New Research Explains Why Water Worlds May Run Dry

Findings have been released from a team of researchers from three universities on the rate of water loss on water worlds, a kind of exoplanet, as well as the related conditions that contribute to the loss.
Mario L. Major

A team of astrophysicists from Harvard, Princeton and the University of Michigan have released findings from a study in which they explain that water worlds have water supplies which they may not be able to support for long periods of time, news which could alter scientists’ thinking about the idea of habitable planets.

Findings from the study, titled “The Dehydration of Water Worlds Via Atmospheric Losses”, was published in last month’s Astrophysical Journal of Letters. Briefly, the study examines the rate of exoplanet water ion loss, provided through computer simulations of the conditions of a water world.

But first, how did we come to this point of focus in the body of research?

With the surge in space technology and space travel capabilites we’ve experienced in the 21st century, combined with the scramble for resources that is affecting life in every corner of the globe, many have begun to look beyond the borders of our planet for future life-sustaining possibilities.


This has given NASA’s work on charting the planets in our galaxy more renewed meaning. As of now, NASA has confirmed the existence of 3,545 exoplanets, going to great lengths to classify everything from the atmospheric conditions, to the precipitation patterns of exoplanets. This research is an important piece in this monumental task of “building an understanding of how many and what kinds of planetary systems exist in the galaxy.”

There is a fine distinction between an exoplanet and a habitable zone. Also known as the “Goldilocks Zone”, as the name suggests, it indicates exoplanets that have a common set of characteristics for being habitable: the distance from its respective star makes it not too hot, and not too cold for supporting liquid water, a fundamental ingredient for sustaining life.

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Within this paradigm are water worlds, planets which are composed of up to 50 percent water, producing surface oceans with staggering depths that reach hundreds of kilometers to the core.

Led by Chuanfei Dong from the Department of Astrophysical Sciences at Princeton University, the team conducted computer simulations that took into account what kind of atmospheric conditions water worlds would be subject to.

"It is fair to say that the presence of an atmosphere is perceived as one of the requirements for the habitability of a planet. Having said that, the concept of habitability is a complex one with myriad factors involved. Thus, an atmosphere by itself will not suffice to guarantee habitability, but it can be regarded as an important ingredient for a planet to be habitable," said Dong.

Through observing the combined effects of coronal mass injections, atmospheric ionization and stellar magnetic fields, towards G-type and M-type stars—the Sun and Proxima Centauri among them—the team could develop a model that came close to explaining the life cycle of an exoplanet:

"We developed a new multi-fluid magnetohydrodynamic model. The model simulated both the ionosphere and magnetosphere as a whole.


The findings revealed, however, that planets based around M-type stars are more unpredictable:

"Our results indicate that the ocean planets (orbiting a Sun-like star) will retain their atmospheres much longer than the Gyr timescale as the ion escape rates are far too low...In contrast, for exoplanets orbiting M-dwarfs, they could have their oceans depleted over the Gyr timescale due to the more intense particle and radiation environments that exoplanets experience in close-in habitable zones.”

As Dr. Dong indicates future projects that will be carried out:

"Given the importance of atmospheric loss on planetary habitability, there has been a great deal of interest in using telescopes such as the upcoming James Webb Space Telescope (JWST) to determine whether these planets have atmospheres and, if so, what their composition are like.”

These are all signs indicating that efforts towards an expanded understanding of exoplanets and the evolution of planets in our Solar System are being actively undertaken.