Earth-Like Planets? Not Quite

Author Tim Barnett Published on 03/16/2018

Every once in a while, the mainstream media buzzes over a newly discovered Earth-like planet. These headlines can give the impression that planets like Earth—which are capable of sustaining complex life—are common. We closely associate “Earth-like” with life-filled. But what do scientists mean by Earth-like?

In a recent blog post, particle physicist Michael Strauss describes three ways the term “Earth-like” is being used by scientists.

When scientists say that an Earth-like planet may have been discovered, they actually mean one of three things. Either (1) the planet is in such an orbit around its central star that allows the temperature on the planet to possibly harbor liquid water, or (2) the planet is about the same size as the earth, or (3) the planet is solid and rocky rather than gaseous.

Unfortunately, when scientists use the term “Earth-like,” most people immediately think of the planet’s ability to sustain life. If it’s “Earth-like,” then it must be able to support life, like Earth. But none of these three qualities—distance to the Sun, size, and rocky composition—means the newly discovered planet will support life. Much more is required.

Strauss continues,

Of course any one of these criteria, or even all three, does not actually give us a true Earth-like planet. We know that our moon is in the correct location to contain liquid water, but it is not “Earth-like.” We know Venus is about the size of the earth, but it is not “Earth-like.” We know that Mercury is rocky and not gaseous, but it is not “Earth-like.” So none of these criteria really give an Earth-like planet. Headlines and sound-bites are not meant to be precise but to draw attention, and it is much more exciting to proclaim an “Earth-like” planet has been found rather than a “Venus-like” planet (if even that could be claimed).

Beware of mainstream articles that are meant to sensationalize scientific findings. This happens all the time. If you’re not properly informed, you can easily be misled. So the next time you see a headline describing an “Earth-like” planet, ask yourself if the phrases “Moon-like,” or “Venus-like,” or “Mercury-like” would be equally appropriate. Chances are the article is more accurately describing a lifeless planet—that happens to be rocky, or Earth-size, or in the habitable zone, rather than anything like our life-filled planet.