Recent research frames Mars as a useful analogue for “marginal” rocky exoplanets—small, likely rocky worlds for which determining habitability is challenging. Because many such planets are far from Earth, scientists cannot easily measure whether they have long-term conditions suitable for life. The studies argue that Mars’s evolutionary history can help fill that gap. Mars is described as being near the threshold of habitability: it transitions from an earlier period that was warmer and wetter, with potentially hospitable conditions, to a later state that becomes colder and drier and generally inhospitable. By studying processes that shaped Mars’s decline—such as tectonic activity and atmospheric escape—researchers can better understand how similar mechanisms might influence atmospheres and surface conditions on other rocky planets near the habitable boundary. This approach aims to improve interpretation of what happens when a planet’s environment changes over time, particularly for exoplanets where direct observations of habitability are limited.