Planets form in protoplanetary discs surrounding newly formed stars, where dust
grains clump and form km-sized planetesimals. As the dust grains start to grow to mm-cm
sized pebbles, they drift inwards very rapidly due to the gas drag within the disc. As the
pebbles drift inwards towards the hotter disc regions, they can evaporate and enrich the
inner disc with their vapor to largely...
Exoplanetary demographic statistics shows that super-Earths are the most
abundant exoplanets, orbiting approximately every other solar-like star. In our own solar system, however, the inner terrestrial planets did not grow beyond Earth in mass. A possible explanation could be provided by the presence of gas giants in our own system, that might have influenced the growth of the inner...
Understanding and testing possible formation mechanisms is crucial to
understanding the history of planetary systems. While observationally there is a prevalence of evenly sized and spaced systems (“peas-in-a-pod” - Weiss et. al 2018), there is also an observational trend between the presence of a Cold Jupiter and inner system non-uniformity (He et. al 2023). Recent work explored in Best et....
Microlensing surveys are sensitive to giant planets on 1—10 au orbits typically around 0.05–0.8 solar-mass hosts. In Zhang (2025; ApJL 995, L55), I performed a statistical analysis of ~80 giant planets detected by microlensing. I show that there exists a statistically significant truncation to the giant-planet mass-ratio distribution at q~0.02, above which the occurrence rate density sharply...
The growth of outer gas giants naturally destabilizes the orbits of nearby
planetesimals. These are scattered in all directions -- many are ejected, but some are scattered inward toward the growing rocky planets (if they exist). In the Solar System, both the C-type asteroids and water delivery to Earth can be explained as a simple byproduct of Jupiter and Saturn's growth. I will explain the...
In the coming decades, the search for life beyond the Solar system will begin in earnest. But how should we choose the best targets for that search? In order to maximiseour chances of success, it is important to consider the many and various factors that could render one planet more or less habitable than another. In this talk, I will describe how dynamical simulations can reveal the role that...
Whether or how giant planets affect the formation and orbital assembly of terrestrial planets has been a longstanding question in planetary astrophysics. In our solar system, Jupiter and Saturn have played a fundamental role in defining the extent and architecture of the asteroid belt, and have been crucial to promoting terrestrial planet formation by confining the process to interior to 1.9...
Jupiter, the archetype of cold giant planets, played a key role in controlling the transport of volatile materials like water and organics between the inner and outer Solar System since its birth. While an extensive body of work highlights how its formation and migration dynamically excites the surrounding planetesimal disk, very few studies investigate the global collisional implications of...
ALMA’s observations of circumstellar discs highlight the wide variety of properties and morphologies of their gas and dust. In particular, the widespread presence of rings and gaps in the dust component of discs is generally considered the direct signature of massive planets forming therein. These gaps and rings often appear at tens of au from the host star, raising the question of whether...
Transiting extrasolar comets have been detected for four decades. Their gaseous components are revealed through spectroscopy, while their dusty tails produce characteristic photometric signatures - remarkably consistent with predictions made 25 years ago. Recently, automated searches for exocometary transits in Kepler and TESS datasets have led to the identification of several dozen new...
Giant planets are key architects of planetary systems: they sculpt protoplanetary disks, shape the formation and long-term stability of inner rocky worlds, and likely mediate the delivery of volatiles needed for habitable conditions. Yet the occurrence, architectures, and dynamical impact of cold Jupiters remain only loosely constrained. Our main detection techniques each probe a limited and...
The dependence of cold Jupiter occurrence on host-star parameters (e.g. mass or metallicity) remains a key question in giant-planet demographics. In particular, current statistics for intermediate-mass stars (1.5 - 4 M⊙) can still be improved, as the number of reported planets around these targets is low (<250) and affected by stellar-variability false positives (e.g. oscillations). I will...
While we know with great detail the magnetic field of Jupiter and several works have successfully reproduced several features, including the atmospheric winds, the only studies for giant exoplanet magnetism rely on scaling laws. We present a novel approach, as shown in Elias-López et al. 2025, A&A, 696: we run 3D dynamo simulations (solving the anelastic MHD equations with MagIC) with the...
At least half the stars in the galaxy are orbited by planets smaller than Neptune and orbital periods less than a year. The demographics of these mini-Neptunes, super-Earths, and terrestrial exoplanets are constrained by transit and radial velocity surveys, often in synergy. In this talk I will give an overview of the statistical properties of these inner planets and planetary systems. I will...
Giant planets are expected to predominantly form beyond the water ice line and occasionally undergo inward migration. Unlike hot Jupiters, which can result from high-eccentricity tidal migration, longer-period giant planets are in many ways more challenging to explain because they reside outside the tidal influence of their host stars. Orbital eccentricities offer important clues about the...
Humanity's search for Earth analogs is enriched by the fact that Earth-like planets do not form in isolation. The interplay between Earth-like planets and their siblings is an emerging new research topic. A prevalent pattern that represents one of the most common modes of planet formation is that planets in the same system tend to have similar sizes and regular orbital spacing, like...
We learned from NASA’s Kepler mission that small inner planets are common around Sun-like stars (50–100%). Separately, ground-based radial velocity (RV) surveys have shown that long-period gas giants are somewhat rare (~16%). To find the conditional occurrence of distant giants in systems with a close-in small planet, I conducted the Distant Giants Survey, a three-year RV search for giant...
Unveiling the architecture of planetary systems is crucial for understanding how planets form and migrate. In this talk, I investigate the occurrence rate of Cold Jupiters (CJs) in systems that host inner Small Planets (SPs), aimed at understanding if giant planets shield or disrupt their smaller inner siblings. I will present results based on an extensive dataset of over 5000 radial...
The connection between outer gas giants and inner super-Earths reflects their formation and evolutionary history. Past work exploring this link has suggested a tentative positive correlation between these two populations, but these studies were limited by small sample sizes and in some cases sample biases. In this talk I will highlight my recent collaborations with Eve Lee where we take a new...
The discovery of planets orbiting at less than 1 au from their host star and less massive than Saturn in various exoplanetary systems revolutionized our theories of planetary formation. The fundamental question is whether these close-in low-mass planets could have formed in the inner disc interior to 1 au, or whether they formed further out in the planet-forming disk and migrated inwards....
The presence of cold Jupiters may strongly influence the formation and survival of inner low-mass companions, yet the observational evidence remains incomplete. Radial-velocity (RV) surveys provide the most direct approach to probe this connection, enabling searches for short-period sub-Neptunes and super-Earths in systems already known to host long-period giants. Although high-precision,...
It is believed that Jupiter played a significant role in the history of the Solar System’s terrestrial planets, likely affecting their mass, volatile budget and orbits. The detection of complete Solar System analogs around other stars is not currently within reach, yet we can still learn about the history of both ours and other systems’ architecture by investigating the "outer giant planet -...
Despite the great advancements made in the exoplanetary field over the last decades, it is not yet clear whether our Solar System's architecture is common. To shed light on this topic, the GAPS team in 2012 started a program aimed at monitoring 16 systems known to host giant planets on a Jupiter-like orbit to detect potential inner smaller companions. After 13 years of observations and a few...
Studies from recent years have reached different conclusions regarding how frequently super-Earths are accompanied by long-period giant planets and vice versa. This relation has been predicted to be mass dependent by planet-formation models. We investigate that as the origin of the discrepancy using a radial velocity sample: the California Legacy Survey. We perform detection completeness...
A defining feature of our Solar System is the presence of multiple giant planets beyond the snowline, yet this architecture appears to be uncommon: only ~6% of stars are known to host Jupiter-like planets between 1–10 AU. Moreover, the Jovian analogs we do find are typically closer in and more eccentric than Jupiter or Saturn, raising questions about the long-term survivability of inner...
We present the identification and characterization on new scaled Solar-System analog, based on intensive radial velocity monitoring performed with HARPS-N at TNG and additional literature datasets. The system includes a previously known giant planet in a moderately wide orbit, a newly discovered one in a Jupiter-like orbit, and additional low-mass planet candidates from TESS light curves and...
Long-period planets play an important role in their systems, as they can interact with material and small mass planets, and modify their orbits. These modifications can result in dynamical instabilities within the system. One such system is that of Tabby’s star. Its Kepler light curve shows unusual dips with no clear periodicity or cause. The most plausible explanation is a family of...
The growing field of comparative exoplanetology increasingly relies on the synergistic combination of detection techniques with complementary sensitivity domains to fully characterize planetary system architectures. Yet, estimates of exoplanet occurrence rates often remain constrained by the detection capabilities of individual instruments, surveys, or techniques. The resulting heterogeneity...
The exact role of outer giant planets in the formation of super-Earths and sub-Neptunes remains unclear. Observationally, measuring occurrence rates of these planet populations brings crucial insights, and RV surveys play a major role in this effort. While large sample sizes are key to obtain precise occurrence rates, strong detection limits on each system are equally important. Commonly, RV...
The dynamical stability of planets with outer giant companions depends on the parameters of the outer companion(s). The inclusion of constraints from stability in the calculation of detection limits can in principle help rule out regions of parameter space where inner planets could not exist in individual systems. We will present preliminary results from a project where, using a synthetic...
PLATO, the 3rd Medium class ESA’s mission, is being built to detect and characterize extrasolar planets by photometrically monitoring a large number of stars. PLATO will detect small planets around bright stars, including terrestrial planets in the habitable zone of Sun-like stars. PLATO will also study the (host) stars using asteroseismology, allowing us to determine the stellar properties...
While Gaia DR3 itself contained limited exoplanet results, Gaia DR4 is expected to include the discovery, orbits, and masses of thousands of exoplanets. I will briefly review exoplanet results of Gaia DR3, including from its combination with Hipparcos. I will discuss the reasons for the continued value of Hipparcos measurements in the face of higher Gaia precision, and the scaling of Gaia...
In 2029, the European Extremely Large Telescope (ELT) will shine its first light on the sky. The high angular resolution and large collecting capacity, combined with the extreme sensitivity and versatility of the ELT's instruments, will allow unprecedented observations of worlds orbiting stars other than the Sun. It will provide a unique opportunity to address fundamental questions related to...
One of the primary goals of the astronomical community in the next few decades is to characterize temperate terrestrial exoplanets to search for life. To address this challenge, the US Astro2020 Decadal survey recommended the pursuit of a technical and scientific study for the Habitable Worlds Observatory (HWO), an ultraviolet/visible/ near-infrared (UV/VIS/NIR) “high-contrast direct imaging...
A Galactic Census of Exoplanets from the Nancy Grace Roman Space Telescope Abstract: The Nancy Grace Roman Space Telescope (Roman) is NASA’s next major
astrophysics mission, scheduled for launch in late 2026. Roman will feature a wavelength range, aperture, and angular resolution comparable to the Hubble Space Telescope but with approximately 100 times the field of view and 1,000 times the...
With its location from ASTEP (Antarctic Search for Transiting Exoplanets) has been contributing to the discovery of many interacting planetary systems on long periods (tens to hundreds of days). The chopping signal from the planet-planet interactions can yield significant TTVs that can be measured with no ambiguity, allowing constraints on the planetary mass. The extremely small densities of...
Radial velocity (RV) surveys have revealed a rich population of cold Jupiters and Solar System analogues, but the long-standing degeneracy between planet mass and orbital inclination continues to limit what we can infer about their true architectures. The upcoming Gaia Data Release 4 (DR4), expected within the next year, will change that by providing epoch astrometry for more than a billion...
Perhaps the greatest mysteries of gas giant and brown dwarf formation reside at the youngest (few Myr) ages, when such objects are being born in their natal circumstellar disks and the corresponding theoretical models predict an enormous range of luminosities. In practice, this means that any observations of such objects help open a window into the earliest stages, and increasing the current...
The atmospheric characterization of giant exoplanets has so far relied primarily on transit spectroscopy, a technique intrinsically biased toward short-period planets and therefore largely inaccessible for cold, long-period giants. High-contrast imaging (HCI) fills this gap by providing a complementary route to study the atmospheres of wide-orbit giant planets directly. However, conducting...
The study of Gyr-old cold gas giants is on the verge of a revolution: the forthcoming Gaia data releases will precipitate their detection, and, thanks to the ESA/ARIEL space mission, the number of such Jupiter-like planets with well-characterized atmospheric composition will also skyrocket in the years to come. Interpreting the results of these forefront campaigns requires a significant leap...
