Scientists have been trying to explore the universe and beyond for decades. With the advancement of technology came our ability to probe the fringes of the massive universe and discover many interesting components we may have never even heard of before.
In the past three decades, we have found a wide variety of unusual planets that we were unaware even existed and that is unlike anything else in our solar system. Among these interesting parts of the universe are super-Earths. Super-Earths are a unique class of planets that are heavier than ice giants like Neptune and Uranus yet more massive than Earth. They can be comprised of rock, gas, or a combination of both. They range in size from being up to twice the mass of Earth to being twice its size.
The term “super-Earth” exclusively refers to exoplanets that are larger than Earth and smaller than Neptune. However, it does not imply that they are similar to Earth in any way. With the ongoing observations about these planets, the real composition is yet to be uncovered unlike any planets in our solar system, despite being widespread among planets discovered so far in our galaxy. Super-Earths have the potential to be up to 10 times as large as Earth. We don’t yet understand these planets well enough to predict when they might cease to have rocky surfaces.
A super-Earth planet called Gliese 581c was found as early as 2007. It is located in the Gliese 581 system, which is quite close to Earth at a distance of 20 light-years on cosmic terms. Early studies suggested that Gliese 581c might have liquid water on its surface since it is in the “habitable zone” of its star, but more recent studies imply that it may have a Venus-like atmosphere.
For years, Gliese 581c had been at the forefront of studies investigating planets that resemble the qualities of Earth which may also cater to live and might have liquid water. The year 2007 saw the publication in the journal Astronomy and Astrophysics of the discovery of Gliese 581c. Stephane Udry, an astronomer at the Geneva Observatory, led the paper which catapulted the investigations on this planet further. Two super-Earth planets, both at the star’s periphery of the habitable zone, were discovered by his team, including Gliese 581c.
The radial-velocity approach was used to discover Gliese 581c, which meant that pulls on its parent star were used to find it. The HARPS spectrograph on a 3.6-meter telescope operated by the European Southern Observatory in Chile was the tool that made the finding.
Gliese 581c was just five times as massive as Earth at the time, according to the researchers, who claimed it to be “the known exoplanet which most closely resembles our own Earth.” While the super-Earth was described as the closest resemblance to our planet, scientists have already warned that due to the limited data on the planet, there is no concrete evidence of its actual conditions. In fact, being in a “habitable zone” does not automatically mean that the conditions of the planet are fit for human habitation.
The atmospheric conditions of Gliese 581c are also unknown and data on this are crucial in determining indicators of climate activity and the magnitude of the greenhouse effect.
Gliese 581 is the star that Gliese 581c is derived. It is an M-class dwarf star
Its habitable zone would be closer to our solar system since it is cooler than the sun. M dwarfs are preferred for planetary searches because they are fainter, making it simpler to spot planets that are transiting the star. The planet’s and star’s relative sizes are smaller, therefore their gravitational impacts are likewise more pronounced.
The core portion of an M-class dwarf star like Gliese 581 fuses hydrogen at a fraction of the rate of the Sun due to its much lower mass. Astronomers have calculated an effective temperature of 3200 K and a visual brightness of 0.2 percent of that of the Sun based on the apparent magnitude and distance. Moreover, Gliese 581 is the 89th closest star to the Sun in terms of distance, with an estimated mass of around one-third that of the Sun. Due to its low star activity, there is a greater chance that its planets will retain considerable atmospheres and that stellar flares won’t have as much of a sterilizing effect.
In further determining the characteristics of Gliese 581c, astronomers needed to first identify the exact number of planets orbiting Gliese 581. Calculating the radius of Gliese 581c is challenging because scientists have yet to know the precise number of planets. Astronomers can only infer the properties of the planet from Gliese 581c’s effects on the star and other planets because it hasn’t been witnessed moving directly across the face of its star. The planet’s radius would then determine things like whether it is closer to a Neptune-like planet or an Earth-like planet with a smaller atmosphere or with a much thicker atmosphere.
Many astronomers think that Gliese 581c is tidally locked because of how near it is to its star. This indicates that the planet remains on the same side facing the sun throughout its orbit. The moons of Jupiter and Saturn in our own solar system frequently experience this occurrence. Additionally, the moon of Earth is tidally locked to our planet. Due to this, there will be no day-night cycle as one side remains dark and the other remains day. If humans were to live there, it is uncertain how life could endure in a place where either continuous day or perpetual darkness prevailed.
However, it is theorized by scientists that there is a portion called the ‘twilight zone’ where the temperature would only be sufficient to support life. However, this is not the only issue concerning the habitability of the planet.
In 2011, scientists have confirmed that Gliese 581c is too hot to be habitable. This means that it showed more ‘Venus-like’ temperature and atmospheric conditions that living species could not grow due to its proximity to its parent star. Although research is still ongoing, scientists have already rejected the idea of habitation in the super-Earth Gliese 581c.
However, studies on this planet have laid the groundwork for this research area which benefits current investigations on other Earth-like planets like Proxima Centauri b which is only four light-years away from our planet.