In the end, a million pieces of hardware scattered throughout the solar system will do a lot for us and the capability is mostly in place while the economics are not too much behind.
When we do launch a craft to another planet, we will have ample
images to inform us about our target. That craft will be fast and
sent to collect high resolution data. It will also be a lot sooner
than anyone thinks. We are on an exponental curve.
It will still be a serious challenge.
To Build the
Ultimate Telescope
by PAUL
GILSTER on AUGUST 20, 2014
In interstellar
terms, a ‘fast’ mission is one that is measured in decades
rather than millennia. Say for the sake of argument that we achieve
this capability some time within the next 200 years. Can you imagine
where we’ll be in terms of telescope technology by that time? It’s
an intriguing question, because telescopes capable of not just
imaging exoplanets but seeing them in great detail would allow us to
choose our destinations wisely even while giving us voluminous data
on the myriad worlds we choose not to visit. Will they also reduce
our urge to make the trip?
Former NASA
administrator Dan Goldin described the effects of a telescope
something like this back in 1999 at a meeting of the American
Astronomical Society. Although he didn’t have a specific telescope
technology in mind, he was sure that by the mid-point of the 21st
Century, we would be seeing exoplanets up close, an educational
opportunity unlike any ever offered. Goldin’s classroom of this
future era is one I’d like to visit, if his description is
anywhere near the truth:
“When you look on
the walls, you see a dozen maps detailing the features of Earth-like
planets orbiting neighboring stars. Schoolchildren can study the
geography, oceans, and continents of other planets and imagine their
exotic environments, just as we studied the Earth and wondered about
exotic sounding places like Banghok and Istanbul … or, in my case
growing up in the Bronx, exotic far-away places like Brooklyn.”
Webster Cash, an
astronomer whose Aragoscope concept recently won a Phase I award
from the NASA Innovative Advanced Concepts program (see ‘Aragoscope’
Offers High Resolution Optics in Space), has also been deeply
involved in starshades, in which a large occulter works
with a telescope-bearing spacecraft tens of thousands of kilometers
away. With the occulter blocking light from the parent star, direct
imaging of exoplanets down to Earth size and below becomes possible,
allowing us to make spectroscopic analyses of their atmospheres.
Pool data from fifty such systems using interferometry and
spectacular close-up images may one day be possible.
Image: The basic
occulter concept, with telescope trailing the occulter and using it
to separate planet light from the light of the parent star. Credit:
Webster Cash.
Have a look at
Cash’s New Worlds pages at the University of Colorado
for more. And imagine what we might do with the ability to look at
an exoplanet through a view as close as a hundred kilometers,
studying its oceans and continents, its weather systems, the
patterns of its vegetation and, who knows, its city lights. Our one
limitation would be the orbital inclination of the planet, which
would prevent us from mapping every area on the surface, but given
the benefits, this seems like a small issue. We would have achieved
what Dan Goldin described.
Seth Shostak, whose
ideas we looked at yesterday in the context of SETI and political
will, has also recently written on what large — maybe I should say
‘extreme’ — telescopes can do for us. In Forget Space Travel:
Build This Telescope, which ran in the Huffington Post, Shostak
talks about a telescope that could map exoplanets with the same kind
of detail you get with Google Earth. To study planets within 100
light years, the instrument would require capabilities that outstrip
those of Cash’s cluster of interferometrically communicating space
telescopes:
At 100 light-years,
something the size of a Honda Accord — which I propose as a
standard imaging test object — subtends an angle of a
half-trillionth of a second of arc. In case that number doesn’t
speak to you, it’s roughly the apparent size of a cell nucleus on
Pluto, as viewed from Earth.
You will not be
stunned to hear that resolving something that minuscule requires a
telescope with a honking size. At ordinary optical wavelengths,
“honking” works out to a mirror 100 million miles across. You
could nicely fit a reflector that large between the orbits of
Mercury and Mars. Big, yes, but it would permit you to examine
exoplanets in incredible detail.
Or, of course, you
can do what Shostak is really getting at, which is to use
interferometry to pool data from thousands of small mirrors in space
spread out over 100 million miles, an array of the sort we are
already building for radio observations and learning how to improve
for optical and infrared work on Earth. Shostak discusses a system
like this, which again is conceivable within the time-frame we are
talking about for developing an actual interstellar probe, as a way
to vanquish what he calls ‘the tyranny of distance.’ And, he
adds, ‘You can forget deep space probes.’
I doubt we would do
that, however, because we can hope that among the many worlds such a
space-based array would reveal to us would be some that fire our
imaginations and demand much closer study. The impulse to send
robotic if not human crews will doubtless be fired by many of the
exotic scenes we will observe. I wouldn’t consider this mammoth
space array our only way of interacting with the galaxy, then, but
an indispensable adjunct to our expansion into it.
Image: An early
design for doing interferometry in space. This is an artist’s
concept of the Terrestrial Planet Finder/Darwin mid-infrared
formation flying array. Both TPF-I and Darwin were designed around
the concept of telescope arrays with interferometer baselines large
enough to provide the resolution for detecting Earth-like planets.
Credit: T. Herbst, MPIA).
All this talk of huge
telescopes triggered the memory of perhaps the ultimate instrument,
dreamed up by science fiction writer Piers Anthony in 1969. It was
Webster Cash’s Aragoscope that had me thinking back to this one, a
novel calledMacroscope that was nominated for the Hugo Award in
the Best Novel Category in 1970. That’s not too shabby a
nomination when you consider that other novels nominated that year
were Ursula Le Guin’s The Left Hand of Darkness (the
eventual winner), Robert Silverberg’s Up the Line, and Kurt
Vonnegut’s Slaughterhouse Five.
The ‘macroscope’
of the title is a device that can focus newly discovered particles
called ‘macrons,’ a fictional device that allows Anthony to
create a telescope of essentially infinite resolution. He places it
on an orbiting space station, from which scientists use it to
discover exoplanets, observe alien races and even study their
historical records. The macroscope is also a communications device
used by intelligent aliens in ways the human observers do not
understand. When a signal from a potential Kardashev Type II
civilization is observed, a series of adventures ensue that result
in discoveries forcing the issue of human interstellar travel.
So much happens in
Macroscope that I’ve given away only a few of its secrets. Whether
the novel still holds up I don’t know, as I last read it not long
after publication. But the idea of a macroscope has stuck with me as
the embodiment of the ultimate telescope, one that would surpass
even the conjectures we’ve looked at above. Anthony’s macrons,
of course, are fictional, but complex deep space arrays and
interferometry are within our power, and I think we can imagine
deploying these technologies to give us exoplanet close-ups as a
project for the next century, or perhaps late in this one. What
images they will return we can only imagine.
David Herne August
20, 2014 at 13:50
So many of our
troubles today would doubtless evaporate if instead of looking
inwards at our differences and fighting each other over them, we
looked outwards to see a much, much bigger picture. Though I’m not
necessarily a fan of the tactics employed by nation builders such as
Otto von Bismark and Giuseppe Garibaldi, these gentlemen understood
this and engendered through their cunning, the creation of two
great, modern nations. Remarkably, perhaps we might make for
ourselves a similar, unifying opportunity.
As a member of the
Murchison Widefield Array, radio telescope community, I am familiar
with the emergent capabilities and issues surrounding terrestrial,
low-frequency interferometric arrays but haven’t kept abreast of
the near-term potential for realisation of instruments such as the
TPF, in whatever form recognised today as most promising. However,
were interested parties able to rouse governments around the world
to support creation of an instrument capable of imaging worlds
beyond our solar system by each adopting and funding a single
component mirror, singly or together with others, perhaps the
project could ‘fly’. Many, many nations would then have
ownership of what would surely rank as one of the most significant
endeavours ever. School children would talk to each other across
borders and together imagine together the discoveries that might be
accomplished. We would have something big in common.
For the science
community however, the risks would be enormous. We’d need to throw
away traditional rivalries and notions of natural leadership, we’d
need to be quite confident in the capabilities of such an instrument
and most of all, we’d need to promise that the telescope would be
built, on time and on budget. Naturally, a few nations would provide
leadership through the knowledge and technologies that they would
provide and for those countries, sharing ownership equitably might
be politically impossible.
Those familiar with
the costs and logistics of operations in space might regard this
concept as quite naive… and it might be. However, the rewards too
would be enormous. A good friend living in Mumbai, India, an
engineer who has a passion for helping local school children gain
insights into the world of science, is constantly astounded and
delighted by the responses of her charges to the opportunities for
expression that her classes provide. She acts out of her deep desire
for children to be given the opportunity to experience a world that
we take for granted. Surely, everyone on Earth having some stake in
such a project would result in enormously positive outcomes, not
least of which being the astounding advance of our knowledge of the
universe (even if out to only 100 ly lol).
Food I hope, for
thought.
“At ordinary
optical wavelengths, “honking” works out to a mirror 100 million
miles across. You could nicely fit a reflector that large between
the orbits of Mercury and Mars. Big, yes, but it would permit you to
examine exoplanets in incredible detail.”
Even assuming that a
perfect telescope of this size could be built it would not achieve
the “theoretical” resolution. EM scintillation in the ISM would
impose a limit. But I don’t know if anyone has done the
calculation. The resolution limit would vary by direction and
distance and wavelength.
The new telescopes
have completely turned around astronomy. We actually can imagine
seeing photos of alien continents and biospheres within our
lifetimes which is an amazing thing to consider.
Science Fiction almost always imagined interstellar travel first then discoveries of alien planets upon arrival, and lately I have heard SF authors jokingly complaining that exoplanet discoveries make their job more difficult.
Personally I can recommend also the fascinating novel Blind Lake by Robert Charles Wilson which touches on future imagined telescope and consequences of such discovery.
I have also stumbled upon an amusing concept called Galactic Life Imager on he net, however I don’t think we will see it soon ;)
The above article of
course gives us some data for Fermi Paradox. It is now rather
obvious that any advanced civilization would be able to detect our
planet, biosphere and civilization since considerable length of
time(biosphere since billions, civilization between around 2000 to
200 years from today).This silences the objections to sending
messages into outer space that are sometimes voiced as warnings, but
it also means such messages shouldn’t be really necessary.
Of course this also means that if they exist most likely they know of our existence-leaving the question-why don’t they want contact? Personally I believe that due to time difference, as millions of years of evolution both technological and biological will make them unable to communicate with us or at least without us losing our unique culture and development.
Of course there is also the possibility that they simply faded away or never existed at all.
Intriguing possibilities.
Still, we should have tools to provide some answers soon-at least within next 50 years.
Until we can get
ships to velocities closer to the speed of light, telescopes are
much much more interesting to me than interstellar probes. For me it
is even hard to choose between massive telescopes and interplanetary
missions that might discover life. As daunting as some of these
telescopes seem, they seem much more achievable than getting close
to the speed of light right now.
If we could directly
image an earth “twin”, even if it is just a pale blue dot, it
would be incredible to me. There would be a certain easing of cosmic
loneliness that would be priceless. As exciting as the current
exoplanetary discoveries are to me, I want to be able to observe
something more direct. If we could get even closer to be able to
say, look at a (hopefully) green continent sitting in a blue ocean…
wow. The level that is talked about in this article, basically
getting a google maps view of a life bearing planet, well I don’t
think I can come up with the appropriate adjectives. Of course, it
may be likely that nothing within a 100 light years will bear
obvious life forms, but still, the gamble seems worth it because of
all the other discoveries we would make.
Would anyone venture
a guess as to how long it would take to build a device of the size
that Shostak proposes? Personally, I think it should be the next LHC
style project.
The effect of seeing
a green exoplanet with continents would be galvanic – there could
be no more certain way to focus humanity’s attention upon our
stellar neighbours than this. That is why such ambitious telescopes
are important for all of u.
I’m a fan of
Maccone’s grav scope (using our own sun as a gravitational lens).
Has anybody produced simulations of the sort of images which could
be extracted from such a device?
City lights? Honda?
Let’s see:
Energy of one photon:
e = 3.3 * 10^-19 J
Approximate world-wide use of power: P = 2 * 10^13 W
Number of photons generated by city lights (per planet): N = P/e ~ 6.6 * 10^31 s^-1 (per second)
Area of sphere of 100 ly radius: A = 4 pi r^2 ~ 1.2 * 10^37 m^2 (square meters)
Number of photons impinging on telescope aperture: N/A ~ 5*10^-6 s^-1 m^-2 (photons per second per square meter)
So, it seems that
detection of all the city lights of a planet is barely theoretically
possible with a really large regular telescope and longish exposure
times. But what if you want to resolve an image? That Honda you want
to make out probably has an area about 10^-12 smaller than that of
the entire planet, and the number of photons you would get from it
would be correspondingly less. An aperture of roughly 10^16 m would
be necessary, i.e. the total mirror area would be 10,000 times that
of the Earth. And because this is about light gathering power, not
resolution, there is no cheating with interferometry.
That should be
10^16 square meters (not meters) there near the end ….
So if we wanted to
realize that 1-Honda resolution telescope as a formation-flying
swarm of (relatively) small elements each with a 1 m mirror, we’d
need to fly 10^16 of them, or 10 million billion. Talk about big
budgets….
A quick question to
those who know: assuming you had the resolution you need to resolve
a honda accords @100ly, would you actually collect any photons to
image it? Whay kind of physical collection area do you need to
actually capture optical-wavelenght photons from an object that
far-away?
There must be some
fundamental limits on what you can see at particular distance, no
matter how big the collecting area?
@ljk (from previous
thread) It is SO frustrating to have just one data point for
something so important.
To me this is why the
telescope will not supplant the space probe. To study biology and
related fields, we will need to send a probe to the life bearing
exo-planets. A telescope can point the way, but it will not be
sufficient to study the planet.
The notion that
telescopes will obviate probes it patently absurd. To the contrary,
better telescopes will always increase the motivation for a probe.
Whatever a telescope may show will always cry out for a next step of
investigation, and there are many things no telescope could ever
show.
Imagine we have a
super-scope that shows an exoplanet at the level of detail that
Schiaparelli and Lowell saw Mars at. What if someone decided it
looked like there were canals? Does anyone really think that there
is a level of resolution at which all important questions can be
answered? Think again….
There must be some
fundamental limits on what you can see at particular distance, no
matter how big the collecting area?
Depends on how
fundamental you want to get. If you only take the diffraction
equation and photon number into account, you could arbitrarily
increase resolution by increasing baseline, and arbitrarily increase
sensitivity by increasing collection area or exposure time.
However, on the next
level of practicality, I am pretty sure that there will be
decoherence due to varying conditions in interstellar space or near
the detectors, which could put a strict (nearly fundamental) limit
on how large the baseline can be. And the inevitable presence of
unrelated photons will put a limit on sensitivity simply because the
few photons that come from the target drown in the noise.
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