Astrobiology: Modern Science Targets an Ancient Question
By Andrew Ng
If you asked someone ten years ago what “astrobiology” is, you may have gotten a blank stare in return. As a scientific pursuit, astrobiology is relatively new. But the underlying disciplines—astronomy, physics, chemistry, biology, geology—have been around for ages, and the underlying question—“Are we alone?”—is an ancient one.
Simply put, astrobiology is the study of life in the universe. This study includes life on Earth, but with our knowledge of Earth’s processes as simply one data set of hopefully many to come.
“For a long time, astrobiology was seen as science without data,” says Caleb Scharf, director of the Columbia Astrobiology Center. “But then the game changed, and suddenly we were in a position to study it.”
The turning point that Scharf refers to was the surge in the detection of “exoplanets”—planets that orbit other stars—over the past decade or so. The first confirmed discovery of a planet around a sunlike star happened in 1995, and the rate of discovery has been almost exponential ever since. Today nearly a thousand confirmed exoplanets and a few thousand more candidates have been detected, thanks to both ground-based and space-based telescopes. Astronomers use several techniques to infer the presence of exoplanets, but the most common involve looking for tiny changes in a star’s velocity due to the gravitational influence of planets and looking for the dimming of a star’s light as a planet crosses in front of it.
While these exoplanet discoveries were surging, a more gradual realization had been building in the field of microbiology. Scientists were discovering bacteria living in places on Earth that were once thought inhospitable—from hot springs and deep-sea vents to deep within the crust and even up in the clouds. If life on Earth could thrive in these extreme locales, then the prospect of life on other worlds was becoming more and more enticing.
So in 2005 the time was ripe for Scharf, who had spent the previous five years at Columbia as a research scientist studying galaxy clusters and testing cosmological models, to contact fellow scientists at Columbia and two other institutions on Manhattan’s Upper West Side—the NASA Goddard Institute for Space Studies (GISS) and the American Museum of Natural History (AMNH)—to gauge their feelings on astrobiology.
“Our initial workshops were like confessionals,” Scharf says, “where people from different disciplines would raise their hands and admit, ‘Yes, I’m interested in astrobiology.’ We quickly realized that many of us were already doing research that could be broadened into addressing the question of life in the universe.”
From these workshops and meetings, the Columbia Astrobiology Center was born—not a physical center per se, but a virtual collective of scientists with a common interest in the topic. The center includes scientists from the Departments of Astronomy, Physics, and Psychology, Columbia’s Astrophysics Laboratory, the Lamont-Doherty Earth Observatory, the Earth Institute, and Barnard College. Scientists from GISS and AMNH are also part of the collective. As the list of departments and organizations indicates, astrobiology is not one singular discipline but an inherently interdisciplinary pursuit with many lines of inquiry.
Daniel Wolf Savin, senior research scientist in the Astrophysics Laboratory, represents one of the biggest successes of a member of the center. Savin has built an experimental apparatus at Columbia’s Nevis Laboratories in Irvington, New York, to investigate how carbon combines with hydrogen under the conditions that one would find in interstellar space. Organic molecules like these seed the universe with the ingredients for life, and thus are of great interest to astrobiologists. While similar experiments have faced technical challenges in the past, Savin’s team is using their unique instrument to better control the temperatures and energies of the chemical reactions and circumvent these past limits.
Another project on the horizon involves “Model E,” which is a state-of-the-art climate model for the Earth developed by GISS scientists. Scharf and GISS colleagues are hoping to kick-start a five-year project to make Model E applicable to any planet or moon. With millions of lines of computer code and parameters that are currently fine-tuned for Earth, generalizing the model is not a trivial endeavor. But armed with such a model, which would first be calibrated by studying the environmental history of familiar worlds such as Mars, Venus, and Titan, scientists would be able to characterize the climate systems of exoplanets and determine their suitability for life.
The allure of astrobiology is pulling in the next generation of scientists as well. Aaron Veicht, M.A. ’10, M.Phil. ’11, Physics, started his doctoral program at Columbia with a research focus on nuclear physics and no astronomy background whatsoever. But he eventually switched to exoplanetary research after a series of events led him to discover his true scientific passion.
Around 2009 Veicht began tinkering with graphics processing units, or GPUs, purely as a hobby. GPUs were invented to handle complex computer visuals, like those found in video games and other graphics-heavy programs. However, with their ability to process massive amounts of data in parallel, GPUs have found an alter ego as inexpensive supercomputers, with applications ranging from quantum mechanics to molecular modeling.
For his own enjoyment, Veicht created a program that modeled physical systems forward in time, given a set of initial parameters. To test the program, he decided to input something he thought had a known answer—how the orbits of planets around stars evolve over millions of years. He contacted Caleb Scharf, who promptly informed him that the problem was, in fact, still at the core of modern planetary science.
A year later, Veicht continued stoking his burgeoning interest in astronomy by taking a seminar on exoplanets at Columbia. The seminar revealed to him just how fertile the field was for new scientific discoveries.
“It blew my mind,” says Veicht. “This was a field in which I thought I could make a large impact. So I switched my research focus to exoplanets. My advisers at Columbia were very supportive of my proposal to change projects and follow my passion, and they ensured a smooth transition.”
With Scharf’s encouragement, Veicht joined the lab of Ben Oppenheimer, an astrophysicist at AMNH and another member of the Astrobiology Center. Veicht currently works on two projects in Oppenheimer’s lab.
The first is direct imaging of exoplanets—an extremely difficult endeavor, given how much brighter and larger a star is compared to its planets. Several times a year, Oppenheimer’s team travels to the Palomar Observatory near San Diego, California, where the Hale Telescope resides. To conduct their observations, the team points the telescope at a given star and employs a high-tech suite of instrumentation and software to block out its light, allowing them to find planets normally overwhelmed by the light of the star. Incredibly, their technique has allowed them to find planets that are up to one million times fainter than the star itself. Once they have isolated the faint light coming off the planets, they can deduce the abundance or absence of chemicals in the planets’ atmospheres by examining their light spectra—the unique and telltale “fingerprints” created by different chemicals. Earlier this year Oppenheimer’s team published a paper in The Astrophysical Journal detailing this “reconnaissance” method on HR 8799, a star about 128 light-years away with four gas giant planets orbiting it. Although these planets are probably inhospitable (they average 1,340 degrees Fahrenheit with ammonia or methane atmospheres), the same techniques can hopefully be applied to more Earthlike planets in the future.
In addition to this cutting-edge research, Veicht continues working on the project that brought him to astronomy in the first place: the modeling of planetary orbits. Observations of an exoplanetary system do not give precise values for attributes like mass, location, and orbits of the planets. Rather, the best one can do is to infer a range of possible values. A computational model can help winnow down these possible values by running simulations on them—those that result in stable orbits over the next 10 to 100 million years are considered more “true,” whereas those that result in chaos (i.e., planets falling into the star, crashing into one another, or getting flung out of the system) are discarded.
Running these simulations requires substantial computing power. The number of simulations for each planetary system could be anywhere from 100,000 to 1,000,000, with more than a thousand possible systems to model. The use of GPUs helps considerably, but Veicht and his advisers are also hoping to recruit the public’s help by starting a citizen science project that will allow people to lend their computers to run these simulations over the Internet.
“Today’s graduate students, like Aaron Veicht, comprise the generation that will see the greatest leaps in astrobiology,” says Scharf. “If you want to be a scientist, astrobiology is an excellent option—there are so many interesting things happening in this field, right now and in the foreseeable future.”
In addition to promoting astrobiology within academic circles, Scharf is spreading the word among the general public. He has written articles and op-eds for The New Yorker, Wired, and Nautilus magazines, as well as The New York Times. He maintains a blog on Scientific American’s website called Life, Unbounded, which covers a wide range of space-related topics and drew an audience of more than 350,000 last year. And in 2014 he will publish an astrobiology-themed popular science book called The Copernicus Complex.
“Copernicus’ heliocentric model removed us—humankind and the Earth—from the center of all things, and spurred the notion that we are not that special,” Scharf explains. “But new discoveries in astrobiology indicate that the story is not that simple. As we continue to learn the details of other planetary systems, it appears that our solar system is not typical. For example, most exoplanets’ orbits are more elliptical than those found in our solar system. Also, exoplanets ranging between Earth-sized and Neptune-sized are very common, but our solar system does not have any of those.”
These discoveries and more continue to fuel the interests of scientists in the Columbia Astrobiology Center. For Scharf, astrobiology sits right alongside evolution and the Big Bang as science topics with the potential for huge impacts on human culture. If scientists find an exoplanet tomorrow with strong and clear indications of life, the impact on society would be as exciting to imagine as the discovery itself.
“Before 1968, when the iconic photo of Earth rising over the moon was released, many people still didn’t have a genuine vision that we lived on a sphere,” says Scharf. “If just a picture of our planet can dramatically shift our thinking, how will evidence that we are not alone change our culture? It would be revolutionary.”