Finding All Earth-Like Exoplanets Orbiting Sun-Like Stars Within 30 Light Years

A new NASA NIAC phase 1 study is analyzing a 20-meter class infrared space telescope.

It is currently impossible to find Earth-like planets in the habitable zones (where the temperature supports liquid water) of Sun-like stars. It is even harder to measure the composition of their atmospheres. But this is necessary if we want to find life as we know it on other worlds, or find another planet that we could easily inhabit. A new design called Diffractive Interfeo Coronagraph Exoplanet Resolver (DICER) should make it possible to find “Earth 2.0.” DICER would be about the would have the equivalent mirror size of some large ground telescopes which are still under construction. However, it wouuld use two smaller mirrors like the Keck ground telescope made in 1996. This is proposing using mirrors sizes we have already proven capable of making.

The James Webb Space Telescope is an infrared telescope and has a 6.1 meter mirror. The proposed DICER space telescope would be over 3 times wider and have a light collecting area over ten times greater. The new DICER space telescope for finding Earth like worlds would use a differnt light collecting system instead of mirrors.

The Status of Large Ground Telescopes

The Extremely Large Telescope (ELT) is an astronomical observatory currently under construction and is targeting 2017 completion. When completed, it is planned to be the world’s largest optical/near-infrared extremely large telescope. Part of the European Southern Observatory (ESO) agency, it is located on top of Cerro Armazones in the Atacama Desert of northern Chile.

The design consists of a reflecting telescope with a 39.3-metre-diameter (130-foot) segmented primary mirror and a 4.2 m (14 ft) diameter secondary mirror, and will be supported by adaptive optics, eight laser guide star units and multiple large science instruments.The observatory aims to gather 100 million times more light than the human eye, 13 times more light than the largest optical telescopes existing in 2014, and be able to correct for atmospheric distortion. It has around 256 times the light gathering area of the Hubble Space Telescope and, according to the ELT’s specifications, would provide images 16 times sharper than those from Hubble.

The Thirty Meter Telescope (TMT) is a planned extremely large telescope (ELT) to be built in Hawaii. The project won a court case but construction is still halted due to protests and opposition.

The Giant Magellan Telescope (GMT) is a ground-based extremely large telescope under construction, as part of the US Extremely Large Telescope Program (US-ELTP), as of 2022. It will consist of seven 8.4 m (27.6 ft) diameter primary segments, that will observe optical and near infrared (320–25000 nm) light, with the resolving power of a 24.5 meter (80.4 ft) primary mirror and collecting area equivalent to a 22.0 meter (72.2 ft) one, which is about 368 square meters.The telescope is expected to have a resolving power 10 times that of the Hubble Space Telescope and four times that of the James Webb Space Telescope, although it will be unable to image in the same infrared frequencies available to telescopes in space. As of May 2021, six mirrors have been cast and the construction of the summit facility has begun.

A total of seven primary mirrors are planned, but it will begin operation with four. The US$1 billion project is US-led in partnership with Australia, Brazil, and South Korea, with Chile as the host country.

DICER Space Telescope

Finding an exoplanet like the Earth requires a very large space telescope that can resolve an Earth-like planet from a Sun-like star to distances of at least 30 light years, where the maximum angular separation of the star and planet is only a few hundred thousandths of a degree. Within this volume, it is expected that there are of order a few rocky, Earth-like planets, highlighting the need to find Earth-analog planets regardless the orientation of their orbit to our line of sight. Detecting an Earth analog exoplanet also requires that the light from the star be blocked so that it does not overwhelm the light from the planet; in the infrared where the Earth is brightest in emitted light, the Sun is a million times brighter than the Earth.

A 20m-class infrared space mission would enable Earth-like planets to be resolved from a host Sun-like star to the required distance, thus enabling the discovery of planets with face-on orbits. However, launching and deploying a 20m-class space telescope is not technologically feasible at this time because it is very difficult to get telescope mirrors that large into space. DICER achieves the diffraction limit of optics that are ~20 meters in length, while requiring two mirrors that are only a few meters in diameter.

The light is instead collected with two or more flat diffraction gratings that are ten meters in length. Furthermore, the system would use a simple coronagraph that could extinguish the light from the star by a factor of a million. This design does not require that multiple components fly through space in precise formation, as has been required for some of the other designs aimed at measuring the atmosphere of a habitable, Earth-like world.

Current models of DICER support the idea that this primary objective grating space telescope might be able to detect all Earth-like planets around G/K stars (stars that are similar to the Sun) within 30 light years. For each planet, orbital periods, semimajor axes, infrared luminosity/temperature, and the presence or absence of atmospheric ozone (a key signature of life as we know it) could also be determined.

However there are a lot of optical, thermal, mechanical, launch/deployment tradeoffs that must be considered to make sure that this design is feasible, cost effective, and produces the highest quality science.

With funding from this proposal, they aim to reduce the estimated size and cost of the current proof-of-concept DICER design so that it can be imagined as a probe-class mission, while showing that it will enable the detection of Earth 2.0.

This activity primarily advances the goals of NASA’s Science Mission Directorate, addressing the mission to “Search for life elsewhere.” We address the astrophysics science theme of Exoplanet Exploration (ExEP).

14 thoughts on “Finding All Earth-Like Exoplanets Orbiting Sun-Like Stars Within 30 Light Years”

  1. I don’t believe K-type stars are good candidates for life as they produce a great deal of radiation in their early life, including in the x-ray range. Yes, they can persist in maintaining themselves on the main sequence for around 3 times as long as our own G-type star, but:
    1) A 35 billion year lifespan doesn’t help much when the universe is only 13.8 billion years old, plus planets probably have a shelf-life (due to things like cooling cores) and, after the expiration date, it simply is not going to happen.
    2) The Goldilocks zone is smaller around a K-type star and planets are much less likely to stay in it as long as around a G-type star.
    3) Many or most K-type stars that formed early enough in the galaxy’s habitable zone to have settled down their radioactivity were probably formed too early to have a proper metallicity.
    4) The galaxy itself may not have been conducive to the evolution of life until not long before the Solar system formed.
    5) There is only about a 20% chance we would be in orbit around a G-type star if K-type stars were good candidates for supporting life like us.


    Of course, I also think our chances of finding a move-in ready Earth 2 are astronomically unlikely, but searching is imperative, both to rule them out and to determine if there are any potentials for terraforming some day — although the latter assumes that our distant descendants will still care about living on planets capable of supporting organic life on the surface.

  2. We have to start thinking about assembling large telescopes in space. Self-assembly would be best. Robotic arms like that of the International Space Station could gather and join the segments together. And move from segment to segment like an inch worm.

  3. You need a proof reader.

    “DICER would be about the would have the equivalent mirror size of some large ground telescopes which are still under construction. However, it wouuld use two smaller mirrors like the Keck ground telescope made in 1996.”

    Anyway, it’s about time to bite the bullet and start building orbiting segmented telescopes designed to achieve arbitrarily large apertures.

    At a sufficient focal length compared to segment size, the segments can be optical flats, which are enormously cheaper to manufacture than curved mirrors. (This observation isn’t original to me.)

    I suggest we develop a standardized free flying optical flat capable of fractional wavelength station keeping under really low gravity situations like the Lagrange points. These could be mass produced, sent into orbit hundreds at a time, and assemble to form mirrors potentially kilometers in diameter. Due to the segments being independently station kept, there would be no settling time, vibrations couldn’t propagate. And segments could be added as they were manufactured.

    Then the image could be observed by a secondary, also free flying system. Multiple imaging arrays could use the same mirror array at the same time to observe different targets.

    Time to start thinking big, and actually exploit the advantages space has for telescope operation, instead of just transplanting ground style telescopes to space. And to think in terms of mass production, not insanely expensive bespoke hardware.

    • The kind of shift in mindset many are now resisting as if their livelihood depends on it.

      All the threats of lawsuits against Starlink et al because they spoil the heavens for land telescopes, are a direct threat for the next big future of kilometer wide telescopes imaging exoplanets.

      There simply is no way that growing the industrialization of space leaves the sky untouched.

      • Ive always found those arguments odd. The way things are headed, tens of thousands of satellites in LEO will not be an issue since large space telescopes will be more feasible.

    • Giant, assembed in space, space telescopes, constructed by drones/robots are the near term future. I am saying near tern, because tech (AI in particular) is moving now so fast, that it’s not possible to know what kind of tech/capabilities our civilization will have after 2030.

      We need to mass manufacture them cheaply and send to space (also cheaply) on Starship (hopefully), if not(because it may fail and will need to be redesigned), via some small reusable rockets which are easier to develop than still theoretical Starhip and they work already.

      We could have 1km orbital telescopes before 2030

    • There just 31 class G stars within 10 parsecs, most of them at the far edge.
      If you also need the planet to rotate the star “Face-On” to earth, e.g. cross directly between the star and earth, then you will get just a few percentage of thus stars with such alignment.
      It seems that the chances that the suggested DICER space telescope to actually find an earth like planet are very close to zero.

      • That seems at odds with the statement in the article:

        “Current models of DICER support the idea that this primary objective grating space telescope might be able to detect all Earth-like planets around G/K stars (stars that are similar to the Sun) within 30 light years.”

        • Looking it up on Wikipedia, there are
          9 G class stars between 25 and 30 LY of Earth.
          2 G class stars between 20 and 25 LY
          7 G class stars within 20 LY of Earth.

          So, 18 candidates just for G class.

          11 K class stars between 25 and 30 LY
          9 K class stars between 20 and 25 LY
          15 K class stars within 20 LY

          Another 35 if you include K class.

          • Hi Bert,

            Your numbers are correct (14 more in the 30 light year range), but look at Snazster comment, the chance of life at a red dwarf (K class star) are very slim.
            Anyway I hasn’t done yet the calculation of the percentage of planets around a sun sized planet in the goldilocks zone (1AU) to be “Head-On’ but is very low.
            Probably it will be down to 1/2 stars with maybe 1 to 4 planets or even a round zero.

            • You say “Probably” and “maybe”.
              Exactly the reasons to do the mission.
              Then we will find out if you are spot on or dead wrong.

            • Well, actually, a K-type dwarf star is called an orange dwarf. These are more massive than red dwarfs, called M-type. Red dwarfs range in size from 0.1 to 0.6 solar masses, while G-type stars like our own are called yellow dwarfs* and range from .9 to 1.1 solar masses.

              K-type orange dwarfs fill the range in between on the primary sequence.

              But yes, as regards M-type red dwarf stars, it has become very difficult to posit life (especially any sort of advanced life) on them without resorting to increasingly more creative and less likely possibilities. Habitable planets simply have to be too close to the primary, where flares and tidal effects (especially tidal locking) would appear to pose insurmountable barriers to life, especially advanced life, without frequent application of a very active imagination. This is even before considerations such as visible light being too poor to support photosynthesis.

              *Yellow dwarf seems a strange name when our star is more massive than 93% of all stars, and is actually white, not yellow, as G-type stars include both yellow and white. Older scientists don’t like changing nomenclature, however (recall the whole Pluto and planet thing). To digress, it is much in the same way, we refer to space-time as though it were composed of space and time, while it would probably be more accurate to say that space and time, at least as we perceive them, are attributes of space-time, not components. It’s not unlike if we called coffee, which is made of coffee beans and water, bitter-wet, even though it is not made of bitter or wet and, in fact, these things don’t even have an existence of their own, merely being attributes of coffee, not its ingredients.

      • @ Com Engineer: I believe you misinterpret the wording. “face-on to earth” does NOT mean that the planet must pass directly between the star and Earth. Elsewhere, the article highlights the need to be able to detect the potential Earth-like planets regardless of the orientation of their orbits relative to the line of sight from Earth, which is wording that is more clear.

        Thus, I believe your objection that nearly 0 planets would be candidates for detection is based on a misunderstanding of the wording, and so should be disregarded.

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