Do Aliens Exist?

Are we alone? Or is there life on other planets? Ask Science discusses the two major breakthroughs in the search for extraterrestrial life making headlines this week.

Sabrina Stierwalt, PhD
5-minute read
Episode #156

Talk of extraterrestrial life—or life originating off of our planet—made science headlines twice in the past week. I’m not talking about claims of UFO sightings or the latest alien abduction story. The news items I’m talking about offer examples of millions of dollars being spent on the human urge to search the vastness of space to find more of ourselves out there.

First, the Russian millionaire Yuri Milner recently pledged $100 million dollars toward the search for ET over the next decade. The funds will go toward developing new technologies, recruiting new students, and more guaranteed telescope time, all of which will make the search for life larger, faster, and more efficient.

Then, just a few days after this game-changing announcement, NASA’s Kepler mission released the news of the most Earth-like planet to be discovered so far. At 1,400 light years away, the planet, called Kepler 452b, is 1.6 times the size of the Earth and orbits its sun at a similar rate, making its year 385 days.

Together these announcements mark a potential turning point in the search for other forms of life in space. We now have the resources to look for it, and we’re figuring out where to look.

Are We Alone?

Whether or not the search for life will be successful depends on what you would call “life.” Studies of extrasolar planets (planets outside of our solar system, also called exoplanets for short) have started by looking for planets with the key ingredients for life rather than for life itself.

One key ingredient for life as we know it is water. Planet hunters can predict the temperature on the surface of an exoplanet based on how far the planet is from its star (and what kind of star it orbits). Every star has a “habitable zone,” also called the “goldilocks zone” where the temperature is just right for water to be a liquid—not too hot (i.e., too close to the star) and not too cold (i.e., too far from the star). When an exoplanet falls in its stars habitable zone, it could potentially host liquid water.

According to the NASA Exoplanet Archive, a total of 1,879 exoplanets have been discovered as of July 2015. Considering the first exoplanet was only discovered in 1992, that’s over 80 entire new worlds discovered each year.

However, early on the search techniques favored the discovery of planets that were much more massive than the Earth and in orbits that were much closer to their stars. These exoplanets are called “Hot Jupiters” because they are closer to the mass of Jupiter than to that of the Earth. The dominance of the more massive planets in the current exoplanet count is what makes NASA’s recent discovery of Kepler 452b so compelling. By comparison, Kepler 452b is so similar to Earth that scientists are calling it Earth’s bigger, older cousin. (It’s star is roughly 1.5 billion years older than our Sun.)

Of course, in order to get a better estimate of an exoplanet’s temperature, we also have to know something about its atmosphere. Remember that Mercury, the closest planet to our Sun, is a blistering 426 degrees Celsius (about 800 degrees Fahrenheit), but it is still not the hottest planet in our solar system. That honor goes to Venus at a sweltering 462 degrees Celsius (864 degrees Fahrenheit). Even though Venus is further from the Sun, its atmosphere acts as a blanket that traps heat and warms the surface.

Planetary atmospheres thus offer clues as to whether or not a planet can host life via their effect on the planet’s temperature but also through their chemical composition. Scientists are just now starting to infer the properties of atmospheres around exoplanets. One of those atmospheres may contain oxygen, a strong indication that the planet could harbor life.


Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.