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Fraser
2005-Jun-13, 07:12 PM
SUMMARY: Astronomers have found the most Earthlike extrasolar planet discovered so far. This new planet is about 7.5 times the mass of the Earth, and has twice the radius of our own planet. It whips every two days around a nearby star called Gliese 876, which is only 15 light years away - this star also possesses two additional giant, Jupiter-class planets. This is the first time that a rocky (or terrestrial) planet has been discovered around another star.

View full article (http://www.universetoday.com/am/publish/large_rocky_planet.html)

What do you think about this story? Post your comments below.

Greg
2005-Jun-13, 08:01 PM
This is very exciting. It is amazing that already a telescope the size of the keck will be able to detect earth-sized planets to a reasonable distance around more than 150 nearby M-dwarf stars. Looks like the next phase in planet finding has already brgun! It will be interesting to see what kind of solar systems will be detected around these kinds of stars. I believe I recall speculation not that long ago about these stars being unlikely candidatres for terrestrial planets, especially for life-harboring planets. With what we know about inward migration of planets, these might be some of the best candidates for harboring life.

Guest
2005-Jun-13, 08:05 PM
Gliese 876 is one of the most exciting planetary systems yet discovered; it has two large gas giants fairly close togetehr, in harmonic orbits with each other, and now this large terrestrial. If it has a rocky core, it probably has a gravity of something like 2 gee; that means it will have a hot, dense atmosphere, maybe something like Venus'.

If the pressure at the bottom of the atmosphere is high enough and the temperature not too high there could be an ocean of superheated water; Ilike to think there could be extremophile life at the bottom of such an ocean (but to be honest the prospect is unlikely).
In fact the range of temperatures given for this world is 200-400 celsius.



"The planet's mass could easily hold onto an atmosphere," noted Laughlin, an assistant professor of astronomy at UC Santa Cruz. "It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that's intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune."


Exciting stuff!

eburacum45
2005-Jun-13, 08:07 PM
Logs in to claim previous post.

piersdad
2005-Jun-13, 08:07 PM
Every time I read about yet another more precise measurement of remote orbits and planet predictions I am amazed.
measaurements now of wobble in the range of 1 meter per sec --incredable--

Its like having a digital zoom camera and each time the zoom gets to its limit you use a better camera.

om@umr.edu
2005-Jun-13, 09:30 PM
This is great news, Fraser.

We have known that rocky planets orbit the pulsar, PSR 1257+12, for over a decade, but this is the first report of Earth-like planets orbiting a Sun-like star.

Most of the elements that comprise rocky planets - Fe, O, Si, S, Ni - are made by nuclear reactions that occur in the deep interior of a supernova.

Is the surface of Gliese 876 metal-rich? Or is this system like an evolved star turned inside-out?

With kind regards,

Oliver
http://www.umr.edu/~om

dave_f
2005-Jun-13, 09:40 PM
Originally posted by fraser@Jun 13 2005, 02:12 PM
This is the first time that a rocky (or terrestrial) planet has been discovered around another star.

Amazing article, though the picture is probably misleading; it looks like a picture of Earth with the blue converted to red in Photoshop with some visible volcanic activity going on in the dark side of the planet. Seeing how this planet will be experiencing a runaway greenhouse gas effect in its atmosphere (if it has one at all) due to to the small distance between it and the star, wouldn't the planet more closely resemble Venus?

I know that's speculation, but if I could put money down on this I'd bet on the atmosphere being totally opaque. Adding to that speculation is a guess that only on side of this planet faces the star; the other side is dark at all times. The tidal forces at that proximity to the star would drag its rotation down relatively quickly in the grand scheme of things.

Greg
2005-Jun-14, 01:20 AM
This is a M-dwarf. M-dwarves have quite a long life, but most likely this one is relatively young. For it to have a terrestrial planet in orbit mandates a higher metallicity and therefore a younger age IMHO. I do not know the specifics on this star as yet. The fact that it is 15 light years away also indicates that it is likely yo have a higher metallicity. It is als othe reason it is a bit easier to study.
Her eis a link to some basic data on Gliese 876:
http://www.obs-hp.fr/www/nouvelles/gl876.html
Here is a nicer link with a graphic of the first 2 planets in their projected orbits, also a note of the stellar metallicity est .33-.5 Solar:
http://www.solstation.com/orbits/gl876sys.htm

The relatively low metallicity surprised me, especially considering this system has 2 large gas giants. Yhe system is quite bizzare by our standards, any thoughts on why?

aeolus
2005-Jun-14, 04:29 AM
Originally posted by Greg@Jun 14 2005, 01:20 AM
The relatively low metallicity surprised me, especially considering this system has 2 large gas giants. The system is quite bizzare by our standards, any thoughts on why?
...Because ours is the only complete system with which we have to set the standard. I'm sure the canoe people in the remote parts of Papua New Gineau who have never come in contact with modern civilization would similarily condsider the watercraft at any of our boatshows "bizarre".

It's already been said, but I'll say it again. The advance of extrasolar planetary exploration and discovery is crazy exciting! So exciting that it merits using an adjective as an adverb...

John L
2005-Jun-14, 04:05 PM
As for habitability in this star system, although the planets are in very tight orbits that are probably tidally locked, the moons of those planets would not be. Two of the three planets are gas giants and therefor could harbor large terrestrial moons. As this system now appears to have at least one large terrestrial world as well, the likelyhood of the gas giants having terrestrial moons is increased. It is very possible that those moons are or could be made habitable. And at only about 15ly distance, this is a system that a few trillion dollars and only minor advances in technology could have a manned mission in this century. Maybe we should send an unmanned probe first...

antoniseb
2005-Jun-14, 04:31 PM
Originally posted by John L@Jun 14 2005, 04:05 PM
Maybe we should send an unmanned probe first...
A prudent idea! It worked for the Moon and Mars (well we still haven't sent a manned probe to Mars).

I'm guessing that this Century might be a little aggressive for a manned mission.

aeolus
2005-Jun-14, 04:39 PM
Originally posted by John L@Jun 14 2005, 04:05 PM
It is very possible that those moons are or could be made habitable.
Wow, John, I've never thought about it like that. I've been dismissing these systems with hot Jupiters as discoveries that are means to an end. But thinking of it like that, sure, maybe these hot Jupiters aren't habitible, but if they have terrestrial-like satellites, we may be looking at habitible systems without even knowing it right now. cool.

Greg
2005-Jun-14, 08:55 PM
I was thinking that planet c could have habitable moons as well. It spends a little less than 1/2 its elliptical orbit in the habitable zone. I suppose it is possible for another terrestrial planet or two to be found in the middle of the habitable zone since there is a pretty big space between c and d. Whomever runs that website just added the d planet graphic after I posted the link yesterday. This is the same link: http://www.solstation.com/orbits/gl876sys.htm

reddog
2005-Jun-14, 09:34 PM
Hi all,
I am new and confused about precession rates. "Slow turning of the long axis of a planet's eliptical orbit." Can anyone try to help me understand what that means?
Perhaps a picture. Thank you.

antoniseb
2005-Jun-14, 09:51 PM
Originally posted by reddog@Jun 14 2005, 09:34 PM
Hi all,
I am new and confused about precession rates. "Slow turning of the long axis of a planet's eliptical orbit." Can anyone try to help me understand what that means?
Perhaps a picture. Thank you.
Hi Reddog, welcome to the UT forum,

You can think of an elliptical orbit as having an axis that goes from the closest point of ellipse to the star to the furthest point on the ellipse. There are factors that make the direction of this axis move a little bit, so that this axis spins around over the eons. In the case of the Earth, this axis goes completely around the Sun once every 100,000 years or so. The planet Mercury has a more elliptical orbit, and is closer to the Sun, and so its axis goes around the Sun much faster.

eburacum45
2005-Jun-15, 06:37 AM
The best model I have seen of Gliese 876 d gives it a gravity of about two gee, a diameter twice that of Earth, a temperature above 400k, and a minimum molecular weight retention between 2 and 3 (not sure what that means exactly);
but it should hold onto Helium if not Hydrogen, and any heavier gases as well.
So it would have a dense atmosphere, but there is a lot of uncertainty as to how thick.

If the pressure at the bottom of the atmosphere is twenty or thirty times as great as on Earth a water ocean is possible at 200 celsius; however the greenhouse effect would probably make the surface temperature even higher than that. If the temperature gets above 700 celsius the rocky core (if any) would be molten at the surface.

Here is my own image of Gliese 876 d using Celestia; the version they have made available since has a radius 600km larger but is otherwise the same.
http://img66.echo.cx/img66/9905/d0fb.jpg

reddog
2005-Jun-15, 02:07 PM
Thank you, antoniseb. I think I've got it: If you drew a line from the tip of the far end of the elipse, through the star to the other far end, that line would slowly turn like a spoke on a wheel. Is that correct?

antoniseb
2005-Jun-15, 02:32 PM
Originally posted by reddog@Jun 15 2005, 02:07 PM
that line would slowly turn like a spoke on a wheel. Is that correct?
Yes, or perhaps another way to see it, the whole ellipse turns like a cam on an axle.

Duane
2005-Jun-15, 07:05 PM
Gliese 876 is an M-type dwarf that is thought to be metal poor and approximately 10 billion years old. Stars of this size can last upwards of 100-billion years due to the slower reaction rate of hydrogen in it's core.

This link has a good discussion about it: http://www.astrobio.net/news/article1603.html

It is also interesting to realize that the habital zone is 0.06 to 0.22 AU from this star, and both of the Jupiter-massed planets orbit within that zone (0.21AU and 0.13AU) so I'ld imagine the moons of these two planets may be very interesting indeed, assuming there are any.

reddog
2005-Jun-15, 08:55 PM
Thanks antoniseb, I have a good visual now.

Guest
2005-Jun-17, 07:47 AM
I'd imagine the moons of these two planets may be very interesting indeed, assuming there are any.

Perhaps so;
here is an image I have made of such a world.
http://img66.echo.cx/img66/3194/aardwolf8wz.jpg

On the other hand there is a problem with the magnetic field of these two giant planets. If the Earth-like moon orbits within the magnetic field, it will be bathed in particles trapped there that were orginally emitted by the red dwarf- is this star prone to flares at all I wonder?

dave_f
2005-Jun-17, 09:43 AM
Perhaps so;
here is an image I have made of such a world.
http://img66.echo.cx/img66/3194/aardwolf8wz.jpg

On the other hand there is a problem with the magnetic field of these two giant planets. If the Earth-like moon orbits within the magnetic field, it will be bathed in particles trapped there that were orginally emitted by the red dwarf- is this star prone to flares at all I wonder?


WOW!!! Nice work on your image! I am impressed. Hopefully others are as well.

I am entranced by the "terrestrial planet around a Jupiter-class planet" idea. Why? I like to imagine that there is a big ginormous orb in the sky when I look up to the stars.

One killjoy is, well, radiation. Jupiter-class planets are prone to exuding huge amounts of radiation. Unless a planet has a strong enough magnetic field to stave off the local radiological effects of the planetary system, I'm doubtful a terrestrial planet can survive at all in such an environment

:ph34r:

Duane
2005-Jun-18, 05:26 PM
Well if Earth is any example, the magnetic field generated by this planet would protect it from the radiation trapped by the gas giant. The aurora's would be incredible!