Earthlike Planet Orbiting Nearby Star

The Bad Astronomer writes "Astronomers in Europe have announced the discovery of a planet with only 5 times the Earth's mass, orbiting a red dwarf star 20 light years away. It orbits the star so closely that it only takes 13 days to go around... but the star is so cool that the temperature of the planet is between 0 and 40 Celsius. At this temperature there could be liquid water. Models indicate the planet is either rocky like the Earth or covered in an ocean. While it's not known if there actually is liquid water on the planet, this is a really big discovery, and indicates that we are getting ever closer to finding another Earth orbiting an alien star."

More links:

[Beolach]

The BBC [bbc.co.uk] and Scientific American [sciam.com] have good quotes from Stephane Udry of the Geneva Observatory, lead author of the scientific paper reporting the results. Others [world-science.net] are already calling it "possibly habitable".

Very cool news!

Re:Only 5X the mass of Earth!

[644bd346996]

You forgot to account for the fact that the radius is 1.5 times that of Earth. The best estimate puts that planet at around 2.25 times earth gravity.

More information...

[Barkmullz]

The link in the blog seems to be broken. There is some more information about the planet (Gliese 581 c) on Wikipedia [wikipedia.org], MSN [msn.com], and Space.com [space.com].

quick maths on gravity

[quenda]

Assuming its the same density as Earth, cube root of 5 is 1.7, so 1.7x the radius. Gravity is mass/r^2, 5/1.7^2 x earth, so 1.7 or 70% more. ie surface gravity only goes up with the cube root of mass, for a constant density, so 5x isn't as bad as it sounds. But if it has more rock, and less iron core, the surface might me much nicer.

Re:This is worth sending a probe.

[plasmacutter]

as i said.. sent 10 years from now.. 20 light years at an average of 0.4 times the speed of light.. 2058 would be the arrival time.. then it communicates back data by laser.. 2078 would be the time we see the signals. of course this would require an international effort to prevent losing track of this project should a certain bloated government disappear *cough*.

still, this is within the realm of practicality, and if it returns promising results it could usher in a new era of colonization.

Re:When do tickets go on sale?

[Scott Ransom]

Actually, this is not the smallest planet yet found. The first extrasolar planets are still the smallest known: the planets around the millisecond pulsar B1257+12: http://en.wikipedia.org/wiki/PSR_B1257+12 [wikipedia.org]

The optical planet hunters often conveniently forgot this system (or dismiss it for various reasons).

Re:How long to get there?

[Wonko the Sane]

Don't think so. If that were the case, it could be 2,000,000,000 light years, and it would still be instantaneous. It doesn't make any sense. Of course, neither does the ability to travel at light-speed.

As you approach the speed of light, your perception of time changes with respect to a stationary observer. If you could actually achieve the speed of light (you can't) the transit time would be 0, no matter how much distance you had traveled.

Re:Only 5X the mass of Earth!

[b.b.rodriguez]

FTA:

The surface gravity is more than twice that of Earth's (22 m/s/s versus 9.8 m/s/s on Earth)

No info on the atmosphere but its certainly exciting news.

Re:Rocky like Earth?

[creativeHavoc]

actually the article I read before (maybe the same one) suggested it would be rocky or "a frozen ice ball with liquid water on the surface." I suppose this would be seen as covered in an ocean. This however is not at all sembling an earthly ocean.

Ion drive not up to the task

[StefanJ]

No.

The best theoretical ion drive I've read about has an Isp of 10,000 seconds. That translates into an exhaust velocity of 100 kps (rounding up a bit).

Speed of light: A touch less than 300,000 kps.

Plugged into the rocket equation:

Mf+Mp / Mp = e^{300000/100) = 2.72 ^ 3000

Well, the Windows calculator tells me that's 5.0899334329769958439246007097416e+1303

That's the ratio of ("fuel" and payload) to payload.

Um, even if I screwed up somewhere, and I'm off by a factor of a million, that ain't good.

Re:5x the mass = impossible gravity

[germansausage]

Sorry if I sound like a dick, but pretty much everything you've said is wrong. Somebody else already 'splained the surface gravity being about 2.2g so I'll skip that bit.

Gravitational pressure? WTF?

I think you are confusing water pressure (which is equivalent to the weight of the water column above you) with gravity which is pretty much the same at the bottom of the sea as it is on the surface. I will also point out that life happily exists at the bottom of our deepest ocean trenches, 35,000 feet down, where the pressure is about 16,000 psi. The fishies down there are made of "organic cell structures" and are not "instantly crushed from the pressure". "How can this be?" I hear you ask. Because the cells are filled with water, which as you have stated correctly (about the only thing correct in you entire post) does not compress.

Gliese 581

[skeptictank]

Here is a link to more information about the star http://www.solstation.com/stars/gl581.htm [solstation.com].

The star is a variable, so it may periodically hammer planets in a close orbit with massive flares. If the planet was covered in a sea that might offer enough protection from the hard radiation of the flares to let life develop. It's surprising that a planet in this new orbit wasn't disrupted by the Neptune size giant closer to the star.

Re:How long to get there?

[Wonko the Sane]

The Calculus result after you take the limit is physically meaningless, in my opinion

I agree, but isn't the whole discussion physically meaningless? You can't physically travel at the speed of light. But if you could, the time dilation equation tells you that your perceived time is 0. Yes this breaks other equations, but the whole thing is impossible to begin with.

Re:Probably not tidally locked.

[Roger W Moore]

Based on our system...

Seems like a very big conclusion to leap to based on a sample size of one and even that single system contains an exception. Is there an underlying model which explains why planets above a certain mass must have dense atmospheres? Mars doesn't and I thought it's gravity was sufficient to stop heavier molecules escaping.

Re:How long to get there?

[Rei]

The problem isn't acceleration G forces. It's energy density. Even a "beamed core" antimatter annihilation system, to go 0.4 c with 100 mT of payload, would require about a thousand mT of antimatter [psu.edu]. 10:1 antimatter/payload ratio. That's not even slightly realistic, even in the long term, and we're talking about only 0.4c.

About the most we could realistically hope for is somewhere between 0.01c to 0.1c. Antimatter-induced microfusion, dusty fission fragment rockets, thermal rockets, nuclear saltwater rockets, various kinds of sails, etc, seem to be the most realistic options. But probably not during our lifetimes.

Re:Probably not tidally locked.

[AJWM]

Mars is small compared to Earth or Venus, only half the diameter. Its gravity will keep heavier molecules escaping, but e.g. a CO2 molecule is nearly twice the weight of an N2 molecule (48 vs 28 AMU), and almost three times the weight of a molecule of water (18), ammonia (17) or methane (16). It also depends on the temperature (hence velocity) of the molecules.

As for our system, it's not a sample size of one, it's a sample size of six planets of Venus size or greater. Yes, there's an exception, but we're reasonably sure we know why -- the same reason that we have a moon (formerly Earth's eighth continent ;-). We've got models of solar system formation, of course -- and some of those indicate that late-formation super-impacts may not be that rare -- but they're pretty much all based on our one known solar system and approximations of known physics. (Approximations being necessary to the modelling process.) There are a lot of unanswered questions both in planetary system formation and in planetary geology yet, that's another reason to learn whatever we can about extrasolar planetary systems.

Re:Rocky like Earth?

[rm69990]

Ummm...they're talking about rocky (eg. Mercury, Venus, Earth, Mars) as opposed to Gas Planets (eg. Jupiter, Saturn, Neptune, Uranus). Whether or not there is water on the surface is completely irrelevent.

Re:Uninhabital new worlds

[init100]

Surface gravity does not scale linearly with planet mass.

If the planet radius is constant, it does, at least according to Newton's gravitational laws. But gravity also is inversely proportional to the square of the planet radius (given a constant mass), so a low density planet (large, but low mass) has lower gravity than a high density planet (small, but high mass), and the gravity decreases faster with increasing radius than it increases with increasing mass.

The planet in the article would have a gravity of approx. 2.223g according to my calculations.

Re:Uninhabital new worlds

[Filip22012005]

From Pubmed:

ORL J Otorhinolaryngol Relat Spec. 1995 Jul-Aug;57(4):189-93.
Effect of prolonged hypergravity on the vestibular system: a behavioural study.Sondag HN, de Jong HA, Oosterveld WJ.
Vestibular Department ENT, University of Amsterdam, The Netherlands.

Golden hamsters were exposed to conditions of 2.5 times normal gravity (hypergravity, HG) for 4 months. During this period, tests were carried out to study equilibrium maintenance, swimming behaviour and open-field behaviour of these HG hamsters and of control hamsters living in a normal-gravity environment. The tests proved to be useful devices for detecting differences in perceptive-motor behaviour between HG hamsters and control hamsters. The HG hamsters had more difficulties in balancing on tubes and orientation during swimming. In the open-field study, the HG hamsters showed less locomotor activity than control hamsters. However, no differences were observed between the groups in washing, rearing and number of times having defaecation. These findings indicate that the daily transition from 2.5 to 1 g was not experienced as stressful by the hamsters, although performance on several perceptive-motor tasks was decreased, especially during the first weeks.

Re:New discoveries...

[robcraine]

Gravity...

OK. We know that F = G Mm/r^2
So, if the Mass is five times bigger... and the radius is twice that of earth, the force will be 5/2^2 = 1.25G

I don't think that we are able to accurately measure the size of the planet, but the site above quoted 1.5 times earth's radius. That would give us 5/1.5^2 = 2.22G

Plug your own numbers in and take your choice

Re:How long to get there?

[QuoteMstr]

Arthur C Clark addressed this issue in Songs of Distant Earth, actually. I was impressed. His solution? Put a big chunk of ice in front of the spacecraft and let it ablate away as the craft encounters bits of space debris; in fact, the plot involves the need to obtain another ice shield.

2.25G in a car?

[Dan Stephans II]

1) 2.25 times that of our own gravitational pull would not be ideal for us to live but, it doesn't mean nothing could live there. I pull 2.25g's with my car on a dry skid pad, I have not died yet.

Is your daily driver a formula 1 prepped vehicle? If not I seriously doubt you pull more than 1G on a dry skid pad. (when you say "my car" I'm assuming you are speaking of the vehicle you regularly drive). One of the best production cars for skidpad grip is the Ferrari Enzo and it "only" pulls about 1.05G.

2.25 G

[AdamThor]

WARNING: PEDANTIC

Do you really pull 2.25g in your car?

Let's give you the benefit of counting the Earth's gravity toward what you are feeling in your car on the skidpad. So you've got 1g straight down plus a lateral component N, and the total is 2.25.

The vectors form a right triangle, so a^2 + b^2 = c^2, right?

a = 1, b=N, c= 2.25
a^2 = 1, b^2 = N^2, c^2 = 5.0625
1 + N^2 = 5.0625
N^2 = 4.0625
N = 4.0625^.5 = ~2.01

Sports cars with special tires pull lateral around 1.0 G. Formula 1 cars and other extreme ground effects cars pull 2 g and more, but most people are never in one of those.

So, either
1) I've screwed up my physics
2) You've got a very uncommon car
3) Even adding regular gravity to what you can pull on a skidpad, you're maxing out your automotive G's closer to sqrt(2) = ~1.4

Well, that was fun. BTW, I agree with your point. 2.25G wouldn't kill us, tho I bet it would greatly reduce the lifespan of one's knees, hips and back. Certainly SOMETHING could live there tho. Probably alien warrior badasses who, should they come to Earth, could jump 50 feet and throw cars around like they were toys. That'd be cool, apart from how much it would suck. Hopefully we could get them hooked on television.