Proxima Centauri header on Frontier Channel, background image by ESA/Hubble

Regarding Rumors of Earth-Like Planet Orbiting Proxima Centauri

By ESA/Hubble, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29263039
By ESA/Hubble, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29263039

We’ve been here before: the media gets wind of a possible discovery made by a long-running science project and before there is a peer-reviewed scientific paper published and a press conference, speculation runs wild. In the age of social media, gossip spreads at the speed of the share, and in this digital game of telephone, the results are often more indicative of our collective imagination than of reality. What is often true about these occurrences is that there is indeed something interesting to announce. What is often not true are the specifics dreamed up by the rumor mill.

Yesterday, my Twitter feed erupted with links to articles like “Scientists to unveil new Earth-like planet: report” from Phys.org and “An Earth-like Planet Might be Orbiting Proxima Centauri” from Discover Magazine. These were articles written quickly in response to the original report, “Wissenschaftliche Sensation: Mögliche zweite Erde in unserer Nachbarschaft entdeckt“, that appeared in the German weekly Der Spiegel.

What’s so potentially exciting about this news is that Proxima Centauri is the nearest star to our Sun. It’s 4.2 light years away, just a little closer even than the other two stars it seems to be gravitationally bound to, Alpha Centauri A and Alpha Centauri B. If there is a planet orbiting Proxima Centauri that is Earth-like, then it is by far the closest Earth-like exoplanet (planets around other stars) yet discovered.

But what exactly does “Earth-like” mean? To a scientist, the comparator “-like” often indicates characteristics like rough diameter or mass. Even though Venus is a hellish world of temperatures hot enough to melt lead underneath a thick atmosphere of carbon dioxide with clouds of sulfuric acid, it is “Earth-like” in terms of its diameter and mass. Recent “3-D climate simulations” of Venus carried out by scientists at NASA’s Goddard Institute for Space Studies suggest the possibility that Venus in the distant past was potentially habitable (Way, M. J.A. D. Del GenioN. Y. KiangL. E. SohlD. H. GrinspoonI. AleinovM. Kelley, and T. Clune (2016), Was Venus the First Habitable World of our Solar System?Geophys. Res. Lett.43, doi:10.1002/2016GL069790.) Being approximately the same diameter and mass as the Earth or being potentially habitable doesn’t imply that Venus was ever really all that much like Earth, though, let alone had liquid water on the surface or gave rise to life.

So the discovery of an Earth-like planet around another star isn’t the discovery of aliens, though this is certainly what many people would like to hear, and that’s where the speculation often tends to go. But the only real information we can glean about exoplanets using current technology and research is limited to one or more or fewer of the following: a range of possible diameters and masses, approximate distance from the parent star, and whether or not that orbit is within a theoretical region around the parent star known as the “habitable zone.” This zone is a region where models suggest a planet with the right atmospheric pressure, composition, and mass could support liquid water on its surface. The Earth seems to be in just the right zone in our solar system for temperate climates with long-standing bodies of surface water, and since this is the only example of such conditions we know of in the entire universe, scientists have modeled where these same conditions might exist around other stars, some of them like our Sun, and others very different, whether bigger or smaller, hotter or colder, solitary or part of binary or greater collections of gravitationally-bound stars.

The habitable zone sounds nice, but both Venus and Mars are in the modeled habitable zone around our Sun, and look how unpleasant and free of long-standing bodies of surface water they are. Even given an Earth-sized planet at an Earth-like distance from a Sun-like star, it is unlikely that such a planet would have all the other conditions required for oceans or life as we know it.

The truth is that you and I and the media don’t have any information about this rumored planet in orbit around Proxima Centauri. All the articles published to date are just rumor, with none of the details necessary to put constraints on what is supposed to be announced. I’m not saying that there isn’t going to be an announcement (the rumors say that this will happen at the end of August), but we certainly don’t have anything to go on other than an initial report that is light on details and doesn’t include confirmation from any of the scientists alleged to be involved. If the rumor turns out to be true, that’s wonderful, but even then, it’s not yet clear that this planet will be described as “Earth-like” or “potentially-habitable.” I can predict with nearly 100% confidence, however, that scientists won’t be announcing the discovery of surface bodies of water or alien life.

That’s the pace of science: glacial compared to the pace of rumor. Knowledge progresses at the pace of data gathering and analysis, confirmation, peer-review, additional studies, new research approaches, and the accrual of additional evidence. This is a step-by-step process, so even if there is an Earth-like planet in the habitable zone of Proxima Centauri, there will be much more investigation required and technology and techniques to be refined and even invented before scientists can give us a clear picture of just what might be out there.

Today, though, all we have are a rumor, speculation, and the possibility that nothing will be announced after all.