Astronomers analyze masses, orbital properties and atmospheric characteristics of six exoplanets

A newly discovered solar system with six confirmed exoplanets and a possible seventh improves astronomers’ knowledge of planet formation and evolution. Drawing on a global arsenal of observatories and instruments, a team led by researchers at the University of California, Irvine has compiled the most precise measurements to date of the masses, orbital properties and atmospheric characteristics of exoplanets.

In an article published today in The astronomical journal, researchers share results from the TESS-Keck survey, providing a detailed description of exoplanets orbiting TOI-1136, a dwarf star in the Milky Way more than 270 light-years from Earth. The study follows the team’s initial observation of the star and exoplanets in 2019 using data from the Transiting Exoplanet Survey Satellite. This project provided the first estimate of the mass of exoplanets by recording variations in transit time, a measure of the gravitational pull that orbiting planets exert on each other.

For the most recent study, the researchers combined the TTV data with an analysis of the star’s radial velocity. Using the Automated Planet Finder telescope at Lick Observatory on Mount Hamilton in California and the high-resolution Echelle spectrometer at WM Keck Observatory on Mauna Kea in Hawaii, they were able to detect slight variations in stellar motion via shift red shift and blue shift of the Doppler effect, which helped them determine planetary mass readings with unprecedented precision.

To obtain such precise information about the planets in this solar system, the team built computer models using hundreds of radial velocity measurements superimposed on the TTV data. Lead author Corey Beard, a UCI Ph.D. candidate in physics, said the combination of these two types of readings yielded more insight into the system than ever before.

“It took a lot of trial and error, but we were really happy with our results after developing one of the most complicated planetary system models in the exoplanet literature to date,” Beard said.

The large number of planets is one of the factors that prompted the astronomy team to conduct further research, according to co-author Paul Robertson, associate professor of physics and astronomy at UCI.

“We view TOI-1136 as being very advantageous from a research perspective, because when a system has multiple exoplanets, we can control the effects of planet evolution that depend on the host star, allowing us to helps us focus on the individual physical mechanisms that led to these planets having the properties that they do,” he said.

Robertson added that when astronomers try to compare planets in distinct solar systems, many variables can differ based on the stars’ distinct properties and their locations in disparate parts of the galaxy. He said examining exoplanets in the same system allows one to study planets that have had a similar history.

By stellar standards, TOI-1136 is young, only 700 million years old, another feature that has attracted exoplanet hunters. Robertson said the young stars are both “difficult and special” to work with because they are so active. Magnetism, sunspots, and solar flares are more prevalent and intense during this stage of a star’s development, and the resulting radiation explodes and sculpts planets, affecting their atmospheres.

The confirmed exoplanets of TOI-1136, TOI-1136 b to TOI-1136 g, are classified as “sub-Neptunes” by experts. Robertson said the smallest measures more than twice the radius of Earth, and others measure up to four times Earth’s radius, comparable to the sizes of Uranus and Neptune.

All of these planets orbit TOI-1136 in less than the 88 days it takes Mercury to orbit Earth’s sun, according to the study. “We’re packing an entire solar system into a region around the star so small that our entire planetary system here would be outside of it,” Robertson said.

“These are strange planets for us because we don’t have anything like them in our solar system,” said co-author Rae Holcomb, a doctoral student at UCI. candidate in physics. “But the more we study other planetary systems, it appears that they may be the most common type of planet in the galaxy.”

Another strange element of this solar system is the possible but unconfirmed presence of a seventh planet. The researchers detected evidence of another resonant force in the system. Robertson explained that when planets orbit close to each other, they can attract each other gravitationally.

“When you hear a chord played on a piano and it sounds good to you, it’s because there is resonance, or even spacing, between the notes you hear,” he explains. “The orbital periods of these planets are equally spaced. When exoplanets are in resonance, the tugs are in the same direction each time. This can have a destabilizing effect, or in special cases it can serve to make the orbits more stable.”

Robertson noted that far from answering all of his team’s questions about the exoplanets in this system, the survey made researchers want to deepen their knowledge, particularly on the composition of planetary atmospheres. This line of inquiry would be best addressed with the advanced spectroscopy capabilities of NASA’s James Webb Space Telescope, he said.

“I’m proud that UCO’s Lick Observatory and the Keck Observatories were involved in characterizing a truly important system,” said Matthew Shetrone, deputy director of the UC Observatories. “Having so many mid-sized planets in the same system really allows us to test formation scenarios. I really want to know more about these planets! Could we find a molten rock world, a water world, and a ice world, all in the same solar system. ?It almost sounds like science fiction.