Discovering Glese 667; Potential Habitability in a triple Star System

Just under three decades ago, our understanding of the cosmos lacked any concrete evidence of planets beyond the boundaries of our own solar system. Today, due to remarkable technological advancements and dedicated scientific exploration, we have unveiled a staggering total of over 5,300 exoplanets - distant realms awaiting our exploration.

Initially, these findings primarily consisted of colossal gas giants, but as our scientific capabilities have expanded, we've begun to uncover smaller, Earth-like exoplanets. Among these discoveries, scientists have identified more than 50 exoplanets sharing Earth's mass and over 800 with radii less than half of our planet's.

Though the number of known planets situated within their parent stars' habitable zones - where life-supporting conditions could prevail - remains limited, this is gradually changing. As our pursuit of habitable planets persists, we are beginning to encounter entire planetary systems with multiple potentially life-sustaining worlds, including at least one such system within our cosmic vicinity.

Our Milky Way galaxy hosts numerous compact systems, characterized by stars akin to our own Sun. However, planets orbiting closely to these stars are typically too scorching to support life. Yet, around cooler, dimmer stars, the habitable zone is significantly closer. Enter Gliese 667 (GJ 667), a triple star system located approximately 23 light-years away in the Scorpius constellation. It holds the distinction of being the first known system where a low-mass star harbours multiple potentially habitable rocky planets orbiting within the so-called Goldilocks Zone.

Much like Alpha Centauri, this system comprises three stars. GJ 667 A, the largest, is a K-type main-sequence star with 73% of the Sun's mass, 76% of its radius, and only 12% of its visual luminosity. Orbiting at an average distance of 12.5 astronomical units (AU) is its companion, GJ 667 B, another K-type orange-red dwarf, with roughly 69% of the Sun's mass and a mere 5% of its visual luminosity. However, the most intriguing component is the third star, Gliese 667 C, an M-type red dwarf with a third of the Sun's mass and radius, emitting a mere 1.4% of the Sun's luminosity, and featuring a surface temperature of 3,775 Kelvin, far colder than our Sun.

Despite its diminutive size, GJ 667 C boasts a surprisingly rich planetary system. Initially, scientists believed it housed only three exoplanets, but upon re-evaluating existing data and conducting further observations, they now suspect there may be as many as six planets within the system, with three or even four of them residing within the potentially habitable super-Earth category.

But what exactly is a "super-Earth"? This term refers to planets larger than Earth but smaller than gas giants like Jupiter and Saturn. Super-Earths may be composed of rock, ice, or a combination thereof, with atmospheres that could support diverse life forms.

The closest planet to Gliese 667 C, Gliese 667 Cb, is a scorching world with temperatures reaching 200°C (392°F). As the most massive planet in the system, roughly 5.5 times Earth's mass, it likely possesses a thick atmosphere and orbits its host star in just seven days.

The three potentially habitable planets within the Gliese 667 system are situated farther from their host star, boasting masses between one and five times that of Earth, making them promising candidates for habitability. Gliese 667 Cc, the nearest of the trio, orbits the inner edge of its star's habitable zone, boasting a mass around 3.8 times that of Earth, a radius 1.8 times Earth's, and a year lasting a mere 28 Earth days. With an Earth Similarity Index of 0.85, it's often referred to as the "holy grail" of exoplanets. Due to its proximity to star C, the habitable zone extends from 0.11 AU to 0.23 AU, entirely contained within the orbit of Mercury. In comparison, Earth resides at approximately 1 AU from the Sun, making it an icy world if it orbited star C at such proximity.

GJ 667 Cc's proximity to its parent star, approximately 0.12 AU, likely results in tidal locking, with one side in eternal day and the other in eternal night. This drastic temperature difference could significantly impact the planet's global climate. Although it receives approximately 10% less light than Earth does from the Sun, most of it is in the form of infrared radiation, which could help retain water on the surface and lead to a climate resembling Earth's if the planet possesses an Earth-like atmosphere.

However, the absence of conclusive information about the planet's atmosphere and its thickness makes it impossible to predict the exact surface temperature on Gliese 667 Cc. If it does possess an atmosphere resembling Earth's, it would distribute heat evenly across the planet, resulting in a pleasant 30°C (86°F) on the night side.

Living on such a planet would be a vastly different experience. GJ 667 Cc receives a faint reddish light from its star. The other two stars, Gliese 667 A and B, are positioned at a considerable distance of about 230 AU, much farther than the Sun-Pluto distance, and outside the planetary system. Nonetheless, these stars would still appear as a bright pair during the day and shine as brightly as a full moon at night, while our Sun would seem like a distant star.

Unfortunately, the nearby red dwarf is known for emitting flares and intense bursts of radiation, with energetic particles up to a thousand times stronger than those emitted by our Sun. This poses potential challenges for any life on the surface of Gliese 667 Cc, given its proximity to this flaring star. Additionally, the red dwarf's strong magnetism can result in starspots, reducing its energy output by up to 40% for extended periods, coupled with a lack of ultraviolet light emissions, further complicating the potential for life as we know it.

Living on Gliese 667 Cc would be an entirely unique experience, primarily due to its substantial mass. The higher mass of the exoplanet translates to a different gravitational acceleration on its surface, which could be up to 60% stronger than what we experience on Earth. Consequently, an individual weighing 75 kg (165 lbs) on Earth would weigh as much as 120 kg (265 lbs) on Gliese 667 Cc. Moreover, a planet with a higher mass can retain a more substantial atmosphere, leading to higher atmospheric pressure at the surface. If the exoplanet possesses an atmosphere akin to Earth's, the atmospheric pressure would be only a few times higher, but if it were more reminiscent of Venus, the pressure could be hundreds of times greater, akin to the water pressure several kilometres deep in Earth's oceans.

Despite its location within a habitable zone, Gliese 667 Cc may offer conditions distinct from Earth's, including fluctuations in lighting, potentially high atmospheric pressure, and frequent solar flares.

Nevertheless, these differences don't preclude the possibility of life on this world, as Earth us numerous examples of life's adaptability.

The other two potentially habitable planets, Gliese 667 Ce and Cf, are nearly identical. Located farther from their parent star, they receive.