"This planet has been studied well in the past, both by ourselves and other teams, but measuring its colour is a real first — we can actually imagine what this planet would look like if we were able to look at it directly."TRESCA database. HD189733b has over 90 such observations from astronomers around the world.
"We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star. From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured."The planet's azure blue colour does not come from the reflection of a tropical ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light. Earlier observations using different methods have reported evidence for scattering of blue light on the planet, but these most recent Hubble observations give robust confirming evidence, say the researchers. Looking out - Looking in! It is thought that inside the atmosphere the sunsets on HD 189733b could be red. If sodium absorbs red light and dust scatters red light, the atmosphere will redden light shining through it, but will appear blue in reflected light. The colours of Jupiter and Venus are both due to unknown particles within the atmospheres of the planets. Earth looks blue from space because the oceans absorb red and green wavelengths more strongly than blue ones, and reflect the blueish hue of our sky. The shorter blue wavelengths of sunlight are selectively scattered by oxygen and nitrogen molecules in our atmosphere via a process called Rayleigh scattering. So there we have it an azure blue planet that rains glass - I'll stop right there before I start to think of quirky analogies about what it takes to make glass ceilings come down. ;-) The new paper, titled "The deep blue colour of HD 189733b: albedo measurements with HST/STIS at visible wavelengths", will appear in the 1 August issue of the journal Astrophysical Journal Letters. The Hubble Space Telescope is a project of international cooperation between ESA and NASA.