# Do moons of gas giants affect the habitable zone?

##### March 7, 2012 by Ray Sanders weblog

(PhysOrg.com) -- If you aren’t familiar with the Drake Equation, or how it may actually apply to exomoons, continue reading to learn more about the famous equation. Additionally, what conditions could make a habitable moon like Pandora as depicted in Avatar, or the forest Moon of Endor as seen in Return of the Jedi?

What exactly is the ? Created in 1961 by SETI founder Frank Drake, the Drake Equation attempts to explore the specific factors that may affect the development of intelligent civilizations elsewhere in our Galaxy.

The equation is as follows (Courtesy of SETI):

N = R* • fp • ne • fl • fi • fc • L

Where:

• N = The number of civilizations in The whose electromagnetic emissions are detectable.
• R* =The rate of formation of stars suitable for the development of intelligent life.
• fp = The fraction of those stars with planetary systems.
• ne = The number of planets, per solar system, with an environment suitable for life.
• fl = The fraction of suitable planets on which life actually appears.
• fi = The fraction of life bearing planets on which intelligent life emerges.
• fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
• L = The length of time such civilizations release detectable signals into space.
By adjusting one (or more) parameters in the equation, you can come up with estimates for habitable worlds (with intelligent life) in our Galaxy. While there isn't any specific solution to the Drake Equation, many researchers use the equation as a basic learning and exploration tool. When new discoveries are made, such as exoplanet discoveries, additional data can be used in the Drake Equation. Keep in mind that the Drake Equation was created 34 years prior to the confirmation of the first exoplanet in 1995!

So how does all this fit in with the habitable zone?

The image above is an infographic showing where the habitable zone would be in our Solar System, given different classes of stars. The habitable zone is merely a region where, given proper atmospheric conditions, liquid water could exist in a stable form on the surface of a body. As you can see, a smaller, dimmer star would produce a habitable zone closer to the central star, and a larger, brighter star would push this habitable zone further out.

In short, the habitable zone is (mostly) determined by the luminosity of the central star.

But wait, there’s more!

Just because a world isn’t in the habitable zone doesn’t necessarily mean it can’t have liquid water. Look at moons such as Europa or Enceladus. While the first impression of these icy worlds is that of a giant ball of ice, it is theorized that tidal flexing may heat the interiors of these worlds and provide an environment where subsurface liquid water may exist.

Keep in mind that the distance between a world and its host star can only provide an educated guess as to whether or not can exist on its surface. There are other factors such as the composition of the world itself (both surface and atmospheric), and that the mechanism for providing planets with water still isn’t completely understood.

To sum everything up, if astronomers detect a gas giant planet outside the habitable zone of its parent star, there’s still a chance it may harbor habitable moons - well, at least habitable for basic life. If a Jupiter-class planet is detected in the of its parent star, it is well within the realm of possibilities for an Earth-like habitable moon to exist in orbit around said planet.

Of course, said detections are still a few years away - currently researchers can detect exoplanets a bit smaller than Mars, and are working on ways to detect moons orbiting around large exoplanets. As for updating Drake’s famous equation - we can probably just replace planet with world and continue our search for life elsewhere in our Galaxy.

Explore further: Avatar's moon Pandora could be real

## Related Stories

#### Avatar's moon Pandora could be real

December 17, 2009

In the new blockbuster Avatar, humans visit the habitable - and inhabited - alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. With NASA's Kepler ...

#### Weird orbits of neighbors can make 'habitable' planets not so habitable

May 24, 2010

Astronomers hunting for planets orbiting nearby stars similar to the sun are looking for signs of rocky, Earth-like planets in a "habitable" zone, where conditions such as temperature and liquid water remain stable enough ...

#### Habitable zones

August 22, 2011

(PhysOrg.com) -- The "habitable zone" is the region around a star where a suitable planet could sustain the conditions necessary for life. Most astronomers take it to be the region where the balance between stellar radiation ...

#### Greenhouse effect could extend habitable zone

August 26, 2011

The distant region beyond Saturn is too cold for liquid water, a necessity for life as we know it. But new research indicates that rocky planets far from their parent star could generate enough heat to keep water flowing ...

#### Goldilocks moons

January 16, 2012

The search for extraterrestrial life outside our Solar System is currently focused on extrasolar planets within the ‘habitable zones’ of exoplanetary systems around stars similar to the Sun. Finding Earth-like planets ...

#### Could 2012 be the year we find extraterrestrial life?

January 19, 2012

Last year came to an exciting end with the discovery of an Earth-like planet, Kepler-22b, orbiting a sun-like star outside of our solar system. It was found by NASA’s Kepler mission and is the first planet detected orbiting ...

## Recommended for you

#### Boiling water may be cause of Martian streaks, study says

May 2, 2016

The results of Earth-bound lab experiments appear to back up the theory that dark lines on Martian slopes are created by water—though in an otherworldly manner, scientists said Monday.

#### Hubble sees galaxy hiding in the night sky

May 2, 2016

This striking NASA/ESA Hubble Space Telescope image captures the galaxy UGC 477, located just over 110 million light-years away in the constellation of Pisces (The Fish).

#### NASA research gives new insights into how the moon got 'inked'

May 2, 2016

A powerful combination of observations and computer simulations is giving new clues to how the moon got its mysterious "tattoos"—swirling patterns of light and dark found at over a hundred locations across the lunar surface.

#### Curiosity cores hole at 'Lubango' fracture zone

May 2, 2016

NASA's Curiosity Mars Science Laboratory (MSL) rover successfully bored a brand new hole in Mars at a tantalizing sandstone outcrop in the 'Lubango' fracture zone this past weekend on Sol 1320, Apr. 23, and is now carefully ...

#### Scientists assemble fresh global map of Pluto comprising sharpest flyby images

May 2, 2016

The science team leading NASA's New Horizons mission that unveiled the true nature of Pluto's long hidden looks during the history making maiden close encounter last July, have published a fresh global map that offers the ...

#### Phase two of ExoMars mission delayed to 2020

May 2, 2016

The second part of a joint European-Russian mission to probe Mars for traces of life has been delayed two years, with a new launch date set for July 2020, officials said Monday.

##### CapitalismPrevails
Mar 07, 2012
This comment has been removed by a moderator.
##### Lurker2358
3 / 5 (2) Mar 07, 2012
Pandora?

Yeah. "Pandora" was the name of the habitable MOON on the movie Avatar.
##### Modernmystic
1 / 5 (1) Mar 07, 2012
The problem with the Drake equation is that it's horribly outdated. The more we know the more variables are added and the narrower and narrower the odds become.

On edit: Also I'm not sure why one would even look at the moons of gas giants. It's my understanding the hard radiation that is present in their magnetic fields are exquisitely lethal...
##### Lurker2358
4 / 5 (4) Mar 07, 2012
On edit: Also I'm not sure why one would even look at the moons of gas giants. It's my understanding the hard radiation that is present in their magnetic fields are exquisitely lethal...

If you had a moon the size of the Earth or larger, then it could have it's own magnetic field.
##### nkalanaga
4.3 / 5 (6) Mar 07, 2012
Not always. Saturn has a very mild radiation environment, probably because the rings absorb much of it. Also, an Earth-sized rocky moon would likely have its own magnetic field, which would shield the surface. Finally, the magnetic field probably varies with rotation speed, so a slowly rotating Jovian should have a weaker field and less radiation.
##### nkalanaga
3.7 / 5 (3) Mar 07, 2012
Lurker: Looks like we answered at the same time!
##### d_robison
4.5 / 5 (2) Mar 07, 2012
The problem with the Drake equation is that it's horribly outdated. The more we know the more variables are added and the narrower and narrower the odds become.

On edit: Also I'm not sure why one would even look at the moons of gas giants. It's my understanding the hard radiation that is present in their magnetic fields are exquisitely lethal...

The problem with the Drake equation is that it is pure speculation.

That being said, I do BELIEVE that there is an extensive variety of life in the universe, but trying to put any numbers at this point in time to how many planets/moons may contain life is a complete guess.

@Lurker and @nkalanaga /like
##### Modernmystic
1 / 5 (1) Mar 07, 2012
In any case we'll know with a relatively high degree of certainty within the next few decades just how prevalent life bearing bodies are in this neck of the woods anyway...

My bet is on finding simple life in most systems, and not a single one with complex life of any kind within 10,000 LY...just my speculative guess.
##### julianpenrod
1.5 / 5 (2) Mar 07, 2012
Among other things, current planetary evolution theory has that gas giants can develop only far enough away from their primary that the gas is super cold. In any habitable zone, they will loose the major part of their atmosphere just from warming or gases could have been pushed out of their neighborhood before major accretion begins. If liquid water was the only criterion, incidentally, anything that kept the environment warm, like a constant regular barrage by meteorites could be considered. And the Drake Equation is nothing to be so excited about. It's a simple joint probability calculation assuming, without proof, that all the variables are independent. In fact, it can be indicative of how little understanding someone has of the world if they consider it such a breakthrough.
##### nkalanaga
4 / 5 (5) Mar 07, 2012
True, gas giants probably FORM far from their stars. But many are being FOUND in close orbits. Simulations have shown that it's quite possible for Earth-mass planets to be captured as moons by migrating Jovians. If the Jovian has stopped, or then stops, in the habitable zone, the captured moon will also be there.

Another possibility, not directly relevant to the article, is a rocky planet captured as a Trojan to a giant planet. Those have also shown up regularly in simulations, and wouldn't have the radiation issues of a moon.
##### Llewellian
not rated yet Mar 08, 2012
Another effect that could broaden the habitable zone with an earth sized moon around a Jupiter is that this kind of Jupiter reflects a lot of Sunlight and Heat from the sun to his moon... at least for half the time of the revolution it would take for that moon. Much like camping between the fireplace and a reflector foil behind you.
##### HydraulicsNath
4.7 / 5 (3) Mar 08, 2012
I just hope that when the day comes that either we do find a planet with intelligent life or not i will still be alive and well enough to witness it even if i were 100yrs old.
##### d_robison
5 / 5 (1) Mar 08, 2012
I just hope that when the day comes that either we do find a planet with intelligent life or not i will still be alive and well enough to witness it even if i were 100yrs old.

The moment may come much sooner than that (unless you are currently 90 years old). Between ground-based telescopes and Kepler we have been finding an increasing amount of extrasolar planets, not to mention the planets we find hidden in older data. As of today there are 709 confirmed extrasolar planets and 2,321 candidates, giving a total of 3,035 and this list is almost entirely consisting of planets found within the last decade. It is only a matter of time now. http://planetques...asa.gov/
##### antialias_physorg
not rated yet Mar 11, 2012
What exactly is the Drake Equation? Created in 1961 by SETI founder Frank Drake, the Drake Equation attempts to explore the specific factors that may affect the development of intelligent civilizations elsewhere in our Galaxy.

No. The Drake equation was created as a humorous way of presenting an agenda at a conference at Green Bank in 1961. Nothing more. For 'scientific exploartions' it's completely useless, since any formula containing even one variable that is pure guesswork (and the Drake equation contains several) can produce any arbitrary result.

As for habitable zones: Every planet that is still hot inside has a habitable zone at certain depths. This is completely independent of where (or even whether) it orbits a star.
##### MurphDog
1 / 5 (1) Mar 11, 2012
I know that the common concept is to believe that there is life out there and that some of it will be intelligent and that we will find it someday. I look at the complexity of life here, what it took to shape our planet into a vessel that would even sustain life, multiple catastrophes, having a moon, water, the just right but problematic environment to start life.
How many times did life start somewhere then fizzle out, right here on earth. The complex dance of evolution itself. I have come to the conclusion that there may not be any life in the universe but here.
Life is anathema to the universe, it doesn't care about nor need life, it has been constantly trying to eradicate life here since it began.

##### antialias_physorg
not rated yet Mar 11, 2012
I look at the complexity of life here, what it took to shape our planet into a vessel that would even sustain life,

And the puddle said "how come this hole fits me so perfectly?"

Life is anathema to the universe,

How so? Life is part of the universe as we speak.

it doesn't care about nor need life

it has been constantly trying to eradicate life

Make up your mind. Either it doesn't care or it is trying to eradicate life. Can't have both.

##### ZombieArmy
not rated yet Mar 15, 2012
Out of curiosity, how would a moon world fair with tidal forces from the host planet? I would imagine it'd be somewhat significant, but I'm not too sure on that subject, so some insight would be nice.