Using data from NASA’s Transit Exoplanet Survey Satellite (TESS) and the Next Generation Transit Survey (NGTS), astronomers have discovered a Saturn-like exoplanet in transit surrounding NGTS-11 (also known as TOI- 1847 and 2MASS J01340514-1425090), a K-type half-star located 624 light-years away in the constellation Cetus. Named NGTS-11b (TOI-1847b), the planet has an equilibrium temperature of just 162 degrees Celsius (324 degrees Fahrenheit), making it one of the coolest known gas giants in transit.
Artist’s impression of a Saturn-sized exoplanet. Image credit: Sci-News.com.
NGTS-11b has a radius of 0.82 times that of Jupiter and a mass of 0.34 Jupiter masses.
The planet orbits its host star every 35 days at a distance 5 times closer than Earth to the Sun.
“NGTS-11b has a temperature of only 162 degrees Celsius, colder than Mercury and Venus,” said lead author Dr. Samuel Gill, an astronomer at the Center for Exoplanets and Habitability and the Department of Physics at the University of Warwick.
“Although it is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets, which typically have temperatures above 1,000 degrees Celsius.”
“This planet is in a thirty-five day orbit, which is a much longer period than we generally encounter them. It is exciting to see the Goldilocks area within our view, ”added Dr. Daniel Bayliss, an astronomer in the Physics Department at the University of Warwick.
The researchers initially identified NGTS-11b from a single transit event detected by the TESS spacecraft.
“TESS uses the transit method to detect planets, scanning the star indicator light that indicates that an object has passed between the telescope and the star,” they explained.
However, TESS only scans most sections of the sky for 27 days. This means that many of the longer period planets only transit once in the TESS data. And without a second observation, the planet is effectively lost. ”
The team tracked the system using NGTS telescopes in Chile and observed the host star for 79 nights, and finally captured the transiting planet for the second time nearly a year after the first detected transit.
By chasing that second transit down we have found a longer period planet. Hopefully, it is the first of many findings that push longer periods, ”said Dr. Gill.
“These discoveries are rare but important, as they allow us to find planets of longer periods than other astronomers are finding. Longer period planets are colder, more like planets in our own Solar System. “
“The original transit appeared only once in the TESS data, and it was our team’s painstaking detective work that allowed us to find it again a year later with NGTS,” said Professor Pete Wheatley, astronomer at the Center for Exoplanets and Habitability. and the Department of Physics at the University of Warwick.
The discovery is reported in a document in the Astrophysical charts.
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Samuel Gill et al. 2020. NGTS-11 b (TOI-1847 b): A warm Saturn in transit recovered from a single transit event TESS. ApJL 898, L11; doi: 10.3847 / 2041-8213 / ab9eb9
