Using data from NASAs Transiting Exoplanet Survey Satellite (TESS) and the Next-Generation Transit Survey (NGTS), astronomers have discovered a transiting Saturn-like exoplanet circling NGTS-11 (also known as TOI-1847 and 2MASS J01340514-1425090), a mid K-type star located 624 light-years away in the constellation of 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 transiting gas giants.

An artists 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 the Earth is to the Sun.

NGTS-11b has a temperature of only 162 degrees Celsius cooler than Mercury and Venus, said lead author Dr. Samuel Gill, an astronomer in the Centre for Exoplanets and Habitability and the Department of Physics at the University of Warwick.

Although this 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 (1,832 degrees Fahrenheit).

This planet is out at a thirty-five days orbit, which is a much longer period than we usually find them. It is exciting to see the Goldilocks zone within our sights, added Dr. Daniel Bayliss, an astronomer in the Department of Physics 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 spot planets, scanning for the telltale dip in light from the star 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 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 followed up the system using NGTS telescopes in Chile and observed the host star for 79 nights, eventually catching the planet transiting for a second time nearly a year after the first detected transit.

By chasing that second transit down weve found a longer period planet. Its the first of hopefully many such finds pushing to longer periods, Dr. Gill said.

These discoveries are rare but important, since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own Solar System.

The original transit appeared just once in the TESS data, and it was our teams painstaking detective work that allowed us to find it again a year later with NGTS, said Professor Pete Wheatley, an astronomer in the Centre for Exoplanets and Habitability and the Department of Physics at the University of Warwick.

The discovery is reported in a paper in the Astrophysical Journal Letters.

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Samuel Gill et al. 2020. NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event. ApJL 898, L11; doi: 10.3847/2041-8213/ab9eb9

Link:

Astronomers Discover One of the Coolest Transiting Gas Giants | Astronomy - Sci-News.com