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Title: The California-Kepler Survey V. Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced
Author: Lauren M. Weiss, Geoffrey W. Marcy, Erik A. Petigura, Benjamin J. Fulton, Andrew W. Howard, Joshua N. Winn, Howard T. Isaacson, Timothy D. Morton, Lea A. Hirsch, Evan J. Sinukoff, Andrew Cumming, Leslie Hebb, Phillip A. Cargile

We have established precise planet radii, semi-major axes, incident stellar fluxes, and stellar masses for 909 planets in 355 multi-planet systems discovered by Kepler. We find that planets within a single multi-planet system tend to be closer in size than planets drawn randomly from the collection of multi-planet systems. This is true even when considering systems with similar host stars; we find, at most, a weak correlation between planet radius and stellar mass. Evidently, it is not the stellar mass but some other property or process that enforces the similarity of planet sizes. When adjacent planets in a multi-planet system are not similar in size, the inner planet is smaller in 656% of cases. The tendency for the inner planet to be smaller is especially pronounced when the inner planet has a short period (\lesssim 10 days) or equivalently, high radiation flux (\gtrsim 150 times the Earth's insolation). This could be the result of photoevaporation. We also find that adjacent planets within a given system tend to be spaced in a regular geometric progression, with a typical semi-major axis ratio of 1.5. Using empirical mass-radius relationships, we estimate the mutual Hill separations of planet pairs. We find that 93% of the planet pairs are at least 10 mutual Hill radii apart, and that a spacing of 10-30 mutual Hill radii is most common.

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Unexpected Classification of Exoplanets Discovered

Since the mid-1990s, when the first planet around another sun-like star was discovered, astronomers have amassed an ever-expanding collection of nearly 3,500 confirmed exoplanets.
In a new Caltech-led study, researchers have classified these exoplanets in much the same way that biologists identify new animal species and found the majority of exoplanets fall into two distinct groups: rocky Earth-like planets and larger mini-Neptunes. The team used data from W. M. Keck Observatory and NASA's Kepler mission.

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NASA Releases Kepler Survey Catalogue with Hundreds of New Planet Candidates

NASA's Kepler space telescope team has released a mission catalogue of planet candidates that introduces 219 new planet candidates, 10 of which are near-Earth size and orbiting in their star's habitable zone, which is the range of distance from a star where liquid water could pool on the surface of a rocky planet.
This is the most comprehensive and detailed catalogue release of candidate exoplanets, which are planets outside our solar system, from Kepler's first four years of data. It's also the final catalogue from the spacecraft's view of the patch of sky in the Cygnus constellation.
With the release of this catalogue, derived from data publicly available on the NASA Exoplanet Archive, there are now 4,034 planet candidates identified by Kepler. Of which, 2,335 have been verified as exoplanets. Of roughly 50 near-Earth size habitable zone candidates detected by Kepler, more than 30 have been verified.

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New Branch in Exoplanet Family Tree

Planets are born out of swirling disks of gas and dust called protoplanetary disks. The disks give rise to giant planets like Jupiter as well as smaller planets mostly between the size of Earth and Neptune. Researchers using data from the W. M. Keck Observatory and NASA's Kepler mission discovered that these smaller planets can be cleanly divided into two size groups: the rocky Earth-like planets and super-Earths, and the gaseous mini-Neptunes.
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Hubble's Tale of Two Exoplanets: Nature vs. Nurture

Astronomers once thought that the family of planets that orbit our sun were typical of what would eventually be found around other stars: a grouping of small rocky planets like Earth huddled close to their parent star, and an outer family of monstrous gaseous planets like Jupiter and Saturn.
But ever since the discovery of the first planet around another star (or exoplanet) the universe looks a bit more complicated - if not downright capricious. There is an entire class of exoplanets called "hot Jupiters." They formed like Jupiter did, in the frigid outer reaches of their planetary system, but then changed Zip code! They migrated inward to be so close to their star that temperatures are well over 1,000 degrees Fahrenheit.

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Title: No snowball on habitable tidally locked planets
Author: Jade Checlair, Kristen Menou, Dorian S. Abbot

The TRAPPIST-1, Proxima Centauri, and LHS 1140 systems are the most exciting prospects for future follow-up observations of potentially inhabited planets. All orbit nearby M-stars and are likely tidally locked in 1:1 spin-orbit states, which motivates the consideration of the effects that tidal locking might have on planetary habitability. On Earth, periods of global glaciation (snowballs) may have been essential for habitability and remote signs of life (biosignatures) because they are correlated with increases in the complexity of life and in the atmospheric oxygen concentration. In this paper we investigate the snowball bifurcation (sudden onset of global glaciation) on tidally locked planets using both an energy balance model and an intermediate-complexity global climate model. We show that tidally locked planets are unlikely to exhibit a snowball bifurcation as a direct result of the spatial pattern of insolation they receive. Instead they will smoothly transition from partial to complete ice coverage and back. A major implication of this work is that tidally locked planets with an active carbon cycle should not be found in a snowball state. Moreover, this work implies that tidally locked planets near the outer edge of the habitable zone with low CO2 outgassing fluxes will equilibrate with a small unglaciated substellar region rather than cycling between warm and snowball states. More work is needed to determine how the lack of a snowball bifurcation might affect the development of life on a tidally locked planet.

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Volunteers spot four super-Earths orbiting sun-like star

This new planetary system, 597 light years away in the constellation Aquarius, has dips from four different planets. The planets take only 3 to 13 Earth days to orbit their star. The smallest is just shy of twice Earths size, and the largest is 2.74 times as big.
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20 ExoWorlds are now available for naming proposals

The NameExoWorlds contest, organised by the IAU and Zooniverse, is now entering its next stage. The 20 most popular ExoWorlds have been made available for naming proposals from registered clubs and non-profit organisations.
Although people have been naming celestial objects for millennia, the IAU has the task of assigning scientifically recognised names to newly discovered celestial bodies by its member countries. The NameExoWorlds contest provides not only the first opportunity for the public to name exoplanets, but also, for the first time in centuries, to give popular names to some stars - those that have known exoplanets in orbit around them.

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Spitzer, OGLE Spot Planet Deep Within Our Galaxy

NASA's Spitzer Space Telescope has teamed up with a telescope on the ground to find a remote gas planet about 13,000 light-years away, making it one of the most distant planets known.
The discovery demonstrates that Spitzer - from its unique perch in space - can be used to help solve the puzzle of how planets are distributed throughout our flat, spiral-shaped Milky Way galaxy. Are they concentrated heavily in its central hub, or more evenly spread throughout its suburbs?

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NASA's Spitzer Spots Planet Deep Within Our Galaxy

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Title: Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars
Author: Lewis C. Roberts, Jr., Andrei Tokovinin, Brian D. Mason, Reed L. Riddle, William I. Hartkopf, Nicholas M. Law, Christoph Baranec

We discuss two multiple star systems that host known exoplanets: HD 2638 and 30 Ari B. Adaptive optics imagery revealed an additional stellar companion to both stars. We collected multi-epoch images of the systems with Robo-AO and the PALM-3000 adaptive optics systems at Palomar Observatory and provide relative photometry and astrometry. The astrometry indicates that the companions share common proper motion with their respective primaries. Both of the new companions have projected separations less than 30 AU from the exoplanet host star. Using the projected separations to compute orbital periods of the new stellar companions, HD 2638 has a period of 130 yrs and 30 Ari B has a period of 80 years. Previous studies have shown that the true period is most likely within a factor of three of these estimated values. The additional component to the 30 Ari makes it the second confirmed quadruple system known to host an exoplanet. HD 2638 hosts a hot Jupiter and the discovery of a new companion strengthens the connection between hot Jupiters and binary stars. We place the systems on a color-magnitude diagram and derive masses for the companions which turn out to be roughly 0.5 solar mass stars.

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