New insights into sub-Neptunes and orbit resonance

New insights into sub-Neptunes in our galaxy reveal a correlation between planetary density and orbit resonance, according to research from the Universities of Geneva and Bern.

Scientists have found that sub-Neptunes, planets between the size of the Earth and Neptune, show different densities depending on the resonance of their orbits, thus excluding observational biases as the cause, which raises new questions about the formation of planetary systems.

New insights into sub-Neptunes in our galaxy reveal a correlation between planetary density and orbit resonance, according to research from the Universities of Geneva and Bern.
Photo by: Domagoj Skledar/ arhiva (vlastita)

Most stars in our galaxy have planets. The most common are sub-Neptunes, planets between the size of Earth and Neptune. Calculating their density poses a challenge for scientists: depending on the method used to measure their mass, two populations stand out, dense and less dense. Is this due to observational bias or the physical existence of two different populations of sub-Neptunes? Recent work by NCCR PlanetS, the University of Geneva (UNIGE), and the University of Bern (UNIBE) supports the latter. Learn more in the journal Astronomy & Astrophysics.

Exoplanets are abundant in our galaxy. The most common are those between the radius of Earth (about 6,400 km) and Neptune (about 25,000 km), known as "sub-Neptunes." It is estimated that 30% to 50% of Sun-like stars contain at least one of these planets.

Calculating the density of these planets presents a scientific challenge. To estimate their density, we must first measure their mass and radius. The problem: planets whose mass is measured by the TTV (Transit-Timing Variation) method are less dense than planets whose mass is measured by the radial velocity method, another possible measurement method.

„The TTV method involves measuring variations in transit times. Gravitational interactions between planets in the same system will slightly change the moment when planets pass in front of their star,“ explains Jean-Baptiste Delisle, a research fellow in the Department of Astronomy at UNIGE's Faculty of Science and co-author of the study. „The radial velocity method, on the other hand, involves measuring variations in the star's velocity caused by the presence of planets around it.“

Eliminating Bias
An international team led by scientists from NCCR PlanetS, UNIGE, and UNIBE has published a study explaining this phenomenon. It is not caused by selection or observational bias but by physical reasons. „Most systems measured by the TTV method are in resonance,“ explains Adrien Leleu, an assistant professor in the Department of Astronomy at UNIGE's Faculty of Science and the study's lead author.

Two planets are in resonance when the ratio between their orbital periods is a rational number. For example, when one planet makes two orbits around its star, the other planet makes exactly one. If several planets are in resonance, it forms a chain of Laplace resonance. „Therefore, we wondered if there is an intrinsic link between density and resonant orbital configuration of the planetary system,“ continues the researcher.

To establish a link between density and resonance, astronomers first had to rule out any bias in the data by rigorously selecting planetary systems for statistical analysis. For example, a large low-mass planet detected in transit requires more time to be detected in radial velocities. This increases the risk of observational interruption before the planet becomes visible in radial velocity data, and thus before its mass is estimated.

„This selection process would lead to bias in the literature in favor of higher masses and densities for planets characterized by the radial velocity method. Since we don't have their mass measurements, less dense planets would be excluded from our analyses,“ explains Adrien Leleu.

After this data cleaning was done, astronomers were able to determine through statistical tests that the density of sub-Neptunes is lower in resonant systems than in their non-resonant counterparts, regardless of the method used to determine their mass.

The Question of Resonance
Scientists suggest several possible explanations for this link, including the processes involved in the formation of planetary systems. The main hypothesis of the study is that all planetary systems converge towards a state of resonance chain in the early moments of their existence, but only 5% remain stable. The other 95% become unstable. The resonance chain then breaks, generating a series of "catastrophes," such as collisions between planets. Planets merge, increasing their density, and then stabilize in non-resonant orbits.

This process generates two very different populations of sub-Neptunes: dense and less dense. „Numerical models of planetary system formation and evolution that we have developed in Bern over the past two decades reproduce exactly this trend: planets in resonance are less dense. This study, moreover, confirms that most planetary systems were the site of giant collisions, similar to or even more violent than the one that gave rise to our Moon,“ concludes Yann Alibert, a professor in UNIBE's Department of Space Research and Planetary Sciences (WP) and co-director of the Center for Space and Habitability and co-author of the study.

Source: UNIVERSITY OF GENEVA

Creation time: 02 July, 2024
Note for our readers:
The Karlobag.eu portal provides information on daily events and topics important to our community. We emphasize that we are not experts in scientific or medical fields. All published information is for informational purposes only.
Please do not consider the information on our portal to be completely accurate and always consult your own doctor or professional before making decisions based on this information.
Our team strives to provide you with up-to-date and relevant information, and we publish all content with great dedication.
We invite you to share your stories from Karlobag with us!
Your experience and stories about this beautiful place are precious and we would like to hear them.
Feel free to send them to us at karlobag@ karlobag.eu.
Your stories will contribute to the rich cultural heritage of our Karlobag.
Thank you for sharing your memories with us!

AI Lara Teč

AI Lara Teč is an innovative AI journalist of the Karlobag.eu portal who specializes in covering the latest trends and achievements in the world of science and technology. With her expert knowledge and analytical approach, Lara provides in-depth insights and explanations on the most complex topics, making them accessible and understandable for all readers.

Expert analysis and clear explanations
Lara uses her expertise to analyze and explain complex scientific and technological topics, focusing on their importance and impact on everyday life. Whether it's the latest technological innovations, research breakthroughs, or trends in the digital world, Lara provides thorough analysis and explanations, highlighting key aspects and potential implications for readers.

Your guide through the world of science and technology
Lara's articles are designed to guide you through the complex world of science and technology, providing clear and precise explanations. Her ability to break down complex concepts into understandable parts makes her articles an indispensable resource for anyone who wants to stay abreast of the latest scientific and technological developments.

More than AI - your window to the future
AI Lara Teč is not only a journalist; it is a window into the future, providing insight into new horizons of science and technology. Her expert guidance and in-depth analysis help readers understand and appreciate the complexity and beauty of the innovations that shape our world. With Lara, stay informed and inspired by the latest developments that the world of science and technology has to offer.