Starts With A Bang

What An Earth-Like World Around Proxima Centauri Would (And Wouldn’t) Mean (Synopsis)

Planets with the same mass and radius as Earth, even in a star’s habitable zone, could have vastly different properties today. Image credit: J. Pinfield / RoPACS network / University of Hertfordshire.

“To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field sown with millet, only one grain will grow.” -Metrodorus of Chios

Later tonight, the European Southern Observatory is expected to make an announcement, and the smart money is on the discovery of an Earth-like planet orbiting Proxima Centauri, the nearest star to our Sun. As incredibly exciting as this news is, however, it’s important to keep in mind that “Earth-like,” to an astronomer, means something very different than what we think of as “actually like Earth.”

The Earth (L) in visible light, compared with Venus (R) in infrared light. While Earth’s reflectivity will vary over time, Venus’ will remain constant. Image credit: NASA/MODIS (L), ISIS/JAXA (R), stitching by E. Siegel.

The only information we can glean from our present observations is the planet’s mass, size and orbit around a star. This is enough to tell us some of its properties, including a few ways (like tidal locking) that are quite different from Earth, but questions about its atmosphere, surface temperature, magnetic field and much more remain unanswered.

An illustration of a panet around a red dwarf star. Only gas giant worlds are large enough to have their atmospheres detected at this point in time. Image credit: ESO.

Come learn what the discovery of a new planet around our closest star would and wouldn’t tell us!