Exo-Jupiters’ Commonality and Exclusivity Highlighted in Two New Studies

A pair of recent studies conduct in-depth analyses of Jupiter-sized exoplanets, also known as Exo-Jupiters, and were published in Nature Communications and The Astronomical Journal, respectively. The study published in Nature Communications was conducted by an international team of researchers and examines how Exo-Jupiters could be more common than previously thought, while the study published in The Astronomical Journal was conducted by one researcher and examines exoplanetary system, HD 141399, and how it is comprised entirely of Exo-Jupiters with no additional planets.

These two studies hold the potential to help astronomers better understand the formation and evolution of gas giant exoplanets, which are exoplanets that are between the size of Jupiter and Saturn. It is currently estimated that 1,756 confirmed gas giant exoplanets exist out of the total 5,535 exoplanets confirmed by NASA.

For the Nature Communications study investigating common Exo-Jupiters, the researchers analyzed 30 stars within what’s known as the ß (Beta) Pictoris Moving Group (BPMG) using high-contrast imaging techniques along with high precision astrometry conducted by the European Space Agency’s Gaia satellite. A moving group consists of a young group of stars who all simultaneously move throughout space together, and the BPMG is estimated to be approximately 115 light-years from Earth and between 20 to 26 million years old. The BPMG is also estimated to be comprised of 17 exoplanetary systems with a total of 28 stars, meaning that 11 of those systems are comprised of binary star systems (two stars).

The study builds on previous radial velocity (RV) surveys that indicated a 6 to 20 percent rate of Jupiter-like exoplanets orbiting Sun-like stars, but the researchers are quick to note these surveys accounted for Jupiter-size exoplanets ranging in size from 0.3 Jupiter masses to 20 Jupiter masses. This most recent study challenges those previous surveys by showing that 20 of the BPMG exoplanetary systems could potentially contain at least one Jupiter-like planets with stable orbits, suggesting that Jupiter-like exoplanets could be more common than previously thought. So, what could a large number of Jupiter-like exoplanets teach us about the formation and evolution of exoplanetary systems?

“We do not think that there are more Jupiter-like planets around old stars in the general field than indicated by RV surveys,” Dr. Raffaele Gratton, who is the Research Director at INAF – Istituto Nazionale di Astrofisica in Italy and lead author of the study, tells Universe Today. “We rather think that this frequency depends on the characteristics of the site where stars form and, on their age, and that this is important to understand the planet formation mechanisms. We think planet formation can go undisturbed in a quiet environment like the beta Pic moving group. In this case the natural outcome is the formation of Jupiter-like planets. The situation is likely different in more massive star forming regions where the planet formation is disturbed by massive neighbors.”

The study published in The Astronomical Journal investigated HD 141399 and its system of four giant planets orbiting a K dwarf star outside of the Habitable Zone (HZ) with sizes ranging from approximately 0.45 Jupiter masses to 1.36 Jupiter masses and no additional known planets in the system. While past studies have explored systems with only Jupiter-size planets, this most recent study notes how exoplanetary systems that mirror our own—terrestrial planets orbiting inside the snow line and gas giants orbiting beyond the snow line—are rare. The snow line is referred to as the boundary where water ice goes from a solid to a gas, or liquid if the atmosphere allows it, as on Earth.

Dr. Stephen Kane of the Department of Earth and Planetary Sciences at the University of California, Riverside, and sole author of the study, tells Universe Today, “Planetary systems with giant planets at large separations (like Jupiter) are relatively rare, but systems with many giant planets scattered throughout (like HD 141399) are exceedingly rare! These systems therefore show that even extreme planetary architectures are possible, and likely require very special circumstances to form and remain stable.”

For the study, Dr. Kane used computer simulations to model the functions and evolution of the system, including experimenting with different scenarios, including inserting Earth-size planets into hundreds of the simulations over 10 million years. These results demonstrated most of the simulations did not last the full 10 million years and noted that those few that survived ended up in highly eccentric orbits that would not be exhibiting habitable environments. Dr. Kane notes in this paper that better understanding solar system architecture, especially pertaining to how our solar system is rare, will help determine the habitability potential of a particular system and its planets.

“Whether or not a planet can maintain long-term temperate surface conditions depends on many factors,” Dr. Kane tells Universe Today. “One of the important factors is the architecture of the system, and exoplanet discoveries have shown that the solar system architecture is rare. Does having two giant planets like Jupiter and Saturn matter? What if we had more giant planets, or less? Through studying the diversity of other planetary systems, we gain critical insights into how the solar system architecture has contributed to Earth’s habitability.”

Both studies highlight the importance of further investigations into solar system architecture, specifically pertaining to how Jupiter-size planets affect a system’s evolution and habitability.

What new discoveries will researchers make about Exo-Jupiters in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!