by Astronomers have discovered an exoplanet orbiting an aging star for the first time. The last exoplanet to be found by the Kepler space telescope is destined to get closer and closer to its expanding star until it crashes into it and disappears.
Giving us our first look at a solar system so late in its life cycle, the discovery provides new insights into the gradual process of planetary orbital decay. Many worlds, including Earth, are predicted to experience stellar death in the next 5 billion years. Kepler-1568b is an exoplanet less than 3 million years old.
First author Shreyas Vissapragada said, “We have previously detected evidence of exoplanets orbiting their stars, but we have never seen such a planet around an evolved star before.”
“For sun-like stars, ‘evolved’ refers to those that have fused all of their hydrogen into helium and passed into the next stage of their lives. In this case, the star has begun to expand into a subgiant. Theory predicts that evolved stars are very efficient at absorbing energy from the orbits of their planets, and now we can test these theories with observations.”
The ill-fated exoplanet is known as Kepler-1658b. Its discovery was made possible by the Kepler space telescope, a pioneering planet-hunting mission that launched in 2009. As the first new exoplanet candidate Kepler ever saw, it was given the name KOI 4.01, or the 4th object of interest discovered by Kepler.
KOI 4.01 was initially rejected as a false positive. Before the data didn’t match the model, scientists thought they were modeling a Neptune-sized object around a sun-sized star. a decade would pass as she watched seismic waves travel through her star. After scientists proved that the planet and its star are much larger than first thought, the object was officially added as the 1,658th object in Kepler’s catalog.
Kepler-1658b is the so-called hot Jupiter. This distance for Kepler-1658b is only one eighth of the distance between our Sun and Mercury, which has one of its closest orbits. Kepler-1658b orbits its star in just 3.8 days, as opposed to Mercury’s 88-day orbit.
Kepler-1658b is about 2 billion years old and is in the last 1% of its life. Its star has reached the stage of its stellar life cycle where it has begun to grow, as our Sun is predicted to do, and has entered what astronomers refer to as the subgiant phase. The core structure of evolved stars, unlike hydrogen-rich stars like our Sun, should more easily lead to the dissipation of tidal energy taken from the orbits of host planets, according to theoretical predictions. As a result, the decay process of the orbits would be accelerated, making consideration of a human-relevant time scale simpler.
Orbital decay and collision are inevitable for hot Jupiters and other planets near their Sun. But because the process is so excruciatingly gradual, tracking how exoplanets cycle through the drains of their stars has proven difficult. According to the current analysis, the orbital period of Kepler-1658 b is decreasing by 131 milliseconds (milliseconds) per year.
Scientists noted, “Detecting this decline required many years of careful observation. The clock began with Kepler and was taken by Palomar Observatory’s Hale Telescope in Southern California, and finally the Transiting Exoplanet Survey Telescope, or TESS, which launched in 2018. All three instruments recorded transits, the term for when an exoplanet crosses the face of its star and causes a very small decrease in the star’s brightness. Over the past 13 years, the interval between the passes of Kepler-1658 b has decreased slightly but steadily.”
“The same phenomenon responsible for the daily rise and fall of Earth’s oceans: tides.”
“The drag distorts the shape of each body, and energy is released as the planet and star respond to these changes. Depending on their distances to each other, their sizes, and their rotation rates, these tidal interactions can result in the bodies pushing each other apart—in the case of the slowly outward moving Earth and Moon—or inward, as with Kepler-1658b toward the star.”
“Many researchers still do not understand these dynamics, particularly in star-planet scenarios, so astrophysicists are eager to learn more from the Kepler-1658 system.”
Ashley Chontos, the Henry Norris Russell Postdoctoral Fellow in Astrophysics at Princeton said, “Although of course, this exoplanet’s system is very dissimilar to our solar system – our home – it can tell us a lot about the efficiency of these tidal diffusion processes and how long these planets can survive.”
Journal Reference:
- Shreyas Vissapragada et al. The possible tidal collapse of Kepler’s first planetary system. The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/aca47e
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