The window for observing TOI-1355 b's eccentric orbit closes around 2033

This account describes two different changes to the orbit. The journal paper is titled "Discovery of an eccentric hot super-jupiter leaving the transiting geometry of the early-A-type star TOI-1355" ^[17]. The summary of the work attributes the closing window to the planet's evolving orbit ^[6]. Watanabe described the later change in the orbit's shape as slow: "It is considered that the planetary orbit had become highly elliptical initially due to gravitational interaction with other celestial bodies, such as other giant planets, and shrunk gradually later due to the tidal effect of its host star," he said ^[13]. Whether the transits end because the alignment drifts or because the eccentricity decays is not stated. The two imply different things for an observation taken in 2032.

The detection started in data already on the ground. "When we investigated the change in brightness of TOI-1355 from prior data, we found that the secondary eclipse, a phenomenon in which a planet passes behind a star, occurred earlier than the timing assumed for a circular orbit," Watanabe said ^[9]. Both the mass and the eccentricity came out of changes in stellar and planetary brightness recorded by TESS ^[11]. Watanabe said the mass was the hard part: "The biggest challenge so far has been to measure the planetary mass from the brightness change in the TESS data. We had to derive more complex model equations due to its elliptical orbit" ^[14]. The report does not include a value for either the mass or the eccentricity ^[18].

The star's surface runs about 2,900 C hotter than the sun's ^[1]. A two-day orbit comes round roughly 180 times a year ^[3], and about seven years remain from publication ^[2].

On the phys.org account, an eccentric hot Jupiter around a hot star supports a history of dynamic migration, with planets perturbing each other into a highly eccentric orbit that tides later circularise ^[12]. A single eccentric system is consistent with that history without measuring how often it happens. Watanabe was direct about the gap: "Planet surveys around stars as hot as or cooler than the sun are flourishing, and thousands of planets have been discovered around such stars. But planet surveys around hotter stars are still not advanced," he said ^[8].

Two follow-ups are under way. The group is preparing a paper on how much the planet's orbit is inclined relative to the star's rotation ^[15], and is planning a proposal to observe the system with NASA's James Webb Space Telescope ^[16].