The three “planets” were discovered by the Kepler space telescope, but now – years later – it turns out they weren’t planets at all.
Instead, they are small stars, the researchers wrote this week Astronomical Journal† In the paper they also refer to a fourth planet that may not be a planet at all.
The researchers based their conclusions on new measurements of the size of some putative planets. These measurements indicate that three of the four planets are too large to be classified as planets and should instead be classified as small stars. The fourth model lies on the boundary between the planet and the star in terms of mass and is given the benefit of the doubt at the moment. But it is very likely that he will also lose his place on planet Earth in the future.
“Most exoplanets are about the size of Jupiter or much smaller,” explains researcher Prajwal Niraula. “Jupiter’s size is questionable already twice its size.” If it is a much larger object, then it cannot be a planet in most cases. And that’s what researchers have now established for three things. In concrete terms, we are thus three poorer exoplanets: Kepler-854b, Kepler-840b and Kepler-699b Anyway the smoke will rise as a planet. Then it rises from the ashes like a small star.
Meanwhile, Kepler-747b retains its “planet” character, but has its own “suspicious” character. New measurements indicate that this planet is about 1.8 times larger than our own Jupiter. This allows it to compete with the largest of the planets whose existence has now been conclusively proven. So it’s not impossible that Kepler-747b really is a planet, but it’s not clear either, given the large distance from the parent star. For the same money, it’s just a little star. But this is not difficult at the moment.
Ironically, the astronomers who are now stripping three Kepler planets of their planetary status, weren’t looking for false positives from the rich database of the Kepler space telescope. Instead, they were actually looking for systems with clear signs of tidal distortion. “If you have two objects that are close to each other, the gravitational force of one will make the other elliptical or elliptical,” Niraula explains. For example, a parent star can use its own gravity to give a nearby planet dimensions similar to a rugby ball. The degree of distortion can tell us more about the mass of the planet and the mass of the parent star.
While searching for distorted planets in the Kepler database, scientists stumbled upon something strange in the Kepler-854b system. “Suddenly we had a system where we saw a huge elliptical signal and knew right away that it couldn’t come from a planet,” said study researcher Avi Shporer. “Then we thought: It’s not true.”
So the researchers decided to zoom in closely on both the star and the alleged planet. Kepler deduced the existence of this alleged planet in 2016 – as always – from dips in the brightness of the parent star (see box).
The Kepler space telescope discovered the planets using the transit method. The telescope stared at the stars for a long time, hoping to see their brightness decrease on a regular basis. This regular decrease or decrease in the brightness of the star’s light may indicate the presence of a planet, which – as it orbits around the star – sometimes interferes between Kepler and the parent star, creating a (small) portion of the star’s light.
However, a dip in starlight can’t only reveal a planet orbiting a star. It can also provide more information about the size of this planet. For example, the rate at which a star’s brightness decreases says more about how the size of a planet compares to that of its parent star. Thus, if you know the size of a star, you can also see what size the planet should be from the degree to which that star’s brightness decreases. In 2016, researchers estimated the size of Kepler-854b based on the observed dip and an estimate of the size of the parent star. They decided that the object must be a planet.
But now, more than 5 years later, researchers are better able to determine the size of the star – and thus also the size of the planet it orbits. All thanks to Gaia, the observatory that has been mapping the properties of millions of stars in the Milky Way since 2013. In 2016, Gaia had not collected data on Kepler-854, and based on the information available, researchers estimated the Kepler-854’s size and distance So Kepler-854b. But now in 2022, thanks to Gaia, researchers have more accurate measurements of Kepler 854. And now researchers have captured them. This has far-reaching implications for Kepler-854b. Based on new stellar measurements, the hypothesized planet should be no less than three times larger than Jupiter. “It’s impossible for the universe to make a planet that big,” said Sporer. “It just doesn’t exist.”
Shporer is very clear above: there is no planet three times larger than Jupiter. Are there really no bigger planets known? We checked it out and quickly found HD 100546b, which takes the cake with an estimated size of about 7 times the radius of Jupiter. How can the existence of this huge planet be explained? We asked Schpurer. First, he explains: “We can determine the size (radius) of planets in two ways.” “Through experimental evidence and theoretical understanding. Experimental evidence includes, for example, hundreds of planets that we’ve seen moving in front of their stars and that we’ve been able to directly measure their masses. A theoretical concept, on the other hand, is an understanding of the physical processes that determine a planet’s radius, such as gravity that make the planet shrink and the pressure that the particles in the planet put on each other and cause the planet to expand..Based on the latter, we know that planets can be up to twice the radius of Jupiter.There may be some strange exceptions: planets that get bigger, for example Because they are very small and therefore they are actually still in the process of being born and therefore still collecting gas and contracting. But these planets are not only very rare, they are very difficult to measure accurately.” Wherever it is difficult to measure the planet HD 100546b, which we just mentioned and which will be approximately seven times larger than Jupiter. “This is a directly observed planet, so its radius has been estimated using theoretical models, given in particular the brightness of the planet. Therefore, no direct measurements have been made. The margin of error is therefore large; nearly 3 times the radius of Jupiter. Plus However, the estimated radius is suspected to be formed by both the planet itself and the disk of gas in which it is still accumulating. This makes it very difficult to estimate the radius of HD 100546b.” So the planet could be an exception that proves the rule, but it could be much smaller than we think.
Few other planets have been detected
The detection of Kepler-854b naturally raised the question of whether there were more false positives hidden in the Kepler data. Researchers have taken a closer look at 2,000 other planets discovered by Kepler. Using Gaia data, they determined the size of each of these planets based on more accurate measurements of their parent star. Thus a few other planets were found that were so underestimated that they could not be planets. “Now we have three bodies that are not planets and the fourth is probably not a planet,” Nyiraula concluded.
According to the researchers, it is unlikely that more planets will die in a similar way in the future. They point out that the corrections come from a better understanding of the parent stars. This understanding is constantly improving, but with Gaia a very big step has been taken. This doesn’t mean we know everything now, but it does mean that future corrections are likely to be much smaller and won’t directly lead to the collapse of the planet.
Saying goodbye to some planets might now seem like a bad thing. But we have to see it differently, says Schpurer. “In fact, our study makes the current list of planets more complete. People rely on this list when they study the population of the planet as a whole. If this list contains some intruders, your results may be incorrect. So it is important that the list is correct.”
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