When we talk about life outside our planet, it's crucial to understand how life has evolved on Earth over time. Not because we expect potential extraterrestrial life to be just like us, but because we need a benchmark for comparison. Earth is our only known planet where life not only emerged but also spread and really thrived. Our planet has an incredibly intricate mix of different life forms and ecosystems, and each one has left its own mark in our atmosphere and on the surface.
Earth's cycles—like carbon, nitrogen, and water—have shaped our world into a cozy place for life. Studying these cycles helps us figure out if similar processes are happening on other planets out there. Earth has also had some catastrophic periods, with asteroid impacts and volcanic eruptions. Understanding how life bounced back from these events teaches us about its robustness and how it might survive in various conditions.
This is why I studied the Phanerozoic environmental factors, like oxygen levels, global surface temperatures, runoff rates, and carbon dioxide levels, shaping a detectable biosphere. The findings aid understanding of exoplanetary biospheres, guiding our search for extraterrestrial life through space missions and observations. You can read more about my work on using Earth’s natural history as a framework for habitability here and here.
Light, essential for photosynthesis, has shaped life on Earth around our Sun, a G dwarf star. While much focus in searching for extraterrestrial life has been on cooler red dwarf stars (M dwarfs), they pose challenges like tidal forces and intense radiation. Alternatively, K dwarf stars, abundant and longer-lived than our Sun, offer more stable environments with less radiation. Planets in the habitable zones of K dwarfs, unlike M dwarfs, are less prone to tidal locking, allowing for more stable climates conducive to life. These stars, often termed 'Goldilocks stars,' present promising candidates for potentially hosting life-supporting planets.
In the realm of my research, I explore how photosynthetic organisms behave under alternative light conditions. I conducted experiments in which I exposed these organisms to a simulated K dwarf star spectrum. The results were eagerly awaited and showed that garden cress (Lepidium sativum) had similar growth and photosynthetic efficiency under K dwarf radiation as it does under Earth's solar illumination. More intriguing was the discovery that the cyanobacterium Chroococcidiopsis sp. CCMEE 029, displayed significantly improved photosynthetic efficiency and growth when exposed to K dwarf radiation compared to standard solar conditions. These findings emphasize the potential habitability of exoplanets located within the habitable zones of K dwarf stars and highlight the importance of prioritizing these specific planetary systems in our pursuit of finding and characterizing extraterrestrial life.
You can read more on my experimental design and work with simulated K dwarf radiation in my publication here!
Studying the atmospheres of planets around K dwarf stars and analyzing their spectral characteristics is crucial to determine if these planets could support life. Despite a planet being potentially super-habitable with abundant life, this life might not be visible in observational data.
I am particularly interested in the intersection of laboratory experiments and theoretical modeling. This drives my goal to blend findings from my lab work involving photosynthetic organisms under simulated K dwarf starlight with theoretical models that portray potential exoplanetary atmospheres. By simulating various changes in both planetary and stellar characteristics linked to superhabitable conditions, I seek to establish the limits of superhabitability and identify observable cues indicating a thriving extraterrestrial biosphere.
Stay tuned to read more on my theoretical work!
At the end of the last century, technological advances made it possible to detect planets outside our solar system. Since the discovery of the first extrasolar planet by Mayor & Queloz in 1995, over 4000 such planets have been confirmed. Many of these are super-Earths orbiting M dwarf stars, which make up around 75% of all the main-sequence stars in the Milky Way Galaxy. This has led to questions about the characteristics of these worlds and the potential for extraterrestrial life. Discussions about planetary habitability often focus on life as we know it on Earth, where molecules like oxygen, nitrous oxide, and methyl chloride are considered biosignatures because they require biological processes to be present in significant amounts. Methane, while produced by biological sources, can also form through abiotic processes, making it a less reliable biosignature on its own. Instead, the simultaneous presence of multiple gases such as ozone, water, and carbon dioxide is considered a strong indicator of life, known as the "triple signature." The detection of both methane and oxygen would also suggest biological activity, as these gases typically react and reduce each other's presence.
The study of exoplanetary atmospheres must also consider the possibility of "false positives" and "false negatives" in detecting life, where abiotic processes might mimic biological signatures or where life might be present but undetected. To better understand the impact of life on a planet's atmosphere, we use "dead" Earth scenarios as benchmarks. Using 1-D coupled climate-chemistry models, I explored scenarios with reduced oxygen, no biomass, and varying carbon dioxide and humidity levels around the M dwarf star AD Leonis. We find that biomass significantly influences atmospheric composition, particularly for gases like chloromethane, which serves as a good biosignature due to its strong dependency on biological activity. We also find that changes in carbon dioxide and surface relative humidity impact planetary transmission spectra more than oxygen levels or biomass alone. The detectability of gases like methane and oxygen is feasible under certain conditions using advanced telescopes like the Extremely Large Telescope (ELT). To read more about this study, click here!
