Active Cryovolcanism on Europa?

This is an excerpt from my post on

Title: Active Cryovolcanism on Europa?
Authors:  William B. Sparks, Britney E. Schmidt, Melissa A. McGrath, Kevin P. Hand, John .R. Spencer, Misty Cracraft, and Susana E. Deustua
First Author’s Institution: Space Telescope Science Institute
Status: Submitted, open access

Europa, one of Jupiter’s Galilean moons, is one of the most exciting places in the search for alien life in our solar system, rivaling both Mars and Saturn’s moon Enceladus.  Underneath a 15-25 km surface layer of ice, Europa very likely has a thick (~100 km) ocean of salty water with a rocky seafloor.  Chemical reactions on the icy surface caused by high-energy particles from Jupiter’s radiation belts could provide some of the essential ingredients for life, but only if this material could somehow reach the liquid water beneath it.  These geological properties make Europa a prime candidate for potential alien life.

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The Scientific Process in a Search for Lost Planets

This is an excerpt from my post on Yale Scientific's The Scope:

New planet discoveries have been coming in fast these last few years. Yesterday, The Astronomical Journal published another such planet discovery in a project I led with assistance from Dr. Jon Jenkins of the NASA Ames Research Center and my advisor Professor Debra Fischer.

Science is celebrated for its results, but the process of obtaining those results is where all the uncelebrated real work happens. This post gives the nitty gritty, behind-the-scenes details of just how science works, at least in this one case.

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A Volcanic Hydrogen Habitable Zone

This is an excerpt from my post on

Title: A Volcanic Hydrogen Habitable Zone
Authors:  Ramses Ramirez and Lisa Kaltenegger
First Author’s Institution: Cornell University
Status: Accepted in The Astrophysical Journal Letters, open access

The search for life beyond the solar system has long focused on the habitable zone (HZ).  This is the region around a star where a planet with the right properties could maintain liquid water on its surface for a substantial period of time. The classical inner edge of the HZ was set using the runaway greenhouse effect, in which a positive feedback loop causes oceans to evaporate creating an oven-like world similar to Venus.  The classical outer edge of the HZ was set using the maximum greenhouse effect from carbon dioxide, which is the distance at which adding carbon dioxide to a planet’s atmosphere starts cooling the planet (due to scattering the light or condensation).  There have been many other calculations of the HZ edges using different assumptions, such as a nearly desert planet and planets with different masses.  In this paper, the authors try to use volcanoes to expand edges of the HZ.  They calculate the HZ edges for atmospheres with significant amounts of hydrogen gas produced by volcanoes, another powerful greenhouse gas.

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Discovery of Water on 51 Peg b

This is an excerpt from my post on

Title: Discovery of water at high spectral resolution in the atmosphere of 51 Peg b
Authors: J. L. Birkby, R. J. de Kok, M. Brogi, H. Schwarz, and I. A. G. Snellen
First Author’s Institution: Harvard-Smithsonian Center for Astrophysics
Status: Accepted into the Astronomical Journal, open access

51 Peg b was the first exoplanet ever discovered orbiting another main sequence star (51 Peg). This Jupiter-sized planet, found orbiting in a 4-day orbit, revolutionized astronomy and upended our understanding of planet formation. It was discovered by measuring the star’s spectrum and seeing periodic shifts in the star’s radial velocity. This radial-velocity shift was caused by the planet gravitationally pulling on the star, which indirectly proves the existence of the planet. However, even early on, it was realized that astronomers should be able to see a similar radial-velocity shift in the light reflected by the planet. Critically, this method could used to determine the planet’s inclination, mass, and atmospheric composition, properties that would otherwise be near impossible to measure. First used in 2010, it has now been used on several hot Jupiters.

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The Lowest Mass Planet with a Detected Atmosphere

This is an excerpt from my post on

Title: Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b
Authors:  John Southworth, Luigi Mancini, Nikku Madhusudhan, Paul Mollière, Simona Ciceri, and Thomas Henning
First Author’s Institution: Keele University (UK)
Status: Submitted, open access

With more and more exoplanets being discovered that border on potential habitability in terms of their size and temperature, the need to measure their atmospheres to test that habitability becomes more imperative.  Astronomers have been trying to measure exoplanet atmospheres for more than a decade with very mixed results.  Almost all of these studies have focused on hot Jupiters (typically 1,000-2,000 K), with GJ 1214 b, a cooler, lower mass planet (~550 K and 6.6 Earth masses) being a notable exception (and also with mixed results).  This new study, led by John Southworth of Keele University, marks one of the most ambitious attempts at measuring an exoplanet’s atmosphere:  a planet with just 1.6 times the mass of Earth at a temperature of just 600 K.

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A New Planetary Architecture: Hot Earths

This is an excerpt from my post on

Title:  A population of planetary systems characterized by short-period, Earth-sized planets
Authors: Jason H. Steffen and Jeffrey L. Coughlin
First Author’s Institution: University of Nevada, Las Vegas
Status: Published in the Proceedings of the National Academy of Sciences (PNAS)

The Kepler space telescope has discovered just over 2500 exoplanets to date, which is more than 70% of all exoplanets found so far.  It has discovered planets and systems vastly different from what we see in our own solar system, such as Super Earths and tightly packed planetary systems.  While both of these are quite easy to visually recognize in the data, other types of systems might not be so apparently obvious.  The authors of this paper claim to discover one such hidden planetary architecture: a population of systems whose main signature is having a short-period (~1 day), Earth-sized planet.

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Why Are Pulsar Planets Rare?

This is an excerpt from my post on

Title:  Why Are Pulsar Planets Rare?
Authors: Rebecca G. Martin, Mario Livio, and Divya Palaniswamy
First Author’s Institution: University of Nevada
Status: Accepted in the Astrophysical Journal

Pulsar planets were the first type of planet ever discovered beyond the solar system, and it shocked the astronomical world.  These were not the planets we expected: solar system-like planets around a Sun-like star.  Instead, these planets orbited a pulsar, a rapidly rotating neutron star (the extremely dense core of a massive star that exploded as a supernova). However, since their initial discovery in 1992, only five such pulsar planets have been found, making them quite rare.  Fewer than 1% of pulsars have been found to host planets.  In this paper, the authors explore how these planets may have formed as a way to explain the rarity of pulsar planets.

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Earth's New Neighbor: Proxima b

This is an excerpt from my post on

Title:  A terrestrial planet candidate in a temperate orbit around Proxima Centauri
Authors: Guillem Anglada-Escudé, Pedro J. Amado, John Barnes, et al.
First Author’s Institution: Queen Mary University of London
Status: Published in Nature

Earth just got a new neighbor.  Proxima Centauri, the closest star to Earth at just 4.22 light years away, appears to host a planet, but not just any planet.  The planet, Proxima b, is potentially Earth-mass and lies within the habitable zone where liquid water might exist on its surface. The quest for a truly Earth-like planet is the Holy Grail of exoplanet research.  The fact that we might have to go only one star over to find another habitable planet indicates that Earth-like planets are either very common or that we got very lucky.  Whatever the case, this makes Proxima b one of the most interesting planets in the search for extraterrestrial life.

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A Planet Living on the Edge

This is an excerpt from my post on

Title:  Direct Imaging Discovery of a Jovian Exoplanet Within a Triple Star System
Authors: Kevin Wagner, Dániel Apai, Markus Kasper, Kaitlin Kratter, Melissa McClure, Massimo Robberto, and Jean-Luc Beuzit
First Author’s Institution: University of Arizona
Status: Published in Science

There’s a tug-of-war in the HD 131399 system.  A planet, HD 131399Ab, is being pulled in two directions.  On one side is the massive star HD 131399A.  On the other is a pair of smaller stars HD 131399B and HD 131399C.  The more massive HD 131399A is winning, but the battle is the most evenly matched that has ever been observed.  The planet’s orbit is just barely stable.  Orbiting far away from its primary host, it could be sent crashing inwards or tossed out of the system altogether.

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Living Under a Dying Star

This is an excerpt from my post on

Title:  Habitable Zones of Post-Main Sequence Stars
Authors: Ramses Ramirez and Lisa Kaltenegger
First Author’s Institution: Cornell University
Status: Published in ApJ

In a billion years, Earth will be a desert planet, roasted by an ever brightening Sun.  All life on the surface will be extinct.  Four billion years after that, Earth may be swallowed up by the Sun as it expands into a red giant.  The Goldilocks zone that the Earth currently lives in, where it’s neither too hot nor too cold for liquid water to exist on Earth’ surface, is not a permanent region around the Sun.  Instead, the boundaries of a star’s habitable zone (HZ) evolve as the star does.  As a star in the main sequence (the core hydrogen burning phase) becomes older, it gradually becomes larger and brighter, which pushes the HZ around it farther out.  Once a star begins burning hydrogen in a shell around the core, and then later burning helium, things start changing much more drastically.  It is the HZ at this stage of a star’s life that the authors explored.

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