Researchers develop model for identifying habitable zones around star

Jan 30, 2013
The graphic shows habitable zone distances around various types of stars. Some of the known extrasolar planets that are considered to be in the habitable zone of their stars are also shown. On this scale, Earth-Sun distance is one astronomical unit, which is roughly 150 million kilometers. Click on the image for a higher resolution version. Credit: Chester Herman

Researchers searching the galaxy for planets that could pass the litmus test of sustaining water-based life must find whether those planets fall in a habitable zone, where they could be capable of having liquid water and sustaining life. New work, led by a team of Penn State researchers, will help scientists in that search.

Using the latest data, the Penn State Department of team has developed an updated model for determining whether discovered planets fall within a habitable zone. The work builds on a prior model by James Kasting, Evan Pugh Professor of Geosciences at Penn State, to offer a more precise calculation of where habitable zones around a star can be found.

Comparing the new estimates with the previous model, the team found that habitable zones are actually farther away from the stars than previously thought.

"This has implications for finding other planets with life on them," said post-doctoral researcher Ravi kumar Kopparapu, a lead investigator on the study, which will be published described in .

For the paper, Kopparapu and graduate student Ramses Ramirez used updated absorption databases of (HITRAN and HITEMP). The databases have more accurate information on water and carbon dioxide than previously was available and allowed the research team to build new estimates from the groundbreaking model Kasting created 20 years ago for other stars.

Using that data and super computers at Penn State and the University of Washington, the team was able to calculate habitable zones around other stars. In the previous model, water and were not being absorbed as strongly, so the planets had to be closer to the star to be in the habitable zone.

The new model has already found that some previously believed to be in habitable zones may, in fact, not be.

The new model could also help scientists with research that is already under way. For example, the model could be used to see if planets the NASA Kepler mission discovers are within a habitable zone. The Kepler mission has found more than 2,000 potential systems that could be investigated.

The data could assist with a Habitable Zone Planet Finder a team of scientists in Penn State's Department of Astronomy and Astrophysics is building. In 2011, that team received a National Science Foundation grant to develop an instrument to find planets in habitable zones. The precision spectrograph, which is under construction, will help scientists find Earth-sized planets in the Milky Way that could sustain .

In the future, the model could also be useful for research done with Terrestrial Planet Finder telescopes, which would guide users of the supersized telescopes on where to look.

While in the Earth appears to be situated at the very edge of the , the model doesn't take into account feedback from clouds, which reflect radiation away from the earth and stabilize the climate.

Explore further: Astronomers: 'Tilt-a-worlds' could harbor life

More information: Paper: arxiv.org/abs/1301.6674

An interactive calculator to estimate Habitable Zones is online: depts.washington.edu/naivpl/content/hz-calculator.

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User comments : 15

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Egleton
1.4 / 5 (10) Jan 30, 2013
The habitable zone is good, and we should find living planets fascinating. But please drop any Startrek (Holiwood)wet dream of dropping down their gravity well and having sex with scantily clad aliens.

Wells had it nailed down pat in his "War of the Worlds." Our microbes ate the invading bad guys from Mars. Except that in this case we would be the Aliens.
And if one of us broke wind, our microbes would party with their microbes, destroying any large life.
Your scantily clad nymphette would dissolve into snot.
Egleton
1 / 5 (4) Jan 30, 2013
And so would you. And then the two puddles of ikky goo could flow together.
Hey, Whatever turns you on.
yep
1 / 5 (4) Jan 31, 2013
Thats Hot!
Kedas
3 / 5 (3) Jan 31, 2013
They changed the requirement for the zone, nothing more.
It is not a model, that would be based on confirming which zones are OK and then try to put all this data in a model.
alfie_null
4.5 / 5 (2) Jan 31, 2013
Interesting to see Earth and Mars on the two edges of the habitable zone. So, no way a planet in a Venus-type orbit around a Sun like ours can ever hope to be habitable?
I wonder if the borders of the zone will increase as we learn more about potential effects of e.g. magnetic fields, and constituents of planetary atmospheres.
philw1776
4.2 / 5 (5) Jan 31, 2013
Around 700,000,000 years ago the Earth almost froze over in Snowball Earth. And in the couple billion years before that the sun was tens of percent fainter. Given this were the Earth nearer the outer edge of this newly drawn HZ it would never have developed complex surface life. Habitable zones move as stars age. The brighter late F and G stars move further and more quickly. For the fainter K and faint Ms, not so much and very, very slowly.
antialias_physorg
4.4 / 5 (7) Jan 31, 2013
Researchers searching the galaxy for planets that could pass the litmus test of sustaining water-based life must find whether those planets fall in a habitable zone, where they could be capable of having liquid water and sustaining life.

On any planet that has still a molten core (which should be almost all of them bigger than, say, the Moon) and is not a gas-giant the temperature conditions for having liquid water are a given. You just have to go far enough down.

For surface water it's also not clear, as atmospheric conditions can alter surface temperatures quite drastically (c.f. Venus)

Even planets that are completely frozen due to distance from the sun can exhibit areas of liquid water due to volvanic activity or persistent vents (or even tidal heating from a nearby, massive moon)or heating due to high content of radioactive materials.

I really think we shouldn't artificially limit our search space - when the limit is not necessarily a hard one.
Sinister1811
2.8 / 5 (13) Jan 31, 2013
Looks like they've just made adjustments to the previous model. There's no doubt that surface temperatures and the existence of liquid water are only two factors in defining a planet's habilitability. And even those lines are blurred when you consider extremophile organisms and their adaptability to inhospitable conditions.
dusanmal
3.3 / 5 (3) Jan 31, 2013
This is still needlessly way too Earth-centric. What is needed is a kick of finding (maybe even in the Solar system) non-water, non-carbon, non-common... based life. Than we can start seeking for life signatures everywhere, not for "habitable zones". Search for habitable zones (particularly when we can't go there) is quite pointless. By laws of Physics life is inevitable and complex life almost inevitable. So it will "try" to emerge in any form anywhere. Proper search: for life signatures visible at astronomical distances.
antialias_physorg
4.2 / 5 (5) Jan 31, 2013
By laws of Physics life is inevitable and complex life almost inevitable

It is? Why? With one datapoint we can't really make that statement. One datapoint still is as likely a fluke as not.

So it will "try" to emerge in any form anywhere

We've been looking in some places already (with landers on the Moon, Mars, Venus and Titan) and haven't found any (at least none that is immediately obvious). So I'd reserve judgement on whether life starts up as easily as all that until we find some elsewhere.

Proper search: for life signatures visible at astronomical distances.

Subterranean life, subaquatic life (or even surface life on planets with dense atmosphere) is likely not to show up in a visible signature.
EverythingsJustATheory
5 / 5 (5) Jan 31, 2013

I really think we shouldn't artificially limit our search space - when the limit is not necessarily a hard one.


You are correct, but it does make sense to focus most of the resources on the areas that are easiest to detect life, given the stage we are at in the process (onset).
lengould100
3.4 / 5 (5) Feb 02, 2013
The most interesting lesson here, presuming accurate, is how near earth is to being too hot for water-based life. Just a small additional amount of CO2 in the atmosphere ......
Torbjorn_Larsson_OM
5 / 5 (1) Feb 05, 2013
@Egleton: It's astrobiology constraining conditions for life, not colonization plans.

Indigenous life would most likely win, they are adapted to the previous environment which remains the largest environmental factor.

@Kedas: Reading the paper, they do a little bit of both redefinition and prediction.

@philw: Yes, the better parameters for GW atmospheres would make Earth's Young Sun problem lesser. They didn't check that, though.

@dusanmal: It is the usual perturbation analysis around Earth conditions. Other chemistry is looked at differently.
Torbjorn_Larsson_OM
not rated yet Feb 05, 2013
@antialias: One observation _is_ enough to test stochastic process models as any other models - life was fast on Earth, so it is an easy and/or rapidly repeating process.

You can't derive "by the laws of physics life is inevitable" from that observation. But as it happens, recently thermodynamics of replicators have constrained them to RNA (among known carbon compounds), and shown that given phosphate activated nucleotides replicators will inevitably "crystallize" out. [I think I gave refs here recently; in any case, I don't have them handy right now.]

It takes ~ 30 000 years for a population to become a pure "crystal", one species of replicator only. That could happen in hydrothermal vents, today's vents becomes maximum 100 000 years.
antialias_physorg
1 / 5 (1) Feb 05, 2013
You are correct, but it does make sense to focus most of the resources on the areas that are easiest to detect life

I think any planet we find should be checked. Currently all we can do is look at the spectra, anyhow, and see what kind of composition the atmosphere has. That's not such a costly procedure.

One observation _is_ enough to test stochastic process models as any other models - life was fast on Earth, so it is an easy and/or rapidly repeating process.

I disagree. One occurence cannot be distinguished from a fluke.

If I tell you that I just rolled a 6 you don't know how often a 6 will turn up (you don't even know how man sides the die has).
You only know that the die has at least one side and has at least one 6 on it - but no more than that.

Since it looks like that all life on Earth has a common ancenstor that was that one "roll of 6".

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