University of Kansas astronomers unveil largest exoplanet survey yet

Astronomers from the University of Kansas (USA) have just presented a comprehensive new catalogue of information about exoplanets. Using the Keck Observatory and the TESS (Transiting Exoplanet Survey Satellite) space telescope, they detected 15 previously unknown exoplanets and determined the mass of 126 others.

"These two facilities (TESS and Keck) work synergistically to study exoplanets," said Alex Polanski, the lead author of the study, which was published in "The Astrophysical Journal Supplement Series". He added: "TESS is a satellite orbiting above Earth's atmosphere, scanning the sky for exoplanets using the transit method."

The transit detection method involves observing changes in the brightness of stars when planets move across their disks. "By detecting and measuring these transit events, researchers can determine the planet's orbital period and size. Larger planets block more light, making them easier to detect. However, transit data doesn't provide information about the planet's mass, which is crucial for understanding its composition," explained the researcher.

To assess the mass of the planets, scientists used the Keck Observatory located on Mauna Kea in Hawaii, which allows for measurements of the star's vibrations caused by the planet's movement. "This method involves observing the host star and measuring its spectrum. Stars contain elements like hydrogen, helium and iron, which create characteristic absorption lines in their spectra. As a planet orbits its star, the star experiences slight gravitational pull, causing it to wobble. This wobble shifts the star's spectral lines due to the Doppler effect — similar to how a siren's pitch changes as it moves towards or away from you. The amount of shift in the spectral lines is related to the planet's mass; larger planets cause greater shifts," explained Polanski.

Scientists remind us that this method detected the first exoplanets around sun-like stars in the 1990s, known as hot Jupiters. These are massive objects the size of Jupiter with short orbital periods of about 10 days. However, more minor planets, especially those sized between Earth and Neptune, cause much smaller spectral shifts and require more sensitive instruments, such as those working at the Keck Observatory.

The new study was conducted as part of the TESS-Keck Survey program—the most extensive analysis program of planets detected by the TESS satellite. "Catalogs like this help astronomers place individual worlds in context with the rest of the exoplanet population," said Prof. Ian Crossfield, co-author of the achievement.

"This paper is the largest of its kind to date. The last similar one that came out was, I think, a sample of 27 exoplanets. This is up to 126 planets," emphasized Polanski.

Some planets have amazed scientists. For example, TOI-1824 b, a super-dense so-called sub-Neptune, is 19 times more massive than Earth but only 2.6 times larger. Typically, planets of this kind are 6 to 12 times more massive than Earth.

Meanwhile, TOI-1798 is a so-called orange dwarf—a type K star, around which two planets orbit—TOI-1798 b and TOI-1798 c. The first is also a sub-Neptune, where a year lasts only about 8 days, and the second is a super-Earth, which orbits the star even faster, in just 12 hours.

"While the majority of planets we know about today orbit their star faster than Mercury orbits the Sun, USPs take this to the extreme," said Prof. Crossfield.

"We used to believe Earth was the center of the universe. Then we learned it isn't even the center of the solar system. From there, we discovered Earth is just one planet among many in a galaxy, which is one among billions of galaxies. However, our solar system might be more unique than we thought. About half of all Sun-like stars have a binary companion. Our Sun does not. Only about 10% of Sun-like stars have gas giants like Jupiter or Saturn. This suggests our solar system might be less typical than we assumed," emphasized Polanski.