiki/Life_on_Mars#Possible_biosignatures)

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m3kw9
The probability of no other intelligent life other than ours is near zero. The
reason most question it is because we are relatively unintelligent, given we
can’t even exit our solar system, and also see anything clearly in the next
closest system.

~~~
ravenstine
No, they question it because there's no evidence that there's intelligent life
elsewhere. Not only do we only have one known example of sapience in the
universe, but only one example of sapience on a planet with over a million
species of animals. _As much as I admire crows, dolphins, and greater apes for
their intelligence, they don 't even come close to the intellectual capability
of humans._

The fact that there are habitable planets out there gives us hope that we will
find extraterrestrial life, perhaps intelligent, but to assert that there must
be life out there is speculation. To say that those who question whether
there's extraterrestrial intelligence is pure arrogance.

~~~
m3kw9
I just looking at the billion billion galaxies out there, what are the chances
there is no life or even slightly intelligent given the physics and chemistry
laws are the same in every planet.

~~~
behnamoh
Some scenarios:

1\. ET life formed and vanished so quickly that they didn't even get to the
stage where they generate electromagnetic signals.

2\. ET life formed and got to generate EM waves, but:

\- they're either too far from us that we haven't detected those waves yet;

\- they only recently got to this stage and the signals they produce have not
reached us yet;

\- or both.

3\. ET life formed way sooner than we did; figured out how to generate EM
waves, and then vanished entirely. So, any signals of their civilization they
must have sent out there have already reached earth, but before we began
listening for such signals.

4\. Then again, since there are practically infinite number of planets with
habitable conditions for ET life, statistically speaking, we must have already
received a signal from at least one of them.

Which leads me to this:

5\. ET life doesn't exist, because the universe as we know it is most probably
a simulation inside a computer and the computational resources can only render
so many different objects at a time. (This is serious stuff, researchers have
already proposed methods for verifying this:
[https://www.washington.edu/news/2012/12/10/do-we-live-in-
a-c...](https://www.washington.edu/news/2012/12/10/do-we-live-in-a-c...)).

~~~
JackFr
(5) is not serious. It’s nonsense, and I wish people would stop bringing it
up.

~~~
behnamoh
Can you say why it's nonsense? It's a speculation and can either be proved or
discarded. I wouldn't do neither without proof.

~~~
varjag
It's essentially solipsism and there are strong philosophical arguments
against it.

~~~
JackFr
That's it in a nutshell.

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surfsvammel
Even if there are Earth like planets everywhere, we don’t know the probability
that life appears spontaneously. Right?

How does this change our outlook if one assumes The Great Filter hypothesis?
Does this lower or increase that such a filter would be behind us or before
us?

~~~
Iv
The last years have given us two estimates of previously unknown factors in
the Drake equation, that's why everybody is excited.

Yes, life could be very improbable to appear, but there is a counterargument
to this hypothesis: on our planet, life appeared almost immediately once the
crust solidified and oceans appeared.

If there had been a 3 billion years period, there may have been an argument
that maybe we got very lucky it appeared at all, but we have fossils that are
just 100 mil years younger than the apparition of oceans. And we keep finding
older ones.

If life was a really rare occurrence that would mean we would have been lucky
twice: that it appeared at all and that it appeared that early.

> Does this lower or increase that such a filter would be behind us or before
> us?

When so many things are unknown, it makes little sense to talk about
probabilities. It removes a possibility for a filter behind us.

I still have doubts that evolution necessary leads to intelligent life. When I
started getting interested into evolution, my main surprise was that there is
no "optimal" unicellular life-form. Why isn't the earth covered by a green
pellicule of photosynthesis-able cells that would be a Kardashev I organism
without ever reaching intelligence?

I still don't understand why it did not happen. Evolution favored competition
to optimality and the reasons are unclear. I would not be surprised that
evolution in other ecosystems would result in one organism "winning" over all
the others.

My personal opinion is that we will find a lot of life on other planets, but
many will be unicellular and many will show an evolutionary process that is
stuck in a dead-end.

I expect intelligent life to be rare, and that the "great filter" is that we
will find things much more worthy of our time and energy than colonizing the
universe or doing mega-engineering projects. Maybe we'll colonize a few star,
build a Dyson star or two, but then we will discover that everyone prefers to
spend time in another dimension, or in infinite pocket-universes. Maybe the
real party is inside the black holes or the neutron stars and all the advanced
civilizations are waiting for us to figure it out.

The idea that an intelligent species would colonize the universe assumes that
it does not manage to handle its demography or views its growth as a good
thing. I doubt that this is a rational conclusion once you reached the state
of full automation.

~~~
xornox
Green unicellular life-form is perfect food and energy source same way as
energy of sun is. Evolution does not stop if there are easy energy sources
available everywhere.

Nature does not care if energy of sun is used optimally or not. It just cares
if offsprings live or not.

~~~
Iv
I think it is very easy to imagine a local minima in which evolution would be
stuck. Making a membrane far too hard to pierce could starve a predator into
extinction instead of making it evolve.

If you reach a point where one organism developed enough mechanisms to resist
simple predators and that their advanced predators die out, I think it would
be impossible for evolution to get out of that dead end. I am not sure that
getting unstuck is a universal feature of life.

Emergence of sexual reproduction, of multi-cellular organisms, are all very
weird phenomenon that I think are risky to take for granted.

I mean, it feels like playing Conway's game of life: Often, when you start a
random one, it all dies out. It often gets stuck in a position where just a
few things vibrates. Some last longer. Others go on forever but are rarer.

My intuition (which can be dismissed without argument) is that life is
similar: if the conditions are right, it may lead to emergent evolutionary
behaviors that eventually can lead to intelligent life, but that's not the
most common outcome.

~~~
DiogenesKynikos
> If you reach a point where one organism developed enough mechanisms to
> resist simple predators and that their advanced predators die out, I think
> it would be impossible for evolution to get out of that dead end.

If all the predators died out, then those defense mechanisms would become
wasteful, and organisms that didn't have those defense mechanisms would be
more efficient. That would open the door to the development of new predators.
The situation you're describing is not a true equilibrium, in other words.

~~~
Iv
True, but in such case, defense mechanisms don't just disappear from the gene
pool, they just get deactivated. The second time they are going to be much
faster to re-evolve, making the disappearance of the second appearance of
predators even faster.

~~~
DiogenesKynikos
The predators will never disappear in the first place.

The fewer predators there are, the more wasteful defense mechanisms are, and
therefore the more disfavored they are by natural selection. The more
predators there are, the more defense mechanisms are favored. The equilibrium
is neither zero defenses nor 100% effective defenses against predation. It's
somewhere in-between.

The predators get to evolve too, by the way. There's no 100% effective defense
against all forms of predation.

------
kornork
My physics isn't great, but why does it matter that these are white dwarfs?

The article says "researchers studied six white dwarfs whose _strong
gravitational pull_ had sucked in shredded remnants of planets" and "if they
stray near its _immense gravitation field_, they “will be shredded into dust,
and that dust will begin to fall onto the star and sink out of sight.”

Isn't it the case that the gravitation field will be as strong as it was
before the star died, or even weaker from blowing off its outer layers?

~~~
_Microft
White dwarfs are interesting because they make up almost all of the current or
future outcomes of most stars in the milkyway. ->
[https://en.wikipedia.org/wiki/White_dwarf](https://en.wikipedia.org/wiki/White_dwarf)

The Roche-limit (the radius at which a satellite would be ripped apart) for
the Sun-Earth system is at ~ 550000km. That's inside the current size of the
Sun. So if the sun shrank a lot (white dwarfs are basically small, 'dead'
stars which shrank to that size after the nuclear fusion stopped which had
counteracted the attraction of the star's mass), Earth could actually be in
such a low orbit and therefore fall apart due to the Sun remnant's attraction.

-> [https://en.wikipedia.org/wiki/Roche_limit](https://en.wikipedia.org/wiki/Roche_limit)

~~~
prewett
Why would a decrease in the sun's radius cause a change in Earth's orbit? From
those to articles it sounds like the mass of the sun will remain about the
same, so the orbit should remain about the same. And less mass will cause the
orbit to migrate outwards.

~~~
the8472
Shrinking of the star simply makes it _possible_ to come within the roche
limit without being inside the star. The inspiral would happen due to separate
processes e.g. friction as the star sheds its envelope or due to interactions
between multiple planets.

~~~
bigwavedave
When the Sun enters the red giant phase, will the radius have expanded enough
to consume the earth? I'm trying to remember if that was something my physics
professor said years ago or if I heard it from someone less reliable and am
merely attributing it to him...

~~~
_Microft
Wikipedia says the sun is expected to expand out to roughly the orbit of Venus
(consuming it and Mercury) and turning Earth into a blob of molten rock.

------
SubiculumCode
I am not an astronomer, but in terms of empirical evidence, for the longest
time the only prior we had was our own solar system. Thus the natural best
guess should have been that (at least for stars similar to our own) earth-like
rocky planets near our size should be the most frequent occurrence.

------
sbmthakur
Assuming there are intelligent species living in nearby systems(with not such
advanced tech), it's unlikely that they can notice us unless we can control
the light intensity of our Sun. Because that's the only object they're
probably looking at.

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andrewflnr
So, to be clear, are they doing spectroscopy on the spectra of these white
dwarfs? Do they have to be looking at it at the exact moment the planet gets
shredded or do the chemicals they're looking for remain in the star's
atmosphere?

~~~
acqq
From their paper (link in my other message):

"(White dwarfs) WDs are the remnant cores left behind when a star ejects its
hydrogen-rich outer layers after the red giant phase. These remnant cores are
~0.5 M (solar masses) and about the same radius as Earth, are no longer
powered by fusion, and slowly cool over time. Because of their high densities,
and thus strong gravitational fields, elements heavier than helium rapidly
sink below their surfaces, becoming unobservable. Nonetheless, spectroscopic
studies show that the atmospheres of up to half of WDs with effective
temperatures <25,000 K are “polluted” by elements heavier than He (3–5). The
source of these heavy elements is exogenous, coming from accretion of debris
from rocky bodies that previously orbited the WDs (6–9). We exploit this
pollution to measure the elemental constituents of extrasolar rocky bodies."

So the answer is "the later."

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acqq
The paper:

[https://science.sciencemag.org/content/366/6463/356](https://science.sciencemag.org/content/366/6463/356)

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ropiwqefjnpoa
The science here and although it's different, makes me think of the "I’m
Convinced We Found Evidence of Life on Mars" article posted here a few days
ago. If they are able to draw these conclusions with such limited data, I
doubt they've missed anything obvious on the surface of Mars.

