Rocky Planet Discovered 331
Fraser Cain writes "Astronomers have discovered a rocky, terrestrial planet orbiting a nearby star, Gliese 876. The planet has approximately 7.5 times the mass of the Earth, double its radius, and orbits its parent star once every two days. This is the most Earthlike extrasolar planet discovered so far." Reader Karthik Narayanaswami points out that "the planet was discovered by the famed Berkeley astronomer Geoff Marcy," and adds a link to the news release from Berkeley.
Let's do the time warp again! (Score:4, Funny)
Hey, Rocky, Watch me pull a Planet out of my Hat! (Score:2)
/monster emerges from hat.
N: What we do with Moose and Squirrel?
Re:Let's do the time warp again! (Score:2)
So while it's "earthlike", I guess they won't be growing grass [watching-grass-grow.com] anytime soon there ...
Berkeley Press Release (Score:5, Informative)
And oh, looks like Slashdot is continuing to mirror Boing Boing [boingboing.net].
Re:Berkeley Press Release (Score:3, Informative)
Re:Berkeley Press Release (Score:3, Insightful)
Re: (Score:2, Interesting)
Re:Heh (Score:3, Funny)
light curve method (Score:3, Informative)
minimum mass (Score:3, Interesting)
It seems that planet's gravity is quite big for "earthlike" planet. Is life possible at all under such gravity? Any examples?
Re:minimum mass (Score:2, Funny)
Well, there's the Klingons on Uranus.
Re:minimum mass (Score:3, Funny)
Re:minimum mass (Score:2, Funny)
Re:minimum mass (Score:3, Funny)
Re:minimum mass (Score:3, Informative)
g_newplanet = G(7.5M_Earth)/4(r_Earth^2), where g is the gravitational field strength and G is the gravitational constant. This is less than 2g_earth.
Seems close enough for life. Although I'm not sure why a stronger gravitational field would necessarily be a huge constraint on the development of life.
And to preempt the trolls, my little convenient formula is good enough. R
Re:minimum mass (Score:2, Informative)
Using Google to come up with necessary constants gives me:
((6.67300 × 10E-11) * (7.5 * 5.97200E24)) / ((2 * 12 756 300)^2)
(I used a theoretical 1 kilogram test mass, at the planet's surface, to simplify things.)
So, call it about 4.7 times the gravity of Earth. Life? Possibly - but I
Real estate speculators swarm over rocky planet (Score:2)
A story on the housing market in the Gliese 876 system reported a slight rise in new housing starts, but the real news is the frenzy of speculation. According to the Gliese 876 Housing Market Letter, permits for new homes on the rocky planet and its Jupiter-like siblings "totaled 5,294,101 in April, down nearly 2 percent over the past 12 months."
The sales are phenomenal. "New-home sales reached 4,886,393 in April, up 26.2 percent from 3,871,936 in April of l
Radius of Earth (Score:2, Informative)
Earth: 9.785 N
New planet: 18.366 N
So the grandparent poster is correct, the surface gravity would be about 1.9 times that of Earth.
Parent is wrong (Score:5, Insightful)
Re:minimum mass (Score:2)
You probably meant 4.7Gs
Re:minimum mass (Score:4, Informative)
And where do you propose we find such examples? In space perhaps?
Re:minimum mass (Score:2)
Re:minimum mass (Score:3, Insightful)
YOU can live under such gravity! (Score:4, Insightful)
Of course I put many questions aside like how would they get there, does it have any continents, how sensitive processes like childbirth are to the gravity, does its atmosphere shield properly from radiation, isn't it too cold/hot there (although this can be fixed) etc etc...
Re:YOU can live under such gravity! (Score:3, Insightful)
Right, except that with the majority of our earth at well below 50 people per square kilometer [mapsofworld.com], we're hardly falling over each other.
Over populated might be a better word; sure, we're doing a great job of stripping our earth's resources bare at such a rate you'd think future generations are going to think we thought it was just a funny thing to do.
Sorry, it's just I find any talk of "terraforming" a pathetically distant rock, let alone mars, utterly utterly so beyond stupid it makes
Re:YOU can live under such gravity! (Score:3, Funny)
Re:minimum mass (Score:3, Informative)
Of course life would be possible with that gravity. Microorganisms don't care particularly about gravity, and any multicellular life that might evolve would adapt to whatever the local conditions are.
What would make life untenable would be a lack of liquid water. This world is very close to the star and would be tidally locked to the star. Unless there are deep ocean basins on the nightside to permit the water to cycle back, the water would eventually freeze out on
Polar zone... (Score:3, Interesting)
Re:minimum mass (Score:2, Insightful)
Re:minimum mass (Score:2)
If you have N times as much gravity, anything human would probably have to be 2/N me
Re:minimum mass (Score:2)
Re:minimum mass (Score:2)
We could never colonise this planet.... (Score:5, Funny)
Re:We could never colonise this planet.... (Score:2)
Re:We could never colonise this planet.... (Score:2)
Dramamine for my birthday (Score:2)
Re: (Score:2)
Re:We could never colonise this planet.... (Score:2)
Re:We could never colonise this planet.... (Score:4, Funny)
Re:We could never colonise this planet.... (Score:2)
Once every two days? (Score:5, Insightful)
The thing has gotta be mighty close to the star. Mercury orbits in 60 days, right? This thing may not be a gas giant, but it must totally bake on the sunny side, and aren't there going to be some horrendous tidal forces with an orbit that close? It probably has no shortage of volcanism. Hey! It's Vulcan, maybe... if it can hold an atmosphere without having the stellar wind blow it all away. Whatever, it can't be Earth-like.
Mating Rituals (Score:3, Funny)
If it is, does that mean Spock mates once every 14 days?
Re:Mating Rituals (Score:2)
Re:Once every two days? (Score:2)
Re:Once every two days? (Score:2)
Re:Once every two days? (Score:5, Interesting)
wobble is only one way (Score:2)
wobble is the only way (Score:3, Informative)
In practical terms, if you want to find earthlike planets, you use the doppler method.
Re:Once every two days? (Score:2)
Re:Once every two days? (Score:2)
Re:Once every two days? (Score:2)
Seems like crowded house were onto something (Score:2)
Now we're getting somewhere! (Score:2)
I'd love to stay and chat, but I'd better be home soon.
Re:Depends on length of day (Score:2)
It would be tidally locked to the star, especially if it's in a circular orbit. No sunrise, no sunset, no seasons.
Hey SETI (Score:5, Interesting)
which is only 15 light years away
So why not send some radio traffic which would obviously not be of natural origins. Surely 30ish years isn't that long to wait for a reply? (assuming the place has lifeforms which developed radio...)
Re:Hey SETI (Score:5, Funny)
Re:Hey SETI (Score:2)
Re:Hey SETI (Score:2)
Oh yeah, sure. a planet with 7.5 G's and 400 degrees celsius surface temperature, constantly hit by solar storms, ripping away any possible atmosphere and inundating it with harsh radiation. That place is more sterile than a grandmother's womb. Its only two frikkin million miles away from its sun! There's nothi
If you read this like I did... (Score:2)
shai (Score:2)
Here we go again (Score:2)
If we'd spend less gazing at stars (at least in the optical range) and more to actually develope an inexpensive space route the public might show more intrest in space. LONG CHAIN THE NANO-TUBES
Interesting, but method is flawwed (Score:2, Insightful)
Re:Interesting, but method is flawwed (Score:5, Interesting)
Yes, our Sun wobbles like that. Its wobble is done mostly by Jupiter, but the Earth contributes as much as +/- 3 meters/s, if I recall correctly. And for these guys, it's not impossible to detect such perturbations.
That said, the wobble method (Dopper detection) is good for all sizes of planets. If it is not a single planetary system, that will show up in the radial velocity curve (like it does here..non sinosoidal curve, I mean).
What you should be asking is this: how the hell do they know about the radius of the planet? The mass isn't too hard to determine (Kepler's law would tell you); but the radius isn't. Not in the accuracy claimed here (2 earth radius). Since I don't have an access to the article yet, it's hard for me to judge the accuracy of the radius value. Nontheless, that's where all of you should be pondering about, not about the wobble method.
Amazing that FARK readers are pointing this out better than Slashdot readers...what did we go wrong?
Re:Interesting, but method is flawwed (Score:2)
You're just not going to find anything heavier than iron in any significant quantities. That's basic astrophysics.
It's certainly possible that the composition of the planet will be different from our own, but not very likely. We're assuming that planetary formation follows the same two courses throughout the galaxy (rocky planets and gas giants), and that pro
Re:Interesting, but method is flawwed (Score:2)
If the radius had been determined by the rate of occultation, etc., then I would have believed that the rocky planet solution CAN indeed exist; but if the radius is assumed based on the assumption that the planet must be rocky, then I'm not sure how solid (or shall I say "unique" mathematically) this rocky interpretation is. Sure, astronomers can make the assumption that the cosmic abundance is more or less the same
Re:Interesting, but method is flawwed (Score:2)
Re:Interesting, but method is flawwed (Score:2)
By observing the harmonics in the wobble for any star for long enough we should be able to determine how many bodies are orbiting it and their period. The only limitations on this are how long we observe for and how sensitive our equipment is at watching it.
On a stellar scale, we "listen" to the details of wobble of
Doesn't sound very earthlike (Score:5, Interesting)
Re:Doesn't sound very earthlike (Score:3, Informative)
Rocky Planet Discovered (Score:5, Funny)
One dude's impression (Score:3, Interesting)
Orbital Velocity? (Score:3, Interesting)
In fact, even Earth seems like it should have centripetal effects. We rotate 1000MPH; we're orbiting at something like 70,000MPH, right? Shouldn't Earth gravity be balanced by detectable acceleration along the tangents to those circular motions?
Re:Orbital Velocity? (Score:2)
Re:Orbital Velocity - significant acceleration? (Score:5, Informative)
No.
A body moving in a circle of radius R at a uniform speed V experiences an acceleration a = (V*V)/R towards the center of the circle. In neither of the cases you mention does any centripetal acceleration come close to the local gravitational acceleration at the surface of the planet.
Case 1: The Earth: orbital speed V = 30 km/s, and R = 150 million km, so (V*V)/R is of order (10^8)/(10^11) m/s^2, or about 10^(-3) m/s^2. The local gravitational acceleration is about 10 m/s^2, of course. If you speak of the Earth's rotational motion at the equator, then very roughly V = 500 m/s and R = 6,400,000 m, so (V*V)/R has magnitude roughly (2.5 x 10^5) / 6.4 x 10^6 = 0.03 m/s^2; again, much less than 10 m/s^2 due to the gravitational pull of the Earth.
Case 2: The new planet. Its orbital radius is about 2 billion meters, so the circumference is about 7 billion meters; if it travels that distance in a period of 2 days = 170,000 seconds, then it speed is about V = 40,000 m/s. The orbital centripetal acceleration is therefore of order (16 x 10^8)/(2 x 10^9) = 0.8 m/s^2. That's much larger than the Earth's orbital centripetal acceleration, but still far less than the likely gravitational acceleration at the surface (or cloudtops) of this planet.
Re:Orbital Velocity - significant acceleration? (Score:3, Insightful)
But this is
Re:Orbital Velocity - significant acceleration? (Score:3, Informative)
Re:Orbital Velocity - significant acceleration? (Score:2)
Re:Orbital Velocity? (Score:2, Informative)
It is, that's why we haven't flung off into the void, or been dragged into the Sun.
Also, we really can't judge what it's semimajor axis is unless we know how massive the star is, but if we know that, then we also have the velocity.
(6.67e-11)*M=(v^2)(r)
where M is the mass of the star.
Also, the centripetal force has a magnitude of v^2/r.
HTH
Re:Orbital Velocity? (Score:2)
If the earth suddenly disappeared, we would all remain in orbit around the sun. See what I mean?
I'm sure the force differentials you're talking about would be detectable, but only by sensative equpment.
That is if I understood what you're asking...
Re:Orbital Velocity? (Score:2)
What does it mean to discover a planet? (Score:4, Interesting)
So essentially this planet was discovered solely on observation of its gravitational effect on other planets. In other words the scientists built a computer model which includes the star and two visible gas giants, and found a planet which they could insert in it so it causes the star and the gas giants to behave as they in the model as they do in observation. Then they declared that they have discovered a new planet.
How did they know it was a rocky planet? Well, correct me if i am wrong but it seems like they decided that by elimination -- the planet is too small to be a gas giant and too close to the star to have anu liquid water on it. Therefore, it must be a rocky planet.
Admittedly I do not know much about modern astronomy but all of this is a little troubling. I mean should we not obtain direct observation from something before we proclaim it "discovered"?
I am sure modeling solar objects is very useful but modeling is limited to our current knowledge. If rely too much on modeling we will never discover anything that we do not already know about.
Re:What does it mean to discover a planet? (Score:2)
Re:What does it mean to discover a planet? (Score:2)
I was just suggesting that astronomers rething the language they use in their press releases.
Re:What does it mean to discover a planet? (Score:2)
Re:What does it mean to discover a planet? (Score:3, Insightful)
The majority of scientists consider the 'wobble' to be an effect of the planet(s) revolving around the star. If you don't accept that planets are the most probable cause, then what your best guess as to what is the cause of the 'wobble'? If you're answer is "I don't know, but they don't know either.", then I think you simply don't know enough to be critical of these PhDs who have made this discovery. (But then again, this is Slashdot, right?).
I think you over-simplify your estimation of how they decided i
whatever you do... (Score:3, Funny)
the first rule (Score:2)
Whatever (Score:5, Funny)
Larger rocky planets? (Score:3, Insightful)
Is there some physical reason why massive rocky planets cannot form, or are we assuming that massive planets in other solar systems must resemble massive planets in our solar system?
Now if we could find one... (Score:2, Interesting)
Adrian!! Adrian!! (Score:4, Funny)
Not the first rocky planet? (Score:2)
Why are we constantly finding these rocky planets orbiting M-Class red dwarf stars? Is there some correlation? (Possibly, these are the aged, burnt-out cores of old gas giants whose gassy layers have been blown off by their parent star?) Or is this the only type of star being surveyed for rocky planets?
Re: (Score:2, Informative)
Krypton? (Score:3, Interesting)
Sound familiar? Perhaps, even, super?
No possible life? (Score:3, Informative)
From TFA:
Um, no, that's not true - there certainly are bacteria which can survive these temperatures and have adapted to them (those living near hydrothermal vents at the bottom of the ocean, for example). Whether this new planet could (even theoretically) host life is another question entirely, of course, but the statement that we do not know life that can endure such temperatures is simply not true.
Te first time? (Score:2, Funny)
Apart from the one we're standing on? :)
Re:my god man, think of the gravity! (Score:2)
So, relative to the Earth, the gravity on this planet will be 7.5/(2^2) = 1.875 Earth.
Not even 2x.
Re:Interesting (Score:2)
Re:You would weigh approximately twice as much... (Score:2)
Re:You would weigh approximately twice as much... (Score:2)
Mass 7.5x
Radius 2x
Gravity is inversely proportional to the square of the distance, so it's 7.5 *
On the other hand, it's not clear to me from TFAs how they measured the radius. It may be only an estimate based on the mass and an assumption of average density!