The study of planets found outside our solar system has been booming over the past few decades, with over two-thousand of these fascinating exoplanets having been cataloged. One of the next obvious steps for researchers is to attempt to detect signs of life on them, although the technology to directly determine if anything is living that far away has yet to be developed. In the meantime, studies are underway to help determine the best candidates to focus on, using what we know about life on Earth, and what information we can currently gather from the exoplanets themselves.
Previous studies done on ocean circulation that might occur in an ocean on an exoplanet have so far assumed that both salinity and ocean depth would be similar to what we have here on Earth. However, a new study, conducted at the University of East Anglia in Norwich, England, took a look at salinity levels that would be higher than what is found in Earth’s oceans, and found that a saltier ocean could actually make for a better environment to support life.
Ocean salinity is one of the major drivers behind ocean currents: on Earth, warm waters flow toward the poles, where they cool and sink to the ocean floor, then begin to circulate back toward the equator. The study found that if a planet’s oceans were much saltier than Earth’s, the opposite would be true, with the ocean floor being flooded with warm water and causing warming at the poles — increasing the planet’s habitability for potential lifeforms if it’s orbit lies outside the system’s "Goldilocks Zone", the distance from a given star where the temperature is neither too hot, nor too cold.
"Previous studies on ocean circulation on other planets have made the assumption that fundamental ocean properties – such as the salinity and depth of water – would be similar to that on Earth," explains study co-author David Stevens. "We wanted to find out what might be happening on other planets which might appear superficially similar to Earth, but where conditions such as salinity are radically different to our own planet… Our research helps to answer whether or not these planets could sustain alien life."
Another research team from the University of Washington, has developed a planetary habitability index, based on how an exoplanet appears as it transits the face of the star it orbits. However, when Earth’s data was applied to the "Habitability Index for Transiting Exoplanets" (HITE), it was found that our home was only had an 82 percent likelihood of being habitable. This could be an important indicator in the likelihood of other exoplanets harboring life, as there are not only a number of candidates with a similar probability to Earth’s, but there are also planets that have significantly higher indexes, with probabilities ranging between 92 and 96 percent.