A decade after its launch and months after its mission ended, glimmers of data detected by NASA’s Kepler Space Telescope in 2009 have been confirmed as evidence for a Jupiter-like exoplanet orbiting a star 2,600 light-years from Earth.
An artist’s concept of the Kepler-1658 system. Sound waves propagating through the stellar interior were used to characterize the star and the planet. Image credit: Gabriel Perez Diaz / Instituto de Astrofísica de Canarias.
Kepler-1658b is a so-called hot-Jupiter. The planet is about 1.1 times the size of Jupiter, 5.7 times as massive, and whips around its parent star, Kepler-1658, every 3.85 days.
Compared to the Sun, Kepler-1658 (also known as KOI-4.01 and KIC 3861595) is 1.45 times more massive and three times larger. While it is younger than the Sun, having more mass means it has burned through its hydrogen fuel faster and is already expanding towards becoming a red giant.
From the planet’s surface, the star would appear 60 times larger in diameter than the Sun as seen from Earth. The planet will eventually spiral into the star.
“Confirming that Kepler’s first exoplanet candidate really is a planet is a wonderful legacy result, which brings things full-circle, now that Kepler has finished taking data,” said University of Birmingham’s Professor Bill Chaplin.
Despite being the very first planet candidate discovered by Kepler, which launched on March 7th 2009, Kepler-1658b had a rocky road to confirmation.
The telescope uses the transit method — small dips in brightness as planets cross in front of a star along our line of sight — to reveal ‘planet candidates’, but further analysis is required to confirm them as genuine planets.
The initial estimate of Kepler-1658 was off, so the sizes of both the star and the planet were vastly underestimated.
It was later marked as a false positive — that is, astronomers thought the data did not really point to a planet — when the numbers didn’t quite add up for the effects seen on its star for a body of that size.
Kepler-1658b moved from planet candidate to false positive and back until new software was used to refine the data and reclassify it, changing it from a data anomaly to possible planet.
“Our new analysis, which uses stellar sound waves observed in the Kepler data to characterize Kepler-1658, demonstrated that the star is in fact three times larger than previously thought,” said University of Hawai’i graduate student Ashley Chontos.
“This in turn means that the planet is three times larger, revealing that Kepler-1658b is actually a hot Jupiter.”
“We were able to extract this astroseismic signal from the data using two different techniques, and in so doing pin-down the size of the star with great precision,” said University of Birmingham’s Dr. Guy Davies.
With this refined analysis, everything pointed to a planet, whose presence was confirmed beyond all doubt by follow-up observations from a ground-based telescope.
Sitting at an orbital distance of only 0.05 AU, which is even closer than Mercury is to our Sun, Kepler-1658b is one of the closest known planets to a future version of our Sun.
It reveals new constraints on the complex physical interactions that cause planets to spiral into their host stars.
“Kepler-1658 is a perfect example of why a better understanding of host stars of exoplanets is so important. It also tells us that there are many treasures left to be found in the Kepler data,” Chontos said.
The research will be published in the Astronomical Journal.
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Ashley Chontos et al. 2019. The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet. AJ, in press; arXiv: 1903.01591
