23 research outputs found
Interior and Evolution of the Giant Planets
The giant planets were the first to form and hold the key to unveiling the
solar system's formation history in their interiors and atmospheres.
Furthermore, the unique conditions present in the interiors of the giant
planets make them natural laboratories for exploring different elements under
extreme conditions. We are at a unique time to study these planets. The
missions Juno to Jupiter and Cassini to Saturn have provided invaluable
information to reveal their interiors like never before, including extremely
accurate gravity data, atmospheric abundances and magnetic field measurements
that revolutionised our knowledge of their interior structures. At the same
time, new laboratory experiments and modelling efforts also improved, and
statistical analysis of these planets is now possible to explore all the
different conditions that shape their interiors. We review the interior
structure of Jupiter, Saturn, Uranus and Neptune, including the need for
inhomogeneous structures to explain the data, the problems unsolved and the
effect that advances in our understanding of their internal structure have on
their formation and evolution.Comment: Review paper published in the special issue "Remote Sensing
Observations of the Giant Planets
Rocky sub-Neptunes formed by pebble accretion: Rain of rocks from polluted envelopes
Sub-Neptune planets formed in the protoplanetary disk accreted
hydrogen-helium (H,He) envelopes. Planet formation models of sub-Neptunes
formed by pebble accretion result in small rocky cores surrounded by polluted
H,He envelopes where most of the rock (silicate) is in vapor form at the end of
the formation phase. This vapor is expected to condense and rain-out as the
planet cools. In this Letter we examine the timescale for the rainout and its
effect on the thermal evolution. We calculate the thermal and structural
evolution of a 10 Earth masses planet formed by pebble accretion, taking into
account material redistribution from silicate rainout (condensation and
settling) and from convective mixing. We find that the duration of the rainout
in sub-Neptunes is on Gyr timescale and varies with envelope mass: planets with
envelopes below 0.75 Earth mass rainout into a core-envelope structure in less
than 1 Gyr, while planets in excess of 0.75 Earth mass of H,He preserve some of
their envelope pollution for billions of years. The energy released by the
rainout inflates the radius with respect to planets that start out from a plain
core-envelope structure. This inflation would result in estimates of the H,He
contents of observed exoplanets based on the standard core-envelope structure
to be too high.We identify a number of planets in the exoplanet census where
rainout may operate, which would result in their H,He contents to be
overestimated by up to a factor two. Future accurate age measurements by the
PLATO mission may allow the identification of planets formed with polluted
envelopes.Comment: accepted to A&A Letter
How planets grow by pebble accretion. III. Emergence of an interior composition gradient
During their formation, planets form large, hot atmospheres due to the
ongoing accretion of solids. It has been customary to assume that all solids
end up at the center constituting a "core" of refractory materials, whereas the
envelope remains metal-free. Recent work, as well as observations by the JUNO
mission, indicate however that the distinction may not be so clear cut. Indeed,
small silicate, pebble-sized particles will sublimate in the atmosphere when
they hit the sublimation temperature (T ~ 2,000 K). In this paper we extend
previous analytical work to compute the properties of planets under such a
pebble accretion scenario. We conduct 1D numerical calculations of the
atmosphere of an accreting planet, solving the stellar structure equations,
augmented by a non-ideal equation of state that describes a
hydrogen/helium-silicate vapor mixture. Calculations terminate at the point
where the total mass in metal equals that of the H/He gas, which we numerically
confirm as the onset of runaway gas accretion. When pebbles sublimate before
reaching the core, insufficient (accretion) energy is available to mix dense,
vapor-rich lower layers with the higher layers of lower metallicity. A gradual
structure in which Z decreases with radius is therefore a natural outcome of
planet formation by pebble accretion. We highlight, furthermore, that (small)
pebbles can act as the dominant source of opacity, preventing rapid cooling and
presenting a channel for (mini-)Neptunes to survive in gas-rich disks.
Nevertheless, once pebble accretion subsides, the atmosphere rapidly clears
followed by runaway gas accretion. We consider atmospheric recycling to be the
more probable mechanisms that have stalled the growth of these planets'
envelopes.Comment: Accepted for publication in A&
Planetary Exploration Horizon 2061 Report, Chapter 3: From science questions to Solar System exploration
This chapter of the Planetary Exploration Horizon 2061 Report reviews the way
the six key questions about planetary systems, from their origins to the way
they work and their habitability, identified in chapter 1, can be addressed by
means of solar system exploration, and how one can find partial answers to
these six questions by flying to the different provinces to the solar system:
terrestrial planets, giant planets, small bodies, and up to its interface with
the local interstellar medium. It derives from this analysis a synthetic
description of the most important space observations to be performed at the
different solar system objects by future planetary exploration missions. These
observation requirements illustrate the diversity of measurement techniques to
be used as well as the diversity of destinations where these observations must
be made. They constitute the base for the identification of the future
planetary missions we need to fly by 2061, which are described in chapter 4.
Q1- How well do we understand the diversity of planetary systems objects? Q2-
How well do we understand the diversity of planetary system architectures? Q3-
What are the origins and formation scenarios for planetary systems? Q4- How do
planetary systems work? Q5- Do planetary systems host potential habitats? Q6-
Where and how to search for life?Comment: 107 pages, 37 figures, Horizon 2061 is a science-driven, foresight
exercise, for future scientific investigation
A massive hot Jupiter orbiting a metal-rich early-M star discovered in the TESS full frame images
Observations and statistical studies have shown that giant planets are rare
around M dwarfs compared with Sun-like stars. The formation mechanism of these
extreme systems remains under debate for decades. With the help of the TESS
mission and ground based follow-up observations, we report the discovery of
TOI-4201b, the most massive and densest hot Jupiter around an M dwarf known so
far with a radius of and a mass of ,
about 5 times heavier than most other giant planets around M dwarfs. It also
has the highest planet-to-star mass ratio () among such
systems. The host star is an early-M dwarf with a mass of $0.61\pm0.02\
M_{\odot}0.63\pm0.02\ R_{\odot}0.52\pm 0.08$ dex). However, interior
structure modeling suggests that its planet TOI-4201b is metal-poor, which
challenges the classical core-accretion correlation of stellar-planet
metallicity, unless the planet is inflated by additional energy sources.
Building on the detection of this planet, we compare the stellar metallicity
distribution of four planetary groups: hot/warm Jupiters around G/M dwarfs. We
find that hot/warm Jupiters show a similar metallicity dependence around G-type
stars. For M dwarf host stars, the occurrence of hot Jupiters shows a much
stronger correlation with iron abundance, while warm Jupiters display a weaker
preference, indicating possible different formation histories.Comment: 21 pages, 11 figures, 4 tables, submitted to A
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planetâs birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25â7.8 ÎŒm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10â100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed â using conservative estimates of mission performance and a full model of all significant noise sources in the measurement â using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL â in line with the stated mission objectives â will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
Enabling planetary science across light-years. Ariel Definition Study Report
Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution
Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution
The low luminosity of Uranus is a long-standing challenge in planetary science. Simple adiabatic models are inconsistent with the measured luminosity, which indicates that Uranus is non-adiabatic because it has thermal boundary layers and/or conductive regions. A gradual composition distribution acts as a thermal boundary to suppress convection and slow down the internal cooling. Here we investigate whether composition gradients in the deep interior of Uranus can explain its low luminosity, the required composition gradient, and whether it is stable for convective mixing on a timescale of some billion years. We varied the primordial composition distribution and the initial energy budget of the planet, and chose the models that fit the currently measured properties (radius, luminosity, and moment of inertia) of Uranus. We present several alternative non-adiabatic internal structures that fit the Uranus measurements. We found that convective mixing is limited to the interior of Uranus, and a composition gradient is stable and sufficient to explain its current luminosity. As a result, the interior of Uranus might still be very hot, in spite of its low luminosity. The stable composition gradient also indicates that the current internal structure of Uranus is similar to its primordial structure. Moreover, we suggest that the initial energy content of Uranus cannot be greater than 20% of its formation (accretion) energy. We also find that an interior with a mixture of ice and rock, rather than separated ice and rock shells, is consistent with measurements, suggesting that Uranus might not be âdifferentiatedâ. Our models can explain the luminosity of Uranus, and they are also consistent with its metal-rich atmosphere and with the predictions for the location where its magnetic field is generated