A groundbreaking new planet-hunting technology now being studied under NASA’s Innovative Advanced Concepts (NIAC) program could detect and then search for biosignatures from literally every Earth 2.0 within thirty light-years of our solar system.
Known as DICER (The Diffractive Interfero Coronagraph Exoplanet Resolver), key to this NIAC study’s revolutionary means of detecting these planets is that unlike traditional optical space telescopes – which use curved, highly polished mirrors to collect starlight – this mission is flat would be sets of so-called diffraction gratings.
These gratings would act as superprisms to redirect starlight hitting them onto smaller curved mirrors. Not only would this significantly reduce the weight of the infrared telescope, but it would also make such a high-resolution exoplanet mission cost-effective.
We have a base design that uses three sets of two grids, Heidi Jo Newberg, an astrophysicist at Rensselaer Polytechnic Institute in Troy, New York, and DICER project leader, told me via email. Each set of two 10-meter-long gratings can detect light in a small portion of an exoplanet’s emission spectrum, says Newberg, the recipient of a $175,000 NIAC Phase I grant.
By precisely aligning these gratings, the observatory would achieve the resolution of a 20-meter optical space telescope.
This new DICER technology won’t produce pretty images of the planets it might discover. But it should allow Newberg and his colleagues to collect enough spectra to detect exo-Earths in a star’s habitable zone. This is currently defined as the place where a planet can hold liquid water on its surface.
The mission’s coronograph would make these detections possible by removing all starlight in the center of the telescope’s field of view. Thus, in fact, any Earth-like planet could be detected near the star.
If this initial nine-month study is successful, the team can apply for a two-year, $600,000 Phase II study. The hope is that this $1 billion DICER mission will see its full development over the next decade.
Unlike previous extrasolar planet-finding techniques, DICER would be able to find and study planets at all inclinations, including frontal orbits. And it would be able to determine if a planet has an ozone-rich atmosphere (O3), a telltale signature of oxygen.
The observatory would be sent to the Sun-Earth gravitationally stable Lagrange point 2 (L2), located about a million miles from Earth. It would operate for at least a few years, as the mission would need enough time to spot a planet like our Earth orbiting its parent star.
Although terrestrial planets are easier to spot near smaller red dwarf (M) stars that dominate the nearby galaxy, this proposed new mission concept would target so-called G- and K-type stars, which are more similar to our Sun.
G and K stars are long-lived and don’t have large magnetic storms that would disrupt a planet in the habitable zone like M stars do, Newberg says. Exoplanets in the habitable zone of M stars are also more tidally dependent (so the same side faces the host star), which would make weather patterns drastic, she says.
Therefore, G and K stars could be the sweet spot.
K stars are the faintest of the more stable main sequence stars, Newberg says. But the Sun is a G star, which is slightly more massive and brighter than a K star, she says. And it’s the only star we know of that harbors intelligent life, says Newberg. That’s why we’re designing DICER to find exoearths around G and K stars, she says.
Nevertheless, the team has a daunting task ahead of them.
Think how difficult it is to find a planet as small as Earth around a star millions or billions of times brighter, Newberg says. Then imagine dividing the tiny amount of light that reaches us from this planet into a spectrum, she says.
There are 62 known G and K stars within 33 light years of Earth. Only one, Tau Ceti, is known to host either a super-Earth or mini-Neptune.
We don’t know how many habitable exoplanets DICER would find; it could be zero or fifty, Newberg says. If we find Earth-like exoplanets and then oxygen, there’s a good chance it was produced by life, she says. It’s the kind of discovery that would prompt another mission to simply study this planet, Newberg says. If we find Earth-like exoplanets and don’t find oxygen, there could still be anaerobic life, she notes.
As for the start?
The optimistic timescale is 2033 with a Falcon Heavy rocket, Newberg says.
But at this point, the mission concept is very fluid.
The team is considering options to maximize the science of the concept while attempting to simplify the spacecraft’s mechanical system. It is a process that takes into account what Newberg calls the usual trade-off between time, cost and scientific productivity.
The first priority of the mission is to simply find these hidden exoearths and then search for ozone.
Ozone is the biosignature we think would be easiest to find, Newberg says. But we might also consider looking for methane, carbon dioxide and water, she says.