The Search for Life Across Light-Years

Image: NASA

For centuries, people peered into the night sky, looking for signs of other civilizations, trying to answer the fundamental questions of where we came from and whether are we alone in the universe. Today, astrobiologists search other solar systems for exoplanets—Earth-like cousins that may have atmosphere, water, and possibly the right life-spawning mixture of inorganic and organic compounds—to understand how they function, persist through cataclysms and what is involved in the lifecycle of planets.

Caleb Scharf, director of the Columbia Astrobiology Center, says that understanding how similar planets developed, used their resources and survived different perturbations can help scientists make realistic predictions about what our world may look like 100, 300 or 500 years from now—not only in terms of climate change but in the overall progression and resilience of planetary life.

“We want to know how planetary systems with life function,” Scharf says. So far, everything we know after four billion years of Earth’s evolution is based only on our planet’s experience—which is essentially only one scientific experiment, Scharf explains. “It would be so extraordinary to have other experiments, so we can compare us with other independent planetary systems that support life.”

Brian Greene, a professor of physics and mathematics who is working to establish an Origins Institute at Columbia, believes that studying other planets can inform us about our own past and future. “The wonderful thing about the universe is that as we look out, we can see the universe at different stages of evolution,” Greene says. “You can look at a planet that may be at a different part of the evolutionary timeline than Earth, and that can be an insight either where we came from or where we are going.”

Columbia’s research in this field spans a full spectrum—from searching for the exoplanets, which orbit stars outside of our solar system, to replicating cosmic conditions that formed those planets, to simulating various biological and climatic environments that may be on them.

Searching for Exoplanets and Exomoons
This search starts with finding suitable exoplanet candidates. But how does one decide which interstellar body, perhaps millions of light years away, fits the bill? David Kipping is an assistant professor of astronomy whose research focuses on the development of novel exoplanet detection techniques. He searches for planets that have moons. Kipping postulates that having a moon increases a planet’s chances of being habitable, and he draws parallels with our own satellite. “Our moon stabilizes the Earth’s tilt, keeping it at 23 degrees, which gives us seasons,” he says.

Without this impact, our seasons would last six months as perpetual days and nights, which would not benefit the development of civilizations. The moon also causes ocean tides, which on ancient earth were large enough to roll over the continents, creating pools of water on the ground that were “great starting places for life,” Kipping says. And there’s also a chance that some exomoons may have just the right conditions to be habitable themselves.

In his exomoon search, Kipping looks at the light and shadows created by the eclipses occurring in the distant solar systems. As planets pass in front of their suns, they briefly block the stars’ light. If one of the planets has an orbiting moon, that moon also blocks the star’s light, shortly before or after the planet’s eclipse, alerting astronomers to its presence. Another way is to note the planetary “wobbles,” Kipping says. With their gravity, the moons pull at their respective planets, affecting the exact timing of the eclipses, so that the planets transit in front of the stars either a few minutes earlier or a few minutes later than expected.

Identifying the Universe’s first Hydrocarbons
Daniel Wolf Savin, a senior research scientist in Columbia’s Astrophysics Lab, investigates how planets were formed from the elemental molecular components available in space. His team looks at the chemical inventory of the interstellar clouds that give birth to planets and stars. These clouds may have helped fuse carbon atoms and hydrogen ions into hydrocarbons—the first organic molecules – which were then scattered around the universe. “The pre-biotic molecules necessary for life may have been synthesized in space and, like seeds across the ocean, got carried to the young planets,” Savin says.

To understand how this fusion may have occurred, Savin reproduces the conditions of interstellar space using vacuum tubes, into which he beams carbon atoms and hydrogen ions at very cold and low-density conditions. At the end of the 20-meter long tube, the apparatus detects the resulting hydrocarbons by measuring the electrical charge. “The data we generate go into the chemical models so that people can predict what molecules are formed in these clouds to be potentially delivered to the surfaces of young planets,” Savin says. This work may not only help understand how life on earth started, but also point to other planets that may have been “seeded” the same way.

Modeling Exoplanetary Climates
Scharf’s research looks for the biosignatures of life, such as traces of oxygen or water, on other worlds. Using supercomputer-constructed models of how atmospheric and chemical changes may progress on the exoplanets, his team can simulate the planets’ climate states and whether they could sustain life. “There may be planets similar to earth but perturbed in different ways, which can inform us about how an Earth-like planet behaves or responds to different perturbations,” Scharf says. Some Earth-like planets may be further along in their planetary lifecycle and could point to the Earth’s eventual states.

This work has the potential to inform our civilization’s path forward. Enabling scientists to make more accurate predictions and inform the decision making that will affect the future of mankind, including whether we are destined to survive as species or not. “Maybe going to Mars is the best shot for our particular species,” Scharf says, “or maybe we just need to look after this planet a little bit better.”

Next Steps
As it develops from idea to realization, the Origins Institute will address these questions of life in the universe by bringing together the best academic minds from across disciplines. Greene envisions a multidisciplinary team in which biologists and neuroscientists ponder the concepts of life and consciousness from an evolutionary perspective, while physicists and mathematicians tackle these questions using the language of thermodynamics and general relativity, and philosophers and artists seek to understand and convey these questions’ impact on humanity.

“Bringing them together will spark new ideas and connections that will allow us to tell this story in a more unified, coherent and intrinsic way,” Greene says.

— Lina Zeldovich

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