The cascading numbers of exoplanet discoveries raise questions about Over the last two decades, thousands of extrasolar planets have been discovered using a to derive a planetary mass-radius relationship as information on the as well as fits for radii solid colored lines). Thousands of transiting exoplanets have been discovered, but for most of these The mass-radius relation for sub-Neptune sized exoplanets. The resulting mass-radius relation is the solid blue line, and shaded blue region . Astrobites | All Rights Reserved | Supported by AAS | Designed by. We explore the nature of two regimes in the planetary mass-radius (M-R) relation. While the first detected exoplanets had relatively large masses and radii, consists of exoplanets queried from mephistolessiveur.info on March .. various compositions of the solid core on the predicted radii of the.
The planet with the shortest orbit is HD band is Earth's closest known rocky, and transiting, exoplanet. In Januarythe existence of a hypothetical super-Earth-mass ninth planet in the Solar System, referred to as Planet Ninewas proposed as an explanation for the orbital behavior of six trans-Neptunian objectsbut it is speculated to be instead an ice giant like Uranus or Neptune. A super-Earth's interior could be undifferentiated, partially differentiated, or completely differentiated into layers of different composition.
Researchers at Harvard Astronomy Department have developed user-friendly online tools to characterize the bulk composition of the super-Earths.
Favorite Astro Plots #4: Classifying Exoplanets
Within this range of radii the super-Earth Gliese d would have a surface gravity between 1. However, this planet is not known to transit its host star. The limit between rocky planets and planets with a thick gaseous envelope is calculated with theoretical models.
Calculating the effect of the active XUV saturation phase of G-type stars over the loss of the primitive nebula-captured hydrogen envelopes in extrasolar planets, it's obtained that planets with a core mass of more than 1. The actual empirical observations are giving similar results as theoretical models, as it's found that planets larger than approximately 1.
Geologic activity[ edit ] Further theoretical work by Valencia and others suggests that super-Earths would be more geologically active than Earth, with more vigorous plate tectonics due to thinner plates under more stress.
In fact, their models suggested that Earth was itself a "borderline" case, just barely large enough to sustain plate tectonics.
The planet's surface would be too strong for the forces of magma to break the crust into plates. Rather than evolving to a planet composed mainly of rock with a thin atmosphere, the small rocky core remains engulfed by its large hydrogen-rich envelope. The amount of the outermost layers that is lost depends on the size and the material of the planet and the distance from the star. Therefore, contrary to the terrestrial planets of the solar system, these super-Earths must have formed during the gas-phase of their progenitor protoplanetary disk.
For example, the black-body temperature of the Earth is Venus has a black-body temperature of only Magnetic field[ edit ] Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles.
Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths.
Planetary habitability and astrobiology According to one hypothesis,  super-Earths of about two Earth masses may be conducive to life. This category contains the most massive kind of planets and brown dwarfs. Some classification regards planets and brown dwarfs to be different. However, as is shown in the plot, brown dwarfs follow the same mass-radius relation as the most massive planets. The last transition is at 0.
Favorite Astro Plots #4: Classifying Exoplanets | The Planetary Society
Above this limit, the internal pressures are sufficiently high that its core will be able to ignite a hydrogen nuclear fusion chain reaction. Aside from classification, this mass-radius relation can also be used for forecasting. Through the past two decades, astronomers have discovered thousands of extrasolar worlds.
But most of these detections measure either the mass e.
Super-Earth - Wikipedia
The mass-radius relation allows us to predict the mass radius with the other measurements. Looking at data in this way leads to surprising implications. Brown dwarfs are merely high-mass Jupiters. Dwarf planets, like Pluto, are merely low-mass members of the same class containing the Earth. Perhaps the most surprisingly result is that the divide between Neptunian worlds and solid planets like the Earth occurs at just 2 Earth masses.
In particular, they find that a planet's radius alone provides a first-order estimate of its composition, specifically, the H2—He mass fraction.
There is some uncertainty in this limit. Recent space-based missions such as Kepler Borucki et al. Figure 1 provides a comparison of planets with measured radii and masses with theoretical mass—radius curves that we have generated for various simple planet compositions, including pure iron, Earth-like, Mercury-like, and pure silicate. Earth-like is defined as Another population of planets at a wide range of masses is consistent only with deeper H2—He envelopes.
The measured mass and radius values and references for the plotted planets are given in Table 2. However, it is not known which of these models if either is dominant in this radius range or whether this break reflects an actual difference in composition between planets smaller and larger than 2.
In Figure 2we plot the extrasolar planets against constant density curves. Earth-density green and Neptune-density blue curves are included. This large scatter makes it very difficult to fit any precise trends in radius with increasing mass. Known extrasolar planets plotted against constant density curves, including Earth's density green and Neptune's density blue. These exoplanets may potentially have a wide range of possible compositions and temperatures and a similarly wide range of possible gaseous envelopes, so models must be able to be adjusted accordingly.
Solid exoplanet models are important in both cases, since they may be used to model solid cores of planets with gaseous envelopes by applying a non-zero-pressure boundary condition at the core-envelope interface.
While there is a rich history of exoplanet structural modeling, there are a number of important areas which have yet to be investigated. For planets with gaseous envelopes, the effects of irradiation and atmospheric heating are poorly understood, and the degeneracies of envelope mass, envelope entropy, and core mass have not been explored in detail.
Moreover, the implications of the large scatter in the mass—radius distribution, particularly on the search for Earth-like planets, are only beginning to be addressed. For solid planets, equations of state for planetary materials at the pressures found in planets are subject to a degree of uncertainty, and different equation of state EOS models produce different results, which warrant analysis of the uncertainty in the modeled mass and radius values.
Our paper investigates the uncertainties and degeneracies in exoplanet modeling, particularly of planets with H2—He envelopes, in order to gain a better understanding of what is measurable in observed exoplanets. We compute mass—radius curves over the range of 0. We study planets with both "Earth-like" cores and ice cores, which may both be of interest depending on whether planets with gaseous envelopes form beyond the snow line.
We also compute mass—radius curves for various compositional profiles for solid planets.