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“Over the past few decades, astronomers have uncovered thousands of new exoplanets. Some of them are rocky; some are temperate; some have water. However, the idea that exoplanet K2-18b is rocky, Earth-like, and has liquid water is absurd, despite recent headlines. Light filters through K2-18b’s atmosphere when it passes in front of its star, enabling us to measure what’s absorbed. Based on those absorption lines, the presence of many chemicals can be inferred, including water. K2-18b is, truly, the first known habitable-zone exoplanet to contain water. However, it is not rocky; its mass and radius are too large, necessitating a large gas envelope around it.”
How incredible was that report that came out last week: the first Earth-like, rocky exoplanet with liquid water on its surface has been discovered! If it were true, it would be incredible. Well, what we did find is still pretty remarkable, but it’s very different from what you’ve likely heard.
We did find water on the exoplanet in question, K2-18b, but only in the vapor phase and only in the atmosphere.
The exoplanet is closer to Earth in terms of mass and radius than any other with water on it, but the planet is still too massive and large to be rocky. It must have an envelope of hydrogen and helium, and both have had their presence detected.
If we want to find atmospheric biosignatures around Earth-like worlds, we need better observatories. Let’s build them! Here’s the real story.
All of Mercury Image Credit: NASA/JHU Applied Physics Lab/Carnegie Inst. Washington
Explanation: Only six years ago, the entire surface of planet Mercury was finally mapped. Detailed observations of the innermost planet’s surprising crust began when the robotic have been ongoing since the robotic MESSENGER spacecraft first passed Mercury in 2008 and continued until its controlled crash landing in 2015. Previously, much of the Mercury’s surface was unknown as it is too far for Earth-bound telescopes to see clearly, while the Mariner 10 flybys in the 1970s observed only about half. The featured video is a compilation of thousands of images of Mercury rendered in exaggerated colors to better contrast different surface features. Visible on the rotating world are rays emanating from a northern impact that stretch across much of the planet, while about half-way through the video the light colored Caloris Basin rotates into view, a northern ancient impact feature that filled with lava. Recent analysis of MESSENGER data indicates that Mercury has a solid inner core.
∞ Source: apod.nasa.gov/apod/ap190428.html
Ganymede global geological map and global image mosaic.
USGS Astrogeology Science Center.