
Transit Detection of a Starshade at the Inner Lagrange Point of an Exoplanet - sanxiyn
https://arxiv.org/abs/1705.01285
======
ChuckMcM
Here I was hoping that Kepler had found a star shade.

Interesting point that at some point your observing apparatus gets good enough
that you can 'see' the structures built by sufficiently advanced civilizations
(sure they cloak their ships in orbit but you can see how they make their home
world comfy!)

At one of the SETI seminars there was a discussion about when would be the
"right" time to alert a newly discovered intelligent species that they aren't
alone in the universe. There was a lot of back and forth about indigenous
tribes in the Amazon, some of who learned of other tribes by the arrival of
missionaries, some by loggers, and some who were out walkabout and came upon
the strangers. How you meet outsiders has a different impact on how it affects
you.

So if you were aliens and you didn't want to 'alarm' or 'damage' humans, what
would you use as a signal that it was probably a good time to say "Hello" ?
I've always felt that once you could detect they were having conversations on
other planets you would now "know" we weren't alone and someone could appear
in orbit and say Hi. Others felt it would only be safe if humans felt
reasonably confident in their own ability to meet them at their level (so
perhaps at least colonies on other solar system bodies). One person at our
table was firmly in the only when it is unavoidable, which is to say they are
about to send a probe to an inhabited planet or come across a construction
like a station that is not easily concealed or moved.

~~~
TeMPOraL
Star Trek had its solution: no contact or interference with civilizations that
didn't develop warp drive yet. The goal of the rule was to not contaminate the
development of another civilization. In today's terms, you could generalize it
to: no contact with a civilization until it's about to, or already did, figure
out that there are others in the universe.

Which is kind of in between of the positions you described in the comment.

~~~
ChuckMcM
Which they violated whenever the script required it :-)

It's the 'figure out there are others' bit that made something like the Prime
Directive problematic. Given our advances in sensing and observing technology
we are much more likely to 'see' an advanced civilization before we can
actually fly out to meet them. If you _know_ that there is intelligent star
faring people living on a 'nearby' star, and they happen to have been
observing your progress, do they introduce themselves or wait for you to
figure out how to reach them?

~~~
gorkonsine
>Given our advances in sensing and observing technology we are much more
likely to 'see' an advanced civilization before we can actually fly out to
meet them.

I don't think this is really true (though I could be wrong, I am not an
astronomer). Sure, we may be able to "see" evidence of an advanced
civilization, but without warp drive, we won't have real proof. All we'll have
is some observational data showing that, for instance, the light from their
host star dims in a really weird way that's unlike anything we've seen before
in our observations, or that there's some object sitting in their L1 spot,
etc. We can hypothesize that this data indicates artificial structures,
because what natural phenomenon could possibly cause such things? But that's
not proof; there really could be some natural thing causing those readings.

So the ETs don't really have to establish contact until we have warp drive and
the actual ability to go see these artificial structures up-close. They can
just leave us to sit around our planet wondering what these observations mean,
and slowly come to grips with the idea that there may very well be some
intelligent ETs out there with starshades, and argue over it for a few
centuries as we'd surely do. They have no obligation to come visit us and
clear up the matter. And considering how backwards, irrational, and violent a
species we are, there's no good argument I see for the ETs to rush first
contact with us, and every reason to delay it as long as possible.

~~~
lordnacho
We'll be able to see the spectra from distant planets soon. That will amount
to "seeing" advanced civs.

Going to them with warp drive without landing and talking to them would be
equivalent. What would you be able to do? Basically sense EM radiation from
there with better resolution, but it's essentially the same thing, "seeing".

~~~
gorkonsine
You'll have to explain how seeing spectra from distant planets conclusively
proves intelligent life. I don't see how it does. Spectra will tell you that a
planet has molecular oxygen, for instance, carbon dioxide, etc., which would
indicate an atmosphere like ours, which would indicate life similar to ours
(doing photosynthesis), but you'd get that on a world occupied solely by
plants, or with only non-intelligent life. Anyone looking at Earth before
about 2M years ago (or anyone looking at it now, but more than 2M ly away)
will see exactly this: a life-bearing planet with no life intelligent enough
to build a civilization.

Finally, even if we could conclusively detect a civilization on a distant
planet, that still doesn't explain why they have any obligation to contact us.
They can easily just ignore us, and I for one can see why they would. The only
time they'd really need to strongly consider establishing contact is when we
have sufficient capability to visit them, and that's never going to happen the
way we're going. It'd probably by prudent on their part to spy on us though,
since we're a potential threat.

------
yodon
The article calculates that solar-radiation reducing shields for earth-sized
exoplanets (like some propose for mitigating climate change) will be
detectable by the next generation of astronomical telescopes.

~~~
weberc2
I'm confused... Does this mean we are looking for life sufficiently
intelligent to build these radiation-reducing shields? Or are we looking for
natural shields (i.e., a moon?) that might make a planet naturally resistant
to climate change?

~~~
drostie
The L1 point is a saddle point in the local effective potential: it is
therefore not stable enough for an object to stay there without station-
keeping.

So yes, the goal here would indeed be to detect life capable of creating large
structures and keeping them actively in orbit. There is some tongue-in-
cheekness to this sort of research, but as the abstract notes, also some
seriousness. The tongue-in-cheekness is that we're nowhere near being able to
build something this large between Earth and the Sun; as the abstract notes,
it has to be around as large as the Earth in order to usefully eclipse the
Sun; that's a very very large structure, and we're certainly able to get into
space right now: and yet we have no prospects even in the next many thousand
years for engineering anything at that scale, unless folks are right about an
impending technological singularity.

The seriousness, on the other hand, comes from one consideration: blotting out
the Sun is probably easier than fleeing to nearby star-systems. It's very hard
to say exactly how much energy it takes to flee to a nearby star-system, but a
lower limit for the technology that I can presently envision is maybe 10^20 J
of kinetic energy; my imagination might not be very good though, but I think
that's reasonably conservative. Now the solar power irradiating a disk-that-
blots-out-the-Sun is known to be 10^17 W or so. So the claim is, to even
harvest the level of energy that is required to try and scout out neighboring
star systems, one needs Sun-blotting scales of energy-harvesting technology;
the length scale could maybe be smaller by a couple orders of magnitude to
scout, but one can imagine that the energy needs of billions of entities
fleeing their home planet would be several orders of magnitude larger, too.

~~~
taneq
> blotting out the Sun is probably easier than fleeing to nearby star-systems

If we want to later use the sun-blotter as a solar panel to power our
interstellar exploits, then yeah.

If we just want to make the Earth a little cooler, we'd be far better off
seeding the stratosphere with some dust, creating a mini 'nuclear winter' /
'Krakatoa effect' in a controllable way.

------
ansible
This is some interesting speculation, and I applaud the researchers who think
of things like this to look for.

I still estimate that by the time a civilization has planetary-scale
engineering capability, that they won't need to make things like starshades.

If you have molecular nanotechnology, you can either adapt yourselves to
whatever location you find, or just skip the biological body business, and
directly upload your consciousness to a computer network.

The 2nd option is far more mass and energy efficient to support large numbers
of sophonts, and I expect that any civilization to endure long enough will
have the majority of its population living online instead of offline. If that
even ends up being a thing, and they all don't just merge into a single entity
(going in the direction of Star Trek's borg).

~~~
marcus_holmes
I always think of the "they're made of meat" story when considering this [1].

How do we even know what life looks like out there? Or what it has turned
itself into in order to survive, travel and spread? Or even what it started
out as?

We can't even talk with dolphins, even though we have a very recent
evolutionary common ancestor. They're sentient life, tool-users, do we think
they'd build a starshade to solve this problem? Shame we can't ask them, or
understand their answer.

We know trees are alive, we know they communicate with each other. We don't
think they're sentient. But how would we know? What would a sentient tree do
differently from a non-sentient tree? What would a sentient tree do about the
sun getting hotter?

Even if they started out like us, the evolutionary responses to living on
other planets will change them. We're adapted to the conditions on Earth. If
we live on other planets with different conditions then we will adapt, because
that's what we do. We don't know how far those changes will go, because all
the life we've ever seen has been adapted to Earth. Maybe high-gravity humans
are less like sci-fi dwarves and more like Pratchett trolls.

We seem to be expecting sentient life out there to resemble us and have
similar solutions for their problems. This seems dumb to me.

1:
[http://www.terrybisson.com/page6/page6.html](http://www.terrybisson.com/page6/page6.html)

~~~
fapjacks
Maybe, but this conversation _always_ inevitably ends up in this territory
("But what if aliens are _crystals_?"). And sure, we can't know. But we're
going to have to make some assumptions, and we all do live in one universe,
with a common constituent set of physical laws. Aliens that build spaceships
probably also have airplanes and an internet. I don't think it's dumb to
speculate with some reasonable assumptions, and while I appreciate that this
conclusion always comes up and is not wrong, it's uninteresting.

------
a_gopher
Paper doesn't address what measures the aliens might use to disguise any
obvious signature of the starshade.

You'd think that the aliens might not be too keen to create huge beacon
advertising their presence to all and sundry...

~~~
logfromblammo
One cannot assume that an alien can think in a fashion similar to Earth
animals.

Humans have the ability to imagine a possibility for which no supporting
evidence currently exists--that species alien to our solar system might exist.
That ability might not be shared by the species we can imagine. That is,
humans can imagine a species that cannot imagine humans. Such aliens would not
even realize that building a planet-sized object that cannot be explained by
natural processes might present an existential risk.

We, of course, are afraid of hypervelocity impact weaponry, even while having
no evidence whatsoever that any such weapon exists anywhere in the universe.

Of course, that just means that any species that did fear annihilation by
near-c rocks smashing into their planet would simply disguise their star shade
so well that we could not detect it. Meaning that any solar shade we can
detect was not likely built by any species able to think like us.

We could clean up by selling them insurance.

~~~
ceejayoz
I'm not sure how you propose a species that can't imagine things that don't
exist would advance technologically to space travel.

~~~
logfromblammo
Investigation of serendipitous results.

------
btilly
You know, this sounds like a great idea.

Maybe we should be building ourselves one of these...

~~~
tensafefrogs
But then they could find us.

~~~
mmjaa
Doesn't matter, still had planet supporting life.

------
graycat
So why has ET not used something like a Dyson sphere or a starshade to send us
light signals as a form of "Hello"?

Maybe because by the time a planet is able to send such signals, they have
discovered better means, faster than light speed, communications.

So, the "Hello" communications have been coming to us for maybe millions of
years, but like our planet before we understood radio, we can't detect their
communications.

~~~
downrightmike
We may even misinterpret the "Hello" signals because we don't understand their
mathematics. They could very easily be sending a "Hungry" signal, because they
are a race of locust.

------
mmjaa
Looking for umbrellas in space. What _will_ we think of next?

------
E6300
I know I'm gonna get downvoted for saying this, but this is kinda dumb. Might
as well look for Dyson spheres by looking for gravitational lensing around
dark spots in the sky.

