

Tens of billions of potentially habitable, Earth-size planets in our galaxy - atpaino
http://www.kurzweilai.net/tens-of-billions-of-potentially-habitable-earth-size-planets-in-our-galaxy-say-astronomers

======
JonSkeptic
>One in five stars in our galaxy like the Sun have planets about the size of
Earth and a surface temperature conducive to life

That is a considerable claim that jars with most of the astronomical data I've
seen. 1 in 5 is far more probable, perhaps an order of magnitude more probable
than I've previously heard.

Does anyone have studies that corroborate their claim?

[EDIT] Later in the article data is cited that more closely matches what I've
heard.

>Independently, Petigura, Howard and Marcy focused on the 42,000 stars that
are like the sun or slightly cooler and smaller, and found 603 candidate
planets orbiting them. Only 10 of these were Earth-size, that is, one to two
times the diameter of Earth and orbiting their star at a distance where they
are heated to lukewarm temperatures suitable for life.

It makes for a much less sensationalist title, but it seems to have more
research behind it.

Over all, I would question the method that caused them to arrive at the 22%
idea. I'm not sure that they are accounting for the missed planets correctly;
if they are, I would like to see their estimates corroborated.

[EDIT 2] Thank you, Tuna-Fish. Typo corrected.

~~~
Tuna-Fish
> astrological

UGHH. Astro _nomical_.

The previous studies have mostly been lower bounds, not attempts to estimate
the most likely count. We are still essentially terrible at locating earth-
sized planets in earth-like orbits, we are much better at finding larger
planets in closer orbits. Because of this, most of the planets that we do find
are larger and/or closer, however, this obviously should not be used to deduce
that most planets are larger and closer.

This study is using honest statistical analysis to estimate the likelihood of
earth-like planets from the data available.

~~~
radley
Psychics at Cal Tech...

[http://www.youtube.com/watch?v=M3DoDMfDa_Q](http://www.youtube.com/watch?v=M3DoDMfDa_Q)

------
Diederich
In my mind, Fermi's Paradox looms very large.

[http://en.wikipedia.org/wiki/Fermi_paradox](http://en.wikipedia.org/wiki/Fermi_paradox)

~~~
unepipe
Honestly, I've come to disagree with the "paradox". The ability to send
physical evidence of other intelligent life is based on a certain speed limit
of the universe. So that doesn't serve as much of a lack of evidence.
Habitable planets are too far apart for much interstellar travel to occur
readily given that the speed limit is c.

Beyond that, the power of a radio signal is inversely proportional to the
square of the distance, and we have things like magnetic eddies at the edge of
our heliosphere, so it might just be incredibly improbable for any
civilization to have generated the types of signal creation that we would pick
up.

In the hypothetical/fantastical, other advanced civilizations might have long
distance, superluminal communication technology, but that's not something our
civilization could actively intercept.

tldr; I don't buy Fermi's paradox.

~~~
Pxtl
The Fermi Paradox doesn't necessarily say that intelligent life doesn't exist.
The impossibility of interstellar travel is compatible with the Fermi paradox.

The point is that _if_ interstellar colonization is possible, the age of the
universe practically _requires_ galaxy-wide colonization as an inevitability.
Yes, it would take millions of years to colonize an entire galaxy. Tens of
millions, even.

Guess what? 10 million years is only 0.1% of the age of the universe. So if
_one_ civilization develops interstellar colonization, they experience
geometric growth and claim the entire galaxy.

So either there is no civilization that has a 0.1% lead on us (which is
statistically absurd if Earth-like planets are common) or interstellar
colonization is impossible.

~~~
maaku
It goes beyond that. Even if interstellar travel is not plausible, you'd still
expect to find solar systems completely transformed by intelligent life (think
Dyson spheres, although maybe not so extreme). If interstellar travel were
merely supremely difficult, then you'd expect regional clusters of stars
exhibiting these properties. These would be bizarre astronomical oddities that
we'd have likely noticed by now.

~~~
unepipe
I'd still maintain we simply can't detect it.

------
ceejayoz
I've seen this reported as 2
([http://www.theguardian.com/science/2013/nov/04/planets-
galax...](http://www.theguardian.com/science/2013/nov/04/planets-galaxy-life-
kepler)) and 8.8
([http://abcnews.go.com/Technology/wireStory/study-88-billion-...](http://abcnews.go.com/Technology/wireStory/study-88-billion-
earth-sized-planets-20780752)) billion this week. Anyone know why the wildly
different numbers being reported for the same research?

I'm also curious about Earth-sized moons around gas giants in the habitable
zone.

~~~
lxmorj
Don't Earth-sized moons of gas-giants have a few others problems? Less
consistent weather patterns due to a more complicated relationship with the
sun, stripping of the atmosphere due to gas giants gravity, and crazy huge
tidal forces from the same.

~~~
ceejayoz
I'm not an expert, so take these with a grain of salt.

There are plenty of spots on Earth with unusual weather patterns (not to
mention extremophiles). I'm not sure what sorts of weather changes a gas giant
moon would see but I'd imagine they're surmountable via evolution.

Titan has a nice atmosphere, so it's possible for a gas giant moon to retain
one. Gravitational force diminishes pretty quickly with distance, so if a
moon's a reasonable distance from the giant it'll likely be fine there.

Tidal forces give Io troubles, but the other moons of Jupiter seem to be
fairly stable geologically.

~~~
yongjik
Tidal force can be a blessing instead. Some says that plate tectonics plays a
vital role in making Earth a habitable planet. It requires continuous source
of heat from inside, which is supplied by radioactive elements[1] on Earth,
but in a gas giant moon, tidal force could play the same role.

[1]: (Off-topic) The fact that our whole planet's life basically survived
thanks to the gigantic amount of radioactivity buried inside, hot enough to
keep the whole planet's core molten for 4.6 billion years, gives me endless
amusement whenever I see someone ranting about how radioactivity has no place
in nature and is a deadly scourge we're inflicting on Earth.

------
Tossrock
I submitted the actual study for this yesterday and got no traction :\
[https://news.ycombinator.com/item?id=6679443](https://news.ycombinator.com/item?id=6679443)

------
melling
Unfortunately every single one of them is unreachable within several
lifetimes. We're going to be pretty much trapped in our solar system until we
try to solve some of the more difficult problems.

~~~
dm2
We're (other people, not me) at least working on it.

[http://www.nasa.gov/centers/glenn/technology/warp/warp.html](http://www.nasa.gov/centers/glenn/technology/warp/warp.html)

[http://en.wikipedia.org/wiki/100_Year_Starship](http://en.wikipedia.org/wiki/100_Year_Starship)

[http://en.wikipedia.org/wiki/Faster-than-
light](http://en.wikipedia.org/wiki/Faster-than-light)

If they're successful and you warp to a planet that's 100 light years away
then warp back, I don't know how much time would have passed on Earth though.

~~~
thangalin
Depends on their velocity. Assuming a warp of 95% the speed of light, then
~640 years (~320 years one direction). See:

[http://www.fourmilab.ch/cship/timedial.html](http://www.fourmilab.ch/cship/timedial.html)

[http://physics.stackexchange.com/questions/31105/how-to-
calc...](http://physics.stackexchange.com/questions/31105/how-to-calculate-
time-dilation-in-approaching-speed-of-light)

[http://www.phy.olemiss.edu/HEP/QuarkNet/time.html](http://www.phy.olemiss.edu/HEP/QuarkNet/time.html)

t / 2 = 100 / (1 - (0.95 * c)^2 / c^2)^(1/2)

Where t is the time for a one-way trip and c is the speed of light.

~~~
gliese1337
That's not how Alcubierre-derived warp fields work. The time inside a warp
bubble is predicted to remain synchronized with the time in the originating
frame. Thus, if your warp bubble goes at .95c, it'll take you 105.26 years one
way, 210.52 going there and back.

And I'm sceptical of your calculation, anyway. From Earth's unchanging
perspective, if your are going at .95c in a conventional manner relative to
Earth, Earthlings will see your trip as taking the same 210.52 years. Time
dilation will only affect the time that passes for the people on board, which
will make it seem _shorter_ , not longer. So, really, if your warp drive can't
break c, it's better from the passengers' perspective not to use one. This is
explained in the StackExchange article you linked to- you put the factor of
gamma in the wrong spot
([http://physics.stackexchange.com/questions/31105/how-to-
calc...](http://physics.stackexchange.com/questions/31105/how-to-calculate-
time-dilation-in-approaching-speed-of-light/31132#31132)).

~~~
thangalin
I was assuming conventional propulsion at 95% c. An Alcubierre warp field
would be ideal, assuming the problems can be overcome:

[http://en.wikipedia.org/wiki/Alcubierre_drive#Difficulties](http://en.wikipedia.org/wiki/Alcubierre_drive#Difficulties)

[http://arxiv.org/abs/1001.4960](http://arxiv.org/abs/1001.4960)

[http://arxiv.org/abs/1202.5708](http://arxiv.org/abs/1202.5708)

I'd enjoy seeing your calculation of the number of years that would have
passed on Earth for a round-trip of 100 light-years out.

~~~
gliese1337
You've seen it. 210.52 years. The passengers on the ship should only
experience 65.7 years- (210.52)sqrt(1-.95^2). Hence the famous twin paradox-
the twin who goes on a relativistic trip comes back younger than the one who
stayed behind. What you calculated was how much time would pass on Earth for a
trip that took 100 years and 100 light-years _from the perspective of the
people on the ship_ , which is not generally what people mean when they say
that a star is 100ly away.

~~~
thangalin
I found the source of my confusion.

The post I replied to stated, "I don't know how much time would have passed on
Earth though." You stated I calculated "how much time would pass on Earth."

The OP was wondering, "if a person on a ship visited a star 100ly away, how
much time would have passed on Earth when they returned?"

However, the OP was wondering about time frames in terms of a warp drive,
rather than a conventional almost-light-speed drive. Take my upvotes. :-)

------
samoht
1/5 seems to be the accepted number doing the rounds, but there must be other
factors to consider too - I'm sure this number is still overoptimistic?

For example..how many of these habitable exoplanets also do the following
earth things

1\. Rotate around their axis as opposed to having one side facing the star.

2\. have a stabilising moon to stop them from wobbling about.

3\. Also how many of these exo solar sytems similarly have heavier elements
and have evolved from spent star dust - using spent supernova explosions? To
have enough water you need H and enough O

Some other important considerations that should perhaps be factored in?

The Earth went through a couple of "snowball-earth events" which resulted in a
healthy % of oxygen being made available in the atmosphere.

We also have an outerlying and right-sized Jupiter to sweep away most of the
asteroids and space debris.

Even with all the luck in the world, intelligent life only involved in the
last million years of our 4 billion year plus Earth history... and we needed
an asteroid, the right size again, to wipe out the dominant dinosaurs so that
the evolutionary stage was set for our homo sapien species.

How much of this is repeatable?

We may indeed be the only intelligent life in our galaxy.

------
nikcub
I'm curious as to what is next, now that Kepler is dead what do we do to
substantiate this data further?

My impression is that there is not much more we can do to confirm outside of
the statistical models giving us probabilities, it would take some much more
advanced detection tech (or traveling there) to get further, which means we
might be stuck at this point for a little while.

~~~
gchokov
I guess pointing even more antennas to a star which is detected to have earth-
like size and location (SETI like programs). With even larger telescopes -
checking the light spectrum of the planet reflected light for chemical check
of the planet (reflected light spectrum can show what the source is made from,
to some extent).

~~~
maaku
We'd have to find them first.. Kepler was aiming at a distant part of the
galaxy.

------
codeboost
But let's say what we really hope for is true. What if we somehow discover
that a large number of these planets are teaming with life ? What then ? How
would that help us ? Spiritually, economically ? Wouldn't that make us feel
even less significant ?

I'm just wondering, why are we hoping there is life out there and what would
we do if we find it ?

~~~
Tepix
Hopefully, we'd get a little attitude adjustment, question religion more and
work together as a human race in the newfound awareness of our place in the
universe. Perhaps also work towards actually surviving as a race for a while
instead of selfishly exploiting every resource before others do.

~~~
VLM
It'll revolve around the Native American Experience, hopefully minus the
conquest and genocide, more likely as a pattern than an anti-pattern.

In the long run, some high school sports teams controversially named after the
aliens, some B-list movies, some academic interest, and that's about it?

------
VLM
I look forward to the discussion revolving around the concept of ten billion
inhabited worlds colliding with the prevailing HN wisdom that the only place
to do tech in the known universe is SV.

That's nice that you want to do tech, but if you stay on flyover Tatooine
you'll never work on anything more modern than a moisture vaporator, better
boot up the x-wing and fly to SV back on old Earth if you want to get paid to
do stuff with jquery.

~~~
VladRussian2
Yes, Tatooine under Pootine really sucks, doing even jquery in the Valley
beats it by orders of magnitude.

------
w_t_payne
This raises the obvious question .... Where _is_ everybody?

It's like we were born on the Marie Celeste; a place that should clearly be
brimming with intelligent life, yet appears (on the face of it) to be an empty
desert.

The more we learn that the extent to which the galaxy is chock-a-block with
habitable worlds, yet apparently devoid of intelligent life, the more I get a
truly creeped-out feeling that we are living in some horror-movie galaxy where
_something_ is killing _everything_.

~~~
patmcc
I sometimes think the answer is both boring and sad: everybody is just really,
really, unimaginably, far away.

Even if we manage to continue for another 10,000 years without causing our own
extinction, will we come up with anything capable of moving people even 10% of
the speed of light? If we do, will we bother to go to the stars?

~~~
repnescasb
That. Why did I have to scroll down so far to find exactly what I was thinking
all the time? I mean, I absolutely love Asimov and Mass Effect but they are
entertainment stuff. The distances we are talking about here seem to be
completely beyond everyone's mental reach. Even _if_ we could upload ourselves
into spacepods like Kurzweil suggests (or for that matter could just UDP our
souls out into space) we would not break the speed of light - which makes
interstellar travel possible but only in a very constraint range feasible.
Plus the problem that during the four years it had taken me to get to Proxima
Centauri, humanity on earth will probably have seen centuries pass...

~~~
w_t_payne
I think we just have to modify our brains to think a little bit longer term
than we do right now.

------
cschmidt
This news reminded me of Carl Sagan's Cosmos episode about the Drake Equation
([http://en.wikipedia.org/wiki/Drake_equation](http://en.wikipedia.org/wiki/Drake_equation))
that I watched as a kid. It is really an improved estimate for a couple of the
terms.

That segment of Cosmos is online:
[http://www.youtube.com/watch?v=MlikCebQSlY](http://www.youtube.com/watch?v=MlikCebQSlY)

------
carsongross
"Where is everybody?"

[http://en.wikipedia.org/wiki/Fermi_paradox](http://en.wikipedia.org/wiki/Fermi_paradox)

------
samoht
re: my previous post - I realize that 1/5 is for "potentially habitable" ...
but I was thinking too far ahead. What I was trying to get at is what factor
would we then need to multiply it (ie., this 1/5th) with to make intelligent
life a mathematical/chemical/biological certainty - as we know it here on
earth, for example.

Was what happened on earth - us - a unique fluke - would intelligent life
still come about if reran the whole thing 1000 times, even here on earth,
where it was almost an after-thought?

Are there other pathways - sliding doors - that would still have brought about
intelligent life here on earth?

What if we didn't have a magnetic field or if there was no Ozone? - that was
another thing I left out before.

We may be a fluke - the end result of a set of rare and unrepeatable
circumstances?

------
strikespeed
I'm only surprised that astronomers haven't concluded this long ago...
Speaking of which, there has been a lot of these new astro sightings this
year. Did they do something to the Kepler? I thought that spacetelescope was
abandoned due to technical problems. What am I missing?

~~~
ceejayoz
Confirming a Kepler planet requires observing multiple transits of the planet,
so it takes several years if it's an Earth-like orbit. On top of that, the
analysis and confirmation and peer review take time.

Incidentally, Kepler's been partially revived - they're going to point it
somewhere else that doesn't require the reaction wheels to stay stable.

