The Philippine Astronomical Society, Inc., in partnership with the Physics Society of the Polytechnic University of the Philippines (PUP), held a set of lectures titled Exoplanets: The Physics and Biochemistry of Searching for the Next Earth at the Claro M. Recto Hall in PUP last November 16.
The event featured advancements in the fields of Cosmology, Telescopy, and Chemistry that have contributed to expanding our current understanding of planets that orbit stars other than our own. Among these include novel methods of detecting rocky exoplanets and new telescopes such as the James Webb Space Telescope—whose launch is scheduled on March 2021—poised to replace the aging Hubble Space Telescope launched in 1990.
Astronomy through the centuries
Ron Darell Aves, a researcher from the National Institute of Physics of the University of the Philippines Diliman, began with his talk titled How the Search for Exoplanets Began. Aves first discussed ancient Greece and Babylon—early civilizations where our first steps toward understanding the Universe began. “For thousands of years, our ancestors studied the stars,” he told the audience, citing how the ancient Polynesians navigated the Pacific with only the waves and stars as their guide.
He then segued into astronomical frameworks derived from the Middle Ages and worked his way through its developments during the European Renaissance and the Age of Enlightenment. Aves also highlighted the work of Tycho Brahe, Nicolaus Copernicus, and Edmund Halley—who were some of the most substantial astronomers of their time.
Aves’ discussion resolved at the mention of Galileo Galilei, who greatly improved the design of the telescope, and how his contributions revolutionized an entire scientific field almost overnight. The researcher then turned to modern Cosmology and highlighted Jim Peebles—who was one of the recipients of the Nobel Prize in Physics earlier this year—and his foundational work on the cosmic microwave background, which is the faint glow left behind from the early Universe.
Discussing the realm of exoplanet detection, Aves listed out and explained the various methods used to search for exoplanets. First among these was the radial velocity method, which he described as “relying upon the ‘wobbling’ that a star exhibits when orbited by another body.” By determining the presence and intensity of this “wobble”, one can surmise whether or not a certain star has a planet orbiting around it and how massive the orbiting planet is.
He then touched upon the transit method, which is based on a very simple principle: since a star emits light, a planet lying on the same plane as the Earth that passes in front of the star will dim the light we perceive. One can determine the size of an orbiting exoplanet based on how much area it dims, while the frequency of dimming gives an estimate of the distance between the host star and the exoplanet. This is possible because of the inverse relationship between distance and orbital velocity, or as Aves explained, “The farther a planet orbits a star, the slower it will do so.”
Aves briefly tackled the differences between ground-based and space telescopes, highlighting that the resolution of the former is hampered by noise created by warm air currents in our atmosphere. He furthered, “[The] thickness of our atmosphere makes it difficult to observe higher wavelengths of light such as x-rays as they get absorbed before we can detect them.”
He ended his lecture on the topic of gravitational lensing, which happens when light passes by massive objects that can appreciably warp the fabric of spacetime, or the four-dimensional space that we live in—three spatial dimensions plus one time dimension. This light is therefore redirected along a curved path, in the same way a lens bends light.
Is anyone out there?
After Aves, Leogiver Mañosca, a Science textbook Outsource Content Editor and Writer from Phoenix Publishing House, Inc. talked about his lecture titled Exploring Exoplanet Biosignatures and other Signs of Life, which revolved around the possible chemical components of extraterrestrial life and the telltale signs that life of all kinds—including extraterrestrial lifeforms—send out into the Universe.
Mañosca relied heavily on the concept of a biosignature, which is a chemical, physical, or electromagnetic sign that points to, as he put it, “the existence of life in a particular region.” In exoplanet Astronomy, the most pertinent biosignatures are those of chemical and electromagnetic origin, as physically visiting exoplanets is far beyond our current capabilities.
Chemical biosignatures can be determined through spectroscopy, which is the analysis of light emitted by matter. One of the strongest chemical biosignatures, Mañosca pointed out, is the abundance of molecular oxygen in an exoplanet’s atmosphere.
Oxygen’s reactivity makes it “suspect for an exoplanet’s atmosphere to contain a high concentration of it,” he explained. A high level of oxygen can be taken to mean that photosynthetic organisms, similar to plants and algae on Earth, are present on the exoplanet.
Another very important chemical biosignature, according to Mañosca, is the presence of water—a known prerequisite to life. Detecting water in an exoplanet’s atmosphere makes it “at least more likely to harbor life.”
Mañosca cautioned, however, that biosignatures are not direct evidence for life, but only the breadcrumbs they leave behind. “Chemical biosignatures are not unique to life alone and that certain abiogenic processes”—those not carried out by living organisms—“like volcanism can introduce these chemicals into [the] atmosphere,” he clarified.
Moreover, there is also the issue of habitability or the general conditions that make it possible for life to exist in the first place. A candidate exoplanet should be in the habitable zone—neither too far nor too close to its star—so that temperatures on its surface are conducive for life. Similarly, exoplanets that orbit blue giant stars are drenched in ionizing ultraviolet rays, which can prevent life from forming in the first place.
After “admittedly dense lectures,” both Aves and Mañosca hoped that they “served as inspirations for those who want to enter the field of Astronomy,” as they closed the event.