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Located 12 light-years away from the Earth, a small, old-fashioned star may be surrounded by two temperate rocky planets. According to today’s announcement by astronomers, the mass of these two new worlds would be identical to that of our planet and their orbits would be compatible with the presence and flow of liquid water on the surface.
Scientists estimate that this stellar host, known as the Teegarden star, is at least 8 billion years old, twice the age of our Sun. We can therefore reasonably infer that the planets orbiting around this star have a similar age, which means that life as we know it has had ample time to evolve. For the moment, the star is remarkably peaceful and has very few signs of events that currently emanate from such cosmic objects as star-tremors or eruptions.
All these factors associated with the relative proximity of the stellar system make it a prime target for astronomers seeking to train next-generation telescopes on other worlds and thus track extraterrestrial signs of life.
“The two planets in the Teegarden system are potentially habitable,” says Ignasi Ribas of the Institute for Space Studies of Catalonia and a member of the team behind the Astronomy & Astrophysics article. “In a while, we will see if they are habitable and, why not, inhabited.”
The two worlds orbit around a star so weak that it was only detected in 2003, when NASA astrophysicist Bonnard Teegarden was raking astronomical data sets in search of nearby dwarf stars if pale that they had previously escaped detection.
The star of Teegarden is a true stellar abort, its mass reaches only 9% of that of our Sun. It is a class M ultra-cold dwarf that radiates in the infrared, just like the star TRAPPIST-1 around which gravitate seven rocky planets. In contrast, the TRAPPIST-1 system is three times farther away from Earth than the Teegarden star. The conditions are therefore ideal to go further in the characterization of the latter.
It is thanks to the researches undertaken by Ribas and his colleagues that these planets could be detected. In recent years, they track down the planets orbiting around 342 small stars and it is in this context that they ended up pointing on this tiny star the CARMENES instrument of the Spanish observatory of Calar Alto.
For three years, CARMENES scanned the star of Teegarden for tremors and other irregularities caused by planets in orbit. In the end, more than 200 measurements suggested that two small exoplanets rubbed the dwarf star, each weighing approximately 1.1 times the mass of the Earth. According to calculations made by the team of scientists, one of the planets named Teegarden’s star b would have an orbit of 4.9 terrestrial days; the other, named Teegarden’s star , would have an orbit of 11.4 days.
Before they could announce the potential existence of these planets, the team had to exclude star-specific phenomena such as stellar spots and eruptions that cause the same variations as planets in orbit and can therefore cause confusion. Sometimes this can be particularly complex for red dwarfs as these stars are known for their tumultuous temper and frequent and massive eruptions. However, Teegarden’s star is strangely calm, and it is therefore all the easier to distinguish the planetary signals.
“The number of readings is so high and the star so quiet that there is very little room for further explanation,” says Riba. “So, from my point of view, this is an obvious case of planet detection. I’m willing to bet my two little fingers that they are there.”
“There are two serious candidates for the planet post,” says Lauren Weiss of the University of Hawaii. “I am impressed by the quality of the data.”
That being said, Weiss evokes some points that make her hesitate. First, scientists do not know the exact period of revolution of the Teegarden star on its axis and this type of movement could very well be confused with the signals of one of the planets.
However, “the rotation of a star could probably imitate the orbit of a planet and not both, so there is at least one planet probably real,” she adds.
Second, she says, it is possible that planets orbit around the star faster than the calculations suggest, which could affect their potential habitability.
“This technical detail remains minor, however,” says Weiss. “If there are really planets around this star but the authors were wrong about the orbital periods, the planets remain planets.”