With thousands of discovered planets around stars beyond our own Sun, why haven’t we found the next Earth?
Over the past 30 years, astronomers have gone from zero known extra-solar planets to thousands.
Periodic changes in a star’s motion or regular brightness dips give them away.
Thanks to these techniques, we’ve revealed the masses and radii of worlds nearby and thousands of light years away.
Over 200 are Earth-sized, with many residing in the so-called habitable zone around their stars.
Yet with everything we’ve found, there are no potentially habitable Earth-like worlds around Sun-like stars.
There are three primary reasons for this.
1.) Most of the small planets we know of are found around red dwarf stars.
Red dwarfs are the most common, and offer the largest planet-to-star size and mass ratios, making planets easier to detect.
2.) Larger planets are easier to find; most are too large to be rocky without a giant gas envelope.
3.) We didn’t observe them for long enough to detect planets with ~1 year orbital periods.
If our own Solar System were at the distance of most stars, we wouldn’t have discovered Earth.
It’s the next generation of planet-finders, like James Webb and PLATO, that will hopefully deliver our first true Earth-like world.
Mostly Mute Monday tells the scientific story of an astronomical object or phenomenon in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.