This is an excerpt from my post on Planet Hunters:

In the 10th paper(!) from the Planet Hunters citizen science program, a stupendously great number, we independently discovered 10 new planet candidates in the K2 *Kepler* data (Campaigns 1 and 3). However, simply discovering them was not the main goal of the new paper. We wanted to explore their neighborhoods.

The environment in which a star is created has a large and enduring impact on how planets form. Under standard planet formation theory, when a star collapses, it forms a disk, called a protoplanetary disk, due to the conservation of angular momentum. It is in this disk of material orbiting the infant star that planets are formed. Solid material clumps together and forms planets. In the inner disk, the material is hotter, so the only solid material is metallic or rocky. In the outer disk, the material is cooler, which allows molecules like ice and frozen ammonia to clump together as well. This extra solid mass in the outer solar system allows the outer planet to grow bigger and eventually capture gas. Interactions between all these planets can then jumble them around.

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This is an excerpt from my post on Astrobites.org:

Title:  The Geology of Pluto and Charon Through the Eyes of New Horizons
Authors: Jeffrey M. Moore, William B. McKinnon, John R. Spencer, et al., including the New Horizons team
First Author’s Institution: NASA Ames Research Center
Status: Published in Science

The New Horizons mission to Pluto and Charon, launched when Pluto was still officially a planet, gave us the best images of the dwarf planet and its largest moon that we might ever see in our lifetime.  Less than a year after its July 14, 2015 fly-by, the New Horizons team has published a preliminary geological examination of the two bodies.  Predicted to have a rather boring landscape unchanged for billions of years, the surfaces of Pluto and Charon have been discovered to be surprisingly complex and, for Pluto, still geologically active!

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This is an excerpt from my post on Astrobites.org:

Title: Could life have arrived on Earth from another planet? Is this even a falsifiable hypothesis?
Authors: Henry W. Lin and Abraham Loeb
First Author’s Institution: Harvard College
Status: Published in ApJ Letters

The origin of life on Earth might not have been in a primordial pool of organic goo, but rather, according to the panspermia hypothesis, it may have come from another planet in perhaps another solar system.  Panspermia is one of the more popular alternative theories for the origins of life on Earth, but is it really testable?  If panspermia isn’t falsifiable, if you can’t make predictions that allow the theory to be tested, it’s not science.    (“A theory that explains everything, explains nothing.” – Karl Popper.)

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This is an excerpt from my post on Astrobites.org:

Title: Terrestrial planets across space and time
Authors: Erik Zackrisson, Per Calissendorff, Juan González, Andrew Benson, Anders Johansen, and Markus Janson
First Author’s Affiliation: Uppsala University, Sweden
Paper status: Submitted for review

When I was born in 1989, there were just nine planets known throughout the entire universe (poor Pluto).  Now there are between 1600 and 2100 confirmed exoplanets (depending on whom you ask).  All these planets are located in a small region of our home galaxy (the Milky Way). However, there are billions of other galaxies. Therefore, you might ask just how many do we expect throughout the entire universe?  This paper attempts to create a “cosmic inventory” of terrestrial (rocky) planets by combining the fields of cosmology, galaxy formation, and exoplanet science to estimate the number of planets around FGKM stars.  (To distinguish stars of different masses, astronomers give them different letters.  The pneumonic, from most massive stars to least massive, is “Oh Be A Fine Girl/Guy, Kiss Me”.  For reference, the Sun is a G-dwarf star.)

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This is an excerpt from my post on Astrobites.org:

Title: Dynamical considerations for life in multihabitable planetary systems
Authors: Jason H. Steffen and Gongjie Li
First Author’s Institution: University of Nevada, Las Vegas, Department of Physics and Astronomy
Status: Accepted to ApJ

We would all like to have good relations with our neighbors, but just how friendly are planetary neighbors?  Could they make your life a disaster, or could they be your best friends?  The authors of this paper explore two aspects of this neighborly relationship:  1) can a planet’s neighbor cause it to tip over more easily, which would cause violent climate change, and 2) can it seed its neighbor with life?

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This is an excerpt from my post on Planet Hunters:

We’re happy to announce the discovery of a new planet discovered by Planet Hunters volunteers, which is now published in The Astrophysical Journal. You can read the article for free on the arXiv here.

The star (PH3/Kepler-289/KOI-1353/KIC 7303287) is young and Sun-like. Two planets in the system, with periods of 35 and 126 days, had been previously validated statistically, the outer planet being a gas giant. However, Planet Hunters volunteers discovered a third transit signal between these two planets at a period of 66 days (PH3 c).

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This is an excerpt from my post on Planet Hunters:

Planet Hunters will soon start work on a new, important question in the field of exoplanets: how common are planets around other stars? This question has become a hot topic in exoplanets, but Planet Hunters has one major, unique advantage. Planet Hunters are sensitive to planets with just one or two transits. The automated computer algorithms require three or more transits; otherwise, they would be overloaded with spurious signals. This allows Planet Hunters to explore much longer periods than the rest of the field.

Until now, Planet Hunters have been looking for planets one quarter at a time. This has been successful in discovering more than 60 new planet candidates and two new confirmed planets (and counting). However, this one-quarter-at-a-time method doesn’t let us figure out how common planets truly are.

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This is an excerpt from my post on Planet Hunters:

We at Planet Hunters are happy to announce the acceptance of the PHVI paper to the Astronomical Journal, in which 14 new planet candidates were discovered. All of these new planet candidates are located far from their host stars. In fact, seven of them lie in their host star’s habitable zone. Unfortunately, all of these planets are too large to be Earth-like.

Two of the new planet candidates are in multiple candidate systems. One of them, the new candidate orbiting KOI-351, is the seventh planet candidate orbiting its host star. Planet Hunters actually detected three new candidates around this star when KOI-351 was only known to have three candidates, showing how great the Planet Hunters can be in discovering multiple planet systems. The planets in KOI-351 also show strong gravitational interactions between the planets, which helps to confirm them as true planets. The gravity from some planets in the system causes other planets to transit before or after what we would otherwise expect, called transit timing variations. In fact, the second-to-last planet transited a full day after we expected it would. Others in the exoplanet field have been working for over a year to determine the masses of these planets.

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