A doomed planet orbiting an aging star has been observed for the first time. Find out what this discovery can contribute to our search for life on other worlds.
Growing up, I was a big fan of Superman comic books from DC. Coming from a rural community myself, I could easily relate to the young Clark Kent being raised by his adoptive parents in Smallville, Kansas.
Despite his many advantages, I always felt sorry for Superman. His birth parents had placed him in an escape rocket to avoid the destruction of his home world, Krypton.
The Canadian band The Crash Test Dummies captured that sense of sympathy in their Superman Song. They wrote, “Folks said, his family were all dead, his planet crumbled but Superman, he forced himself to carry on, forget Krypton, and keep going.”
Doomed Planet’s Orbit Slowly Decaying into its Aging Star
I felt that same, vague sense of sadness reading about a discovery published this month in The Astrophysical Journal Letters. For the first time, scientists have detected a doomed planet whose orbit is slowly decaying into its aging star.
Professor Shreyas Vissapragada is the study’s lead author. He earned his PhD in Planetary Science at the California Institute of Technology, and he recently accepted a fellowship from the Center for Astrophysics | Harvard & Smithsonian. He’s been studying and characterizing the evolution of planets outside of our solar system along with their atmospheres for the past decade.
Professor Vissapragada and his peers have often speculated that planets might sometimes end their lives through an orbital, decay-and-collision process they call “death-by-star.” In fact, there’s a strong possibility that our own sun may obliterate the Earth in the distant future.
“We Have Never Before Seen Such a Planet”
“We’ve previously detected evidence for exoplanets in-spiraling toward their stars, but we have never before seen such a planet around an evolved star,” Professor Vissapragada explained. “Theory predicts that evolved stars are very effective at sapping energy from their planets’ orbits, and now we can test those theories with observations.”
Scientists call the doomed planet Kepler-1658b. It’s named after the Kepler space telescope that discovered it.
NASA launched the Kepler space telescope in 2009 to explore the structure and diversity of planetary systems surrounding other stars. It focused mainly on Earth-size planets orbiting in their stars’ habitable zones.
First Exoplanet Kepler Space Telescope Observed
Although Kepler-1658b was the very first exoplanet Kepler observed, it took an unusually long time for researchers to confirm and name it. That’s why, after almost ten years, Kepler’s first planet ended up cataloged as its 1658th discovery.
Kepler-1658b is what planetary scientists call a “hot Jupiter.” Like many of the early exoplanets astronomers have observed, it’s a gas giant like our solar system’s outer planets.
Unlike Jupiter, the doomed planet orbits unimaginably close to its star. In fact, its orbit is only one-eighth as far from its star as our innermost planet, Mercury, is from the sun.
Star is Aging and Expanding into Sub-Giant Phase
The star the doomed planet orbits is aging and expanding into its sub-giant phase. Our own sun will do something similar in about five billion years, as it expands into a red giant.
Scientists believe that a planet so close to an aging star is nearly certain to experience orbital decay. Although no astronomers have observed it, models suggest that eventually, such planets collide with their stars, destroying them.
Planetary orbital decay is a painfully slow process, as gravity makes each revolution minutely faster. In the case of this doomed planet, its orbital period is decreasing by just 131 milliseconds per year.
Years of Careful Observation and Analysis
Detecting this minute acceleration isn’t easy. It takes years of careful observation and analysis of a planet’s faint transits across the face of its star. In the case of Kepler 1658b’s transits, scientists have been tracking them for the last 13 years.
After NASA retired Kepler in 2018, astronomers continued to follow the doomed planet’s transits using the Mount Palomar Observatory’s Hale Telescope and later with NASA’s new Transiting Exoplanet Survey Telescope (TESS).
The doomed planet’s orbital decay is caused by tidal action. Just as the moon’s gravity affects ocean levels on Earth, any two orbiting bodies affect one another through gravitational interaction.
Orbital Decay Caused by Tidal Action
Astronomers are still in the early stages of discovering planets in other solar systems. So, they’re only beginning to understand tidal dynamics for exoplanets orbiting distant stars.
The doomed planet also seems to be getting hotter and brighter than usual. Tidal effects may also be causing these changes.
Professor Vissapragada used Jupiter’s moon Io as an analogy. Tidal interaction between those two bodies is what causes Io to erupt so much lava and sulfur onto its surface, causing its pockmarked and discoloured surface.
Opportunity to Understand Solar System’s Life Cycle
Humans have always been curious about the world’s origin, its ultimate fate and our place within it. The discovery of Kepler-1658b’s orbital decay, and our ability to follow it in the future, is an opportunity to better understand a solar system’s life cycle.
This doomed planet can help us learn more about our own planet’s fate. Perhaps more importantly, understanding its full life cycle may help to find life on other worlds.
“Now that we have evidence of in-spiraling of a planet around an evolved star, we can really start to refine our models of tidal physics,” Vissapragada concluded. “The Kepler-1658 system can serve as a celestial laboratory in this way for years to come, and with any luck, there will soon be many more of these labs.”
We always have more to learn if we dare to know.
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