It’s all over the news: A team of scientists at UC Berkeley and University of Hawaii used Kepler data to gain one step closer to determining the abundance of potentially habitable extra-solar planets within the Milky Way Galaxy.
In their paper, published yesterday in the journal Proceedings of the National Academy of Sciences, the team states: “We find that 22% of Sun-like stars harbor Earth-size planets orbiting in their habitable zones.”
Although the statistic is simple enough, the media are playing a number flinging game to see who can produce the most earth-shattering headline. Consequently, readers are caught in the midst of confusing, misguiding headlines such as:
“Kepler Space Telescope data suggests up to 40 billion Goldilocks planets” – SlashGear
“8.8 billion habitable Earth-size planets exist in Milky Way alone” – NBCNews
“Two billion planets in our galaxy may be suitable for life” – The Guardian
But my personal favorite is a press release issued by the W.M. Keck Observatory: “One in Five Stars has Earth-sized Planet in Habitable Zone.” To their credit, the authors redeem themselves in the first sentence by specifying Sun-like stars. The University Herald earns no such redemption with their take titled “Kepler Telescope Researchers Estimate One in Five Stars in the Universe Has an Earth-Like Habitable Planet.”
UC Berkeley’s press release, which is worth the read, uses a more accurate headline: “Astronomers answer key question: How common are habitable planets?”
Perhaps the best take on the study’s results are by Bad Astronomer blogger Phil Plait. His impressively detailed look at the paper’s results leads him to estimate that there are roughly four billion Earth-sized planets in their habitable zones orbiting Sun-like stars throughout the Milky Way Galaxy. Not 40, or 8.8, or two, but four billion.
Phil Plait argues that there are about 200 billion stars in our galaxy, 10 percent of which are like our Sun, which means there are roughly 20 billion Sun-like stars in our galaxy. Twenty percent of 20 billion is four billion.
The values that NBCNews and The Guardian boast are more difficult to decipher but stem from a similar calculation to Plait’s. On the other hand, Will Conley at SlashGear merely states “as many as 40 billion planets with climates similar to Earth’s may be calculated to exist in the Milky Way galaxy.” In addition to including a statistic, which he provides no reference for, this statement is particularly egregious since no one knows about the climate (a.k.a. the combination of atmospheric patterns, weather conditions, precipitation, temperature, etc.) of any extra-solar planet. The technology is not sophisticated enough to make such detailed measurements.
Read Seth Borenstein’s piece in the NBCNews, and you’ll get a better sense of where SlashGear likely grabbed the 40-billion-planet claim. According to co-author of the scientific paper, Geoff Marcy, there are 40 billion Sun-like stars in our galaxy – double what Plait argues. Take 22 percent of 40 billion and you get 8.8 billion.
Similarly, Alok Jha at The Guardian claims that the galaxy contains 100 billion stars, 10 percent of which are Sun-like. Therefore, he provides half of Plait’s value, which is two billion. Jha does not give a reference for his value of 100 billion stars.
Unfortunately, the scientific uncertainty for the number of stars in the Milky Way and the percentage of those that are Sun-like has led to the slew of different values smeared across some media headlines. But that does not redeem the lack of attention to detail and accuracy in some of these headlines as well as, in some cases, the text. Other headlines get the point across more clearly such as:
“Kepler Telescope Finds Plethora of Earth-Sized Planets” – Scientific American
“Kepler space telescope finds Earth-size, potentially habitable planets are common” – The Washington Post
“Kepler find Earth-size planets commonplace” – CBS News