An exomoon survey of 70 cool giant exoplanets and the new candidate Kepler-1708 b-i

Exomoons represent a crucial missing puzzle piece in our efforts to understand extrasolar planetary systems. To address this deficiency, we here describe an exomoon survey of 70 cool, giant transiting exoplanet candidates found by Kepler. We identify only one exhibiting a moon-like signal that passes a battery of vetting tests: Kepler-1708 b. We show that Kepler-1708 b is a statistically validated Jupiter-sized planet orbiting a Sun-like quiescent star at 1.6 au. The signal of the exomoon candidate, Kepler-1708 b-i, is a 4.8σ effect and is persistent across different instrumental detrending methods, with a 1% false-positive probability via injection–recovery. Kepler-1708 b-i is ~2.6 Earth radii and is located in an approximately coplanar orbit at ~12 planetary radii from its ~1.6 au Jupiter-sized host. Future observations will be necessary to validate or reject the candidate.

Resolving the Multiplicity of Exoplanet Host Stars in Gemini/NIRI Data

The majority of stars have one or more stellar companions. As exoplanets continue to be discovered, it is crucial to examine planetary systems to identify their stellar companions. By observing a change in proper motion, companions can be detected by the acceleration they induce on their host stars. We selected 701 stars from the Hipparcos–Gaia Catalog of Accelerations (HGCA) that have existing adaptive optics imaging data gathered with Gemini/Near InfraRed Imager (NIRI). Of these, we examined 21 stars known to host planet candidates and reduced their archival NIRI data with Gemini’s DRAGONS software. We assessed these systems for companions using the NIRI images as well as Renormalized Unit Weight Error values in Gaia and accelerations in the HGCA. We detected three known visible companions and found two more systems with no visible companions but astrometric measurements indicating likely unresolved companions.

Orbital Dynamics and the Evolution of Planetary Habitability in the AU Mic System

The diverse planetary systems that have been discovered are revealing the plethora of possible architectures, providing insights into planet formation and evolution. They also increase our understanding of system parameters that may affect planetary habitability, and how such conditions are influenced by initial conditions. The AU Mic system is unique among known planetary systems in that it is a nearby, young, multiplanet transiting system. Such a young and well-characterized system provides an opportunity for orbital dynamical and habitability studies for planets in the very early stages of their evolution. Here, we calculate the evolution of the Habitable Zone of the system through time, including the pre-main-sequence phase that the system currently resides in. We discuss the planetary atmospheric processes occurring for an Earth-mass planet during this transitional period, and provide calculations of the climate state convergence age for both volatile rich and poor initial conditions. We present results of an orbital dynamical analysis of the AU Mic system that demonstrate the rapid eccentricity evolution of the known planets, and show that terrestrial planets within the Habitable Zone of the system can retain long-term stability. Finally, we discuss follow-up observation prospects, detectability of possible Habitable Zone planets, and how the AU Mic system may be used as a template for studies of planetary habitability evolution.

Exciting Mutual Inclination in Planetary Systems with a Distant Stellar Companion: The Case of Kepler-108

We study the excitation of mutual inclination between planetary orbits by a novel secular-orbital resonance in multi-planet systems perturbed by binary companions, which we call “ivection.” The ivection resonance happens when the nodal precession rate of the planet matches a multiple of the orbital frequency of the binary, and its physical nature is similar to the previously studied evection resonance. Capture into an ivection resonance requires encountering the resonance with slowly increasing nodal precession rate, and it can excite the mutual inclination of the planets without affecting their eccentricities. We discuss the possible outcomes of ivection resonance capture, and we use simulations to illustrate that it is a promising mechanism for producing the mutual inclination in systems where planets have significant mutual inclination but modest eccentricity, such as Kepler-108. We also find an apparent deficit of multi-planet systems that would have a nodal precession period comparable to the binary orbital period, suggesting that ivection resonance may inhibit formation of or destablize multi-planet systems with an external binary companion.

3. Beautiful theories, ugly facts

‘Beautiful theories, ugly facts’ evaluates the theories on planetary systems, particularly the Solar System. In 1734, the Swedish polymath Emmanuel Swedenborg proposed that the Sun and all the planets condensed out of the same ball of gas, in what is probably the earliest statement of the nebular hypothesis. The nebular hypothesis entered something close to its modern form in the hands of the French mathematician Pierre-Simon Laplace, who in 1796 made the clear connection to Newtonian gravity. The angular momentum problem and the structure of a protoplanetary disk, the formation of rocky cores, and the gravitational accretion of gas in the disk also come under this topic.

4. What are planets made of?

‘What are planets made of?’ assesses what planets are made of, beginning by looking at the life cycle of stars, and the kinds of stars which populate the Universe. Although the first stars of the Universe could not have formed planetary systems, the process did not take long to get under way. The Milky Way galaxy formed not long after the Big Bang and has been building its stock of heavy elements ever since. Thus, our Solar System incorporates ingredients from a mix of myriad expired stars, most of which have been processed multiple times through short-lived stars.

1. Beginnings

‘Beginnings’ discusses the general processes that form planetary systems, particularly the Solar System. Most of the Universe is made of a mysterious substance called ‘dark matter’, and an even more mysterious substance called ‘dark energy’. After the birth of the Universe in the Big Bang, the tiny bits of stardust which have accumulated contain the heavier elements (baryonic matter) that make it possible to form beings like ourselves, and the planets on which we live. We mustn't forget the importance of the formation of protostars, as well as gas and ice giant planets, the evolution of the proto-Sun, and the formation of inner rocky planets.

2. Creation revealed

‘Creation revealed’ examines key observations on planetary systems. Astronomers at first could probe the Universe only through the medium of visible light. In the early 1600s, the invention of the telescope allowed the Universe to be observed in much greater detail. With the discovery of ‘heat rays’, the seeds of infrared astronomy were planted. Meanwhile, throughout the course of the nineteenth century, one of the grandest unifications in physics was accomplished. It was discovered that the forces of electricity and magnetism were in fact different aspects of the same phenomenon: electromagnetism. Other important topics include blackbody radiation; infrared observations of young stellar objects; and the Atacama Large Millimeter/Submillimeter Array (ALMA).

Planetary Systems: A Very Short Introduction

Planetary Systems: A Very Short Introduction takes the reader on a journey through time and space, exploring how planetary systems such as ours form and evolve, and the conditions under which life may arise. Not long ago, the Solar System was the only example of a planetary system that we knew. Now, we know of thousands of planetary systems, and have even been able to observe the moment of their birth. This VSI reveals the astonishing variety of planetary systems out there. It explores the insights gained about these other worlds from a new generation of telescopes.