Astronomers determine that two super-Earths are not as rocky as previously believed
Using observations from both the Hubble Space Telescope and the now retired Spitzer infrared space telescope, astronomers now think that two super-Earth-sized explanets are not as rocky as previously believed, and are in fact liquid worlds with as much as half their make-up comprised of water. From the press release:
Water wasn’t directly detected at Kepler-138 c and d, but by comparing the sizes and masses of the planets to models, astronomers conclude that a significant fraction of their volume – up to half of it – should be made of materials that are lighter than rock but heavier than hydrogen or helium (which constitute the bulk of gas giant planets like Jupiter). The most common of these candidate materials is water.
“We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths,” explained Björn Benneke, study co-author and professor of astrophysics at the University of Montreal. “However, we have now shown that these two planets, Kepler-138 c and d, are quite different in nature and that a big fraction of their entire volume is likely composed of water. It is the best evidence yet for water worlds, a type of planet that was theorized by astronomers to exist for a long time.”
With volumes more than three times that of Earth and masses twice as big, planets c and d have much lower densities than Earth. This is surprising because most of the planets just slightly bigger than Earth that have been studied in detail so far all seemed to be rocky worlds like ours. The closest comparison, say researchers, would be some of the icy moons in the outer solar system that are also largely composed of water surrounding a rocky core.
This data simply underlines a basic point: The information we have of all exoplanets is sparse, practically nil. Any conclusions about their make-up is an educated guess, at best. Even now the conclusion that these are water worlds should be treated with great skepticism.
Using observations from both the Hubble Space Telescope and the now retired Spitzer infrared space telescope, astronomers now think that two super-Earth-sized explanets are not as rocky as previously believed, and are in fact liquid worlds with as much as half their make-up comprised of water. From the press release:
Water wasn’t directly detected at Kepler-138 c and d, but by comparing the sizes and masses of the planets to models, astronomers conclude that a significant fraction of their volume – up to half of it – should be made of materials that are lighter than rock but heavier than hydrogen or helium (which constitute the bulk of gas giant planets like Jupiter). The most common of these candidate materials is water.
“We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths,” explained Björn Benneke, study co-author and professor of astrophysics at the University of Montreal. “However, we have now shown that these two planets, Kepler-138 c and d, are quite different in nature and that a big fraction of their entire volume is likely composed of water. It is the best evidence yet for water worlds, a type of planet that was theorized by astronomers to exist for a long time.”
With volumes more than three times that of Earth and masses twice as big, planets c and d have much lower densities than Earth. This is surprising because most of the planets just slightly bigger than Earth that have been studied in detail so far all seemed to be rocky worlds like ours. The closest comparison, say researchers, would be some of the icy moons in the outer solar system that are also largely composed of water surrounding a rocky core.
This data simply underlines a basic point: The information we have of all exoplanets is sparse, practically nil. Any conclusions about their make-up is an educated guess, at best. Even now the conclusion that these are water worlds should be treated with great skepticism.
