nearby exoplanet in habitable zone

[Martin]

J'Dona reported

http://www.scienceforums.net/forums/showthread.php?t=12124

the finding of a third planet in the Gliese 876 system 15 lightyears away.

 

This planet is too hot to be considered habitable. However there are two other planets in the system, one at 0.13 AU and one about 0.2 AU.

the absolute luminosity of the star, Gliese 876, is estimated at 0.0124 solar.

 

The middle planet, at distance 0.13 AU receives roughly as much watts per square meter as the earth does.

 

It could have a surface temperature similar to the earth's. It is a massive planet and could have satellites, as Jupiter does, which could also have an earth-like surface temperature.

 

this is admittedly highly speculative. also the smaller star is cooler, and redder, than the sun.

anyone interested in finding out more about the Gliese 876 system can look in J'Dona's thread and also check the various exoplanet listings

 

like for instance the Harvard exoplanet catalog

 

http://cfa-www.harvard.edu/~planets/Gl876.html

__________________

 

anyone know of a closer exoplanet which is in the habitable zone of its star, temperature-wise?

[ydoaPs]

that's cool. if only we had FTL capabilities...

[Martin]

like for instance the Harvard exoplanet catalog

 

http://cfa-www.harvard.edu/~planets/Gl876.html

__________________

 

anyone know of a closer exoplanet which is in the habitable zone of its star, temperature-wise?

 

if you check out the middle planet, on that harvard catalog page

you see that the star's luminosity is 0.0124

 

and the distance squared is 0.13 squared which is 0.0169

 

so very roughly the watts per sq. meter is 124/169 of what we get on earth

 

(this is just practice arithmetic for anybody interested in exoplanets)

 

and the equilibrium temperature of a flat surface facing the light, alternatively of a rotating ball, is the FOURTH ROOT of that, because of the fourth power radiation law, compared with the same thing at our distance from the sun.

 

and the fourth root of 124/169 is roughly the same as one. Newbs try it on your calculator, press the square root button twice.

[ydoaPs]

.9255156037 according to my TI-83+

[Martin]

thanks, so neglecting possible differences in albedo effect and greenhouse effect, temps there should be about 90 percent of what they are here

 

anyone interested in the Gliese system should probably find out the surface temperature of the star (which is only about 1/3 as massive as the sun) and visualize how that affects the mix of wavelengths.

harvard catalog might have relevant information

[Guest amazed]

Thanks for all the posts relating to the estimated temp of the new planet.

Now, if only ITER would forget about fusion, and start on warp drive...

[Martin]

amazed, welcome to SFN

 

Thanks for all the posts relating to the estimated temp of the new planet.

Now' date=' if only ITER would forget about fusion, and start on warp drive...[/quote']

assume you are kidding about "warp"

 

BTW I have heard that ITER fusion reactor is to be built in France at Cadarache, and not (as the japanese hoped) in Japan.

http://www.iter.org/index.htm

 

I do not think that ITER represents the technology relevant to sending a probe to Gliese 876.

 

If people thought it was interesting to send an unmanned probe there they would probably use ION DRIVE, with some more usual type of powerplant.

It would take a long time to go 15 LY, but that's how the world is.

 

at least for now IMO they are more likely to want to build much more powerful orbital telescopes, to get a look at systems like Gliese 876, than to be sending unmanned probes.

[Guest amazed]

Thanx for the welcome, Martin; and no... Me kid? Just ask Scottie, he will tell you are about warp drives...

Which is no more far-feched than SETI. Maybe in the not too distant future, we can send ion powered gizmo's to the near sky, which equipped with a telescope, could render good science. Anything further out would be spitting in the wind.

[Martin]

J'Dona reported

http://www.scienceforums.net/forums/showthread.php?t=12124

the finding of a third planet in the Gliese 876 system 15 lightyears away.

 

This planet is too hot to be considered habitable. However there are two other planets in the system' date=' one at 0.13 AU and one about 0.2 AU.

the absolute luminosity of the star, Gliese 876, is estimated at 0.0124 solar.

 

The middle planet, at distance 0.13 AU receives roughly as much watts per square meter as the earth does....

 

http://cfa-www.harvard.edu/~planets/Gl876.html

[/quote']

 

In post #4 of J'dona thread, Spyman gave this link

 

http://skyandtelescope.com/news/article_1530_1.asp

 

and in this link it says

 

"...The star itself is in easy reach of amateur telescopes. Using a detailed, large-scale star atlas, you can find it glowing orange at right ascension 22h 53m 13s, declination –14° 15' 13" (2000.0 coordinates). It's in the bottom of Aquarius's water bucket, as Sky & Telescope draws the constellation, which is currently (mid-June) low in the southeast just before the first light of dawn."

 

That means in three months, like September, Aquarius will be overhead around midnight and we can take a look at where this orange Gliese 876 star is.

 

I will try to remember 23 hours and 14 degrees south latitude.

 

I am at 37 degrees north, so when Gliese is on the meridian northsouth line then it will be 37 + 14 = around 50 degrees south of dead-overhead.

for me that means the frigging Oakland citylight glow will blind it out even if I had telescope eyes.

 

but anyway the thing is ORANGE, so I will probably stay up past ordinary bedtime some night and go outdoors and think about this orange thing I cant see which has planets I cant see

 

where one of the planets is about the same temperature as earth

 

(the hot rock closer in to the star I do not care about, I care about the jupitersize thing that has equilibrium temp near the freezingmelting point of water)

[ydoaPs]

and it's possible moons

[Molotov]

The problem with red dwarfs is they like to flare up randomly.

[Martin]

The problem with red dwarfs is they like to flare up randomly.

 

great! would love to know more

please give links to online info about this type star

 

it is spectral type M4 V

 

do you know a typical range for surface temperature?

 

this star seems to be low metalicity

 

can you describe a mechanism for variable luminosity of spectal type M4?

 

I'd be glad to learn about this

[Molotov]

great! would love to know more

please give links to online info about this type star

 

http://www.solstation.com/stars/gl876.htm

http://www.extrasolar.net/startour.asp?starid=2

http://www.exoplaneten.de/uvceti/english.html

 

it is spectral type M4 V

 

do you know a typical range for surface temperature?

 

According to extrasolar.net' date=' for Gliese876, the average temperature is 3240 degrees kelvin.

 

M stars typically range from 3500k and under.

 

this star seems to be low metalicity

 

can you describe a mechanism for variable luminosity of spectal type M4?

 

I'd be glad to learn about this

 

From what I have gathered, intense magnetic disturbances will push super heated gasses from the core to the surface of the dwarf star increasing the energy output by as much as a twofold.

 

Also, here is something from solstation.com

 

Many dim, red (M) dwarf stars exhibit unusually violent flare activity for their size and brightness. These flare stars are actually common because red dwarfs make up more than half of all stars in our galaxy. Although flares do occur on our Sun every so often, the amount of energy released in a solar flare is small compared to the total amount of energy that Sol produces. However, a flare the size of a solar flare occurring on a red dwarf star (like Wolf 1055 A or B) that is more than 40 thousand times dimmer than our Sun would emit about as much or more light as the red dwarf does normally.

 

Flare stars erupt sporadically, with successive flares spaced anywhere from an hour to a few days apart. A flare only takes a few minutes to reach peak brightness, and more than one flare can occur at a time. Moreover, in addition to bursts of light and radio waves, flares on dim red dwarfs may emit up to 10,000 times as many X-rays as a comparably-sized solar flare on our own Sun, and so flares would be lethal to Earth-type life on planets near the flare star. Hence, Earth-type life around flare stars may be unlikely because their planets must be located very close to dim red dwarfs to be warmed sufficiently by star light to have liquid water (less than 0.08 AU for Wolf 1055 A or B), which makes flares even more dangerous around such stars. In any case, the light emitted by red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently.

 

 

 

Does anyone know if its even possible for moons to exist in stable orbits around planets that are tidally locked with their star?

[Molotov]

I found the answer to my own question if anyone is interested.

 

 

Yes, moons can exist around Gliese 876 C which is tidally locked with its star.

 

Though it is inferred that the maximum mass could be no greater than that of Pluto or .002 Earths.

 

And the maximum stable orbit around the planet no greater than 570,000km or .003 AU.

 

Too bad, this pretty much kills the notion of a moon with an atmosphere around the planet.

[Martin]

Molotov, I am much obliged to you for this fine informative post!

 

I note that Gliese 876 is 80 times fainter than the sun (abs. luminosity 0.0124) while the two stars most often mentioned in your post are

said to be 40,000 times dimmer than the sun.

 

so there is a factor of 500 difference which may affect the qualitative feel of some of the comparisons.

 

I note that some type M dwarf stars have been identified as flare stars, and others have not. I dont yet know if Gliese 876 has been so identified.

 

I found the answer to my own question if anyone is interested.

 

 

Yes, moons can exist around Gliese 876 C which is tidally locked with its star.

 

Though it is inferred that the maximum mass could be no greater than that of Pluto or .002 Earths.

 

And the maximum stable orbit around the planet no greater than 570,000km or .003 AU.

 

Too bad, this pretty much kills the notion of a moon with an atmosphere around the planet.

 

Indeed I am interested. I was wondering about the possibility of moons several days ago and I would like to see the source.

 

For anyone else reading, the planet of interest Gliese 876 C, has a period of 30 days and a semimajoraxis of about 0.13 AU. Molotov you know a lot more than I do about this planet. Please give me a link to some source. I wonder how they get the upperbound on the possible mass of a moon. Why is it 0.002 earths?

 

I will try the links you have already given and see if that answers this question.

 

thanks

[Martin]

I was wondering how sure we are that Gliese 876 C is tidally locked

 

I was reading one of your links and it said that the NEW ROCKY planet Gliese 876 D is assumed to be tidally locked because it is so close.

 

the one that interests me is further away, but still pretty close, namely 0.13 AU. Do we assume that it is tidally locked too, or is there some possibility that it rotates?

 

sorry if question is naive.

 

here is the quote from your source about the newly discovered rocky planet

". Located only 0.021 AUs (semi-major axis) from Gliese 876, the planet completes its orbit around the star in less than two ... days. Due to its close orbit, the planet is presumed to be tidally locked with one surface eternally facing its host star, and so may have a bright-side temperature around 157-377° C but be extremely cold on the dark side. "

[Martin]

. In any case, the light emitted by red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently.

 

but what is "efficient" depends on what one has as an alternative and what is red depends on the dwarf.

 

the filament of a 100 watt incandescent litebulb temperature is about 2800-2900 kelvin, IIRC

 

this star is hotter than the filament of a litebulb----your source says 3240 kelvin

 

so its light is going to be whiter than that of the litebulb

 

many type M dwarf stars are smaller than Gliese, and cooler, and redder. I think that Gliese is not SO red.

 

earthtype plants only use a small fraction of the sun's photons because much of the sun's light is infrared and they only use a couple of wavelength bands----one in the blue and one in the red

 

so earthtype plants waste a lot of light------and they would waste an even larger percentage of Gliese light. Gliese makes an even smaller percentage of the particular blue and red that earthtype plants use for photosynthesis

 

(you know all this Molotov, I am just summarizing)

 

so I think in this light of Gliese 876, whiter than a litebulb, some earth plants could grow if they were properly sheltered

[Molotov]

I was wondering how sure we are that Gliese 876 C is tidally locked

 

I was reading one of your links and it said that the NEW ROCKY planet Gliese 876 D is assumed to be tidally locked because it is so close.

 

the one that interests me is further away' date=' but still pretty close, namely 0.13 AU. Do we assume that it is tidally locked too, or is there some possibility that it rotates?

 

sorry if question is naive.

 

here is the quote from your source about the newly discovered rocky planet

". Located only 0.021 AUs (semi-major axis) from Gliese 876, the planet completes its orbit around the star in less than two ... days. [b']Due to its close orbit, the planet is presumed to be tidally locked[/b] with one surface eternally facing its host star, and so may have a bright-side temperature around 157-377° C but be extremely cold on the dark side. "

 

You are correct, we do not know if its tidally locked or not. Sorry, I mis-read it being in a 1:2 harmonic orbit with the b planet as being tidally locked.

 

 

From extrasolar.net planet C is "Tidally locked if older than: > 20 Gyr^5"

Is that 20 billion years raised to the power of 5?! I guess it must have alot of angular momentum to wear off.

Also in a side note they say "orbit may be too eccentric for 1:1 tidal lock"

 

Here is the page I get all this info from

http://www.extrasolar.net/planettour.asp?StarCatId=&PlanetId=156

 

I personally trust extrasolar.net as a good source because they get most of their info from the extrasolar planets encyclopedia.

http://cfa-www.harvard.edu/planets/

and

http://exoplanets.org/

[Molotov]

but what is "efficient" depends on what one has as an alternative and what is red depends on the dwarf.

 

the filament of a 100 watt incandescent litebulb temperature is about 2800-2900 kelvin' date=' IIRC

 

this star is hotter than the filament of a litebulb----your source says 3240 kelvin

 

so its light is going to be whiter than that of the litebulb

 

many type M dwarf stars are smaller than Gliese, and cooler, and redder. I think that Gliese is not SO red.

 

earthtype plants only use a small fraction of the sun's photons because much of the sun's light is infrared and they only use a couple of wavelength bands----one in the blue and one in the red

 

so earthtype plants waste a lot of light------and they would waste an even larger percentage of Gliese light. Gliese makes an even smaller percentage of the particular blue and red that earthtype plants use for photosynthesis

 

so I think in this light of Gliese 876, whiter than a litebulb, some earth plants could grow if they were properly sheltered[/quote']

 

Yes I agree, as long as there is a full spectrum(or atleast around 440nm and 660nm) present and enough energy some plant life would likely be able to adapt. Alot of plants don't like large amounts of dark red light and will stop growing in its presence. It would be interesting to do an experiment with a light source simulating the output of Gliese 768 to see what types of plants would do well.

 

(you know all this Molotov, I am just summarizing)

 

 

Please don't assume that, I do this as a hobby. Your post inspired me to brush up on photosynthesis and light spectrums.

[Martin]

 

 

From extrasolar.net planet C is "Tidally locked if older than: > 20 Gyr^5"

Is that 20 billion years raised to the power of 5?! I guess it must have alot of angular momentum to wear off.

Also in a side note they say "orbit may be too eccentric for 1:1 tidal lock"

 

 

what they mean is that the planet is "Tidally locked if older than: > 20 Gyr"

 

and the superscript 5 points to the footnote #5

which you quoted about maybe not getting a simple tidal lock

 

so not to worry about raising to the fifth power, 20 billion years should be enough

 

excellent page Molotov, thanks again!

[Molotov]

Another message board discussion on possible moons around Gliese 876c...

http://www.extrasolar.net/forums/viewtopic.php?t=160

[Martin]

Another message board discussion on possible moons around Gliese 876c...

http://www.extrasolar.net/forums/viewtopic.php?t=160

 

that's an interesting message board discussion

I was not aware of that board (I dont get around much I guess)

 

some side comments about it reminded me of HD28185b

which Ive had recurring thoughts about for several years.

Maybe we should start a thread about HD28185 system

It is farther away from us' date=' I have forgotten, maybe you know the distance from earth. [EDIT: I found a link, it is much farther, around 130 lightyears!']

 

But, if I am not mistaken about the number, it is a star resembling the sun with a Jupitersize planet in not-very-eccentric orbit at roughly 1 AU.

 

 

Molotov do you happen to have collected any information about that system?

 

EDIT: I tried your "extrasolar" site and found this

http://www.extrasolar.net/startour.asp?StarCatId=normal&StarId=130

http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=158

 

it is much more remote, but could have an OK temperature, and a nice color of light, and the larger distance from primary would allow for more massive moons.