This diagram shows how planets are assembled. It can be sorted into two sizes. The rocky cores of the planets are made from smaller pieces. Next, gravity attracts hydrogen gas and helium gas. The planets then become "baked" by starlight, and eventually lose some gas. The Magellan-TESS Survey will provide more information about how formation pathways for super-Earths as well as mini-Neptunes might differ. Credit: NASA/Kepler/Caltech (R. HurtA Carnegie-led study of exoplanet candidates, identified by NASA's Transiting Exoplanets Satellite Survey(TESS), is helping astronomers to understand how the Milky Way’s most common planets formed. It also helps to determine why the pattern of planetary orbits is so unique in our solar system.Johanna Teske from Carnegie, Sharon Wang of Tsinghua University (formerly of Carnegie), Angie Wolfgang (formerly at Penn State University) and Sharon Wang of Tsinghua University (formerly at Carnegie) led the Magellan TESS Survey (MTS), now halfway through its planned three-year duration. In collaboration with an international group of researchers, their mid-survey results will be published in The Astrophysical Journal Supplement Series.NASA's Kepler Mission discovered thousands of planets in our galaxy. They also predicted that billions more may exist. This bounty contains one of the surprising facts: Exoplanets that are between Earth and Neptune in size are the most commonly discovered, despite the fact there is none in our solar system. These "in-between" planets are found in two sizes, roughly one to 1.7 (super Earths) and two to three (mini Neptunes). This indicates that they have different gas compositions.Teske stated that "we want to understand if super-Earths or mini-Neptunes were different from their earliest origins or whether some aspect in their evolution caused them to deviate from one another." "In a way, we want to probe the nature/nurture question for galaxy's most frequent exoplanets. Were these planets created differently or did their environments cause them to diverge? Or is there something else?TESS data and observations from Carnegie's Las Campanas Observatory, Chile are used to survey a selection 30 candidates for small, short-period planets. TESS data shows that objects pass in front of their host star, causing a dip in brightness. The survey team can measure the radius of a candidate planet by measuring the amount of dimming. These observations are combined with the Planet Finder Spectrograph from Las Campanas, which uses a technique known as the radial velocity method. This is the most commonly used way for astronomers measure the masses of individual stars.Artists' conception of the Transiting Exoplanets Satellite Survey (or TESS) that identified the planet candidates. NASA's Goddard Space Flight Center provided the illustration. Magellan Clay telescope at Carnegies Los Campanas Observatory (right), where Planet Finder Spectrograph and other survey teams are used. Credit: Yuri Beletsky courtesy the Carnegie Institution for ScienceThe Magellan TESS survey team is looking at the interaction of key variables that can help astronomers better understand the formation pathways for super-Earth and miniNeptune planets. They are interested in trends in the relationship between a planet's radius and its mass; the properties of its star, including its composition and how much energy it emits onto the planet; as well as the architecture of any planetary systems of which the planet is a part.Wolfgang explained that the underlying relationship between mass and radius for small planets is essential to determine their general compositions via their overall density as well as how much variation they have in their compositions. This relationship can be quantified to determine if there are multiple formation pathways.This survey is different from other previous work because of its scope. The team designed the survey from scratch to avoid biases that might affect how the results are interpreted in a wider context. They want to be able draw solid conclusions about super-Earths, mini-Neptunes planets as a whole population and not just 30 objects.Mid-survey results, which are a significant contribution to the total number of small planets known to have masses and radii, already suggest evidence for small observational biases that could have affected mass measurements. The MTS could provide a framework for future radial velocity research on transiting planets.The next half of the survey will be focused on the completion of the sample. This paper contains 22 of 30 candidates. It also continues to monitor all systems for longer-period, non-detected planets to determine their system architectures. Another step is to check the influence of host star composition. Past work suggests that planets' compositions are related to the stars they orbit.Wang stated, "We hope this multidimensional understanding will significantly enhance our knowledge about exoplanet evolutionary and maybe explain why our solar system seems so unusual."Continue reading Astronomers discover a new large sub-Neptune alien planet
