:INFO
The planet that refused to answer for thirteen years
Every telescope aimed at GJ 1214 b between 2009 and 2022 came back with the same thing: a flat line. A transmission spectrum works by watching starlight filter through a planet's air, and each gas leaves a fingerprint. This one had no fingerprints at all, just a featureless curve, which meant a cloud or haze deck high enough to block the view of everything below it. In 2023 JWST attacked it from a different angle, measuring a full phase curve as the planet went round instead of just the moment it crossed.

:STATS
[icon:TARGET] Radius | 2.733 Earth radii, a mini-Neptune
[icon:CHART] Mass and density | 8.41 Earth masses at 2.26 g/cm3
[icon:CHECK] Equilibrium temperature | 567 K, measured
[icon:CLOCK] One year | 1.58 Earth days
[icon:STAR] Host star | GJ 1214 at 3101 K, a cool red dwarf
[icon:BOLT] Distance | about 48 light-years

:JOURNEY
Thirteen years of getting nowhere, and why it was not wasted
1 A target
2 A flat line
3 A negative
4 A new angle
5 An answer

:NOTE
The measured dayside came in colder than the planet's own equilibrium temperature. That sounds impossible and is not: equilibrium temperature assumes the planet absorbs everything that falls on it. Measure it colder and you have learned that a great deal of the starlight is being reflected straight back out, which is how the haze got characterised without ever being seen through.

:NOTE.half
High metallicity means the air is dominated by things heavier than hydrogen and helium. At 100 times solar or more this is not a scaled-down Neptune, it is a different kind of object, and the category is the most common one in the galaxy while having no example in our own solar system.

:NOTE.half
Thirteen years of flat spectra were not wasted effort. They ruled out a clear hydrogen atmosphere early and forced the haze interpretation, and the phase curve that finally worked was designed around exactly that problem. A null result that narrows the options is still a measurement.

:LINK
https://www.nature.com/articles/s41586-023-06159-5
A reflective metal-rich atmosphere for GJ 1214 b from its JWST phase curve