Featured Research

from universities, journals, and other organizations

A warmer planetary haven around cool stars, as ice warms rather than cools

Date:
July 19, 2013
Source:
University of Washington
Summary:
In a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This is due to the interaction of a star’s light with ice and snow on the planet’s surface.

In a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This artist’s concept illustrates a planet orbiting a red dwarf star.
Credit: NASA

In a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This is due to the interaction of a star's light with ice and snow on the planet's surface.

Related Articles


Stars emit different types of light. Hotter stars emit high-energy visible and ultraviolet light, and cooler stars give off infrared and near-infrared light, which has a much lower energy.

It seems logical that the warmth of terrestrial or rocky planets should depend on the amount of light they get from their stars, all other things being equal. But new climate model research led by Aomawa Shields, a doctoral student in the University of Washington astronomy department, has added a surprising new twist to the story: Planets orbiting cool stars actually may be much warmer and less icy than their counterparts orbiting much hotter stars, even though they receive the same amount of light.

That's because the ice absorbs much of the longer wavelength, near-infrared light predominantly emitted by these cooler stars. This is counter to what we experience on Earth, where ice and snow strongly reflect the visible light emitted by the Sun.

Around a cooler (M-dwarf) star, the more light the ice absorbs, the warmer the planet gets. The planet's atmospheric greenhouse gases also absorb this near-infrared light, compounding the warming effect.

The researchers found that planets orbiting cooler stars, given similar amounts of light as those orbiting hotter stars, are therefore less likely to experience so-called "snowball states," icing over from pole to equator.

However, around a hotter star such as an F-dwarf, the star's visible and ultraviolet light is reflected by planetary ice and snow in a process called ice-albedo feedback. The more light the ice reflects, the cooler the planet gets.

This feedback can be so effective at cooling that terrestrial planets around hotter stars appear to be more susceptible than other planets to entering snowball states. That's not necessarily a bad thing, in the scheme of time -- Earth itself is believed to have experienced several snowball states during the course of its 4.6 billion year history.

Shields and co-authors found that this interaction of starlight with a planet's surface ice is less pronounced near the outer edge of the habitable zone, where carbon dioxide is expected to build up as temperatures decrease. The habitable zone is the swath of space around a star that's just right to allow an orbiting planet's surface water to be in liquid form, thus giving life a chance.

That is the case because planets at that zone's outer edge would likely have a thick atmosphere of carbon dioxide or other greenhouse gases, which blocks the absorption of radiation at the surface, causing the planet to lose any additional warming advantage due to the ice.

The researchers' findings are documented in a paper published in the August issue of the journal Astrobiology, and published online ahead of print July 15.

Shields said that astronomers hunting for possible life will prioritize planets less vulnerable to that snowball state -- that is, planets other than those orbiting hotter stars. But that doesn't mean they will rule out the cooler planets.

"The last snowball episode on Earth has been linked to the explosion of multicellular life on our planet," Shields said. "If someone observed our Earth then, they might not have thought there was life here -- but there certainly was.

"So though we'd look for the non-snowball planets first, we shouldn't entirely write off planets that may be ice-covered, or headed for total ice cover. There could be life there too, though it may be much harder to detect."

Shields' UW co-authors are Victoria Meadows, associate professor of astronomy; Cecilia Bitz, associate professor of atmospheric sciences; and Tyler Robinson, an astronomy research associate. Other co-authors are Raymond T. Pierrehumbert of the University of Chicago and Manoj Joshi of the University of East Anglia.

The work was funded by a National Science Foundation Graduate Research Fellowship and performed as part of the NASA Astrobiology Institute's Virtual Planetary Laboratory Lead Team. ###


Story Source:

The above story is based on materials provided by University of Washington. The original article was written by Peter Kelley. Note: Materials may be edited for content and length.


Journal Reference:

  1. Aomawa L. Shields, Victoria S. Meadows, Cecilia M. Bitz, Raymond T. Pierrehumbert, Manoj M. Joshi, Tyler D. Robinson. The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets. Astrobiology, 2013; 130715061117009 DOI: 10.1089/ast.2012.0961

Cite This Page:

University of Washington. "A warmer planetary haven around cool stars, as ice warms rather than cools." ScienceDaily. ScienceDaily, 19 July 2013. <www.sciencedaily.com/releases/2013/07/130719103151.htm>.
University of Washington. (2013, July 19). A warmer planetary haven around cool stars, as ice warms rather than cools. ScienceDaily. Retrieved December 22, 2014 from www.sciencedaily.com/releases/2013/07/130719103151.htm
University of Washington. "A warmer planetary haven around cool stars, as ice warms rather than cools." ScienceDaily. www.sciencedaily.com/releases/2013/07/130719103151.htm (accessed December 22, 2014).

Share This


More From ScienceDaily



More Space & Time News

Monday, December 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA Prepares for Next Phase of Hubble Successor

NASA Prepares for Next Phase of Hubble Successor

Reuters - Innovations Video Online (Dec. 22, 2014) — Scientists and engineers prepare for the next phase of the James Webb Space Telescope, the scientific successor to the Hubble. Nathan Frandino reports. Video provided by Reuters
Powered by NewsLook.com
Spokesman: 'NORAD Ready to Track Santa'

Spokesman: 'NORAD Ready to Track Santa'

AP (Dec. 19, 2014) — Pentagon spokesman Rear Adm. John Kirby said that NORAD is ready to track Santa Claus as he delivers gifts next week. Speaking tongue-in-cheek, he said if Santa drops anything off his sleigh, "we've got destroyers out there to pick them up." (Dec. 19) Video provided by AP
Powered by NewsLook.com
NASA's Planet-Finding Kepler Mission Isn't Over After All

NASA's Planet-Finding Kepler Mission Isn't Over After All

Newsy (Dec. 18, 2014) — More than a year after NASA declared the Kepler spacecraft broken beyond repair, scientists have figured out how to continue getting useful data. Video provided by Newsy
Powered by NewsLook.com
Rover Finds More Clues About Possible Life On Mars

Rover Finds More Clues About Possible Life On Mars

Newsy (Dec. 17, 2014) — NASA's Curiosity rover detected methane on Mars and organic compounds on the surface, but it doesn't quite prove there was life ... yet. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins