Alan Calder, associate professor in the department of physics and astronomy, gave a talk on astrobiology and the search for life beyond Earth on Friday, Oct. 5. The talk was a part of the department’s “Astronomy Open Night” series.
Calder spent the evening exploring the possibility of intelligent life in the universe. He said that the three fundamental requirements for life are sufficient material, sufficient energy and the presence of water. He then went into detail on what each of these conditions implied for the probability of alien life.
“[Astrobiology is] the study of life in the universe, its distribution and its future,” Calder said. “It brings together different kinds of sciences to understand how living systems emerge, how their worlds form and how they evolve.”
According to Calder, the elements required in order to create life are carbon, nitrogen, oxygen and hydrogen. These form the building blocks of organic compounds which constitute all living organisms.
“These elements may reach planets because of comet impacts,” Calder said.
Furthermore, energy is required for life to exist. Stars like our own sun provide the energy necessary for metabolism, as is the case on Earth. However, it is also theorized that plate tectonics — the movement of the surface of a planet on the inner molten layers — may provide the requisite energy as well. Not all planets have an active inner molten system to make this work. The final requirement for life is the presence of a liquid or gaseous medium for organic reactions to happen in. These reactions are not possible in a solid medium as elements are not free to interact with each other.
In our solar system, Calder mentioned Enceladus and Europa, moons of Jupiter, as two possible candidates that may satisfy all three criteria. Calder said Europa has enough internal heat for a subsurface ocean to be present, where life may exist. A probe to verify this is in NASA’s long term plans. Enceladus has liquid water and energy due to active volcanoes on its surface.
Outside of our solar system, Calder said that the most likely place for life is on Earth-like planets in the Goldilocks Zone of their respective stars. The Goldilocks, or habitable zone, is the region in the vicinity of the star where water stays in its liquid state.
“For our sun, this is from roughly 0.85 AU to 1.2 AU,” Calder said.
An AU, or astronomical unit, is the approximate distance from the Earth to the sun, about 93 million miles.
NASA’s Kepler space telescope has been searching for planets within the habitable zone that may contain liquid water since 2004.
Calder also answered the question of why aliens, if they exist, have not found us yet. He said that there are three possibilities: that they don’t exist, that there is some fundamental limitation regarding space travel that we do not yet know or that they have annihilated themselves.
“We came very close to that as humans — are still close to it,” Calder said.
Calder emphasized that the study of astrobiology is not only about looking for aliens. In his eyes, such research provides valuable insight into the evolution of life on Earth, and can increase our understanding of the future of life on Earth.
“By learning more about life we learn more about what it means to be human,” he said.