![Left: a cross section of Earth showing its interior. Right: a cross section of the blue world, Kepler-138 d with a brown core (rocks & metal) below a dark blue high-pressure water layer that is below a light blue water vapor envelope..](https://science.nasa.gov/wp-content/uploads/2023/04/hubble_kepler138d_stsci-01gksazkgaz65ryzg7bj8wpccz-jpg.webp?w=4096&format=png)
hubble_kepler138d_stsci-01gksazkgaz65ryzg7bj8wpccz
This is an artist's illustration showing a cross-section of the Earth (left) and the exoplanet Kepler-138 d (right). Like the Earth, this exoplanet has an interior composed of metals and rocks (brown portion), but Kepler-138 d also has a thick layer of high-pressure water in various forms: supercritical and potentially liquid water deep inside the planet and an extended water vapor envelope (shades of blue) above it. These water layers make up more than 50% of its volume, or a depth of about 1,243 miles (2,000 kilometers). The Earth, in comparison, has a negligible fraction of liquid water with an average ocean depth of less than 2.5 miles (4 kilometers).
Credits: Benoit Gougeon (University of Montreal)
Image CreditBenoit Gougeon (University of Montreal)
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