Asked by Thomas Davis
The difficulty with observing exoplanets is that they’re so very small in comparison with their stars that we can’t observe them directly. However, it’s possible to calculate the colour of an exoplanet by watching as it moves behind its parent star. We call this a secondary eclipse and it temporarily blocks the light reflected off the planet from reaching us.
By recording the decrease in thermal radiation and light coming from the system before, during and after the event, we can get information about the type of world we’re looking at. We can carefully analyse the changes in the light spectrum as the planet is hidden and observe which wavelengths of light go missing. From this we can deduce what colour the exoplanet should appear.
Answered by Zoe Baily at the National Space Centre
Image Credit: NASA