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Rocky Planet Discovered
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.
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.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
Gravity is only 1.8 from normal - I believe you can get used to it. Meanwhile surface is 3.2 times larger, so if it could be terraformed it will hold a lot of people from our overcrowded Earth.
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...
Its always interesting when we find these new planets in other systems, but the wobble method is just not effective for finding an earthlike planet. For starters, have you ever noticed all the planets found have extremely quick orbits (1 year = 2 days) etc. And infact the longer their year is the bigger the planet is (because although the wobble doesn't occur as quickly it is more pronounced. If a planet were to have orbits similar to ours it would take nearly 2 years to see one wobble back and forth. Sure its neat to find new planets but I don't think we need to be spending all our time looking for wobbling stars. For every star that wobbles there are probably more just sitting still with planets around them more similar to ours that we just cannot detect.
Also, I tend to think if you see a start wobbling back and forth its because there is one large mass in its orbit affecting it, as opposed to many planets balancing things out at various points around the start. Does our Sun wobbel like this? I am not sure, but if not, it hardly seems a good measure to find an earthlike planet, but rather a good way to find large sole planet systems.
Deep-sea life is under far greater pressure. But it's interesting in that this is the first rocky planet found, as far as I know.
Me (Blog)
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?
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.
But this is more than sufficient that if there were intelligent life (fabulously unlikely) then they would quickly notice that things were a few percent lighter at night than during the day.
The planet has about 7 times the mass of Earth and about twice the radius, so the surface gravity will be...pause for algebra...about 2g ~ 20 m/s**2. At night, the orbital centripetal acceleration acts against the surface gravity, so it would be a minimum at midnight of 19.2 m/s**2, and during the day they act together for a max at noon of 20.8 m/s**2, or a little less than a 10% difference.
This is conceptually closely related to tides, and this is another way of pointing out that the tidal effects on such a world are going to be wickedly large.
Blasphemy is a human right. Blasphemophobia kills.
This is pretty simple. Surface gravity for spherically-symmetrical masses scales linearly with mass and inverse-square with radius. The mass makes gravity 7.5 times higher, while the radius would make it 4 times lower, for a total surface gravity of about 1.9G.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Aren't there creatures living at far greater pressures in deep sea environments? Wouldn't that be similar to having creatures living at high gravities (leaving out the other ways the planet clearly isn't very "earthlike" for the moment).
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 it was rocky. They use, as a model, what they've found in our solar system, as well as basic physics.
As far as I know, this star is simply too faint to be directly observed for planets and detecting the wobble is the best method of detecting the likelyhood of a star system containing planets. If you have a better method of detection other than declaring "your method is not good enough!", please let the scientific community know. They could then use your help and your insightful powers of posting on Slashdot.
I watched the live webcast of the announcement of their discovery as they answered questions from the rest of the astronomical community (via phone/e-mail). Believe me, these people who announced this discovery aren't stupid, and they are using the best scientific theory they have at hand (with 3 years of data supporting their theory, yeah they waited that long before announcing this).
Boing Boing and Fark are news aggregators, while CNN is more traditional news. The difference being that Boing Boing and Fark link to sites like CNN, while CNN pays for the Reuters and AP news feeds themselves. What makes Slashdot different is that they're prepetually a day behind everyone else. But I still stick with Slashdot because FARK can be a little risque for work at times and I can generally pretend that Slashdot is somewhat related to the work I do.
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