Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



EXO WORLDS
The answer to planetary habitability is blowing in the stellar wind
by Staff Writers
Plainsboro NJ (SPX) Dec 04, 2017


Star swept.

Is there life beyond Earth in the cosmos? Astronomers looking for signs have found that our Milky Way galaxy teems with exoplanets, some with conditions that could be right for extraterrestrial life. Such worlds orbit stars in so-called "habitable zones," regions where planets could hold liquid water that is necessary for life as we know it.

However, the question of habitability is highly complex. Researchers led by space physicist Chuanfei Dong of the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University have recently raised doubts about water on - and thus potential habitability of - frequently cited exoplanets that orbit red dwarfs, the most common stars in the Milky Way.

In two papers in The Astrophysical Journal Letters, the scientists develop models showing that the stellar wind - the constant outpouring of charged particles that sweep out into space - could severely deplete the atmosphere of such planets over hundreds of millions of years, rendering them unable to host surface-based life as we know it.

"Traditional definition and climate models of the habitable zone consider only the surface temperature," Dong said. "But the stellar wind can significantly contribute to the long-term erosion and atmospheric loss of many exoplanets, so the climate models tell only part of the story."

To broaden the picture, the first paper looks at the timescale of atmospheric retention on Proxima Centauri b (PCb), which orbits the nearest star to our solar system, some 4 light-years away. The second paper questions how long oceans could survive on "water worlds" - planets thought to have seas that could be hundreds of miles deep.

Two-Fold Effect
The research simulates the photochemical impact of starlight and the electromagnetic erosion of stellar wind on the atmosphere of the exoplanets. These effects are two-fold: The photons in starlight ionize the atoms and molecules in the atmosphere into charged particles, allowing pressure and electromagnetic forces from the stellar wind to sweep them into space.

This process could cause severe atmospheric losses that would prevent the water that evaporates from exoplanets from raining back onto them, leaving the surface of the planet to dry up.

On Proxima Centauri b, the model indicates that high stellar wind pressure would cause the atmosphere to escape and prevent atmosphere from lasting long enough to give rise to surface-based life as we know it. "The evolution of life takes billions of years," Dong noted.

"Our results indicate that PCb and similar exoplanets are generally not capable of supporting an atmosphere over sufficiently long timescales when the stellar wind pressure is high."

"It is only if the pressure is sufficiently low," he continues, "and if the exoplanet has a reasonably strong magnetic shield like that of the Earth's magnetosphere, that the exoplanet can retain an atmosphere and has the potential for habitability."

Evolution of Habitable Zone
Complicating matters is the fact that the habitable zone circling red stars could evolve over time. So high stellar wind pressure early on could increase the rate of atmospheric escape. Thus, the atmosphere could have eroded too soon, even if the exoplanet was protected by a strong magnetic field like the magnetosphere surrounding Earth, Dong said.

"In addition, such close-in planets could also be tidally locked like our moon, with one side always exposed to the star. The resultant weak global magnetic field and the constant bombardment of stellar wind would serve to intensify losses of atmosphere on the star-facing side."

Turning to water worlds, the researchers explored three different conditions for the stellar wind. These ranged from:

* Winds that strike the Earth's magnetosphere today.

* Ancient stellar winds flowing from young, Sun-like stars that were just a toddler-like 0.6 billion years old compared with the 4.6 billion year age of the Sun.

* The impact on exoplanets of a massive stellar storm like the Carrington event, which knocked out telegraph service and produced auroras around the world in 1859.

The simulations illustrated that ancient stellar wind could cause the rate of atmospheric escape to be far greater than losses produced by the current solar wind that reaches the magnetosphere of Earth. Moreover, the rate of loss for Carrington-type events, which are thought to occur frequently in young Sun-like stars, was found to be greater still.

"Our analysis suggests that such space weather events may prove to be a key driver of atmospheric losses for exoplanets orbiting an active young Sun-like star," the authors write.

High Probability of Dried Up Oceans
Given the increased activity of red stars and the close-in location of planets in habitable zones, these results indicate the high probability of dried up surfaces on planets that orbit red stars that might once have held oceans that could give birth to life. The findings could also modify the famed Drake equation, which estimates the number of civilizations in the Milky Way, by lowering the estimate for the average number of planets per star that can support life.

Authors of the PCb paper note that predicting the habitability of planets located light-years from Earth is of course filled with uncertainties. Future missions like the James Webb Space Telescope, which NASA will launch in 2019 to peer into the early history of the universe, will therefore "be essential for getting more information on stellar winds and exoplanet atmospheres," the authors say, "thereby paving the way for more accurate estimations of stellar-wind induced atmospheric losses."

Scientists spot potentially habitable worlds with regularity. Recently, a newly discovered Earth-sized planet orbiting Ross 128, a red dwarf star that is smaller and cooler than the Sun located some 11 light-years from Earth, was cited as a water candidate. Scientists noted that the star appears to be quiescent and well-behaved, not throwing off flares and eruptions that could undo conditions favorable to life.

"Is Proxima Centauri b Habitable? A Study of Atmospheric Loss," Chuanfei Dong et al., 2017 Mar. 10, Astrophysical Journal Letters

"The Dehydration of Water Worlds via Atmospheric Losses," Chuanfei Dong et al., 2017 Sep. 20, Astrophysical Journal Letters

EXO WORLDS
Newly Discovered Twin Planets Could Solve Puffy Planet Mystery
Honolulu HI (SPX) Nov 30, 2017
Since astronomers first measured the size of an extrasolar planet 17 years ago, they have struggled to answer the question: how did the largest planets get to be so large? Thanks to the recent discovery of twin planets by a University of Hawaii Institute for Astronomy team led by graduate student Samuel Grunblatt, we are getting closer to an answer. Gas giant planets are primarily made out ... read more

Related Links
Princeton Plasma Physics Laboratory
Lands Beyond Beyond - extra solar planets - news and science
Life Beyond Earth


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

EXO WORLDS
Building for a future in space: An interview with Dava Newman and Gui Trotti

Space Farms: 'Mark Watney in The Martian Was Right to Add Poop to the Soil'

NASA successfully fires Voyager 1 thrusters after 37 years

New motion sensors major step towards cheaper wearable technology

EXO WORLDS
ISRO eyes one rocket launch a month in 2018

Russia to build launch pad for super heavy-lift carrier by 2028

Mechanisms are critical to all space vehicles

Russia loses contact with satellite after launch from new spaceport

EXO WORLDS
Earthworms can reproduce in Mars-like soil

Opportunity Greets Winter Solstice

NASA builds its next Mars rover mission

Scientists developed a new sensor for future missions to the Moon and Mars

EXO WORLDS
Nation 'leads world' in remote sensing technology

China plans for nuclear-powered interplanetary capacity by 2040

China plans first sea based launch by 2018

China's reusable spacecraft to be launched in 2020

EXO WORLDS
Going green to the Red Planet

Orbital ATK purchase by Northrop Grumman approved by shareholders

UK space launch program receives funding boost from Westminster

Need to double number of operational satellites: ISRO chief

EXO WORLDS
Quantum optics allows us to abandon expensive lasers in spectroscopy

Spin current from heat: New material increases efficiency

New catalyst controls activation of a carbon-hydrogen bond

Math gets real in strong, lightweight structures

EXO WORLDS
Scientists identify key factors that help microbes thrive in harsh environments

Exoplanet Has Smothering Stratosphere Without Water

Scientists study Earth's earliest life forms in Nevada hot spring

Traces of life on nearest exoplanets may be hidden in equatorial trap

EXO WORLDS
Pluto's hydrocarbon haze keeps dwarf planet colder than expected

Jupiter's Stunning Southern Hemisphere

Watching Jupiter's multiple pulsating X-ray Aurora

Help Nickname New Horizons' Next Flyby Target




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement