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Astronomers have discovered TIC-65910228 b (also known as NGTS-38 b), a giant exoplanet approximately 4.78 Jupiter masses with a 180.5-day orbital period around a bright F-type star. The planet was detected through a combination of transit observations from TESS and NGTS telescopes, along with radial velocity measurements from CORALIE and HARPS spectrographs. With its moderately eccentric orbit and relatively cool equilibrium temperature of 458 K, this warm super-Jupiter is one of the longest-period transiting giant planets discovered to date.
Why it matters
This discovery adds to the limited population of well-characterized transiting warm Jupiters, which are crucial for understanding planetary formation and migration processes. The planet's bright host star and wide orbital separation make it particularly valuable for future atmospheric studies, spin-orbit alignment measurements, and searches for exomoons or rings.
arXiv:2602.12977v3 Announce Type: replace
Abstract: We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081pm0.047$ R$_text{J}$ and a mass of $4.78_{-0.37}^{+0.40}$ M$_text{J}$ on a long-period ($180.52791pm0.00038$ day), moderately eccentric ($e=0.308pm0.011$) orbit transiting a bright (V=$10.230pm0.020$ mag) metal rich ([Fe/H]=$0.33pm0.09$, ‘dex’) F6V-F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of ~180.5,d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $458pm11$ K, NGTS-38 b joins a small but growing population of well characterised transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b’s bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.
Source: TIC-65910228 b / NGTS-38 b, a 180 day transiting warm super-Jupiter