Since Neptune is about four times Earth’s diameter, these planets are sometimes called “sub-Neptunes.”Ī thick atmosphere on a sub-Neptune planet would trap heat on the surface and raise the temperature.
The new paper shows which chemicals might point to hidden oceans on exoplanets between 1.7 and 3.5 times the diameter of Earth. None of these chemicals alone would be a sign of life, but in combination they would point to the possibility that our planet is inhabited. A chemical profile of Earth wouldn’t be able to reveal pictures of, say, cows or humans on the planet’s surface, but it would show carbon dioxide and methane produced by mammals, and oxygen produced by trees. Some NASA space telescopes equipped with spectrometers can reveal the chemical makeup of an exoplanet’s atmosphere. More than 4,500 exoplanets have been confirmed in our galaxy, with over 7,700 candidates yet to be confirmed, but scientists estimate that hundreds of billions of exoplanets exist in our galaxy. Since liquid water is a necessary ingredient for life as we know it, this technique could help scientists narrow their search for potentially habitable exoplanets, or planets beyond our solar system. In the new study, accepted in the Astrophysical Journal Letters, researchers show how the chemistry of those atmospheres could reveal clues about what lies beneath – specifically, which planets are too hot to support liquid-water oceans. These planets may have rocky surfaces or liquid-water oceans, but most are likely to be topped with atmospheres that are many times thicker than Earth’s and opaque. But around other stars, astronomers have found planets that fall in between – worlds slightly larger than Earth but smaller than Neptune. In our solar system, planets are either small and rocky (like Earth) or large and gaseous (like Neptune).
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