mirage earths

Figure 1 Total amount of water lost during the pre-main sequence phase from an Earth mass planet in the habitable zone (HZ) that formed with 1 Terrestrial Ocean (TO) of surface water, assuming the the oxygen is instantaneously absorbed by the surface, and the escape is energy-limited. The axes correspond to the stellar mass (vertical) and the position of the planet within the HZ at 5 Gyr (horizontal). The "position in habitable zone" is the fractional distance between the Recent Venus (RV) limit and the Early Mars (EM) limit (the empirical HZ). The dashed lines represent the Runaway Greenhouse (RG) and Maximum Greenhouse (MG) limits (the conservative HZ). Colors correspond to the total amount of water lost after 5 Gyr. Dark blue corresponds to less than 0.1 TO; dark red corresponds to complete desiccation. Most planets in the HZ of M dwarfs are completely desiccated; conversely, those close to the outer edge of high mass M dwarfs and throughout most of the HZ of K dwarfs lose little or no water. Interior to the RG limit, planets around stars of all masses are completely desiccated.

Figure 2 Same as the previous figure, but showing the total amount of oxygen in bars produced by photolysis and retained by the planet. For a planet with an Earth-like composition, this oxygen will be absorbed at the surface to form iron oxides. Dark blue corresponds to insignificant oxygen buildup; dark red corresponds to nearly 200 bars of oxygen. Planets that lose significant amounts of water also undergo extreme surface oxidation. Depending on whether or not a deep, convective magma ocean is present, the surface may not be able to absorb all of the oxygen produced in this way. These planets may therefore have detectable levels of oxygen in their atmospheres for prolonged periods of time, potentially confusing future spectroscopic searches for biosignatures in the HZ of M dwarfs.