(Description) Figure 20 GJ 1214 b transmission spectrum. The measurements are shown as black circles (with error bars). The coloured lines are models for different atmosphere compositions used as a comparison. The changes in transit depth are so small that they are measured in a unit called ‘parts per million’ (ppm) – ten thousand times smaller than our more familiar percentage measure (‘parts per hundred’).

Week 7: The Special Ones

This is the measurement of GJ 1214 b’s transmission spectrum made with the Hubble Space Telescope (black dots with uncertainties shown), compared with several models of expected atmospheres. The measured spectrum is so flat that it’s not consistent with any of the predicted atmospheres.

4.2 The small ones: GJ 1214 b and GJ 1132 b