Planet Seeker Telescope

Our mission is to seek out and colonise habitable exoplanets, of course, a number of organisations are aiming to do the same. However, the entire field of interstellar travel seems to be in something of a rut, with even the most optimistic projections of interstellar travel suggesting we will not set foot on a planet under an alien sun for at least a century, probably more. Yet is this truly an accurate assessment? We are of the opinion that it is not, that in fact interstellar travel could be achieved not within ten decades, but within a single decade.

This project is but the first, as we build a iron-hard case, that interstellar travel is in fact far easier, and far more near term, than anyone is currently expecting. Firstly, we must find a suitable exoplanet, no barren rock nor oversized comet will do, we must find a blue and green world potentially capable of supporting human life.

To this end, a new telescope operating on a colossal scale is needed, we have put together a design for just such a telescope, in fact a multipart telescope which we call the ‘Planet Seeker’, to be placed in a geostationary orbit, minimising the cost of deployment, and providing great stability, see below for an overview of the entire telescope.

The telescope will be a visible-light and possibly ultraviolet interferometer, able to directly image even quite small exoplanets with a substantially higher resolution than currently possible with traditional telescopes.

To minimise costs we have decided upon a ‘dumb’ array, consisting of hundreds of thousands of tiny, inexpensive thin-film plastic Fresnel zone plates, what the late Dr. Robert Forward referred to as ‘holographic tissue lenses’ forward1990rocheworld , which can be inexpensively mass produced at a fraction of the cost of conventional lenses doi:10.1021/acsnano.5b03165, allowing the production and launch of upwards of one million individual telescope units.

The basic design will be something like the Hypertelescope, proposed by Prof. Antoine Labeyrie in 1996 HypertelescopeOrg:2020, and which he and his team have steadily worked on for almost three decades. When completed, the array will consist of up to one million units, with a total collection area of over 700 square metres, a baseline of 100 kilometres or more, and an angular resolution of approximately 1.25 micro arc seconds.

For those who are not versed in the field: the resolution of a telescope is the angular size of the smallest resolvable object, a ‘higher’ resolution refers to a smaller minimal resolvable angle, therefore, an angular resolution of 1.25 micro arc seconds is an extremely high resolution, not a low resolution.

Once deployed, the Planet Seeker will possess a high enough resolution to successfully resolve features as small as 600 kilometres on a hypothetical planet in the Ran/Epsilon Eridani system, some 10.5 light years distant, as one example.

The goals of the Planet Seeker are: (1) locate, characterise, and study from afar habitable worlds suitable for human colonisation, (2) investigate exoplanets for signs of intelligent activity, (3) study and locate, known and unknown distant bodies within our solar system, such as confirming and/or studying ‘Planet 9’, and (4) perform scientific study of innumerable cosmic phenomena.

An indefinite mission lifetime is intended, taking advantage of recent advances in space travel, such as the SpaceX Falcon 9, Falcon Heavy, Dragon, and Starship, to perform routine maintenance and upgrades on the interferometer array, and also the massively redundant number of the very simple individual ‘telescopes’, ensuring that the collective system can operate for years or decades with minimal maintenance.

We expect the Planet Seeker to revolutionise astronomy and science in general, and we also expect certain social, political, cultural, and technological changes arising from discoveries the Planet Seeker will make.

With an angular resolution of 1.25 μas, the Planet Seeker could resolve features as small as continents or large islands, at such resolutions it will not only be possible to detect the signature of photosynthetic pigments like chlorophyll or an extraterrestrial equivalent, or other biologically-produced substances, but to resolve large-scale urbanisation. Below you can see on the left a blurred image simulating what Earth at night would look like from ten and half light years away, on the right is a simulated image of a heavily urbanised exoplanet at the same distance.

As you can see, the resolution of the Planet Seeker, while not high enough to make out smaller features, is more than sufficient to detect even the moderate levels of urbanisation on our planet.

Wandering or ‘rouge’ black holes with minimal or non-existent accretion disks could be more readily located, either via direct imaging, utilising the Planet Seeker's large collection area, or indirectly via observation of gravitational lensing, utilising the telescope's very high resolution.

The Nemesis hypothesis, originally put forward by palaeontologists David Raup and Jack Sepkoski in 1984 Raup801, proposes that Sol, our sun, has a low-mass binary companion orbiting on a 26 million year orbit with a semi-major axis of approximately 1 light year. Raup and Sepkoski noted a 26 million year interval between major extinction events, and suggested that there could be a small red or brown dwarf companion disturbing Oort cloud comets at regular intervals.

After decades of debate, in 2010 and 2013 Adrian Melott and Richard Bambach demonstrated that there is indeed a 26 or 27 million year periodicity to major extinction events 10.1111/j.1745-3933.2010.00913.x, i.e. extinctions occur at consistent 26 or 27 million year intervals. An independent study in 2021 by Michael Rampino, Ken Caldeira, and Yuhong Zhu RAMPINO2021101245, found that Earth has a 27.5 million year geological cycle, a ‘pulse’ as they termed it, where major volcanic events, and mass extinctions on the land and in the sea, appear to reoccur with an average interval of 27.5 million years.

However, Melott and Bambach also noted that a sharp peak in extinction events every 27 million years does not appear to be consistent with the Nemesis hypothesis Melott_2013. As they point out, because of Nemesis' great distance from the Sun, it is expected to have been perturbed by passing stars, and therefore should not produce a sharp peak in extinctions, but a more gradual one.

Regardless, the Planet Seeker will be able to answer this question definitively, first of all, a Jupiter-sized object (as Nemesis appears likely to be) at 1 light year is well within the Planet Seeker's imaging capabilities, secondly, with the Planet Seeker's large collection area, and despite the great distance of Nemesis, the very faint light from the Sun should be sufficient for imaging.

We are reaching the limit of what is possible with conventional and ground-based telescope designs, light pollution is ever-increasing, and conventional telescopes with large reflectors quickly become unwieldy. In order to achieve the greatest advances possible, we must instead turn to space-based interferometers.

Interferometers collect the feeble light from distant stars, planets, nebulae, black hole accretion disks (and in principle, Hawking radiation), and galaxies, amongst other celestial objects and phenomena, from multiple individual telescopes. A phased-locked laser beam is sent out to each of the many telescopes, where it interferes constructively and destructively with the incoming light, increasing the brightness whilst preserving contrast. By mixing with the out-going phased-locked beam, a certain frequency and phase signal is embedded within the now-amplified images, specifically the phase and frequency changes with the distance and time travelled.

The amplified images are sent on to a collector unit and combined, and by measuring and analysing the shift in both frequency and phase, a central computer can determine where in space and time each image was taken, sending this information to a ground-based supercomputer which processes the separate images into a single large image with a very high resolution, far higher than what any near-future mirror could achieve, and theoretically expandable to sizes that would be completely infeasible to manage with any single reflector.

This is analogous to taking the mirror out of a conventional reflecting telescope, and instead using several small mirrors, scattered around within the area the large single mirror formerly occupied, the image is just as sharp as before, despite the lack of a single continuous mirror.

The design and operating principle of the Planet Seeker can be broken down into a few primary components.

Very small and extremely low mass plastic Fresnel zone plates 2009ApSS.320..225KrefId0, or ‘holographic tissue-lenses’ forward1990rocheworld, mass produced, and easily suspended via laser light in a free-flying formation, against both Earth's gravitational pull and light pressure from the Sun HypertelescopeOrg:202010.1117/12.460844ognjen-atwater:2019.

We have preliminarily decided on a visible-light, and possibly ultraviolet, telescope, the reasons are as follows:

The potential for stirring up enthusiasm cannot be overlooked, especially as this is one of the primary purposes of the Planet Seeker.

A two-part device, consisting of a housing for the CCDs used to collect incoming starlight, and a separate focusing element, made as a thin-film sheet using the same technique as used to manufacture the individual telescopes, and suspended via laser light a modest distance away.

This design allows for light to be collected from over 1 million individual telescopes, with the etched collecting lenses also functioning in reverse, as demonstrated by Khatri et al KHATRI201577, where a laser beam is sent out through one or more beam-splitters, and then focused to a ‘spot’ at each of the telescopes, making this component a combined Collector-Laser.

Internal measurement arms of a fixed and predetermined length allow comparison of incoming signals with a reference signal, permitting the all-important combination—interferometry—of the many images. See the work by Koechlin et al, on the ‘Fresnel interferometric imager’ 2009ApSS.320..225KrefId0, for more information about this type of lens as used to construct a telescope.

According to Labeyrie and the Hypertelescope team, a laser power of 3 milliwatts is required per telescope HypertelescopeOrg:202010.1117/12.460844, in order to levitate them against Earth’s pull and solar light pressure, this amounts to 3 kilowatts for 1 million telescopes, a relatively modest laser that is easily available, indeed, near-infrared lasers of this power level are frequently used in the manufacturing industry IndustrialLaserSolutions:2020.

The lenses are designed such that near-infrared laser light is unable to completely pass through, only partially penetrating and thereby producing a strong force on the tiny telescopes Ying-Ju-Nelson-Swartzlander:2019ognjen-atwater:2019.

Frequency-doubling material in the lenses converts some of the laser light into visible light Ou:92, that is able to interfere with incoming light in order to amplify the resulting image. Outgoing near-infrared laser light is focused to the individual telescopes by 1 million holographic lenses—etched into the focusing sheet—which, due to their unique properties, will also collect and refocus the incoming 400 to 700 nanometre wavelength starlight to a different spot than reflected 700+ nanometre, near-infrared laser light 2011IAPM...53...77W.

Later on, additional Collector-Lasers—or a larger focusing sheet and a higher power laser—can be added in order to support additional telescopes.

Typically it is the Lagrange Points that are considered for telescope placement, permitting a view uninterrupted by Earth, or in the case of the Earth-Sun point L2, at least partially benefiting from Earth’s shadow. However, we plan on instead deploying the Planet Seeker to a geostationary orbit 10.1117/12.460844, providing a greater orbit stability, and lower launch costs, compared with the Lagrange Points. As the telescopes of the array are very low mass and easily suspended via laser beams, the only parts of the telescope that are in purely gravitational orbits are the Collector-Laser and the Reflector.

The easiest way then to achieve a stable arrangement is to place the Collector-Laser in a geostationary orbit some degrees ahead of, or behind, the Reflector, the telescopes are then suspended via laser light between the two, which will face each other. For comparison, if we wished to take advantage of Earth’s shadow over L2, we would find that over time the Collector-Laser and Reflector would tend to either drift toward the central region of L2, or away, requiring constant adjustment and therefore use of propellant, creating a limited lifetime for the telescope, or else continual refuelling.

By carefully angling the telescopes via adjustment of the outgoing laser beams, and by taking advantage of the new laser ablation manufacturing technique, to make lenses nearly without glare, we can avoid the problem of unwanted light from the Sun spilling into our images. Of course the telescope array would be unable to take images directly away or near the Sun, but that can be managed, such as by waiting for nightfall, and besides, over the course of a year nearly anywhere in the sky could still be imaged.

A central computer aboard the Collector-Laser analyses the frequency and phase shift, as well as the angle, of returning laser beams, now carrying amplified images acquired by the individual telescopes, in order to determine where in space and time the image was taken. This information is beamed down to the ground, where a waiting supercomputer uses raytracing, as well as conventional digital interferometry techniques, to electronically produce a very high-resolution final image, even reproducing the effects of additional, more sophisticated optics, such as the ‘pupil densifier’ designed by Labeyrie et al 10.1117/12.460844, without the added mass and physical complexity such equipment would introduce.

In advance of a space-based telescope array, a ground-based prototype can be developed and built within the next year or so. The prototype would be very minimalistic and non-disruptive to the environment, consisting of little more than an array of lenses on tripods. This way it can be built in a remote location, even in a designated wilderness park, without disturbing or altering the environment. Since 2011, the Hypertelescope team has been developing a similar prototype in the Alpes de Haute-Provence, in France HypertelescopeOrg:2020.

Several of the nearest star systems of a similar type to the Sun are located within the southern sky, such as Alpha Centauri, Ran (formerly known as Epsilon Eridani), Sirius, etc., therefore from the northern hemisphere they are either not visible at all or are visible only near the horizon, where there is greater atmospheric turbulence. It is for this reason, that we propose Central to South America as a possible location for the Planet Seeker prototype, specifically in a region with a mountainous landscape, helping to cut down on light pollution.

It is almost too early to give even rough estimates of the costs involved in this project, however, a very broad overview can be managed.

At this stage it appears the two most expensive aspects of the project will be launch costs, as well as the costs involved in the research and development of the Collector-Laser.

Based on figures given on the SpaceX website, we conclude that the entire interferometer will cost at least $62 million USD SpaceX:2020 to be launched, though probably closer to $70 million USD. The individual telescopes themselves can be launched for less than $3 million USD by making use of SpaceX’s rideshare program for small satellites SpaceXRideshare:2020, as the million lenses are only 30 millimetres across and microns thick, easily fitting within a rather small volume.

The individual telescopes of the Planet Seeker are little more than etched pieces of micron-thick plastic, and using the new technique discussed earlier, the 1 million lenses required for the full array could be mass-produced at a very low cost-per-lens doi:10.1021/acsnano.5b03165, perhaps as little as $0.1 USD or equivalent, though this is only an educated guess. Research, and especially development, is required before a firm estimate on the cost of lens manufacture can be given, as the technology must be scaled up from a lab prototype first, or at the very least, this process must be started in order to begin to make an estimate on the cost.

The primary costs involved in the manufacture of the lenses appears to be the initial cost of the laser equipment and clean room, followed by the cost of vacuum-grade plastic with the correct composition and optical properties, and lastly labour and electricity costs.

The Collector-Laser will be more involved to develop and construct, with the bulk of the cost and effort going into the precise arrangement of the laser splitter or splitters, and in maintaining a clean room environment, that said, such expertise and facilities are already in existence.

One of the primary purposes of this paper, and especially the International Research Institute for Space, is to bring awareness to, and draw the interest of, needed specialists.

This is a call to action, a foundation to get the ball rolling, to get things started. We have the technological prerequisites to design, develop, build, and launch a telescope capable of finding another Earth, another habitable world.

In a year’s time, we could have an organization developing a prototype of the telescope, and in five… We could together be watching its launch, knowing that the Age of Interstellar Discovery is dawning.

To begin with we need to create a flyable design, all the bells and whistles, an absolutely complete and airtight final design. Following this, we will begin research and development of the hardware, and software, needed for the Planet Seeker Interferometer, testing and refining the technology by way of a ground-based prototype.

Ultimately, this is perhaps the grandest and most important project humanity has ever undertaken, we cannot remain on Earth alone forever, nor even within our solar system, sooner or later the Sun will die, and our very distant descendants will die with it, unless we take the actions necessary now, to ensure that we become a star-faring species.

The Planet Seeker is only the beginning of a grand adventure, an adventure of epic proportions, to explore and colonise distant worlds orbiting alien suns. If we take this step, if a brave few of us dare to go against the current, ignore cries of economic irrelevance and the ‘impossibility’ of the task at hand, then our distant descendants will look back on this moment, from their homes amongst the stars, and wonder at the courage and vision of those mighty pioneers.

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