Earth-like exoplanet discovered around Proxima Centauri

[SelfSim]

Interesting article here on space.com that addresses many of the issues surrounding habitability of Proxima b; the flares, the tidal locking, the likelihood of water etc

http://www.space.com/33915-newfound-planet-proxima-b-habitability.html

What comes across from this article is how unconstrained our knowledge is thus far in the observation of exo-planets. For every 'possibility' cited, there are always other aspects to consider. For example (from the article):

However, more recent research has shown that planetary magnetic fields are actually supported by convection, a process by which hot material at the center of the core rises, cools and then returns," Barnes wrote. "Rotation helps, but Dr. Peter Driscoll and I recently calculated that convection is more than sufficient to maintain a strong magnetic field for billions of years on a tidally locked and tidally heated planet. Thus, it is entirely possible that Proxima b has a strong magnetic field and can deflect flares."

.. And we know Mercury has magnetic field .. but not really what we'd call 'an atmosphere' in the conventional sense:

Mercury's magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, though small enough to fit within Earth, is strong enough to trap solar wind plasma. This contributes to the space weathering of the planet's surface.

So, Mercury's 'atmosphere' appears to be a 'solar wind plasma' .. and thus not particularly conducive to 'habitability'.

 

[Belz...]

No .. no contradiction.
You just don't get the differences between my mind's thoughts, someone else's mind's thoughts and something that (supposedly) exists entirely separately from any mind whatsoever.

SelfSim... a mind that exists independently from yours IS objective.

The claim that something is 'mind independent' is a claim that no minds are involved whatsoever

And that's been addressed as well.

Never once have I said that other people are figments of, or are under the control of, my imagination!

Do they exist or not?

You never answered my above request - what is impossible about those underlined parts?

I didn't answer because what I said was a response to the part that _wasn't_ underline.

No

Yes. If objective reality doesn't exist, then there can be no evidence for anything. Of course you don't believe that, but it would be a consequence of it.

The thing is that I have not used anything other than observations of what has been written by minds in this thread.

Not written by minds. Written by physical bodies.

For the umpteenth time, I am not arguing a philosophical solipism here.

Good. Objective reality exists, then.

This depends entirely on what you mean by 'objective’ (and illusion) and you have thus far, not stated what you mean by this.

Define "this".

 

[SelfSim]

SelfSim... a mind that exists independently from yours IS objective.

And yet it takes your mind (in this case) to reach that conclusion.

Your claim that another mind 'exists independently IS objective' is a claim that 'objectivity exists' with no minds being involved at all ... unless you want to change the meaning of the terms 'objectivity', 'independent' or 'exists' to fit your own needs. Is that what you are doing then, choosing some new and unusual meanings of 'independent, objectivity or exists'? Because under normal logic, if something is claimed to be independent of something else, and specific examples of dependence are given, (such as my opening statement), that refutes the claim. In normal logic, anyway.

Do they exist or not?

Let me get this .. you are asking me to use my active mind to reach either of those conclusions? How could I possibly do that in any other way? Unless of course, your mind has conceived of the existence of some all-powerful 'objective' deity that confers 'existence onto 'people'. Which is what I'm beginning to think you're actually saying(?)

I didn't answer because what I said was a response to the part that _wasn't_ underline.

Which would be a clear case avoiding the question .. and until you demonstrate some honesty by at least addressing it, we have no common grounds for rational discussion. Until now, I have offered you the generosity of giving you the benefit of any personally held doubts I may have held (in my mind).

Yes. If objective reality doesn't exist, then there can be no evidence for anything. Of course you don't believe that, but it would be a consequence of it.

The consequence you cite is merely your mind finding the tautological equivalences of your initial untestable posit of: existence equates to 'is true'. This is not science. Science wants to test it. Show me the test, because your attempts thus far, have failed miserably in demonstrating it.

Not written by minds. Written by physical bodies.

And now we have the bizarre notion of 'physical bodies' being detached (ie: 'independent') of their own minds!

Do you see how ridiculous your 'argument' has become?

Good. Objective reality exists, then.

And I have never argued that the scientifc method doesn't produce objective reality, following its objective testing/verification process.

So where is your test which shows unequivocally that some reality can exist completely independently of any mind whatsoever? I'm still waiting for it, in order to substantiate your beliefs, assertions and posits.

Define "this".

Ok ..

If it's not objective, then it's an illusion. You can't have your cake and eat it too, no matter how much you want to.

There ya go .. that's what I meant by "this".

 

[lpetrich]

Linkfest:

Alpha Centauri^WP, Proxima Centauri^WP, Proxima Centauri b^WP

Planet Found in Habitable Zone Around Nearest Star | ESO -- European Southern Observatory. That page has a widely-distributed artist's conception of Pb, my abbreviation for Proxima Centauri b. The two bright stars near Proxima are Alpha Centauri A and B.

That artist's conception is for a mostly-rocky Pb. But if Pb is like GJ 1214b, then it would have a planetwide ocean extending downward for some sizable fraction of its radius.

A terrestrial planet candidate in a temperate orbit around Proxima Centauri : Nature : Nature Research -- professional journal paper

It's now listed in some exoplanet databases, like exoplanet.eu and NASA's exoplanet database.

[1407.4820] The Solar Neighborhood. XXXIV. A Search for Planets Orbiting Nearby M Dwarfs using Astrometry -- no evidence that Proxima has a planet around Jupiter's mass orbiting with a period of around 2 to 12 years.

[1607.03090] Effects of Proxima Centauri on Planet Formation in Alpha Centauri -- A and B can have Earthlike planets closer than about 2 AU, while Proxima can also have some such planets.

[1608.06672] MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri -- about 0.5% of Proxima's total luminosity and about 63 times a day

[1608.06908] Exploring plausible formation scenarios for the planet candidate orbiting Proxima Centauri -- Pb can form in any of them, it seems.

[1608.06813] The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present

"We set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays." This likely makes Proxima b lose hydrogen faster than the Earth, but the authors estimate that the planet lost only an Earth ocean's amount of hydrogen before Proxima settled down on the main sequence, some 100 - 200 million years after it formed.

[1608.06827] The habitability of Proxima Centauri b II. Possible climates and Observability If Pb is tidally locked, with one side permanently facing Proxima, then that side will be warm enough to have liquid water, even with a weak or absent greenhouse effect. The substellar point, where Proxima is at the zenith, will get up to 20 or 30 C.

[1608.06919] The Habitability of Proxima Centauri b I: Evolutionary Scenarios As Proxima settled down to the main sequence, it may have made Pb hot enough to have a Venus-like runaway greenhouse effect. Pb may then have lost much of its water, with hydrogen escaping into space and leaving behind oxygen. That would have been bad news for the origin of life, though the oxygen may eventually be consumed by crustal rocks getting oxidized by it.

[1608.06930] Biofluorescent Worlds: Biological fluorescence as a temporal biosignature for flare star worlds -- as a way of protecting from flares' ultraviolet light.

 

[lpetrich]

Sara Seager et al have written Mass-Radius Relationships for Solid Exoplanets, and I've deduced some size estimates for various mass estimates and compositions.

Proxima b (Pb) has only been observed with radial-velocity measurements of Proxima, and its inferred mass value is thus (mass)*sin(inclination). That value is 1.27 Earth masses. Averaging over possible orbit inclinations gives (4/pi) times this value, or 1.6 Me. Using (that estimate)²/(min estimate) as an upper value gives 2.07 Me.

For an Earthlike composition (70% rock, 30% iron by mass), 1 Earth mass gets 0.96 Earth radii, close to the Earth's observed value. Here are the radii for various masses and compositions, in Earth units:

Composition | Mlow | Mavg | Mhigh
(Mass value) | 1.27 | 1.6 | 2.07
Pure iron | 0.82 | 0.87 | 0.94
70% rock, 30% iron by mass | 1.04 | 1.12 | 1.20
Pure rock | 1.12 | 1.20 | 1.29
Half rock, half water by mass | 1.28 | 1.38 | 1.48
Pure water | 1.44 | 1.54 | 1.66

Here, "rock" is magnesium silicate.

For 1.6 Earth masses and an Earthlike composition, the planet's surface gravity would be 1.29 g's, while for half-rock-half-water, it would be 0.85 g's. The Earth's low-orbit and escape velocities are 7.9 and 11.2 km/s. For an Earthlike Pb, they will be 8.6 and 12.1 km/s. Using Tsiolkovsky's rocket equation and an exhaust velocity of 3 km/s (typical non-cryogenic or partially cryogenic), I find that for the same payload mass, one need 1.7 times as much booster mass, or 1.2 times as much linear dimensions. That's a problem not much discussed for super-Earths: space travel will be very difficult from their inhabitants.

Turning to surface features, mountains' maximum height scales as 1/(acc. of grav.) because too great height means that a mountain cannot hold its shape. This is from stresses in its interior being too great. Mauna Loa and Mauna Kea are about 10.3 km above the ocean floor, and Olympus Mons of Mars has 9.5 km when scaled to the Earth's gravity. So let's use 10 km. On an Earthlike Pb, that height limit is 7.75 km.

That limit also applies to organisms. Tallest tree: 116 m -> 90 m, Elephant max shoulder height: 4m -> 3m. For larger super-Earths, it's even worse, and we'd have to have an elephant's build to survive on them with our body size. We could shrink, but it would be hard to support a large brain and to live long if we were much smaller than our present size.

 

[Belz...]

And yet it takes your mind (in this case) to reach that conclusion.

So what? This seems to be your only answer to everything anyone's ever said in the history of the world.

You're not saying anything of value. We have methods of determining if things are true or not. Yes, sure, it requires minds to interpret (though a computer could do it, too), but it does not change the validity of the conclusion.

 

[JeanTate]

Returning to this ...

<snip>

What I do know is that the Jansky is a unit of flux density used for natural continuum emissions. Since continuum sources are extremely broadband, quantifying their bandwidth is difficult. The assumption is usually that they are broader than the detector bandwidth and therefore the energy is pretty well uniform across the receiver bandwidth. The total power therefore will increase with wider receiver bandwidth. This is where the Watts/m² of the collector area enters as the relevant measurement. That power measurement then gets divided by the bandwidth of the receiver, in Hertz to give the flux density in Watts per square meter per Hertz. (This gets divided by 10²⁶ to adjust for the resulting scale. This then becomes the Jansky.

(Sorry for all that .. I'm sure you already know this but its important to restate it for the next step).

The above only makes sense if the signal is spectrally broad, (ie: so that the recovered power can be assumed to be uniformly distributed across the receiver's detector bandwidth).

This is valid for for continuum sources, but it isn't for the kinds of narrow-band signals being sort by SETI artificial alien technology producing sources. SETI achieves their sensitivity through digital signal processing, which makes the instantaneous channel bandwidth (ie: the bin width) very narrow, thus shutting out much of the broadband background noise. That works if the assumption is that the signal they're setting out to detect is also very narrow (and therefore by definition, it also doesn't have a uniform power distribution across the channel). I think that assumption and technique, makes the Jansky a meaningless unit for SETI narrowband signal detection(?)

The Jansky is fine for characterizing the sensitivity of radio telescopes searching the continuum for natural signals .. but it is rendered by the above assumption as an inappropriate unit of measure for classifying the sensitivity of a SETI receiver. This is why, I think(?), they opt to classify receiver sensitivity in Watts per square meter.

Rather than spend lots of words explaining why this is, um, off, I'll give an "existence proof" of the contrary; Pustilnick&Martin (2016) (link is to the abstract of arXiv:1608.08284), "Study of galaxies in the Lynx-Cancer void. VI. HI-observations with the Nancay Radio Telescope". In particular, look at Fig. 1 ... that's a single-frequency line being studied (HI), not a continuum source. Note the units on the y-axis (yes, they're mJy).

Ok .. will have a look when I get the chance.
Cheers

Here's another that may be better in terms of being somewhat less technical: Padovani (2016) (PDF link to arXiv preprint), "The faint radio sky: radio astronomy becomes mainstream". However, it focuses on extra-galactic astronomy, so it's more of a general background than particularly relevant to Proxima b.

 

[JeanTate]

Umm, no.

We are, IMHO, largely talking past each other.

When I get a chance, maybe some time in the next few days, I'll try to write at some length. For now, radio astronomers observe lines (and bands). In fact if you look at the frequencies reserved for radio astronomy, you'll see quite a few are around things like the 21cm H line.

I hope my last post clears up the confusion over narrow-band and continuum sources, as far as radio astronomy is concerned.

Back to Proxima b and how easily radio astronomers can detect emissions that might point to artificial use of the radio part of the EM spectrum.

First, this thread is about Proxima b, not any other star or planet. It is only ~4 ly distant, a tad more than 1 pc.

Second, for background on radio stars, check out section 3.8.5 ("Radio stars") of the Norris+ (2013) paper I cited earlier; the sorts of radio emissions expected from stars is in there (there are not many of them, and they are pretty easily characterized).

If radio emissions from Proxima Cen (Proxima b is too close to resolve) are not like those of a flare star, or any other known radio star, they could be from an artificial source (i.e. not produced by the kinds of astrophysical processes astronomers are familiar with). Or they could be produced by processes not yet known or understood.

Is it necessary to use only a SETI approach - as SelfSim has outlined above - to study whether such an unusual radio emission may be artificial? I say no.

For example, the properties of airport radars, early warning missile warning systems, TV broadcasts, cellphone networks (and more) are easy to generalize, in terms of frequency, power, variability, polarization, band-width, etc. If radio emission from Proxima Cen were to be shown to have characteristics similar to any of these generalized sources (or any combo), the hypothesis that such emission were artificial would be strengthened, no?

And we can run this in reverse: what would the radio emission from our Sun look like, from Proxima b? How would it have changed, over the past century?

 

[smartcooky]

For example, the properties of airport radars, early warning missile warning systems, TV broadcasts, cellphone networks (and more) are easy to generalize, in terms of frequency, power, variability, polarization, band-width, etc. If radio emission from Proxima Cen were to be shown to have characteristics similar to any of these generalized sources (or any combo), the hypothesis that such emission were artificial would be strengthened, no?

Sorry, I think there is a language difficulty here.

Are you saying that observing radio emissions that appeared to share characteristics with our own artificial emissions would NOT strengthen the view that an advanced civilisation might exist on Proxima b, or that they would strengthen it?

 

[smartcooky]

And we can run this in reverse: what would the radio emission from our Sun look like, from Proxima b? How would it have changed, over the past century?

I would have though that would be obvious.

An observer over that period of time would see a dramatic rise in the amount/level of radio emissions, along with a very noticeable increase in the radio frequencies being used as the technical challenges of transmitting and receiving in the VHF then the UHF then the SHF and EHF bands were resolved. Before WW2, VHS transmissions above 100 MHZ would have been rare indeed.

However there is another thing to consider and that is, at least for broadcasting, in the future we may actually become almost radio silent as more and more broadcasts are watched/listened to over the internet, which will more and more be carried on fibre.

 

[RecoveringYuppy]

What are you assuming about the aliens looking at Proxima that makes it obvious or dramatic? It's debatable whether any repeatable signals even make it that far.

 

[JeanTate]

Sorry, I think there is a language difficulty here.

Are you saying that observing radio emissions that appeared to share characteristics with our own artificial emissions would NOT strengthen the view that an advanced civilisation might exist on Proxima b, or that they would strengthen it?

Sorry 'bout that.

I'll rephrase ... the original "If radio emission from Proxima Cen were to be shown to have characteristics similar to any of these generalized sources (or any combo), the hypothesis that such emission were artificial would be strengthened, no?"

Let "radio emission from Proxima Cen [is/could be/were to be] shown to have characteristics similar to any of these generalized sources (or any combo)" be A

Let "the hypothesis that such emission [is/could be/were] artificial would be strengthened" be B.

Rephrased: If A then B, no?

Alternatives: If A then B, wouldn't you say?/n'est pas?/don't you think?/right?

So, I am saying - in the form of a semi-rhetorical question - that observing radio emissions that appeared to share characteristics with our own artificial emissions WOULD strengthen the view that an advanced civilisation might exist on Proxima b (to use your paraphrase).

I hope that clears things up ...

 

[JeanTate]

I would have though that would be obvious.

It seems that there is at least one fellow ISF member for whom this is anything but obvious

An observer over that period of time would see a dramatic rise in the amount/level of radio emissions, along with a very noticeable increase in the radio frequencies being used as the technical challenges of transmitting and receiving in the VHF then the UHF then the SHF and EHF bands were resolved. Before WW2, VHS transmissions above 100 MHZ would have been rare indeed.

(my bold)

In my response to RecoveringYuppy's post, I'll go into this a bit more, but I think this is not quite right.

Leaving aside the capabilities of Proxima b's radio astronomers and their telescopes, over time, the radio emissions detected, measured in Jy and in carefully defined frequency bins (and polarization, etc) would not necessarily be so much louder than the background noise.

However there is another thing to consider and that is, at least for broadcasting, in the future we may actually become almost radio silent as more and more broadcasts are watched/listened to over the internet, which will more and more be carried on fibre.

Sure.

However, for airport radar, cellphones (etc), early missile warning systems, and so on, less so, right?

 

[JeanTate]

What are you assuming about the aliens looking at Proxima that makes it obvious or dramatic? It's debatable whether any repeatable signals even make it that far.

Indeed.

The signals do/would "make it that far" (unless blocked by a strange patch of the ISM in which the plasma frequency is higher); inverse square relationship etc.

As to "repeatable", well it might help to break it down by type ... (and leaving aside questions of the noise floor, polarization, anisotropy, etc):

• missile warning systems: very strong radio emission, but possibly low repeatability
• airport radar: certainly variable, but equally surely repeatable
• TV broadcast: ditto
• cellphones etc: some variability, but otherwise constant

In any frequency band (suitably defined), the emission in a particular direction from any but the first would vary on a fairly repeatable daily basis (and somewhat less so weekly etc), and over yearly+ timeframes would increase in intensity (power).

A bigger question - one that smartcooky seems to have missed - is what the S/N (signal to noise ratio) would be. In principle, this is pretty straight-forward; however, the details matter a great deal (and I'm not sure how well we could even sketch them out, much less put tight bounds on them).

Missile warning radars are not the only military uses of radio emission; does anyone know how much power there is in other types (e.g. "jamming")? Sure, those emissions will be highly variable, and some also highly anisotropic ... but then maybe they'd be detected as a Wow! signal, on Proxima b?

 

[RecoveringYuppy]

Cellphone towers are fairly low power, 4 KW or so? There are so many of them I would start to wonder about destructive interference, radio signals add up vectorially.

 

[SelfSim]

Indeed.

The signals do/would "make it that far" (unless blocked by a strange patch of the ISM in which the plasma frequency is higher); inverse square relationship etc.

As to "repeatable", well it might help to break it down by type ... (and leaving aside questions of the noise floor, polarization, anisotropy, etc):

• missile warning systems: very strong radio emission, but possibly low repeatability
• airport radar: certainly variable, but equally surely repeatable
• TV broadcast: ditto
• cellphones etc: some variability, but otherwise constant

In any frequency band (suitably defined), the emission in a particular direction from any but the first would vary on a fairly repeatable daily basis (and somewhat less so weekly etc), and over yearly+ timeframes would increase in intensity (power).

A bigger question - one that smartcooky seems to have missed - is what the S/N (signal to noise ratio) would be. In principle, this is pretty straight-forward; however, the details matter a great deal (and I'm not sure how well we could even sketch them out, much less put tight bounds on them).

Missile warning radars are not the only military uses of radio emission; does anyone know how much power there is in other types (e.g. "jamming")? Sure, those emissions will be highly variable, and some also highly anisotropic ... but then maybe they'd be detected as a Wow! signal, on Proxima b?

The biggest issue is sensitivity. See here for the explanation of the design parameters needed for SETI targetted and all-sky surveys leading up to the Phoenix survey which concluded in 2004 with the announcement of:

In March 2004 the Project announced that after checking the 800 stars on its list, it had failed to find any evidence of extraterrestrial signals. Project leader Peter Backus remarked that they had been forced to conclude that "we live in a quiet neighborhood".

(I believe Proxima Centauri was within the included search zone, also).

In particular, note Figure 5 here and included below.

Figure 5 shows the range of sensitivities that may be realized during the observing program in both the sky survey and the targeted observations. For comparison, sloping lines representing a range of transmitter EIRP have been included so that the sensitivity required to detect classes of transmitters having the indicated EIRPs can be deduced as a function of distance to the transmitter.

.. and note the x-axis is sensitivity in Watts/m².

Also note:

Neither of the search modes will be capable of detecting leakage radiation at power levels comparable to our own TV transmitters. However, the planetary radar transmitter at Arecibo could be detected at a distance of 400 light years with the minimum sensitivity of the targeted search or out to about 18 light years at the lowest frequency of the sky survey.

Which, I think, demonstrates the Tarter/SETI's view, which I posted way back in post #118, that when these design exercises were undertaken, (and even up to Tarter's 2004 document), TV broadcasts were beyond the technology of the time. Putting subsequent technology improvements aside for the moment, the Figure 5 graph still encapsulates the theoretical parameter constraints, which are still applicable to the discussion about types of signals, assumed EIRPs, background noise, receiver sensitivities, interstellar distances and search types, needed to establish a proper observational test for ETIs. This test is still the appropriate one for providing the minimum necessary data leading to any scientifically formed hypotheses/questions about ETI's residing on Proxima b.

Also noteworthy is the findings of the most recent 'Project Breakthrough Listen':

It began operations in January 2016, with release of the first batch of data in April 2016.
...
As of April 2016, the targets for the radio search with the Green Bank Radio Telescope in the Northern Hemisphere include the following:

All 43 stars within 5 parsecs
1000 stars of all spectral-types within 50 parsecs
One million nearby stars
Center regions of at least 100 nearby galaxies, including spiral galaxies, elliptical galaxies, dwarf galaxies and irregular galaxies
Exotic Stars: 20 white dwarfs, 20 neutron stars, 20 black holes

Their website mentions they have detected many 'interesting signals', but they have not yet been able to conclude that any of these are isolated to an external ETI source.

 

[smartcooky]

Here are a couple of things that have me thinking.

► Maybe advanced civilizations don't radiate for very much of their existence. If this is true, there are a couple of obvious reasons why that might be;'

1. they get whacked by The Great Filter shortly after achieving the technology, (Cold War ends up in nuclear holocaust rather than peace; their civilsation is wiped out by disease, a planet-killing meteorite or a massive CME.

2. Emissions are reduced because much of their media broadcast goes direct. On Earth, within 20 years there could be no direct terrestrial or satellite media emissions at all. This is already happening. I can listen to almost any major radio station in the world, or watch most of my SkyTV video content, on the internet. Same will apply to TV as providers use high speed fibre internet to get their broadcasts into homes.

► Maybe the S/N ratio really is too low for ordinary "not specifically directed at a star" radio emissions to be picked up over interstellar distances. This is why I think it might be worthwhile directing a very powerful radio signal towards Proxima b. It would be the quickest and cheapest experiment, even if it has a low chance of success. It would be like putting $10 on a horse at 5000:1 odds. Chances are, you will lose your money, but boy, if it wins!!!

 

[SelfSim]

...
► Maybe the S/N ratio really is too low for ordinary "not specifically directed at a star" radio emissions to be picked up over interstellar distances. This is why I think it might be worthwhile directing a very powerful radio signal towards Proxima b. It would be the quickest and cheapest experiment, even if it has a low chance of success. It would be like putting $10 on a horse at 5000:1 odds. Chances are, you will lose your money, but boy, if it wins!!!

Here's what you're after .. 'IETI: The Invitation to ETI' .. (these were the dudes and dudettes who first got their butts kicked whilst standing around on top of a building waving placards, in 'Independence Day'. )

The other idea is that ETI probes are lurking within our system and are listening to web traffic via satellite uplinks. Unfortunately, even the most powerful uplink signal emitted is still many orders of magnitude weaker than the solar flux. Thus, even if you access pages from the IETI website above, and they happen to transit a satellite uplink, there would be zero impact on our terrestrial civilisations as a result of ethereal IETI ideas.

 

[The Great Zaganza]

Unless the "Great Filter" is something that sterilizes or even annihilates a planet, all it would do is reset the development of technology-capable life.

 

[Craig B]

Unless the "Great Filter" is something that sterilizes or even annihilates a planet, all it would do is reset the development of technology-capable life.

Or the filter might operate on the same planet each time a life form develops the appropriate powers of destruction.