Astronomers have discovered four new exoplanets playing hide and seek

An international team of astronomers – using the CHEOPS space telescope and NASA’s TESS satellite – has discovered the existence of four new exoplanets. These worlds are smaller and cooler than the so-called “Hot Jupiter” exoplanets, and harder to find.

As members of NCCR PlanetS, Dr. Hugh Osborne of the University of Bern and Dr. Solen Ulmer-Moll of the Universities of Bern and Geneva collaborated to exploit the unique synergy between CHEOPS and NASA’s TESS spacecraft to find several elusive exoplanets. Planets TOI 5678 b and HIP 9618 c have 4.9 and 3.4 Earth radii, respectively, and are roughly the size of Neptune.

Amy Tuson from the University of Cambridge (UK) and Dr Zoltan Garay from the ELTE Gothard Astrophysical Observatory (Hungary) were two other members of an international team that used the same method to find two similar planets in other systems.

Suspecting the existence of exoplanets, the CHEOPS team devised a mechanism to avoid wasting valuable observing time in hopes of finding more transits. Based on the scant information provided by the transits seen by TESS, they developed a targeted strategy. Based on this, Osborne created a program that suggests and ranks candidate periods for each planet.

Osborne says: “Then we play hide-and-seek with the planets via the CHEOPS satellite.”

“We aim CHEOPS at a specific time, and depending on whether we observe a transit or not, we can rule out some possibilities and try again at another time until we have a unique solution for the orbital period.”

“It took scientists five and four attempts, respectively, to confirm the existence of the two exoplanets, finding that TOI 5678 b has a period of 48 days and HIP 9618 c has a period of 52.5 days.”

The researchers were able to determine the masses of TOI 5678 b and HIP 9618 c as 20 and 7.5 Earth masses, respectively, using ground-based observations using another method called radial velocity combined with newly discovered constrained periods. Scientists can determine a planet’s composition by knowing its density, size, and mass.

Ulmer-Moll said: “However, the density is not high enough for small Neptunes, and there are still several hypotheses about the composition of the planets: they could be rocky planets with a lot of gas, or planets rich in water and very steamy. atmosphere”.

“As the four newly discovered exoplanets orbit bright stars, this makes them a prime target of interest for the James Webb Space Telescope’s JWST mission, which will help unravel the mysteries of their composition.”

“The temperatures of the four new planets we discovered are much more moderate at ‘only’ 217 to 277ºC. This temperature allows clouds and molecules to survive, otherwise they would be destroyed by the intense heat of Hot Jupiters. They can be detected by JWST.

“Smaller in size and with longer orbital periods than hot Jupiters, the four newly discovered planets are the first step in tracking the transits of Earth-like planets.”

Journal Links:

1. HIP 9618 transit biennial Neptune from TESS & Cheops by HP Osborn et al. Published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stad1319
2. TOI-5678 b: 48-day transit Neptune-mass planet, S. Ulmer-Moll et al. Published in Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202245478
3. Refined parameters of the planetary system HD 22946 and the true orbital period of planet d Z. Garai et al. Published in Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202345943
4. TESS and CHEOPS A. Tuson et al. Published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stad1369