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An international team made up of a hundred researchers has just announced the discovery of one of the most distant planets discovered to date. It is called K2-2016-BLG-0005 Lb, it is located 17,000 light years from Earth and had remained hidden since 2016 among the data of the Kepler Space Telescope.
It is the most distant world recorded by Kepler and, curiously, it is remarkably similar to our own Jupiter. It even orbits at the same distance from its star as the giant in our system around the Sun.
The finding is the first confirmation of a series of data from 2016, when the Kepler observatory detected 27 possible planets thanks to the gravitational microlensing technique, and will soon be published in ‘Monthly Notices of the Royal Astronomical Society’, although it can already be found at the arXiv preprint server.
“Kepler was not designed to find planets using microlensing,” says co-author Eamonn Kerins of the University of Manchester, “so in many ways it is surprising that it did.” The ship, which marked a before and after in the search for exoplanets, was launched in 2009 and during its 10-year mission it discovered 3,000 new worlds, more than half of all those known today.
brightness decrease
The findings of this telescope were made thanks to the transit method, which measures the small decrease in brightness of a star when a planet crosses in front of it, revealing its presence. But the gravitational microlensing technique is considerably more complicated, since it takes advantage of a quirk of gravity and a fortuitous alignment. The mass of a body such as a planet creates a gravitational curvature of space-time around it. If that planet then passes in front of a star, that curved space-time acts like a magnifying glass, making light from a dim, faint star appear closer and brighter.
Unlike transit, which works best with nearby exoplanets, gravitational microlensing makes it possible to find worlds at a great distance from Earth, even those of lower mass. Until now, the most distant exoplanet, the size of the Earth, was captured in 2020 thanks to this system at a distance of 25,000 light years.
For this reason, and since Kepler is not specially optimized to use the microlensing technique, the team of researchers thought of analyzing the telescope’s data for these types of events in an observation window of several months during 2016. And they managed to identify up to 27 events, five of them totally new and not yet identified by other telescopes. “To see the effect -explains Kerins- an almost perfect alignment between the planetary system in the foreground and the background star is required. The possibility that a background star is affected in this way by a planet is from tens to hundreds millions against one. But there are hundreds of millions of stars at the center of our galaxy. So Kepler just sat down and watched them for three months.”
One of the five new microlensing events was K2-2016-BLG-0005 Lb, which looked especially promising. So the team looked at data sets from five ground-based surveys that were looking at the same patch of sky at the same time as Kepler, to corroborate their signal.
Extraterrestrial life
Thus, the researchers found that Kepler observed the signal a little earlier and for a little longer than ground-based observatories. This combined data set allowed the team to determine that the exoplanet is about 1.1 times the mass of Jupiter and orbits its star at a circular distance of 4.4 astronomical units. Jupiter’s mean distance from the Sun is 5.2 astronomical units.
“The difference in viewpoint between Kepler and observers here on Earth,” Kerins said, “allowed us to triangulate where the planetary system is along our line of sight. Kepler was also able to observe without interruption from weather or daylight, which allowed us to accurately determine the exoplanet’s mass and its orbital distance from its host star. It’s basically Jupiter’s identical twin in terms of its mass and its position relative to its Sun, which is about 60 percent of the mass of our own Sun.
Although we currently have no further data on that planetary system, the finding has implications for the search for extraterrestrial life. In fact, there is evidence that here in our solar system, Jupiter played a critical role in the conditions that allowed Earth to emerge and thrive. Finding analogues of Jupiter orbiting distant stars could be one way to identify these conditions.
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