The study of exoplanets, those worlds that orbit around stars other than our Sun, is tremendously complicated. In general, the planetary system around any star does not account for more than a small percentage of the mass of the entire star system . In the case of the Sun, the star accounts for 99.8% of the total mass of the solar system , the remaining 0.2% being everything else: the planets, their moons, as well as the millions of asteroids and comets that complete the system. If we add to this that these exoplanets are located light years away , sometimes hundreds or even thousands of light years, the task of studying and characterizing them becomes enormously complicated .
But despite the limitations inherent in the vastness of the universe we live in, those who study them find ingenious ways to reveal their properties . This is the case of 55 Cancri e , a planet on which we could have detected a large volcanic eruption . This is one of five planets detected orbiting the star 55 Cancri, also known as the Copernicus star.
Copernicus is actually a binary system, although the name refers to its central and most massive star. This star, which is slightly less massive than the Sun , with 95% of its mass, has a smaller companion orbiting about a thousand astronomical units (a thousand times the average distance between the Earth and the Sun). This companion is a red dwarf, almost eight times less massive than Copernicus. Around the central star orbit at least five planets , all of them considerably closer to the star than the planets in our own solar system. Four of these planets are gas giants , ranging from a Neptune-sized planet to one 4 times more massive than Jupiter. The fifth planet , which is actually the closest to the star Copernicus, is the only rocky planet discovered in this system and has a radius twice that of Earth and a mass 8 times greater . This makes it what is known in astrophysics as a super-Earth .
This fifth planet is named 55 Cancri eo Janssen , as decided by the International Astronomical Union at the end of 2015 after a popular vote, in honor of the French astronomer Pierre Janssen , discoverer of the chemical element helium. Janssen, the exoplanet, orbits just over 2 million kilometers from Copernicus , taking less than 18 hours to do so. By comparison, Mercury orbits at about 58 million kilometers on average and takes almost 88 days to complete a particular revolution. It is therefore not surprising that temperatures above 2000°C have been detected on the planet Janssen’s surface and that it undergoes a tidal coupling with its star, leaving it with one hemisphere always pointing towards Copernicus. This temperature has been measured by directly detecting the light emitted by the planet itself.
These very high surface temperatures indicate that the planet’s surface will be largely molten, being covered by large oceans of magma , and some volcanism may also occur, in principle. However, we did not have more direct evidence of this until observations over several months measured a drop in temperature on the planet .
This decrease was important, due to the possible causes that it could have. We know that hardly any clouds should form on planets as hot as Janssen, so this drop in measured temperature could not be due to a normal meteorological process and must have had another source. The most plausible explanation and defended by Demory et al in their article published in the scientific journal Monthly Notices of the Royal Astronomical Society would be that of a volcanic eruption that has created a large cloud of dust and ash that has blocked the star’s light and consequently cooled the surface of the planet.
This possibility might seem far-fetched were it not for the fact that we know of several instances of similar events on Earth. The 1991 eruption of Mount Pinatubo in the Philippines lowered global temperatures for two years, and the 1815 eruption of Indonesia’s Mount Tambora , the largest eruption in recent history, triggered what is known as the “year without a summer” the following year, in Global temperatures dropped by almost 1°C.
Furthermore, such violent volcanic eruptions would be very similar to those observed on Jupiter’s moon Io . Io’s volcanism would be caused not by internal heat, as in the case of the Earth, but by the influence of the gas giant , which, due to tidal effects, would heat the interior of the moon , causing these eruptions. On Io the clouds expelled during some of the most energetic events have reached hundreds of kilometers in height . The process observed on planet Janssen could have created volcanic plumes up to 1,500 kilometers high , spreading to obscure much of the planet’s surface.
Referencia:
B.O. Demory et al, 2015, Variability in the super-Earth 55 Cnc e, Monthly Notices of the Royal Astronomical Society, https://doi.org/10.1093/mnras/stv2239
