Thanks to the Hubble space telescope, astronomers have been able to determine the true color of a planet orbiting another star other than the Sun. HD 189733b is a dark blue color, chromatically similar to the appearance of the Earth seen from the outside. Are they alike in something else?
Well no. There the reasonable similarities end. Located about 63 light years from us, this planet is completely different from Earth. Despite its blue color, water will hardly be present as on Earth, since the temperature of its atmosphere exceeds 1,000 degrees Celsius and its winds reach 7,000 kilometers per hour.
But this data is not really new. As Fréderic Pont from the University of Exeter in the UK explains, “We had studied this planet in the past, both ourselves and other teams. However, it is the first time that we have measured what color it is , we actually imagine what the planet would be like if we could be in front of it ”.
To get to know its color, astronomers have measured the amount of light reflected from the surface of the planet HD 189733b, that is, they have calculated its albedo. But, how have they managed to isolate the light that the planet reflects from that emitted by its star? They simply took different measurements at different points in the planet’s orbit around the astro with the Hubble Space Telescope (Hubble’s Space Telescope Imaging Spectrograph). In the words of Tom Evans, from the University of Oxford, in the United Kingdom, “we have seen the brightness throughout the passage in the blue part of the spectrum when the planet passed behind its star”.
The bluish color of the planet is not due to the large masses of water that cover its crust, as in the case of the Earth. On this occasion, it is the atmosphere itself that gives it that azure blue color as the silicates present in it disperse the blue color. However the measurement is neither easy nor exact. As Pont himself explains, “it is difficult to know exactly what causes the color of a planet’s atmosphere, even on planets in the Solar System . But these new observations add one more piece to the puzzle about HD 189733b’s nature and atmosphere. We are gradually painting a more complete picture of this exotic planet ”.
