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We know that there are thousands of exoplanets and many millions more waiting to be discovered. But the vast majority of exoplanets are simply uninhabitable. For the few that may be habitable, we can only determine if they are by examining their atmospheres. LIFE, the Large interferometer for exoplanetsto be able to help.
The search for biosignatures on potentially habitable exoplanets is intensifying. The JWST has successfully collected some atmospheric spectra of exoplanet atmospheres, but it has many other tasks to do and observation time is very demanding. A planned space telescope called LIFE is dedicated to finding biosignatures of exoplanets, and researchers recently gave it a test: Can it detect biosignatures from Earth?
As an interferometer, LIFE is composed of five separate telescopes that will work in unison to expand the working size of the telescope. LIFE is being developed by ETH Zurich (Federal Institute of Technology Zurich) in Switzerland. LIFE will observe in the mid-infrared, where the spectral lines of the important bioindicative chemicals ozone, methane and nitrous oxide can be found.
LIFE will be located at Lagrange Point 2, approximately 1.5 million kilometers (1 million miles) away, where JWST is also located. From that location, it will look at a list of exoplanet targets in hopes of finding biosignatures. “Our goal is to detect chemical compounds in the light spectrum that indicate the existence of life on exoplanets,” explained Sascha Quanz, Professor of Exoplanets and Habitability at ETH Zurich, who leads the LIFE initiative.
LIFE is still just a concept and researchers wanted to test how it works. Since it hasn’t been built yet, a team of researchers used Earth’s atmosphere as a test case. They treated Earth as if it were an exoplanet and tested LIFE’s methods against Earth’s known atmospheric spectrum under different conditions. They used a tool called LIFEsim to work with the data. Researchers often use simulated data to test mission capabilities, but in this case they used real data.
Their results are published in The Astronomical Journal. The research is titled “Large Interferometer for Exoplanets (LIFE). XII. The detectability of Capstone biosignatures in the mid-infrared: sniffing out exoplanetary laughing gas and methylated halogens.The lead author is Dr. Daniel Angerhausen, astrophysicist and astrobiologist at ETH Zurich.
In a real-world scenario, Earth would be just a distant speck, almost impossible to discern. All LIFE would see is the planet’s atmospheric spectrum, which would change over time depending on what views the telescope captured and, crucially, how long it observed it.
These spectra would be collected over time, leading to an important question: how would observational geometry and seasonal variations affect LIFE observations?
Fortunately for the research team, we have extensive Earth observations to work with. The researchers worked with three different observation geometries: two views from the poles and one from the equatorial region. From these three points of view, they worked with atmospheric data from January and July, which represent the greatest seasonal variations.
Although planetary atmospheres can be extremely complex, astrobiologists focus on certain aspects to reveal a planet’s potential to support life. Of particular interest are the chemicals N20,CH3Cl and CH3Br (nitrous oxide, chloromethane, and bromomethane), all of which can be produced biogenically. “We use a set of scenarios derived from chemical kinetic models that simulate the atmospheric response of various levels of biogenic production of N2O, CH3Cl and CH3Br in O2-rich atmospheres of terrestrial planets to produce advanced models for our LIFEsim observation simulation software,” the authors write.
In particular, the researchers wanted to know if LIFE will be able to detect CO2, water, ozone and methane on planet Earth about 30 light years away. These are signs of a temperate world that supports life (especially ozone and methane, which are produced by life on Earth), so if LIFE can detect biological chemistry on Earth in this way, it can detect it too. in other worlds.
LIFE was able to detect CO2, water, ozone and methane on Earth. He also detected some surface conditions that indicate liquid water. Interestingly, the LIFE results did not depend on the angle from which the Earth is viewed. This is important since we do not know from what angles LIFE will observe the exoplanets.
Seasonal fluctuations are the other problem and were not as easy to observe. But fortunately, it looks like that won’t be a limiting factor. “Even if atmospheric seasonality is not easily observed, our study demonstrates that next-generation space missions can assess whether nearby temperate terrestrial exoplanets are habitable or even inhabited,” Quanz said.
However, detecting the desired chemicals is not enough. The critical piece is how long it takes. Building a space interferometer that detected these chemicals but took too long to do so would not be practical or effective. “We used the results to derive the observation times necessary for the detection of these scenarios and applied them to define the scientific requirements for the mission,” the research team writes in their paper.
To get a broader view of LIFE observation times, the researchers developed a list of objectives. They created a “…distance distribution of HZ planets with radii between 0.5 and 1.5 Earth radii around M- and FGK-type stars within 20 pc of the Sun that are detectable with LIFE.” The data for these objectives comes from NASA and other previous research.
The results show that for some targets it only takes a few days, while for others, it could take up to 100 days to detect relevant abundances.
What the team calls “golden targets” are the easiest to observe. The planets in Proxima Centauri are an example of this type of goal. For these planets only a few days of observation are needed. About ten days of observations with LIFE will be needed to observe “certain standard scenarios, such as temperate terrestrial planets around M stars at five pc,” the researchers write. The most challenging cases that are still feasible are Earth’s twin exoplanets about 5 parsecs away. According to the results, LIFE needs between 50 and 100 days of observation to detect the biosignatures.
LIFE remains only a potential mission at this time. It is not the first proposed mission that would focus solely on exoplanet habitability. In 2023, NASA proposed the Observatory of habitable worlds (HWO). Their goal is to directly image at least 25 potentially habitable worlds and then search for biosignatures in their atmospheres.
But, according to the authors, their results show that LIFE is the best option.
“If there are exoplanetary systems of late-type stars in the solar neighborhood with planets exhibiting global biospheres producing N2O and CH3X signals, LIFE will be the most suitable future mission to systematically search for them and eventually detect them,” they conclude.
