New Rankings of Habitable Alien Planets

As orbiting telescopes continue to discover and catalog new worlds, a team of scientists has published a study describing two methods of determining which planets may be the “most liveable.” The habitability, for purposes of the study, is determined on the basis of life as it’s known on Earth.

Some planets that interest astrobiologists, astronomers and exobiologists fall into the narrow range dubbed “Goldilocks planets.” Those planets have all the conditions necessary to create familiar life forms: they are not too hot, too cold, too massive, or too tiny. Habitable worlds have a viable atmosphere, water and a temperature range that can support life. In other words, like the baby bear’s porridge that Goldilocks ate at the three bears’ house, the planets are “just right.”

The authors of the paper, “A Two-Tiered Approach to Assessing the Habitability of Exoplanets,” published in the journal Astrobiology, approach the likelihood of a planet’s ability to support life by measuring it with two new rating systems.

The first rating measures a planet’s similarity to Earth. The study authors call that guideline the Earth Similarity Index (ESI). It rates the data gleaned from observation and determines a planet or large moon’s factors that are like Earth in terms of atmospheric pressure, density, availability of water and other factors.

The second rating metric analyzes another worlds ability to support life—how habitable it might be. If the temperature, orbit, pressure, or atmosphere is too extreme the planet probably cannot easily support life. The team calls that rating system the Planetary Habitability Index (PHI).  

The PHI considers a host of other things such as the composition of a planet’s atmosphere, a moon or moons creating tidal forces, has seas or lakes, the chemistry and probability of organic matter and so on.

“The first question is whether Earth-like conditions can be found on other worlds, since we know empirically that those conditions could harbor life,” co-author Dr. Dirk Schulze-Makuch of Washington State University told the BBC during an interview about the study.

“The second question is whether conditions exist on exoplanets that suggest the possibility of other forms of life, whether known to us or not.”

The study concluded that a surprising number of planets may be habitable. While some are on the very edge of the Goldilocks range, they could support life as defined by science. The distant alien world Gliese 581g [See “Alien life on new planet Gliese 581g 100 percent certain”] discovered in 2010 is a good candidate for supporting life as is the giant moon Titan that orbits Saturn. [“Why scientists believe life may exist on Saturn’s moon Titan”]

Study published in Astrobiology: A Two-Tiered Approach to Assessing the Habitability of Exoplanets

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