Did nature or education shape the most common planets in the Milky Way?

A Carnegie survey of candidate exoplanets identified by NASA’s Transiting Exoplanets Satellite Survey (TESS) lays the groundwork to help astronomers understand how the Milky Way’s most common planets formed and evolved, and to determine why the pattern of planetary orbits and sizes of our solar system is so unusual.

Johanna Teske of Carnegie, Sharon Wang (formerly of Carnegie) of Tsinghua University, and Angie Wolfgang (formerly of Penn State University and now at SiteZeus), led the Magellan-TESS (MTS) survey, which is halfway through way of its expected duration of three years. . The results of the mid-term survey, in collaboration with a large international group of researchers, will be published in the Astrophysical Journal Supplements Series.

NASA’s Kepler mission revealed that our galaxy is teeming with planets, uncovering thousands of confirmed worlds and predicting that there are billions more. One of the surprises in this bounty is that Earth and Neptune-sized exoplanets are the most common discovered to date, despite the fact that none exist in our own solar system. These “intermediate” planets appear to come in two distinct sizes – about one to 1.7 (super-Earth) and about two to three (mini-Neptunes) times the size of Earth – indicating a different gas content in their compositions. .

“We want to understand if super-Earths and mini-Neptunes were distinct from their earliest origins, or if some aspect of their evolution caused them to deviate from each other,” Teske explained. “In a sense, we hope to probe the question of the nature and diet of the galaxy’s most common exoplanets: Were these planets born differently or did they diverged due to their surroundings? Or is it something in between?

The survey uses TESS data and observations from the Magellan telescopes at the Carnegie Observatory in Las Campanas in Chile to study a selection of 30 small candidate planets with relatively short half-lives. TESS data shows drops in brightness as an object passes in front of its host star. The amount of gradation allows the investigation team to measure the radius of a candidate planet. This information is combined with observations collected by the Planet Finder spectrograph in Las Campanas which uses a technique called the radial velocity method, which is currently the most common way for astronomers to measure the masses of individual planets.

The Magellan-TESS study team is interested in the interplay between key variables that could help astronomers better characterize the formation pathways of super-Earth and mini-Neptune planets. They look for trends in the relationship between a planet’s mass and its radius; the properties of its host star, including the composition and amount of energy it radiates to the planet; and the architecture of the planetary system of which it is a member.

“The underlying relationship between the radius and the mass of these small planets is crucial in determining their overall compositions, via their overall density, as well as the variation in their compositions,” explained Wolfgang. “Quantifying this relationship will help us discern whether there is a single path of formation or several avenues.”

What sets this survey apart from previous work is its scope: the team designed the survey from the start to try to account for biases that might skew the way the results are interpreted in a larger context. Their goal is to be able to draw solid conclusions about super-Earths and mini-Neptune planets as a population, compared to a collection of 30 individual objects.

The results of the mid-term survey, which represent a significant contribution to the number of small planets with known masses and radii, already suggest evidence of small observational selection biases that may have affected scientists’ work on mass measurements. The MTS could thus provide an important framework for future studies of radial velocity of planets in transit.

Going forward, the next half of the survey will focus on sample completion – this article contains 22 of the 30 planned candidates – as well as continuing to monitor all systems for planets longer. period not detected by TESS to probe system architectures. Checking the influence of the composition of the host star is another next step, as previous work has suggested that the compositions of the planets may be related to those of the stars they orbit.

“We hope that gaining this multidimensional understanding will dramatically improve our knowledge of the evolution of exoplanets and perhaps explain why our own solar system looks unusual,” Wang concluded.