HD 189733b, the first exoplanet caught passing in front of its parent star in X-rays. NASA's Chandra X-ray Observatory and the ESA's XMM Newton Observatory have been used to observe a dip in X-ray intensity as HD 189733b transits its parent star. The exoplanet itself cannot be seen in the Chandra image, as the transits involve measuring small decreases in X-ray emission from the main star. Astronmers estimate that the percentage decrease in X-ray light during the transits is about three times greater than the corresponding decrease in optical light. This tells them that the region blocking X-rays from the star is substantially larger than the region blocking optical light from the star, helping to determine the size of the planet's atmosphere. The extended atmosphere implied by these results is shown by the light blue color around the planet. Recent observations of HD 189733b with the HST have confirmed that the lower atmosphere of the planet has a deep blue color, due to the preferential scattering of blue light by silicate particles in its atmosphere. Release date July 29, 2013.