Smallest Exoplanet Found

Astronomers recently announced finding a new exoplanet (a planet in another solar system). That alone wouldn’t be a big deal anymore, since in the last 20 or so years we’ve found more than 800 (with a few thousand other “candidates” requiring more study to verify). What’s special about this one is how small it is. Newly discovered Kebler-37b is only 3865 diameters wide, making it smaller than Mercury and barely larger than the Moon.

Aside from setting a new record for smallness, it also represented a unique experiment. Kepler-37, the star the planet orbits, has not been studied much and so astronomers were uncertain of its size (both volume and mass, is my understanding). One way to determine this is seeing how the stellar equivalent of seismic waves behave in the stars interior (a discipline called “asteroseismology“). It turns out that for most stars, the way it oscillates is also linked to its size. You might wonder how this is possible since, on Earth, seismology is a fairly hands on affair with detectors everywhere. With stars, we can look at their light. If you split the light from a star into all the colors (giving you a “spectrum”), you’ll see dark lines appear at some spots.

Spectrum of the sun

These dark lines are where the light is absorbed by the atoms in the star. If you have really sensitive equipment to read the spectrum, you’ll see that these lines actually move slightly over time. This is because of that ubiquitous feature of waves, the Doppler effect. Just like an ambulance siren sounds higher pitched when approaching you and deeper when it passes you and moves away, light does the same thing. So if a segment of a star is expanding toward you when the light is emitted, we see the spectral lines at higher frequencies (or “blueshifted” as it moves closer to the blue end of light) and a shrinking section has lines at lower frequencies (or “redshifted”).

The other cool thing about this discovery was who funded it. The asteroseismology work was not funded by NASA, but actually by a crowdfunding project called Pale Blue Dot. The organization has people “adopt a star”, but instead of pretending to let you name it and making you pay for an expensive diploma (*hem hem*), the money star adopters give goes to fund research groups working with data from the Kepler mission.