So, by now you’ve probably heard about the discovery of 7 new Earth-like planets around the star, TRAPPIST-1.
First, what’s with the name? Usually stars either have a commonly known Arabic name (such as Betelguese or Kochab) or Greek name that go back to at least medieval, if not ancient, times, or they have some catalog name such as HD 172147 that refer to a specific stellar catalog (in the case I mentioned, the Henry Draper Catalog). In this case, “TRAPPIST” is an acronym referring to a telescope in Chile that is dedicated to looking at transiting planets around relatively nearby stars. This is the first star with transiting planets detected by TRAPPIST, therefore its “TRAPPIST-1.” The lead scientist on this project is from Belgium, as are the well-known Trappist monks, hence that particular acronym.
Let’s also be careful how we use the word “Earth-like.” Its not likely that we will see a “carbon copy” of the Earth, as in Journey to the Farside of the Sun or more recently, Another Earth. All we know about these planets for sure is that they are about the same size and mass as Earth (though some might be better called “Mercury-like” or “Mars-like”). They may or may not have atmospheres. We don’t know yet.
All are within just several million miles of their parent star. You might think that would make them extremely hot, but keep in mind that TRAPPIST-1 is a red dwarf star and is much smaller, much less massive, and is giving off much less light (and heat) than the Sun. Therefore several of these planets are likely in a “habitable zone”, that is an imaginary zone around each star in which it would be possible to have liquid water on their surface (although they’d need atmospheres for said water to exist for very long). Of course, that assumes that life would be similar to life on Earth, and we just don’t know yet whether it would. However, its a reasonable place to start.
Another concern is that several of these planets are likely to be tidally locked. If a planet or moon is relatively close to another more massive body such as a planet or, in this case, a star, the planet or moon is likely to have its rotation rate slowed down by the gravity of the bigger object its orbiting through a process called “tidal braking.” Eventually the rotation period of the planet or Moon will become equal to the period of revolution. So, in this case, the “day” of each planet would become equal to its “year.” We see this process at work with our own Moon and with the planet Mercury. Without knowing the details of the planetary composition its hard to definitively predict whether or not they’d be tidally locked in this way (for TRAPPIST-1’s planets), though it seems likely that the closest ones would be.
Under these conditions, one planetary face would always remain hot and the other side, cold. However, it may be possible for an intermediate zone to have more moderate temperatures, especially if there is a stabilizing atmosphere.
Unfortunately, TRAPPIST-1 is also a known X-ray sources, and that level of X-rays might be enough to bake away the atmospheres of these planets (if they every had any atmosphere).
Stay tuned, cause its likely that scientist will likely try to observe the atmospheres of the planets next, if its possible.
And remember, if you like what you see and want more, take a look at my book from McFarland Publishing, The Physics and Astronomy of Science Fiction. Its available from the publisher and Amazon.