A strange ice giant, which cannot be explained by previous theories, was discovered by NASA scientists with the Exoplanet Sleuth Transit Exoplanet Survey Satellite (TESS, which had “first light” on August 7, 2018). The planet TOI-849 b is the most massive planet in Neptune size and the first with a density comparable to that of the Earth. The strange proportions of the planet orbit a star about 750 light years from Earth every 18 hours and are 40 times as massive.
“We are really confused about how this planet formed,” said Chelsea Huang, postdoc at the Kavli Institute for Astrophysics and Space Research at MIT and a member of the TESS science team. “All current theories do not fully explain why it is so massive at its current location. We don’t expect planets to grow to 40 masses of the earth and then just stop there. Instead, it should just keep growing and become a gas giant like a hot Jupiter with hundreds of Earth’s masses. It’s pretty crazy to think what happens to this pressure in the center of a planet. “
Since its launch on April 18, 2018, the TESS satellite has been scanning the sky for planets beyond our solar system. The project is one of NASA’s Astrophysics Explorer missions and is being led and operated by MIT. TESS, which is predicted to discover a handful of habitable extraterrestrial planets, is said to survey almost the entire sky by rotating its gaze every month to focus on a different patch of the sky as it orbits the Earth. TESS uses the “transit method”, which looks for slight drops in star brightness that arise when a orbiting planet, from TESS’s perspective, crosses the star’s face, similar to NASA’s Kepler space telescope, which accounts for about 70% of the more than 4,000 known has discovered alien worlds.
“Tess object of interest”
Data recorded by TESS in the form of a light curve from a star or brightness measurements are first made available to the TESS science team, an international research group with several institutes that is led by scientists at MIT. These researchers get a first look at the data to identify promising planet candidates or TESS Objects of Interest (TOI). These are shared with the general scientific community along with the TESS data for analysis.
Hidden in the data
For the most part, astronomers focus their search for planets on the nearest, brightest stars that TESS has observed. However, Huang and her team at MIT recently had a little more time to check the data in September and October 2018 and wondered if there was anything under the fainter stars. Sure enough, they discovered a significant number of transit-like intrusions from a star 750 light years away and soon confirmed the existence of TOI-849 b.
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“Stars like this are usually not closely scrutinized by our team, so this discovery was a happy coincidence,” said Huang. Subsequent observations of the faint star with a series of ground-based telescopes further confirmed the planet and also helped determine its mass and density.
Earlier theories cannot explain this planet
One hypothesis that scientists have put forward to explain the mass and density of the new planet is that it may have once been a much larger gas giant, similar to Jupiter and Saturn – planets with more massive gas envelopes that enveloped cores that were believed to be that they are as dense as the earth.
As the TESS team suggests in the new study, much of the planet’s gaseous shell may have been blown away by star radiation over time – not an unlikely scenario since TOI-849 b orbits extremely close to its host star. Its orbital period is only 0.765 days or just over 18 hours, exposing the planet to approximately 2,000 times the amount of solar radiation the earth receives from the sun. According to this model, the Neptune-sized planet discovered by TESS could be the residual nucleus of a much larger Jupiter-sized giant.
“If this scenario applies, TOI-849 b is the only remaining planetary nucleus and the largest known gas giant nucleus,” says Huang. “This is something that really excites scientists because previous theories cannot explain this planet.”
The Daily Galaxy, Max Goldberg, on MIT