In a new opinion piece in the journal Astrobiology, Edward Guinan from Villanova University and I caution not to overhype the possible discovery of a second Earth. Although there are now more than 3,000 confirmed planets outside of our Solar System, truly “Earthlike” planets will be exceedingly rare.
Just because a planet is located in the so-called habitable zone of a star does not mean that it is Earthlike. Our moon is also located in the habitable zone, but no one argues that life exists there. Earth 2.0 requires so much more than just the right location, including the existence of multiple environmental habitats and a sizeable biosphere, a suitable atmosphere, a liquid solvent at the planet’s surface, the presence of organic molecules, a geomagnetic field, plate tectonics and so much more. Without these things, Earth as we know it would not exist.
Currently, we do not have the technological ability to measure all these parameters to determine whether a specific exoplanet might be a second Earth. But we will in the near future, with space missions such as PLATO, WFIRST, and the James Webb Space Telescope, as well as the next generation of large Earth-based telescopes such as the GMT and E-ELT. Particularly exciting would be a dedicated spacecraft such as the New Worlds Mission (NWM), which would include a large occulter in space designed to block the light of nearby stars to observe any orbiting planets. With this generation of new missions we can hone in on possible life by determining an exoplanet’s atmospheric composition, land-ocean ratios, and perhaps even detecting the presence of vegetation.
The overhyping of potentially Earth-like planets at the present time does a disservice to science, however. The results of current exoplanet research might easily be misunderstood, and government agencies might set unrealistic expectations. It reminds me of the backlash from the Viking life detection experiments of the 1970s. Expectations had skyrocketed, only to be dashed when the determination of life on Mars was inconclusive. Since then we have not launched a single dedicated life detection mission to any other planet or moon, and the Viking experience is a big reason for that hiatus.
Overhyping today’s exoplanet discoveries could also be a disservice to those scientists who eventually do find a true Earth 2.0, because the public might feel that it has already heard the news. Besides, the new results coming in daily from exoplanet research are exciting enough to stand on their own merit.