Tau Ceti: Sun-like star only twelve light years away may have a habitable planet

Dec 19, 2012 by Tim Stephens
Artist’s impression of the Tau Ceti system. Credit: J. Pinfield for the RoPACS network at the University of Hertfordshire, 2012

(Phys.org)—An international team of astronomers has discovered that Tau Ceti, one of the closest and most Sun-like stars, may host five planets, including one in the star's habitable zone ('Goldilocks Zone').

At a distance of twelve from Earth and visible to the in the evening sky, Tau Ceti is the closest single star that has the same spectral classification as our . Its five planets are estimated to have masses between two and six times the mass of the Earth, making it the lowest-mass yet detected. One of the planets lies in the star's habitable zone – the so-called Goldilocks Zone with it's 'just right' temperatures for supporting liquid water – and has a mass around five times that of Earth, making it the smallest planet found to be orbiting in the habitable zone of any Sun-like star.

The international team of from the United Kingdom, Chile, United States, and , combined more than six-thousand observations from three different instruments and intensively modeled the data. Using new techniques, the team has found a method to detect signals half the size previously thought possible. This greatly improves the sensitivity of searches for small planets and suggests that Tau Ceti is not a lone star but has a planetary system. The team presented its findings in a paper that has been accepted for publication in & Astrophysics.

"This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets," said coauthor Steve Vogt, a professor of astronomy and astrophysics at UC Santa Cruz. "We are now beginning to understand that nature seems to overwhelmingly prefer systems that have multiple planets with orbits of less than 100 days. This is quite unlike our own solar system, where there is nothing with an orbit inside that of Mercury. So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up."

Tau Ceti in the early evening sky in constellation of Cetus on Wednesday 19th December from Hatfield, UK. Credit: Stellarium software

First author Mikko Tuomi of the University of Hertfordshire emphasized the importance of new techniques the team developed. "We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches," Tuomi said. "This significantly improved our noise modeling techniques and increased our ability to find low-mass planets."

Hugh Jones, also at the University of Hertfordshire, said the researchers chose Tau Ceti for this noise-modeling study because they had thought it contained no signals. "As it is so bright and similar to our Sun, it is an ideal benchmark system to test out our methods for the detection of small planets," Jones said.

Over 800 planets have been discovered orbiting other worlds, but planets in orbit around the nearest Sun-like stars are particularly valuable. "Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these in the not-too-distant future. Planetary systems found around nearby stars close to our Sun indicate that these systems are common in our Milky Way galaxy," said James Jenkins of Universidad de Chile, a visiting fellow at the University of Hertfordshire.

The researchers discovered this planetary system using data from three state-of-the-art spectrographs: HARPS on the 3.6-meter telescope at the European Southern Observatory in La Silla, Chile (4864 data points); UCLES on the Anglo-Australian Telescope in Siding Spring, Australia (978 data points); and HIRES on the 10-meter Keck telescope on Mauna Kea, Hawaii (567 data points).

The result is based on spectra from taken as part of the Anglo-Australian Planet Search with the UCLES spectrograph on the Anglo-Australian Telescope, HIRES on the Keck Telescope, and reanalysis of spectra taken with the HARPS spectrograph and available through the European Southern Observatory public archive. This work would have not been possible without the ESO public data policies and the excellent work of the ESO Software development division and the ESO Science Archive Facility.

The international research team consists of Mikko Tuomi, Hugh Jones, John Barnes and David Pinfield (University of Hertfordshire); James Jenkins (University of Chile and University of Hertfordshire); Chris Tinney, Rob Wittenmyer, Jonathan Horner, Jeremy Bailey, Duncan Wright and Graeme Salter (University of New South Wales, Australia); Steve Vogt (UC Santa Cruz); Paul Butler (Carnegie Institution for Science); Simon O'Toole (Australian Astronomical Observatory); and Brad Carter (University of Southern Queensland).

Explore further: Astronomer confirms a new "Super-Earth" planet

More information: The paper (Signals embedded in the radial velocity noise - Periodic variations in the Tau Ceti velocities) is accepted for publication in the journal Astronomy & Astrophysics and is available at star-www.herts.ac.uk/~hraj/tauceti

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ScottyB
3.9 / 5 (14) Dec 19, 2012
Exciting news, hopefully we can create a telescope that will be big enough to actually get a real gimps of this system soon! that would be amazing
Gunzo
4.4 / 5 (7) Dec 19, 2012
Agreed ScottyB. Something this close with the same sun as our own and a potential planet in the habitable zone. Along with Curiosity's spectacular landing, this may be the most interesting space news of the year.
Grallen
2.5 / 5 (13) Dec 19, 2012
A habitable planet around our closest neighboring star? That would be incredible luck. We could colonize that no problem.
Sinister1811
2.5 / 5 (20) Dec 19, 2012
A habitable planet around our closest neighboring star? That would be incredible luck. We could colonize that no problem.


Yeah, maybe with the opening of a wormhole, or close to light speed space travel (neither of these exist yet). Even traveling at a fraction of light speed would take an enormous amount of time to get there. So I wouldn't say it's no problem.
grondilu
4.1 / 5 (9) Dec 19, 2012
Space is so frustrating. An extra-solar planet can be so close and yet so far!
Trewoor
1.9 / 5 (22) Dec 19, 2012
What streaks me most is that astronomers tend to make these unbelievable statements which are nothing more that highly improbably assumption sound as "this is the way it is".
I do love astronomy I and strongly support it, but I do not know is this ignorance or lack of knowledge or what?

So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up


This is based on what? That they fond 854 planets so far in 673 planetary systems. The accuracy of the measurements that they can take comparing it to the number of stars is unbelievably small.

They have not even started to scratch the surface of this subject, jet they make such false statement.

Cam on how long they have been assuming the "mass" of a galaxy based only on visible mass (stars), even kids know this is wrong!!
phillip_hooper2
1.6 / 5 (16) Dec 19, 2012
Even if this planet is in the habital zone, who can live under a constant 5G, I would weigh 875 lbs.
Peteri
1 / 5 (6) Dec 19, 2012
@Grallen: Without some serious genetic engineering to human physiology a planet 5 times the mass of the earth is uninhabitable - unless, that is, you plan to spend all your time in bed! ;-)

@Grondilu: The vast distances of interstellar space are the universe's built-in quarantine system.
NeutronicallyRepulsive
4.1 / 5 (18) Dec 19, 2012
phillip_hooper2: Five times the mass != five times the gravitational acceleration. The gravity is also inversely proportional to the square of its radius. I doubt is it is five times more dense than a molten metal core. So the radius will be probably quite larger, thus decreasing the gravity on the surface.
axemaster
4.1 / 5 (14) Dec 19, 2012
A habitable planet around our closest neighboring star? That would be incredible luck. We could colonize that no problem.


Enjoy being crushed by the 5x stronger gravity. Also, if you go down to the surface, you ain't never getting off it again. Rockets struggle getting out of Earth's gravity well as it is...

Five times the mass != five times the gravitational acceleration.


Assuming no change in density, the radius will increase by a factor of 1.7, thus decreasing the surface gravity by 1.7^2 = 3. The mass increased by 5, so the overall gravity compared to Earth will be (5/3)g.

So yeah, you're right. We overreacted. Thanks for making me rethink, ^_^
Modernmystic
1.6 / 5 (13) Dec 19, 2012
Since Tau Ceti has low metalicity in comparison to Sol, it's possible this planet's internal heat has shut off already, especially given that it's an older system. Also, since it's an older star it's quite likely that this planet hasn't been in a habitable place for long, ASSUMING they're taking into effect that G type stars tend to continue to gain luminosity and gradually heat up at 5 Gyr. Tau Ceti is estimated to be 5.8 Gyr. old.

There are a LOT of factors that go into this, more than is practical to list here. I'm quite sure the people who made this discovery know this, but it would be nice to hear that they do and they don't just look at the orbits, look at the luminosity, and then say "HABITIBLE!"....
Lurker2358
3 / 5 (21) Dec 19, 2012
Even if this planet is in the habital zone, who can live under a constant 5G, I would weigh 875 lbs.


5 planetary masses does not make 5G.

Even if you assume it's the same average composition as the Earth, then you must make a sphere with volume equal to about 5 Earth volumes, and then figure the radius of that:

Re = 6,371,000m = (1 is a simple metric)
Ve = 1,083,206,916,845,753,700,547.12 m^3
Me = 1(simple metric).

then.

Vp =~5Ve = 5,416,034,584,228,768,502,735.58 m^3
Rp = 10,894,256.756277236519168656626977 = 1.71 Earth radii
Mp = 5 Earth masses.

Gravity is mass divided by radius squared. The gravitational constant cancels in this case.

G = 5/1.71^2 = 1.71 Earth Gravities.

This is livable.

If obese people can weight 350 to 400 lbs and live on earth, and even walk around (although being nearly disabled,) then a healthy person can conceivably get around as well or better on that planet than an unhealthy person does here.

You will burn more calories too, so no fatties.
Lurker2358
1.8 / 5 (13) Dec 19, 2012
the problem with "Super Earths" which 5E masses is big enough to be counted as, is that if they actually do have the same average composition as the Earth, then because volume and mass increase more quickly than surface area, the planet will be covered by a very thick atmosphere, and it will be covered by a VERY deep ocean.

We would expect 5 times as much atmosphere by mass, and 5 times as much water by mass, but the surface area would only be 2.9 times greater.

So the atmospheric surface pressure would be at least 5 times greater than on Earth (mass times gravity for weight,) if it had the same surface temperature as the Earth, but you also have to figure other variables like temperature, which can vaporize more material.

Also, if there was proportional amount of water on the planet, then the oceans would be 1.71 times as deep. Doesn't sound like much, but given the higher gravity would erode mountains quicker, all topography should be under water...
Lurker2358
1.3 / 5 (11) Dec 19, 2012
However, having said all that, there's no good reason to assume the planet has the exact same composition as the Earth, so it could range anywhere from a Mars or Mercury-like desert world, to a true water world.

On the other hand, a planet with 5 times the mass could be 5 or more times as volcanic.

This should be the new "first target" for the James Webb, so they can take a look at this planet in infrared.
Pkunk_
2.5 / 5 (16) Dec 19, 2012
A habitable planet around our closest neighboring star? That would be incredible luck. We could colonize that no problem.

The fastest sustained speed anything human-made going out of the system has ever achieved is the Voyager 1 @ 60km/s and at its present speed of abt 18km/s has travelled 1/600th of a light year after more than 30 years of travel. At that rate it will take > 200,000 years for anything we send to reach Tau Ceti.
Any travel that takes more than 50 years(relative) is pretty much impossible to succeed esp. if it involves human passengers. So we need a form of travel which is at least 4000 times faster than Voyager 1. However all bets are off once Voyager enters the Interstellar medium since we don't really know the physics out there.

On another note , Tau Ceti is one of the Stars on which quite a few scifi stories/novels have been written. Nice to find out there might actually something worth visiting out there.
FMM
4.3 / 5 (6) Dec 19, 2012
I assume there is a selection effect here as there is with Kepler -- that is, we can expect to detect the larger planets more easily than those more Earth sized. Am I right?

Regardless, I don't know why planets around Tau Ceti should make be happy, but the news really made my day.
Lurker2358
1.4 / 5 (11) Dec 19, 2012
This super Earth can probably harbor Earth Exremophiles, IF it does not have a run-away greenhouse effect (like Venus).

Here are some other issues I've thought of for "super-Earths".

1, Higher magnetic field protects the atmosphere more from solar and cosmic radiation. Combined with the higher gravity, this could allow Helium from radioactive decay to accumulate in the atmosphere, driving up greenhouse effects.

2, In spite of being much more massive, the Troposphere in a purely "scaled up" Earth will be crushed into a lower altituded, due to the mass of air above itself and due to the higher surface gravity. This means the density of the bottom few kilometers of atmosphere will be several times higher than on Earth.

3, Higher gravity will make convection behave differently, so it will be harder for tall clouds to build because it takes more thermal energy to lift against the gravity. However, this may be offset by pressure or composition differences.
Lurker2358
1.4 / 5 (10) Dec 19, 2012
4, Atmosphere of massive planets may be stratified by composition, so that some molecules only occur at certain altitudes. On Earth the troposphere is well mixed: Oxygen, Nitrogen, and Carbon based molecules, plus water vapor. A "Super Earth" might not work that way, because the enhanced gravity may be enough to "sort" the molecules by density, which would be a problem for most Earth-like life forms.

5, Because the curvature of the planet is less (large spheres curve more slowly,) it would be possible for cyclones to be larger by a factor similar to the ratio of the surface area of the planets, give or take a bit. So no this planet if it was Earth-like composition, the maximum area for a cyclone would be about 3 times greater than on Earth. Since the atmosphere will also be denser in the troposphere, this means the integrated kinetic energy of a storm on such a planet would be far, far greater than a storm of the same wind speeds on Earth.
NeutronicallyRepulsive
1.9 / 5 (9) Dec 19, 2012
axemaster: Still. I reckon, it's no country for obese people. But some of those powered exoskeleton suits could make a difference, once perfected. We're not going anytime soon anyway.
GSwift7
2.3 / 5 (12) Dec 19, 2012
Assuming no change in density, the radius will increase by a factor of 1.7, thus decreasing the surface gravity by 1.7^2 = 3. The mass increased by 5, so the overall gravity compared to Earth will be (5/3)g


Yes, the gravity at the surface should be less than 5G. I wonder what the upper limit would be for long term human life. Probably not more than 3 G, if that. 2 G might even be pushing it.

That's also an estimate of the entire planetary system. If the planet has moons, then the mass of the moons is included in that 5X factor, so the mass of the planet could be less than that.
grondilu
3 / 5 (4) Dec 19, 2012
oops. Wrong. Please someone remove this message.
GSwift7
2.7 / 5 (14) Dec 19, 2012
One great thing about this is that it's so close, and it appears to be a much more common planetary arrangement than we have here. It's still too far for exploration any time soon, but just in terms of catagorizing and observing, it's marvelous. We should be able to eventually learn quit a bit about the characteristics of this super-earth with telescopic observation, due to its relatively close distance. It will make a great target for the advanced telescopes now under construction. Finding planets around nearby stars is a big deal, especially if we are able to find lots of them. The more examples we find, in terms of different types of planets, the more we are able to fill in the missing pieces in our catalogue of planetary types. Once we know what types are possible, and which are most common, we can make better guesses about what the more distant systems are like. You can use comparison and elimination to narrow down the guesses.
TopherTO
4.4 / 5 (7) Dec 19, 2012
Life will do what it always does, adapt. High gravity would mean natural adaptations through evolution. Our digestive, circulatory etc systems are based on our gravity. I don't see it as a blind leap of faith to assume any life, if it ever existed on this planet, would have adaptations to thrive under this sort of gravity.
rubberman
2.1 / 5 (11) Dec 19, 2012
Hey Lurk, don't forget about the requirement for plate tectonics in order to maintain a hydrological cycle, and those processes which generate the magnetic field. GS7 mused about the moons, great catch! At least one would be required to stabilize the rotational axis.
philw1776
1 / 5 (9) Dec 19, 2012
Before we get too excited, this discovery is all statistics. Notice how they injected various patterns of "noise" until they finally got signals of the orbiting planets. They got what they were looking for by playing stats tricks.

In other words, we really need more precise date to confirm or falsify this discovery. The good news is that given the excitement over such a nearby system, the data will be forthcoming over the next few years. Let's not forget that similar data gathering and analysis is ongoing for the even nearer Alpha Centauri system where one close in planet to Alpha Centauri B may have already been discovered.
GSwift7
3.1 / 5 (17) Dec 19, 2012
Before we get too excited, this discovery is all statistics. Notice how they injected various patterns of "noise" until they finally got signals of the orbiting planets. They got what they were looking for by playing stats tricks


No, they used synthetic noise to test their method. They then used the method on the real data and saw evidence for the planets in data from three different sources.

They actually did not find what they expected to find. They picked Tau Ceti exactly because they did not expect to find planets there. Oops.
Lurker2358
1.6 / 5 (11) Dec 19, 2012
philw1776:

With the planet being 5 Earth masses, the Hubble space telescope should be able to detect wobble by taking a few pictures every month or two and comparing them.

Because of the increased potential for atmosphere, I think this planet would actually be most Earth-like if it were at the luminosity adjusted equivalent of 1.31 A.U. Which is to say, where ever the stellar constant is 1365watts/m square, you should multiply by 1.31, and that would give the best distance for this planet to be ideally for actually producing an Earth-like conditions. Tau ceti luminosity is believed to be 0.52. So this puts the ideal distance as, I figure, at 0.6812 A.U. from the star.

This means to detect a wobble we'd need to observe it for several revolutions to work out any noise from the other planets. This will still be a few Earth Years worth of observations to get better idea of exactly how many planets there are and how massive is each planet.
GSwift7
2.9 / 5 (15) Dec 19, 2012
This means to detect a wobble we'd need to observe it for several revolutions to work out any noise from the other planets. This will still be a few Earth Years worth of observations to get better idea of exactly how many planets there are and how massive is each planet


Did you read the story at all?

They used years worth of data from previous observations. They already have years of data. They already detected the wobble. That's what the above story is about. They used a new analysis method on the old data and they were able to tease out the wobble signal from the random noise.

This is common in modern astronomy. New methods used on old data, as computer algorithms and computer performance improve, allow us to make new discoveries all the time, from old data. There are mountains of old data that have never been analyzed by modern computers, simply because nobody has taken the time to digitize it and run the processes.
Lurker2358
1.4 / 5 (10) Dec 19, 2012
Directly from the paper, article link above:

Thus it is plausible that the signals
are caused by a system of five planets with minimum masses
of 2.0, 3.1, 3.6, 4.3, and 6.6 M...

...Given this assumption, we also note that a candidate corresponding to the signal with a period of 168 days would have an orbit inside the liquid water habitable zone as defined by (Selsis et al.,2007)


The 168 day period planet is given as 4.3 Earth masses @ 0.552a.u.

The 642 day period planet is given as 6.6 Earth masses planet at @ 1.35 a.u.

Given things I discussed above, the 6.6 mass planet may actually have a temperature more comparable to Earth than the 4.3 mass planet.

Being slightly too cold is probably better than being slightly too hot.

Given the star's luminosity of 0.52:
The 4.3M planet should have a surface temperature of at least 495K, or 223C or 433F.
The 6.6M planet should have a surface temperature of around 83K, or -190C or -400F.

This doesn't count exotic greenhouse effects.
Lurker2358
1.7 / 5 (11) Dec 19, 2012
And considering how greenhouse effects work, the "real" temperatuers would be greater than or equal to what's posted above.

therefore the 4.3M planet is likely as hot or hotter than Venus at the surface.

the 6.6M planet is likely quite a bit warmer than the initial number I posted above, but 6.6M is large enough that it could be a hybrid gas giant at that size, or else just an enormous ball of ice, because the initial temperature calculation suggests it might be cold enough to liquify nitrogen even at Earth atmospheric pressures, but then again, higher pressure equals more temperature, but it also equals more pressure to liquify...

However, if it has a lot of helium and hydrogen in the atmsphere, as I surmised earlier, it might be able to hold enough heat to overcome the boiling point of liquid nitrogen to keep the atmosphere in tact...but we don't know the phase diagram for nitrogen under such gravity and pressure, and we don't know if it even has nitrogen...
Lurker2358
1.4 / 5 (10) Dec 19, 2012
Ok, so based on the fact some planets in our solar system have significantly different ratios between their solar constant at their position and their actual surface temperature, I figure the 6.6M planet could conceivably be another 80k to 100K warmer than the number I gave above for the Mean temperature, and it might be as much as 200k warmer at the equator during Perihelion.

Which is to say, the equator might have a temperature of about 10C during the perihelion, which is just below the Earth's global mean temperature. So it's probably very much like Hoth on Star Wars.

So I suppose some Earth micro-organisms and possibly even multi-celluar organisms might actually be able to live near the equator, if they don't die from the pressure, gravity, or any exotic chemistry...

As for the 4.3M planet, maybe I'm doing something wrong in my maths, but it seems like nothing we know of would survive there. It's mean temperature is probably slightly hotter than hydrothermal vents.
Modernmystic
1.7 / 5 (11) Dec 19, 2012
Ten degrees above freezing at the Equator I suppose qualifies as habitable? I'm not sure that would qualify as hospitable for abiogenesis or any kind of significant evolution.
Lurker2358
1.7 / 5 (11) Dec 19, 2012
Ten degrees above freezing at the Equator I suppose qualifies as habitable? I'm not sure that would qualify as hospitable for abiogenesis or any kind of significant evolution.


If you want to know how I got that number, I used Mars' mean solar constant to mean temperature ratio, which actually is 2.8, and gives 139K, which is nearly double using the Earth's ratio. Then I figured that on such a large planet, the difference between mean global temperature and max temperature could be a lot more than that, so I adjusted it.

To be sure, I'm probably giving it too much credit with the 10C max equatorial temperature at perihelion, but I don't want to be too big of a pessimist.

In any case, my assumptions about atmospheric pressure and composition are impossible to weigh without more evidence.

We Will need some direct IR measurements from a powerful telescope like James Webb to figure out what the real temperature is and spectroscopy for composition.
Lurker2358
1.7 / 5 (11) Dec 19, 2012
There's also internal heating questions, but it should be warmer than the Earth internally, if it's a similar age, because mass goes up more quickly than surface area.

therefore internal heating could offset some of the solar heating discrepancies.

And again, the extra mass makes it more likely to hold hydrogen and helium, therefore stronger greenhouse effect, and since the initial temperature is nowhere near cold enough to freeze out hydrogen and helium, it may be able to accumulate enough heat to unfreeze the nitrogen and maybe CO2 to get a real atmosphere.

Of course, since it starts out warmer, presumably, due to the extra mass, none of that may be an issue because it may also start out with lots of CO2 gas which would help a greenhouse effect keep it warm.

6.6M would have 1.87g for gravity, if it was Earth-like composition.

I can't imagine what would make the 4.3M planet habitable unless their initial numbers are wrong or something...
Lurker2358
1.2 / 5 (9) Dec 19, 2012
Now remember, planets this size could easily have 300 to 550 Earth atmospheres if they have experienced greenhouse runaways or something like that. Look at Venus, less massive than the Earth, but has 93 Earth atmospheres pressure at the surface, because of the runaway, presumably. I guess it probably started out with high CO2 and just got worse and worse, but that's my theory.
Q-Star
2.3 / 5 (12) Dec 19, 2012
Why must people write a ten or twelve page response to a one page article?

Oh well, at least now I won't have to buy the book.
Lurker2358
1.5 / 5 (11) Dec 19, 2012
Why must people write a ten or twelve page response to a one page article?

Oh well, at least now I won't have to buy the book.


Because the article tells you next to nothing. It can't even give you the mass correctly, as it rounded up from 4.3 to 5.

At least the paper gives the masses and basic orbital parameters, but the authors make no attempt to explain themselves when they claim these planets are in the "habitable zone".

We have no examples of planets in these mass ranges in our solar system, and even within our own solar system Earth and possibly Mars are the only habitable planets.

I was just showing that when you adjust for luminosity, neither of these planets is likely to be habitable, which is quite different than originally though from the article or even the paper.

It's become typical for articles on here to make sensational claims, and even the scientific papers make sensational claims to get headlines.
Q-Star
2.3 / 5 (12) Dec 19, 2012
Because the article tells you next to nothing. It can't even give you the mass correctly, as it rounded up from 4.3 to 5.


Naaaa, that can't be right, I think you should have said:

"Because just like the kid that sat next to you in the 4th, I can't control myself. You remember, the kid who didn't understand the question, only half understood the answer and hopped up and down with his hand raised saying 'I know! I know! Me! Me!' and when the teacher tried to ignore him and called on someone else, he blurted out that answer whether it was right or not."

That is what you should have said. Be that as it may be,,,, carry on professor, at least you're swearing like a street punk today.
Lurker2358
1.5 / 5 (11) Dec 19, 2012
The PDF file of the Paper gives you the orbital parameters and the real mass they calculated in the last few pages.

Then when you take the star's actual luminosity, it is not possible for the temperature of either of the two best candidates to be anything remotely like what the Earth experiences, and I was being VERY generous for the 6.6M planet.

You can calculate the solar constant of each planet from the luminosity of the star and the distance to the planet.

The first one has a solar constant of: 2,329.47 watts/m^2. This is about as high as Venus, and since it has 4.3M it's atmosphere is likely about 4 or 5 times as thick as Venus...

The second one has a solar constant of: 389.47 watts/m^2. This is a little more 28% that of the Earth.

I got the information I used to calculate that from the PAPER written by the scientists, and then did the math myself.

http://star-www.h...aper.pdf
Q-Star
2.3 / 5 (12) Dec 19, 2012
Oh, okay. I'm very impressed with all that.

Who would have thought that so many if's, could's, possible's, might's, maybe's and then's could turn out to be such an exact science.

I thank you for tutoring me.

sirchick
5 / 5 (3) Dec 20, 2012
"Only 12 light years" lol... better book my ticket now.
GSwift7
1.8 / 5 (10) Dec 20, 2012
Oh, okay. I'm very impressed with all that.

Who would have thought that so many if's, could's, possible's, might's, maybe's and then's could turn out to be such an exact science


Exactly. He's trying to work out all this stuff, but none of it is worth anything. There are too many unknowns until direct observation is possible.

What if the planet's rotational axis is highly oblique? Or what if the orbit is highly eccentric? These objects could go from too far in to too far out. The method we use does not tell us the eccentricity of the orbits, only the orbital periods.

There are other factors too.
rubberman
1.4 / 5 (9) Dec 20, 2012
So does this mean I jumped the gun last night when I read this article and designed a faster than light ship to get us there?

Dammit....I was so proud.
GSwift7
1.9 / 5 (9) Dec 20, 2012
So does this mean I jumped the gun last night when I read this article and designed a faster than light ship to get us there?

Dammit....I was so proud


Never mind. I already went there tomorrow and will get back yesterday. There's nothing to see there. If you do go, remember to aim where the star was 12 years ago. I had to make two trips. It looked like nothing there but Mormons. We have those here, so whatever.
rubberman
1.4 / 5 (9) Dec 20, 2012
Hey, did you do any fishing? On a mormon planet you can catch and keep more than one....
Torbjorn_Larsson_OM
5 / 5 (2) Dec 20, 2012
It is actually classified as two habitable planets among astrobiologists, e @ 0.77 ESI and f @ 0.71 ESI. (ESI > 0.7 is considered potentially habitable). [ http://phl.upr.ed...ts/ha... ]

That system alone provides 22 % of the 9 acknowledged potentially habitable planets! Tau Ceti joins Gliese 581 among the exclusive systems which have 2 habitables.

I'm not sure the press release makes sense, but I haven't read the paper, both habitable planets are well outside the 100 day orbit at 168 and 642 (!) days. I would like to see some statistics, where observational bias is considered, on the 100 day orbit claim.

One nice observation is that Tau Ceti has about half the metallicity of Sun. That explains the absence of giants.

Tau Ceti is also older than Sun, so you would expect life there. However it has an observed debris disk that is an order of magnitude more dense than ours (no giants), so that would be troubled life (many mass extinctions).
Torbjorn_Larsson_OM
5 / 5 (2) Dec 20, 2012
@ Trewoor: Astronomers don't do this in general, but this time (not having read the paper) it seems unsubstantiated. For one thing, this system with 2 of 5 planets outside the 100 day orbit criteria, and one habitable with twice the orbital period of ours, the system is a little bit of everything.

Except it isn't special in having 2 habitables, Gliese 581 has 2 too. In fact, 2 out of 7 systems with habitables, or ~ 30 %, have at least two of them. (Some deem Gliese 581 have more IIRC, 3-4 depending on atmospheric models.)

@ Phillip: Effective gravity scales as m*M/R^2 ~ m*R^3/R^2 ~ m*R at same density, so Tau Ceti e at ~ 1.9 Earth radii has ~ 2g gravity acceleration and Tau Ceti f at ~ 2.3 Earth radii much the same.

We can survive there, but we won't like it until we remodel muscles and bones after a year or so. And don't expect to live long, heavy circulation system challenges. Need genetic engineering and/or generations to get back up in lifetime.
Torbjorn_Larsson_OM
5 / 5 (1) Dec 20, 2012
@ Mm: It doesn't matter if the terrestrials are made by much the same composition elements regardless of how much (i.e. star metallicity) there is.

As it happens, Sun has relatively little radioactive isotope elements (mainly uranium), and Earth is a runt as habitable terrestrials goes, so Earth will cool its core faster than most.

At the same time the star and habitable zone lifetime is very dependent on oxygen content, IIRC. I'm not on top of that, but I believe again Earth comes out as shortlived relative to others.

As for (independent) habitability calculations, see the HEC I linked to earlier.
Torbjorn_Larsson_OM
5 / 5 (1) Dec 20, 2012
@ Lurker: Good thinking, water is a huge problem.

The generic ocean is set by the local disk composition - these are within the ice line (habitable zone) - so sufficiently dry, roughly same as Earth. In our case impactors didn't contribute much (see the D/H isotope ratios), despite being many orders of magnitude wetter than inner planets.

It is the Tau Ceti one order of magnitude as dense earlier observed debris disk, so an oom higher impact numbers, that contributes a little bit too much water to my liking. (A larger planet captures more, goes as the cross section area or R^2, while the surface area to disperse over does too. So no net effect there.)
Torbjorn_Larsson_OM
5 / 5 (1) Dec 20, 2012
[cont]

The problem with the hot TC e isn't mature species as extremophiles, but evolution of the first fragile RNA populations. At ~ 70 degC (see the HEC), it is sufficiently cool. RNA duplexes melting is a whole science, but it seems they are somewhat thermally stabler than our DNA duplexes (DNA stability is mostly chemical), and can take at 60 - 100 deg C depending on composition. [ http://online.lie...22860825 ]

Re your list, if we look at it in general (too early for Tau Ceti specifics, as other's say), it is complicated.

1, 4. Planetary magnetic fields shield the atmosphere, it is the solar magnetic atmosphere (~ 90 %) and finally the atmosphere ( ~ 10 %), that shields from cosmic radiation for example. But yes, superEarths will more easily have convective cores (magnetic fields) and mantles (plate tectonics), Earth is marginal on both.
Torbjorn_Larsson_OM
5 / 5 (1) Dec 20, 2012
[cont]

Just from being more massive, a superEarth will retain an atmosphere for ~ 20 billion years or more as compared to Earth ~ 10 billion. So the star life time may set the habitability lifetime (as it does in our case), not the atmosphere, unless we go to M dwarfs that lives for many 10s of billion years.

These atmospheres are well mixed (convective).

2-3. Pressure/gravity isn't a problem for life (see the crustal life), but for traits (as flying, say).

5. ??? But weather and climate is not well understood yet. Certainly both Mars, Venus, and the gas giants have megastorms. But Titan's & Pluto's atmospheres seems calm.

For estimated surface temperatures of TC e&f, see the HEC. They are, of course, potentially habitable (since HEC lists them).
OceanDeep
not rated yet Dec 21, 2012
This is a great discovery. Comments have been generally very interesting, in particular those with objections to certain details in the report. Such objections are good for science.

1. Number of Gs. I think someone has shown it would be about 1.71 G, not 5G.
2. Distance and travel time. Certainly 12 ly is way too far to travel in a human lifetime using current technology.

Still, think about the possibilities. Lowly bacteria don't give up when faced with seemingly insurmountable odds, so why should we? If humanity wants to fulfill the destiny it feels it has in this universe, a planet like the one around Tau Ceti seems like a nice beacon to shoot for.

It needn't be a permanent home. It could be a stepping stone to some other system that is better. And we could use generation star ships one day.

Naturally all that talk is way premature when we haven't even laid eyes on the planet. But if we think in terms of possibilities, we can see the door to the cosmos is nudging open.
SteveInNM
1 / 5 (8) Dec 21, 2012
ok..Proof of intelligent life. 1. Does it have water like has a bluish reflection, like Earth from a distance. 2. On the dark side do you see points of light as indicator of the horrible commuting conditions like we have here in the cities on Earth. 3. Can we pickup TV transmissions of their commercials.
SteveInNM
1.2 / 5 (9) Dec 21, 2012
ok..Proof of intelligent life. 1. Does it have water like has a bluish reflection, like Earth from a distance. 2. On the dark side do you see points of light as indicator of the horrible commuting conditions like we have here in the cities on Earth. 3. Can we pickup TV transmissions of their commercials.
GSwift7
1.8 / 5 (10) Dec 21, 2012
Still, think about the possibilities. Lowly bacteria don't give up


Yes, the possibility is what's at stake here. If we don't find at least one good candidate for a human outpost at one of our nearest neighbors, then the possibility of ever leaving the solar system falls to nearly zero.
SteveInNM
1.3 / 5 (8) Dec 21, 2012
ok..Proof of intelligent life. 1. Does it have water like has a bluish reflection, like Earth from a distance. 2. On the dark side do you see points of light as indicator of the horrible commuting conditions like we have here in the cities on Earth. 3. Can we pickup TV transmissions of their commercials.
baudrunner
1 / 5 (10) Dec 22, 2012
Tau Ceti is a prime candidate for those "giants" mentioned in the bible, or as they are called in some scriptures, the Nephilim. It makes sense that life on a planet with 1.7 times earth's gravity would evolve proportionately larger life forms.

For those who think that it would take too long to get to the next star to make it worthwhile should read Robert Zubrin's book "Entering Space: Creating a Spacefaring Civilization", published in 1999. He envisions a journey to Alpha Centauri which would take less than 50 years using technologies available then. Since then, the state of the art has evolved, including plasma ion rocket engines and the like. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) could get us to Mars in about 30 days, for example. In another 15 years, even that figure will be out of date.
Q-Star
1.4 / 5 (9) Dec 22, 2012
ok..Proof of intelligent life. 1. Does it have water like has a bluish reflection, like Earth from a distance. 2. On the dark side do you see points of light as indicator of the horrible commuting conditions like we have here in the cities on Earth. 3. Can we pickup TV transmissions of their commercials.


You must really wish for an answer, since ya asked three times. Here is the best I can do,,, maybe someone else will be able to give a more thorough assessment.

1) Who knows? Perhaps.

2) Who knows? Perhaps.

3) Maybe, maybe not,,,, Who knows?
flashgordon
1 / 5 (5) Dec 22, 2012
Don't know if this has been mentioned yet; and my post at spacedaily was deleted(getting tired of nazy scientists), but,

Tau Ceti is over a billion years older than Sol(our solar system). Yes, biology could have evolved differently than hear on earth; but, I would think the chances are slimmer that intelligent life arises on older and older solar systems than sooner(the older the solar system, the greater chance of life and civilization destroying impacts and other astronomical devestations).

Something else to bring up about Extraterrestrial Civilizations; the Fermi question implies there must be lots, like millions and billions of intelligent technological species out there; not a needle in the haystack; the arguement against why we havn't detected E.T's from any wavelength astronomy . . . that well, there's lot of space and lots of stars, and we're looking at a needle in a haystack falls apart at this point; i think we can confidently say that technological species is rare;
superaxe
1 / 5 (2) Dec 22, 2012
Again, lack of foresight seems to rule this administration. If Planet Finder hadn't been cancelled.......
Mayday
1 / 5 (3) Dec 23, 2012
I chose Tau Ceti as the destination for my starship novel, Civilization Starship, because, of course, its color, age and mass are similar to our Sol, and it is not a binary system. But also because getting there does not require traveling out through our plane of the ecliptic, plus the way there is relatively free of significant dust lanes.

Civilization Starship was inspired by the efforts of the 100 Year Starship initiative and explores issues of the limits of the human mind in undertaking such a voyage. Would human error intervene? In interstellar travel there is very, very little margin for error. Consider that, to date, no human being has been more than three days away from home. The story is a fun sci-fi romp. Check it out at http://www.starshipnovel.com.
Fleetfoot
5 / 5 (1) Dec 24, 2012
Tau Ceti is over a billion years older than Sol(our solar system). .. I would think the chances are slimmer that intelligent life arises on older and older solar systems ..


All it means is that if it arose there, it would probably have done so a billion years ago.

.. the arguement against why we havn't detected E.T's from any wavelength astronomy ... that well, there's lot of space and lots of stars, and we're looking at a needle in a haystack falls apart at this point; i think we can confidently say that technological species is rare;


If we built an solar-orbiting satellite to receive signals from a similar device at a nearby star, we would make it large enough so that the effective beamwidth excluded the thermal emissions from the star to maximise SNR. For transmit power, the satellite would be within a few AU of the star so the beamwidth would be less than that. Only signals from nearby star pairs perfectly aligned with us would be detectable.
sirchick
not rated yet Dec 24, 2012
Why are we debating what planets are habitable for us humans such as gravity ?

When the journey to get to them is not.. its an irrelevance if its habitable for human life.
What is more important is the chance of other life - namely bacteria at the very least.
C_elegans
not rated yet Dec 24, 2012
Billion year old bacteria, yum. If life starts, it will flourish. Competition favors slow but stable growing multicellular organisms. Biofilms are the predecessors of slime molds.
Spacy
1 / 5 (3) Dec 25, 2012
I must note that Tau Ceti is not yet visible on Stellarium.
When it does show up, we should be able to see the planets. I can only hope.
discouragedinMI
1 / 5 (10) Jan 16, 2013
Humans can't even colonize an ant hill not to mention the moon or Mars. And before we start plans for a "Red Dwarf" spaceship, let us make sure we are not stepping on the neighbors garden plants.

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