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After the discovery of two exoplanets near the star Gliese 581, scientists began to detect strange signals coming from this system. Because of their uncertainty, over time, deciphering them has become an unofficial priority for all researchers of possible life on other planets. Recently, scientists from the University of Pennsylvania said they were able to decipher the signal and determine its source.
Initially, it was believed that the signal came from two planets orbiting a star in a zone suitable for the existence of liquid water. These planets even began to be called “Goldilocks planets,” it was assumed that under their conditions environment are as close as possible to Earth conditions, under which life can exist. However, scientists say the opposite: the planets are silent, and a strange signal comes from the star as a result of processes occurring in its depths.
“This is a very important result for us because for the first time it refutes all previous conflicting assumptions and observations of this intriguing dwarf star. Gliese 581 is significantly smaller than the Sun in mass, and is located only 20 light-years from Earth. But as another result, we found that the number of planets orbiting the star is three,” - Paul Robertson, author of the study from the University of Pennsylvania.
“We also proved that some of these conflicting signals do not come from planets in the habitable zone, but from the star as a result of its activity. In addition, we found that there is no clear evidence that these three exoplanets are in the habitable zone where liquid water can exist,” Suvrat Mahadevan, assistant professor of astronomy and astrophysics at the University of Pennsylvania.
This image shows the locations of three exoplanets confirmed to exist around the star Gliese 581 in 2014. If earlier it was assumed that there were three planets in the habitable zone orbiting the star, now it is known for sure that there is only one planet (shown in blue), the other two turned out to be signals from the star itself. Source: NASA/Penn State University
Astronomers search for exoplanets by recording changes in the spectrum of the stars they orbit. This experiment is also called the Doppler method. The exoplanet and the star interact with each other, resulting in small deviations in the speed of the star's orbit. However, this method is not entirely accurate. Such Doppler changes can appear as a result of various events in the star's magnetic field, such as sunspots, which can give completely incorrect information about the presence of an exoplanet orbiting the star. The research team made its discovery of the star Gliese 581 using the European Southern Observatory's HARPS and Keck Observatory's HIRES advanced spectrographs. Scientists were aimed at searching for the very features that arise as a result of exposure to magnetic fields. By carefully selecting analysis methods, the researchers amplified the signal coming from three exoplanets orbiting the star. But the signals that were previously attributed to two of the three planets disappeared and became indistinguishable from the general noise background of the research. The disappearance of these signals during a detailed analysis of only exoplanets, excluding the star, suggests that the signal comes precisely from the life activity of Gliese 581 itself.
“Such detailed studies of exoplanets give us confidence that we currently have sufficient knowledge and technical skills to study them in this way. And at the same time, we also got a negative result: two promising exoplanets are not what we thought. But I hope that this is more of a plus than a minus, because this is another confirmation of how well developed analyzing equipment is now,” - Paul Robertson.
Older M dwarf stars, such as Gliese 581 in the constellation Libra, have about one-third the mass of our Sun and have so far been very attractive targets for the search for extraterrestrial life because they are less active than ordinary stars. One of important conclusions, drawn from these studies, tells us that stars, as a result of their life activity, can emit signals in the same range as exoplanets located in the habitable zone, which significantly increases the risk of false detections of non-existent planets. One hope to avoid this is the production of new high-precision instruments.
→Gliese 581 g is a so-called exoplanet located in the system of the star Gliese 581 in the constellation Libra, at a distance of about 20 light years from Earth. This planet was discovered by Stephen Vogt from the University of California and Paul Butler from the Carnegie Institution of Washington on September 29, 2010 and was boldly called by scientists a “potentially habitable planet” or “super-Earth.”
The exoplanet was discovered by scientists using the Keck 1 telescope (Hawaii, USA) and the La Silla Observatory telescope (Chile). Stephen Vogt, who led the team of astronomers that discovered the planet, unofficially named the cosmic body "Zarmina" (in honor of his wife). According to Vogt, this object was very difficult to detect - more than 200 measurements were made for this.
However, an employee of the Geneva Observatory, Francesco Pepe, said that Michel Mayor's group (which discovered the first exoplanet - 51 Pegasi b) was unable to find confirmation of the very existence of the planet Gliese 581 g and Gliese 581 f, despite processing data accumulated over six and a half years, but not ruled out the possibility of a planet existing in the habitable zone. In response, Steven Vogt stated that he was confident in the accuracy of his data, complaining about the inability to familiarize himself with the observations of the Swiss team.
According to scientists, the planet, located in the red dwarf system, has a radius equal to 1.5 Earth's, and its mass is 3-4 times that of Earth. The planet's landscape is represented mainly by rocks and rocks, but there is indirect evidence that there may well be liquid water on the surface. The detected gravity gives scientists the opportunity to assume the presence of an atmosphere.
The planet's orbital period around the star is 36.6 Earth days, while its orbit differs only slightly from circular. The acceleration of free fall is 1.1-1.7 times greater than the earth's. According to experts, due to its proximity to the star, the planet always faces it with only one side (the other always remains in the shadow; a similar situation is observed on the Moon). As a result of analyzing the data obtained, scientists determine the temperature range on the planet from -34 degrees Celsius on the unlit side to 71 degrees Celsius on the illuminated side.
The constant rotation of the planet towards the star with only one side can lead to a constant displacement air masses towards the unlit side. However, if there is a dense atmosphere, there is a chance that the heat that the planet receives from the red dwarf will be distributed more evenly by it.
The chemical composition of the planet is not yet known. The discovery of 581 g of oxygen and carbon dioxide on Gliese would be another positive factor existence on the planet of life in one form or another.
Shortly after the discovery of the exoplanet, Australian scientist Raghbir Bhatal made a sensational statement that the flashes that were seen in the area were very reminiscent of the action of a laser, which allowed the scientist to assume that this planet is indeed habitable. These observations were recorded within international project SETI (Search for Extraterrestrial Intelligence), whose task is to search for extraterrestrial intelligence. However, most scientists were very skeptical about this bold statement.
In any case, the discovery of an exoplanet is a very important milestone in space exploration. Since red dwarf systems are the most common type of system in our Galaxy, scientists have concluded that 10-20 percent of these systems may have potentially habitable planets.
Galetich Yulia, Update date - 01/15/2013
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