Kepler-438b Downsizing From Habitable to Unhabitable Exoplanet

Summary: A study in Monthly Notices of the Royal Astronomical Society Nov. 8, 2015, announces the Kepler-438b downsizing from habitable to unhabitable exoplanet.

Planet Kepler-438b, shown in front of its violent parent star, is regularly irradiated by huge flares of radiation that could render the planet uninhabitable in the absence of Earth-like magnetic fields. Here the planet's atmosphere is shown being stripped away: Mark A Garlick/University of Warwick, no usage restrictions, via EurekAlert!

Astrophysicists are downsizing Kepler-438b from status as a potentially habitable to a potentially unhabitable exoplanet, according to a study preprinted Nov. 18, 2015, by the Monthly Notices of the Royal Astronomical Society.

Kepler Object of Interest 438b (Kepler-438b) belongs on lists of Earth-like, star-orbiting planets discovered by the National Aeronautics and Space Agency’s Kepler space observatory since the NASA spacecraft’s launching March 7, 2009. The Kepler telescope contains a photometer to measure about 150,000 dwarf stars in terms of such optical properties as light intensity. It detects non-stellar presences by the transit method of periodically dimmed brightness when exoplanets cross to the front of their host stars.

Kepler-438b emerges as one of 1,030 extrasolar or extragalactic planets.

KOI-3284, the cool red dwarf star around which Kepler-438b orbits every 35.2 days 470 light years from Earth in the constellation Lyra, furnishes 40 percent more light than the sun, the solar system’s bigger, hotter yellow dwarf star.

Astrophysicists guesstimate exoplanet sizes and temperatures from the intervals between transits. Kepler-438b has 0.88 percent agreement with the Earth Similarity Index of bulk density, center-to-surface radius, escape velocity and surface temperature, with 70 percent likelihoods of orbital situations within the Goldilocks zone of year-round availability of flowing surface water, rocky compositions similar to that of Earth and Mars, and surface temperatures between zero and 60 degrees Celsius (32 and 140 degrees Fahrenheit).

Astrophysicists judge the distance between Kepler-438b and KOI-3284 at 0.166 astronomical units (24,833,246.52956 kilometers; 24,833,246,529.56 meters; 15,426,062.92876 miles), in comparison to the Earth’s distance from the sun of 1 AU (14,9597,870.66 kilometers; 149,597,870,660 meters; 92,928,089.93228 miles).

Earth’s magnetic shield keeps the Blue Marble from losing an atmosphere protective against harmful radiation and vital to respirations sustaining carbon-based life forms. Monitoring of light-curves leads to article co-author and research team leader David K. Armstrong of the University of Warwick’s Astronomy and Astrophysics Group detecting radiation from KOI-3284 10 times more powerful than any recorded from the sun.

The shooting of coronal mass ejections and superflares every 200 days makes atmospheric stripping likely in the absence of Earth-like magnetospheres.

Chloe Pugh, co-author and Ph.D. student at the University of Warwick’s Centre for Fusion, Space and Astrophysics, notes: “With little atmosphere [and absent or weak magnetosphere], the planet would also be subject to harsh UV and X-ray radiation from the superflares, along with charged particle radiation, all of which are damaging to life.”

The seven co-authors nevertheless observe for Kepler-22, Kepler-61, Kepler-62, Kepler-174, Kepler-186, Kepler-283, Kepler-296, Kepler-298, Kepler-438b, Kepler-440, Kepler-442, Kepler-443 and KOI-4427: “This [calculation of fluid flows, low-mass star ages, magnetic pressures, mass-loss rates, perceived brightness, X-ray flow rates] leads to an estimate of the magnetospheric standoff distance for the planets, assuming Earth-like magnetospheres, showing that in principle these planets could all maintain an Earth-sized magnetosphere.”

Of 1,030 confirmed planets from Kepler, a dozen are less than twice Earth's size and reside in their host stars' habitable zone. Sizes of diagram's exoplanets are represented by size of each sphere, arranged by size from left to right, and by type of star they orbit, from M stars that are significantly cooler and smaller than the sun, to K stars that are somewhat cooler and smaller than the sun, to G stars that include the sun. Planets' sizes are enlarged by 25 times compared to stars. Earth is shown for reference: NASA/Ames/JPL-Caltech, Public Domain, via NASA

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Kepler-438b: Mark A Garlick/University of Warwick, no usage restrictions, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/103491.php

Kepler planetary system: NASA/Ames/JPL-Caltech, Public Domain, via NASA @ http://www.nasa.gov/jpl/finding-another-earth

For further information:

Armstrong, D.J., et al. 1 January 2016. "The Host Stars of Keplers Habitable Exoplanets: Superflares, Rotation and Activity." Monthly Notices of the Royal Astronomical Society, vol. 455, issue 3 (Jan. 1, 2016): 3110-3125. DOI: 10.1093/mnras/stv2419
Available @ arXIV:1511.05306v1 [astro-ph.EP]

Brennan, Pat. 23 July 2015. "Finding Another Planet." NASA > Jet Propulsion Laboratory > Distant Planets.
Available @ http://www.nasa.gov/jpl/finding-another-earth

Kepler A Search for Habitable Planets. NASA Ames Research Center.
Available @ http://kepler.nasa.gov

Starr, Michelle. 18 November 2015. "Farewell to Hope of Life on Kepler-438b." CNET. Sci-Tech.
Available @ http://www.cnet.com/news/farewell-hope-of-life-on-kepler-438b-it-was-good-while-it-lasted/

Warwick University @warwickuni. 18 November 2015. "Most Earth-like planet uninhabitable due to radiation, @WarwickAstro research suggests." Twitter.
Available @ https://twitter.com/warwickuni/status/666951328866897920