Alien life search: ‘Surprising number’ of exoplanets could boast habitable zone

Earth is alone in our solar system for its hospitality for hosting life as we know it. However, a new study indicates other star systems could have as many as seven Earth-like planets.

And space scientists now believe the absence of a gas giant-like Jupiter may be key in the formation of planets resembling our own.

This made me wonder about the maximum number of habitable planets it’s possible for a star to have

Professor Stephen Kane

This is the conclusion of a study led by University of California, Riverside astrobiologist Professor Stephen Kane.

The search for life in outer space usually concentrates on what scientists have dubbed the habitable zone.

This area typically exists around stars where an orbiting planet could have liquid water oceans.

Water is considered to be a necessary condition for life as we know it.

Professor Kane had focussed on a nearby solar system called Trappist-1.

This cosmic neighbourhood has three Earth-like planets in its habitable zone.

Professor Kane said: “This made me wonder about the maximum number of habitable planets it’s possible for a star to have, and why our star only has one. It didn’t seem fair.”

Researchers created a model system which simulated planets of various sizes orbiting around their stars.

An algorithm accounted for gravitational forces, allowing the scientists to test how the planets interacted with each other over millions of years.

The team was shocked to discover it is possible for some stars to support as many as seven such planets.

And they also learned stars such as our Sun could potentially support six planets with liquid water.

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Professor Kane added: “More than seven, and the planets become too close to each other and destabilise each other’s orbits.”

This study now offers an answer to the question of how this solar system only has one habitable planet if it is capable of supporting six.

It helps if the planets’ movement is circular rather than oval or irregular, minimising any close contact as well as maintaining stable orbits.

The lead researcher now believes Jupiter, boasting a mass two-and-a-half times that of all the other planets in the solar system combined, limited our system’s habitability.

Professor Kane said: “It has a big effect on the habitability of our solar system because it’s massive and disturbs other orbits.”

A minority of stars have been found with multiple planets in their habitable zones.

The researchers now intend to search for additional stars surrounded entirely by smaller planets.

Such stars will be prime targets for direct imaging with NASA telescopes like the one at the Jet Propulsion Laboratory’s Habitable Exoplanet Observatory.

Professor Kane’s study identified one such star, Beta CVn, which is relatively close by at a mere 27 light-years distance.

Although Beta CVn lacks a Jupiter-like planet, it will be included as one of the stars checked for multiple habitable zone planets.

Future studies will also involve the creation of new models examining the atmospheric chemistry of habitable zone planets in other star systems.

Projects such as these offer more than new avenues in the search for life in outer space.

And they also offer scientists insight into forces that might change life on our own planet one day.

Professor Kane said: “Although we know Earth has been habitable for most of its history, many questions remain regarding how these favourable conditions evolved with time, and the specific drivers behind those changes.

“By measuring the properties of exoplanets whose evolutionary pathways may be similar to our own, we gain a preview into the past and future of this planet — and what we must do to main its habitability.”

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