Astro2110 – The Solar System

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This planet, HD 189733b, is the first exoplanet to have its color confirmed. We now know it is a deep, dark blue from a technique called secondary eclipse that scientists used to determine its albedo. As the planet was just about to finish transiting its host star relative to us, scientists measured light emission wavelengths and compared them to those of the star alone. It revealed a deep blue color “quite distinct from the atmosphere colors seen in our solar system.” Scientific American.

However, unlike the Earth and its blue oceans, the coloration of this planet, which lies 63 light years away from Earth, is due to clouds laced with silicate particles. This planet is a hot Jupiter, orbiting its host star in 2.2 days, tidally locking one side of it to be forever in darkness and the other forever in light. The temperature would thus be an average of 1,000 degrees Celsius, based on observations, and a temperature difference between near and far sides of 260 Celsius. This could fuel winds up to 8,700 kph littered with glass. Silicates condense at temperatures above 1300 Celsius, so this planet likely has ripping winds with shards of glass embedded in it. This example shows just how varied and extreme worlds can be in the universe. Nature sometimes stretches the human imagination and renders science fact more strange than science fantasy. Glass Rain.

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In a system 218 light years from Earth, scientists have discovered two planets, Kepler-138 c and Kepler-138 d, which make Earth look like a desert in comparison. Both planets were initially thought by scientists to be rocky super-Earths. However, after closer examination by the Hubble Space Telescope, scientists were able to determine that both planets are three times the volume of Earth, but only twice the mass. Although there are alternative explanations, the most likely one is that 50% of their mass is water. In comparison, the Earth’s mass is only 0.02% water. Source.

This was ascertained by the planet’s higher density than elements like gaseous hydrogen or helium, yet lower than a density equivalent to rock. However, the proximity to their host red dwarf star increases the predicted surface temperature of the planet. Since the presence of an atmosphere is likely with such an abundance of surface water, the planets probably have a thick atmosphere of steam with a water ocean beneath this atmosphere. The ocean might even have strange properties due to a combination of high pressure and high temperature. The most stunning prediction was an average ocean depth before reaching rock of 1,243 miles. Earth’s average ocean depth is around 2 miles. Source 2.

The significance of this discovery is obviously the likely presence of liquid surface water on an exoplanet’s surface. However, it also has implications for planetary formation models which show waterworlds only forming as ice worlds like Europa. This lends credence to the idea of planetary migration. It also opens scientists’ eyes to new possibilities of conditions on exotic, strange new worlds and the potential widening of human knowledge by continuing the hunt for new exoplanets.