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The human being may not be alone in the galaxy of the Milky Way. At least the possibility opens with the results of a study of 53 twin stars of the Sun carried out by researchers from the National Institute of Space Research (INPE), recently published in the Monthly Notices of the Royal Astronomical Society (MNRAS).
Research suggests favorable geological conditions for the emergence and maintenance of life on the rocky planets that revolve around these stars. And that it could be scattered throughout the galaxy and have its origin at any point in its evolution.
- Astronomers observe the farthest star in the universe
To arrive at this conclusion, scientists evaluated the abundance of thorium (232Th) in the (A light-year is the distance traveled during from one year by light in the space, which equates to about 9,500 billion kilometers).
This was done by badyzing high quality optical spectra and wave length resolution, collected with the aid of an ultra-stable spectrograph called HARPS, installed in the telescope. 3.6 m from ESO (European Southern Observatory), Chile.
Although thorium is not the only determinant, this radioactive chemical is one of the necessary conditions for the emergence, evolution and maintenance of life in a given world. For this to happen, it is necessary that the planet's orbit is in the habitable zone around the star, that is to say at a certain distance from it in the which water can remain liquid.
According to researcher André de Castro Milone, of the Division of Astrophysics of Inpe, doctoral advisor to Rafael Botelho, first author of the article, other conditions necessary for the emergence of the Life on a planet is the existence of an atmosphere imprisoned by gravity and a magnetic field to protect it from the flow of energetic and harmful particles to living beings emitted by its host star.
"It is also crucial that it be geologically active, like Earth, with earthquakes and volcanoes, which provide the carbon cycle, which keeps the temperature of our world conducive to life." This is only possible thanks to plate tectonics.
The globe is made up of layers that look almost like an onion. In the center is the nucleus whose center is at a depth of about 6,370 kilometers, with a temperature of 6,000 ºC, similar to the surface of the Sun. Above, the coat is pasty, similar to that of a hot asphalt. , with a thickness of about 2 950 km and 100 ° C in its upper part and 3500 ° C in the deepest, at the interface with the nucleus. This is magma, which can be seen when it is expelled by volcanoes.
It is covered by the crust, the shallowest layer and the least thick of the planet, in which we live, with an average depth of 40 km. With the top of the solid mantle, it forms the lithosphere, 100 km thick, which is itself divided into gigantic rock plates, called tectonics, which float on the mantle of magma, transporting oceans and continents.
There are 10 of these large stone rafts – African, Antarctic, Arabic, Eurasian, Philippine, Indo-Australian, Nazca, North America and Caribbean, Pacific and South America – and several smaller ones. It is these structures that shape the surface of the Earth, raising mountains and causing earthquakes and tsunamis when they collide. What makes these plates float and move around the mantle is a phenomenon called convection, which is a movement of the material up or down because of the heat.
This induces the carbon cycle by releasing much smaller amounts of CO2 (carbon dioxide) and methane (CH4), which makes possible thermal stability in the global atmosphere, creating conditions Natural and life changing scale of billions of years.
"Therefore, the initial concentrations of these elements on a rocky planet contribute indirectly to the livability on their surface, especially because of their long period of disintegration (billions of years)", explains Milone.
The twins studied by the Inpe team have different ages well determined, ranging from 500 million to 8.6 billion years old. "So we can track the abundance of thorium throughout the evolution of the galaxy, as well as stars similar to the Sun," says Milone.
"Another study, done by American researchers, had already shown that our star had a slight thorium deficiency compared to 13 of its twins (seven in common with our study), showing that such stars, if they had rocky planets, would provide internal energy reservoirs sufficient for the emergence of life ".
In other words, research has shown that there is a large amount of available energy due to the disintegration of thorium to maintain mantle convection and tectonism on possible planets rocks that can exist around solar twins.
"What is most exciting, it is that it seems that this element is also abundant in the old solar twin, which means that the galaxy can be full of life, to both in space and in time, "said Botelho.
In addition, according to estimates by Milone and Jorge Luis Melendez Moreno, of the Department of Astronomy of the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) from the University of São Paulo (USP), there should be about 100 million to 1 billion stars relatively similar to the Sun in the Galaxy.
"It is only an order of magnitude, based on an extrapolation of what we know from studies of the solar neighborhood," Melandez explains.
According to another group, about 5% of solar twins could have a planetary system similar to ours (rocky planets relatively close to the Sun and distant gas giants).
"In our galaxy, there are therefore between 5 and 50 million solar-like planetary systems," says Milone. "It seems that we are not alone and therefore in the universe.However, it is worth noting that the results of our work only open up possibilities for the existence and maintenance of the life, and no detection of extraterrestrial life itself. "
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