Goldilocks And The Habitable Zone – The Increased Place In Space

by Tammy Plotner on November 15, 2011

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Artist's impression of a planet orbiting red dwarf GJ1214.

It’s referred to as the “Goldilock’s Zone”, but this area in space isn’t meant for sleepy or hungry bears – it’s the relative area in which life can evolve and sustain. This habitable region has some fairly strict parameters, such as certain star types and rigid distance limits, but new research shows it could be considerably larger than estimated.

In a study done by Manoj Joshi and Robert Haberle, the team considered the relationship which occurs between the radiation for red dwarf stars and a possible planet’s reflective qualities. Known as albedo, this ability to “bounce back” light waves has a great deal to do with surface layers, such as ice and snow. Unlike our G-type Sun, the M-class red dwarf is much cooler and produces energy at longer wavelengths. This means a great deal of the radiation is absorbed – rather than reflected – turning the ice and snow into possible liquid water. And, as we know, water is considered to be a primary requirement for life.

“We knew that red dwarfs emit energy at a different wavelength, and we wanted to find out exactly what that might mean for the albedo of planets orbiting these stars.” explained Dr. Joshi from the National Centre for Atmospheric Science, who carried out the research in collaboration with Robert Haberle from the NASA Ames Research Centre.

What makes this theory even more charming is that M-class stars make up a very substantial portion of our galaxy’s total population – meaning there’s even more possible Goldilock’s Zones yet to be discovered. Considering the lifespan of a red dwarf star also increases the chances – as well as the distance a planet would need to be located for these properties to happen.

“M-stars comprise 80% of main-sequence stars, and so their planetary systems provide the best chance for finding habitable planets, i.e.: those with surface liquid water. We have modelled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M-stars) using spectrally resolved data of the Earth’s cryosphere.” explains Joshi. “In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M-stars may be 10-30% further away from the parent star than previously thought.”

Have we discovered planets around red dwarf stars? The answer is yes. In order to calculate the effects of radiation and albedo, the team chose to use similar M-class stars, Gliese 436 and GJ 1214, and applied it to a simulated planet with an average surface temperature of 200 K. Why that particular temperature? In this circumstance, it’s the temperature at which one bar of carbon-dioxide condenses – a rough indicator of the outer edge of a habitable zone. It is theorized that anything registering below this temperature is too cold to harbor life.

What the team found was high albedo planets register a higher surface temperature when exposed to longer wavelength radiation. This means ice and snow covered planets could exist much further away from a red dwarf parent star – as much as one third more the distance.

“Previous studies haven’t included such detailed calculations of the different albedo effects of ice and snow.” explains Joshi. “But we were a little surprised how big the effect was.”

Original Story Source: Planet Earth OnLine. Further Reading: Suppression of the Water Ice and Snow Albedo Feedback on Planets Orbiting Red Dwarf Stars and the Subsequent Widening of the Habitable Zone.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

HeadAroundU November 15, 2011 at 7:55 PM

Imagine snowy planets with white dinosaur-like bears. LC will build me a ship, I’ll put my predator suite on and we can go to hunt them. Torbjorn Larsson will be my cook and Ivanman will ride a snowy truck. :D

William Sparrow November 16, 2011 at 12:59 AM

Who will supply the psychadelics?

Anonymous November 16, 2011 at 4:09 AM

I call shotgun!

Torbjörn Larsson November 16, 2011 at 1:01 PM

Don’t hire a swedish chef unless you want soured fish (aka “rotten” fish) for lunch every day. Bring the ice drill for fishing, and since most only herring easily ferment by autolysis (due to an enzyme in the skull bones, AFAIK) you would probably need to stock up on some enzyme or yeast supplement too.

Anonymous November 15, 2011 at 10:19 PM

Does it also mean that the inner solar system is 10-30% further away from the parent star because of the same effect that the planet will become a lot warmer ?

HeadAroundU November 16, 2011 at 12:00 AM

Well, I don’t think so. You could have a habitable zone planet as close as possible but with a low albedo. Or, a snowy planet getting closer stops being a snowy planet right?

Now I wonder about white puffy clouds. :D

Torbjörn Larsson November 16, 2011 at 1:27 PM

They also point out another line of investigation of possible mitigation effects, as lowered photolysis effects (lower UV intensity) may mean more CH4 and N2O greenhouse contributions.

It is interesting that more details more often increase habitability than not.

For atmospheres I am reminded of the circulation of higher pressures that mitigate temperature differences on tidal locked planets such as M-star habitables, as well as the thermal mantle convection models that increase magnetic field strength on superEarths.

Another atmospheric effect has been the lowered demand for greenhouse gases that current climate research brought, mitigating the lower initial irradiation from young stars with a larger set of atmospheres.

For planets the biosphere has increased to incorporate land and ocean crust even for multicellular life (nematodes), which mitigate habitability for planets outside the habitable zone (possible Mars habitats for example). It also means an inhabited planet can sustain a much higher impact rate without wholesale extinction, such as our own Late Heavy Bombardment.

It is theorized that anything registering below this temperature is too cold to harbor life.

Well, they point to Kasting’s models, and as I remember them (a bit vaguely at the moment, and I haven’t the ref handy) the condensation point was taken as indication of the runaway freeze out of the atmosphere.

[Say, which has happened on Mars at the current time, about half the CO2 is locked in ices. It is still an open question if Mars is stuck in that state AFAIU, if its tilt changes the partial freeze out may revert.]

So you wouldn’t have any surface life under a dense and moist atmosphere, such as the habitability zone is concerned with regardless if you derive the surface temperature with or without atmosphere models, because the atmosphere is mostly gone.

But if ice locked oceans or heated subsurface crust exist, you can still have “non-atmospheric habitability”, to coin a term.

Anonymous November 16, 2011 at 3:30 PM

There is some complex tuning of various parameters. Bio-active planets around M-class stars probably exist, but I think there is some tricky issues of not just having a goldilocks zone, but also on how one gets the “goldilocks.”

LC

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