On our vacation this year to Rockport, Massachusetts, we spent an hour one night watching the Perseid meteor shower. This is my favorite meteor shower because I can lay outside and not get cold too fast. The night sky is far darker on the end of Cape Ann than it is at home in Delaware, so it was a rewarding activity. There’s really nothing like staring at the stars and pondering the vastness of space to make you realize your puny human problems aren’t worth losing sleep over.

Ancient astronomers were the first to notice that most of the objects in the night sky moved in circular patterns. They also observed that a few did not move this way, and those they named wandering stars. The ancients’ wandering stars are what we today know as planets. Almost since humans recognized that Earth was also a planet, we have wondered whether there could be life in other parts of the universe. Recent technological advancements in astronomy have increased confidence in the probability that there are other forms of life in the universe.

Detection and Identification

The United States National Air and Space Administration (NASA) developed the ongoing Kepler mission to detect other planets in the universe and identify those that are similar to Earth in size, chemical composition, and orbit. Kepler is a spacecraft and photometer that continuously points at the same group of stars. The Kepler mission has identified a number of Earth-like planets in the habitable zones of stars. Since its launch on March 6, 2009, Kepler has identified 12 Earth-like planets in the habitable zones of stars. This is remarkable because the Kepler field of view is just a tiny portion of our galaxy, and the galaxy is a tiny portion of the universe.

Identifying a planet as potentially habitable isn’t enough to say if it is certainly so. The crucial element is water. The habitable zone for humans is identified as the orbital period around a star where liquid water might exist on the surface of the planets. The way that astrophysicists calculate a planet’s temperature is described here. The habitable zone for a star system can also be calculated.

A potentially habitable planet must also have an atmosphere. An atmosphere shields the planet’s surface from impacts and radiation, both of which can be hazardous to life. Some researchers have posited that some planets’ atmospheres could evolve over time. If a big planet forms in an outer orbit, with a rocky core and a thick gaseous atmosphere (similar to Neptune in our solar system), tidal forces in that star system could cause the planet to change and move over time. The star’s gravitational pull would stretch the planet into an ellipsoid and possible pull the planet closer to the star. The friction caused by these movements would cause heat, that could potentially drive surface volcanism or drive off lighter gasses in the atmosphere. If the planet has shifted into the star’s habitable zone, the leftover rocky core could be a habitable planet.

Are We Alone?

Although the existence of a number of planets in the habitable zone of other star systems has been proven, no one has yet seen these planets or captured images of them. There are a number of reasons why the search for other habitable planets matters to all of us. One is of course that the question of “Are we alone?” has fascinated humans since the recognition of Earth as a planet. Another is that the natural evolution of a star means that the Sun will eventually make life on Earth unsustainable, and we definitely don’t want to be in the neighborhood when that happens.

The recent discovery of Kepler 452b has been exciting for astrophysicists because its star is very similar to our Sun and the planet is of similar size, mass, and distance from its star as Earth. Its mass is likely about 5 times that of Earth because it is about 60% larger in diameter. The additional mass would provide many thousands of additional years of protection for the planet’s atmosphere from the increased energy of its star.

The relatively new field of astrobiology offers new opportunities for students interested in an interdisciplinary STEM career. Astrobiology degree programs are currently offered at a number of U.S. universities, including the University of Washington and the University of Hawaii. A comprehensive list of international educational resources can be found here.

Produced by the National Science Teachers Association (NSTA), science writer Becky Stewart contributes monthly to the Science and STEM Classroom e-newsletter, a forum for ideas and resources that middle and high school teachers need to support science, technology, engineering, and math curricula. If you enjoy these blog posts, follow Becky Stewart on Twitter (@ramenbecky).

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