The recent discovery of a solar system with six confirmed exoplanets and a possible seventh exoplanet has improved astronomers' understanding of planet formation and evolution. A team led by researchers at the University of California, Irvine, relied on observatories and instruments spread across the globe to produce the most precise measurements yet of an exoplanet's mass, orbital properties and atmospheric characteristics.
In a paper published on January 29 in The Astronomical Journal, researchers shared the results of the TESS-Keck survey, which provided a detailed description of the exoplanets orbiting TOI-1136, a dwarf star in the galaxy more than 270 light-years away from Earth. This study is a follow-up to the team's initial observations of the star and exoplanets in 2019 using data from NASA's Transiting Exoplanet Survey Satellite (TESS). The project provided the first estimate of an exoplanet's mass by timing changes in transit times, a measure of the gravitational pull of orbiting planets toward each other.
In the recent study, the researchers combined TTV data with 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 Keystone Spectrograph at W.M. Keck Observatory on Mauna Kea in Hawaii, they were able to detect subtle changes in the star's motion through the red shift and blue shift of the Doppler effect -- which helped them determine planet mass readings with unprecedented precision.
To obtain precise information about the planets in this solar system, the team built computer models using hundreds of radial velocity measurements and TTV data. Lead author Corey Beard, a UCLA Ph.D. candidate in physics, said combining the two readings can yield more knowledge about the system than ever before.
"It took a lot of trial and error, but after developing one of the most complex planetary system models to date in the exoplanet literature, we are very pleased with our results," Beard said.
Paul Robertson, co-author of the paper and an associate professor of physics and astronomy at UCLA, said the sheer number of planets is a factor motivating astronomical groups to conduct further research.
"We believe that TOI-1136 is very advantageous from a research perspective because when a system hosts multiple exoplanets, we can control the impact of planetary evolution on the host star, which helps us focus on the individual physical mechanisms that cause these planets to have such properties," he said.
Robertson added that when astronomers try to compare planets in different solar systems, there are many variables that differ due to the different properties of the stars and their locations in different parts of the galaxy. Observing exoplanets in the same system can study planets that have experienced similar histories, he said.
TOI-1136 is very young by stellar standards, only 700 million years old, another feature that attracts exoplanet hunters. Finding young stars is "difficult and special" because they are so active, Robertson said. During this stage of a star's development, magnetism, sunspots, and solar flares are more common and intense, and the resulting radiation can impact and sculpt planets, affecting their atmospheres.
The confirmed exoplanets TOI-1136b to TOI-1136g in TOI-1136 are classified by experts as "sub-Neptunes". The smallest planet has a radius more than twice that of Earth, and others have radii up to four times that of Earth, about the same size as Uranus and Neptune, Robertson said.
According to the study, all of these planets orbit TOI-1136 in less than the 88 days it takes Mercury to orbit Earth's sun. "We fit the entire solar system into such a small region around the star that our entire planetary system here is outside of that region," Robertson said.
"They are strange planets to us because there is nothing exactly like them in our solar system," said co-author Rae Holcomb, a doctoral candidate in physics at UCLA. "But the more we study other planetary systems, the more we think they may be the most common type of planet in the Milky Way."
Another peculiar ingredient of this solar system is the possible existence of a seventh planet, but this has not yet been confirmed. The researchers detected some evidence of another resonant force in the system. Robertson explained that when planets orbit close to each other, they exert a gravitational pull on each other.
"When you hear a chord played on a piano, it sounds nice to you because there are resonances, or even gaps, between the notes you hear," he said. "The orbital periods of these planets have similar gaps. When an exoplanet resonates, the direction of the pull is the same every time. This can have a destabilizing effect, or in special cases, it can make the orbit more stable."
Robertson noted that the survey is far from answering all of his team's questions about the exoplanets in this system, but leaves researchers hoping to gain more knowledge, particularly about the composition of the planet's atmosphere. Research in this area can be better conducted through the advanced spectral analysis capabilities of NASA's James Webb Space Telescope.
"I am very proud that both UC Lick and Keck Observatories have participated in the characterization of this very important system," said Matthew Shetrone, associate director of the UC Observatory. "Having so many medium-sized planets in the same system really allows us to test what planet formation looks like. I want to know more about these planets, will we find lava worlds, water worlds and ice worlds in the same solar system? It feels like science fiction."
Compiled source: ScitechDaily