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).
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