I have much more to say about the Breakthrough Starshot meetings, but last evening I decided to slow the pace a bit. I mentioned in my first report that the discovery of a planet around Proxima Centauri had woven through our San Francisco meetings, creating a bright thread of discussion that continued through all three days. We are also getting papers on Proxima’s planet that inform us more about its potential habitability. In the next couple of days, then, I want to go through some of these before returning soon to the broader issues of Starshot.
I also have to admit that I am still transcribing some of my handwritten notes from San Francisco to get everything in synch with my laptop, a process that is taking longer than I intended, thanks to my murky handwriting…
In any case, whether Proxima b is habitable or not would surely play a large role in any decisions about using it as Starshot’s initial target. So let’s remember what Guillem Anglada-Escudé and the Pale Red Dot team had to say about the planet’s placement, which they describe as “…squarely in the center of the classical habitable zone for Proxima.” I also want to quote briefly from the reliable Andrew LePage, whose Habitable Planet Reality Check: Proxima Centauri b is a post you’ll want to read. Here LePage sums up what we know so far:
Based on the limited data we currently have about Proxima Centauri b, it seems to be potentially habitable, although not very Earth-like. Its MPsini of 1.27 ME suggests that it is a rocky planet instead of a mini-Neptune with little prospect of being habitable in the conventional sense. It is also located inside the habitable zone (HZ) of its host star and detailed 3D global climate models suggest that it could be habitable over a wide range of realistic conditions. Comparing it to other potentially habitable exoplanets currently known (a short list dominated by planets of other red dwarfs), Proxima Centauri b is probably one of the most promising, on par with Kepler 186f…
Image: Announcing Proxima b. On 24 August 2016 at 13:00 CEST, ESO hosted a press conference at its Headquarters in Garching, near Munich, Germany. Speaking here is Dr. Guillem Anglada-Escudé. That’s Breakthrough Starshot executive director Pete Worden behind him at far right. Credit: ESO/M. Zamani.
Note the reference to MPsini, which refers to an essential problem with radial velocity studies. We can’t know how a given exoplanet’s orbit is tilted in relation to our view from Earth. The practical result is that the answer we obtain for a planet’s mass is only a minimum. We can see that it is affecting its star, but we have no way of knowing (unless we have a transit) whether we are seeing the system at a steep or shallow angle. So we’re really dealing with a set of possibilities about the actual range of a planet’s mass.
Anglada-Escudé and team calculate a mass for Centauri b of ~1.3 M? (i.e., 1.3 times the mass of the Earth). As to its size, another quote from LePage:
Based on statistical analysis of Kepler results performed by Leslie Rogers (Hubble Fellow at Caltech) and others, it is known that exoplanets seem to transition from being predominantly rocky to predominantly volatile-rich probably at a radius of about 1.5 RE and certainly no greater than 1.6 RE (see “Habitable Planet Reality Check: Terrestrial Planet Size Limits”). A planet with this radius corresponds to a mass of about 6 ME, assuming an Earth-like composition. With an unconstrained orbital inclination, there is about a 98% chance that Proxima Centauri b with a MPsini of 1.27 ME has an actual mass below this threshold.
LePage also looks at a paper I haven’t studied yet from Martin Turbet (Laboratoire de Météorologie Dynamique, Sorbonne Universités) and colleagues which studies climate models for Centauri b. The finding here is that this planet could support liquid water on the surface, making the case that the planet is at least potentially habitable.
JWST: Focusing in on Proxima b
Avi Loeb is chairman of the Breakthrough Starshot Advisory Committee. The Harvard physicist, who led our discussions in San Francisco, has also produced (with Harvard’s Laura Kreideberg) a new paper on Proxima b that advances our discussion. What Loeb and Kreideberg look at is the question of how we can learn more about the atmosphere of this planet, which in turn goes a long way toward illuminating potential habitability. The paper reminds us early on that the amount of stellar radiation reaching the planet is about two-thirds what we receive on Earth. The prospects for habitability really are enticing but we must have a way to confirm them.
The issues here are more serious than they may seem at first glance. We don’t know whether Proxima b even has an atmosphere. Remember that in order to have suitable temperatures for liquid water, this world must orbit very close to its small star, at about ?0.05 AU. That’s going to make for probable tidal lock, with one side of the planet continuously turned toward Proxima Centauri, the other away from it. It is not inconceivable that an atmosphere can collapse; i.e., we wind up with a world whose atmosphere is largely frozen out on the night side. We also face the possibility that atmospheric erosion from stellar winds can strip the world of its envelope.
We’re going to learn soon, through David Kipping’s work with data from the Canadian MOST satellite, whether a transit can be detected here, but the odds hover around 1 percent. In the absence of a transit, Loeb and Kreideberg look at what they consider the best option for characterizing an atmosphere: Measuring variations in its heat as it orbits Proxima.
The idea is this: A tidally locked planet will expose more or less of its hot dayside to the observer as it orbits the star (as seen from Earth). We should thus get thermal variation, which allows us to compare what we observe with models for a world with various kinds of atmosphere. If the planet has no atmosphere at all, this ‘thermal phase variation’ will be different from what we would see if an atmosphere is present, for an atmosphere would redistribute heat from dayside to nightside, changing the profile of the temperature variation over time.
Image: Figure 2 from the Loeb/Kreideberg paper. Caption reads: Thermal phase curves for a bare rock (left) and a planet with 35% heat redistribution. The models both assume an inclination of 60 degrees and an albedo of 0.1. Credit: Loeb & Kriedeberg.
The James Webb Space Telescope, to be launched in 2018, may be a key component in this work. The paper proceeds to outline the kind of observational test that could confirm the existence of an atmosphere on Proxima b. It is a combination of observing strategies from ground and space that seeks to measure the possible redistribution of heat. From the paper:
In the case of no redistribution, one could infer the planet does not have an atmosphere and is unlikely to host life. By contrast, if we do find evidence for significant energy transport, this would indicate that an atmosphere or ocean are present on the planet to help transport the energy. In that case, Proxima b would be a much more intriguing candidate for habitability. Either way, these observations will provide a major advance in our understanding of terrestrial worlds beyond the Solar System.
Observations with the JWST in the 5 ? 12 micron regime, the paper argues, can distinguish between bare rock and a world with 35 percent heat redistribution to the nightside at a high level of confidence. Longer observations can tell us whether an Earth-like atmosphere exists by detecting ozone absorption. Here it’s interesting that we can use an existing space instrument to begin the investigation:
This model assumes an Earth-like atmospheric composition irradiated by a GJ 1214b-like star. We note that the presence of ozone is sensitive to the ultraviolet (UV) spectrum of the host star (Rugheimer et al. 2015), which can vary for M-dwarfs even of the same spectral type (France et al. 2016). UV spectroscopy of Proxima should therefore be a priority while it is still possible with the Hubble Space Telescope.
A combination of our tools, then, can be applied to this task, one that would mark our first cut into the question of possible life around the star nearest our own. More thoughts on Proxima b’s habitability, as seen in a new paper from Rory Barnes (University of Washington) tomorrow.
Today’s paper is Loeb & Kreideberg, “Prospects for Characterizing the Atmosphere of Proxima Centauri b,” submitted to Astrophysical Journal Letters (preprint).
So Starshot is only for visiting exoplanets that we think are “habitable” or for exploring and discovering what is really out there?
I suspect THEY ( multiple redundancy “swarm” ) will explore whatever gets found in the systems of the three constituent stars of the Alpha Centauri system
1/ because they are easily the nearest
2/because we know of one planet already that is in the habitable zone of Proxima and
3/ As recent calculations show that the maximum limit of stable orbits for A and B are about 2 AU , which is pretty much contiguous with their hab zones too, anything discovered there will be worth targeting too.
In essence the first planet picks itself already along with whatever else hopefully turns up , which unless bigger than 1.5Re is likely to be terrestrial and in the hab zone and potentially habitable by default .
It’s unlikely that the three systems will turn up so many planets as to be unmanageable unless perhaps a remote planet is found orbiting Proxima I suppose. Even a mini Neptune , the most common planet in the galaxy to date , would be worth visiting for that very reason regardless of habitability .
Moons would be a big bonus though perhaps unlikely in closish binary A/B system.
Starshot would only require about 10 minutes to launch a wafersat to 20% the speed of light. This time is dictated by the need to accelerate quickly by directly focusing the phased array laser on the wafersat’s sail and avoid needing a lens 100s of km in diameter in space to focus the laser.
Once you have launched one probe, you aren’t going to stop their, after spending the billions needed to build the phased laser array in the first place. Starshot, if realized, would likely send multiple probes to *all* nearby target stars.
If that is right, and it clearly is, does this not make the Fermi paradox more paradoxical, because other civilisations should have thought the same way and the galaxy should be polluted with millions of miniature alien starchips?
The ease of detection of miniature alien starchips may be overstated if trying apply the Fermi Paradox here.
Think about it for a moment: Other than during the data transmission phase (relatively short given the lifetime of the starchip) most of these would be “inert” small mass/low visibility objects travelling around 0.20c.
If you have a reasonably good detection regime for such I’d love to hear it!
Can astrometric measurements be combined with radial velocity data to approach a best guess for orbital inclination?
The astrometric signal amplitude for Proxima b is 1.5 microarcsec.
The astrometric accuracy of Gaia is only ~30 microarc sec.
So we have to wait for future instruments, like the Theia astrometric mission,
a project to be sumitted to the European Space Agency next October:
http://sci.esa.int/cosmic-vision/57780-call-for-a-medium-size-mission-opportunity-in-esa-s-science-programme-m5/
Not quite true. Your calculation of the astrometeric signature assumes that the Mpsini for Proxima b is the same as its actual mass which is most likely not the case. Assuming your claim Gaia can detect a ~30 microarc second “wobble”, it could detect Proxima b if it were a 25 Earth-mass planet with an inclination less than ~3 degrees. Of course there is only ~0.1% chance of this scenario assuming a randomly oriented orbit, but a null detection by Gaia could still be used to set an upper limit on the actual mass of Proxima Centauri b.
As for the “30 micro arc second” astrometric accuracy you quote, I am curious where you got that number. It is my understanding that for a V=11 red dwarf star like Proxima Centauri, Gaia will have an astrometric accuracy on the order of ~10 microarc seconds. Assuming this figure is accurate for the short orbital period of Proxima Centauri b, that means Gaia could set an even more stringent upper limit on the exoplanet mass of ~8 Earth-masses with orbit inclinations less than ~9 degrees.
In fact, the Gaia astrometric precision will increase with time.
For Proxima:
– there will presumably be no data from the first Data Release
on Sept. 14 2016
– in one year, the forseen precision will be 50 – 100 micro arcsec
– at the end of the mission, the precision is expected to be
5 – 16 micro arcsec
(Gaia internal source)
Which is more than enough for planets around Alpha Centauri A and B, with the limiting factor being the sensors lower range of magnitude v=10 , well above that of the binary system. Is there any way of desensitising the array to allow imaging and to utilise Gaia to look for terrestrial planets around this one unique system? A forerunner of Theia.
Ironically 30mas is for the further stars. The average resolution is 23 mas and the best for close stars is less than 7mas. This still rules out Proxima but not Alpha Centauri ironically . It can’t be imaged sadly as it is too near and consequently bright thus saturating Gaia’s sensors ( unless someone can come up with a clever way of bypassing this )
If there is one mission we really need it is this one. Any search shows that it’s been around for a while in different guises as different teams have tried to make it work. NEAT, STEP, Theia etc . The current 0.8 m iteration seems to be a variant of “NEAT light” though I’m surprised that the decision for a two instrument “formation flying ” version versus a TMA still hasn’t been made yet. I guess that might depend on the performance of PROBA 3 mission when it becomes operational ? If nothing else it should reassure the ESA ( and Nasa too in terms of star shades) on the practicality of formation flying . Searches also reveal the many difficult technical challenges to overcome .
Ironically Guillem Anglada-Escude is also heavily involved with Theia and his comments to me echoed those of Prof Chen (of STEP) and David Spergel ( who has led US efforts at advanced microarc second level astrometry including clever adaptation of WFIRST -described in a detailed AAS Jan 2015 presentation ) – namely that THE big obstacle ( as with coronagraphic direct imaging too ) is the incredible stability required for any such telescope . This was reinforced in a recent review of Gaia on arXiv.
Good luck to all involved . If it’s to be M5 I’m sure the intervening time will allow the technical issues to be ironed out and all well worthwhile . Frustrating delay though . A truly great concept that will offer so much both in terms of mapping out nearby terrestrial planets but also to underpin the inevitable and necessary follow up to Gaia .
The semi-major axis of Proxima Centauri b is 0.0485 AU, so the projected separation is 37 milli arc seconds (mas). The pixel resolution of the Webb telescope NIRCam at 0.6 to 2 microns is 32 mas and it will have a coronograph. I feel fairly sure that the Webb (or the Vortex Coronograph on Keck II, or some new instrument) will be adopted to get an image of this object, and thus determine its inclination directly.
Sadly not. They simply don’t have the resolution and contrast definition to do so. JWST was conceived long before high contract coronagraphs and not with exoplanet imaging in mind unfortunately . Doing it via reflected light and phase transition to calculate the system’s inclination and then using phase thermal transmission from light to dark side is the only way and even then only just. Been done lately with Hubble/Spitzer but only on Hot Jupiters . Certainly using the MIRI instrument on the JWST and possibly the MRS too ,perhaps in combination with extended ground based spectroscopy ( maybe a hundred hours on keck) . This paper has a follow up in today’s arXiv which explains the whole non transiting process as well as it’s limitations. A few equations , but nothing too heavyweight no helps highlight the issues faced with things like ” diffraction limit” and “inner working angle “. Well worth a read .
It’s a big article but one section covers this approach and shows the various apertures required to view Proxima b at given wavelengths . Resolution=1.22 wavelength / aperture , so the shorter the wavelength the greater the resolution in effect . The 2.4m WFIRST for instance could only do it in the UV ( 0.36 nm) which for a predominately IR star like Proxima is no good. Needs a 4m space scope minimum ( up to o.59nm) and ideally 6.5m ( 0.91 nm) but also with a 1e10 contrast coronagrpgh which is way beyond JWST ( or any ground based scope with about 1e6 contrast ) .
ACEsat does have suitable contrast ironically but it’s 0.45m mirror is no where near big enough to image Proxima’s narrow hab zones cording to the equation above . It’s serious stuff approaching Nobel prize level skill.
There is a great review of this combination of high resolution spectroscopy and high definition imaging published on this site by Ignas Snellen, The worlds leading authority on this cutting edge technique . “Here come the Giants ” . Worth a read . He describes in detail what is effect the new science of “High dispersion spectroscopy “. Going to be big on the ELTs.
That’s why there are proposals for launching a free flying coronagraph to operate in tandem with the JWST.
Too late unfortunately. Despite vigorous lobbying over several years the JWST will not get the small but important modifications it requires prior to launch to enable use with a star shade . “Not a cent or day more ” sadly given the huge overspend that even came close ( very close !) to shutting the whole project down . For all the fantastic exoplanet science a star shade would add.
Transit spectroscopy now it’s best ( and still good to be fair ) bet for exoplanet characterisation. Even WFIRST’s exoplanet technology has run into trouble recently ( an unfavourable ” independent” auditor’s cost report on coronagraph inclusion ) through slightly overzealous campaigning for a star shade on what is essentially still a dark energy mission with the coronagraph on board as a secondary ” technological demonstrator ” technology .
The extra research money allocated has succeeded in bringing on coronagraph science by a good decade or so in its pre-formulation phase though.
Hopefully when the time is right , some time next decade , WFIRST , if it’s still working ok , will get a starshade that significantly enhances its exoplanet science ( depending on the size and distance of the shade it could even help exceed the small 2.4m telescope’s Atheoretical diffraction limit ) . In the meantime the battle is on for its many increasingly active advocates to get it star shade adapted (- few tens of millions ) and to the ideal SEL2 Lagrange lissajous orbit for star shade use. It was originally planned to go into a much more limiting ( cheaper launcher and data download friendly ) geosynchronous orbit . All discussed in the papers on arxiv in the last few days . A good introduction to exoplanet direct imaging and a good read. .
The Snellen et al (2015) paper on combining high resolution spectroscopy with imaging is just an extension of the Sparks & Ford (2002) and Riaud & Schneider (2007) papers.
The sooner we see high dispersion spectroscopy on big telescopes the better . I’m only sad that it was felt too risky to build at Dome C ( understandably) which would have allowed for a less intrusive background and allowed imaging further into the IR than the 2.5 microns possible at mid latitudes.
Whilst it is difficult and whilst we should be caref ul not to get overly blinkered on this one world, regardless of the life question, we need to focus attention on this planet to garner as much science as we can from this, the closest, exoplanet.
PCb gives us an opportunity to try out and , potentially, test techniques which can be used to gather information on other exoplanets.
Within reason, we need a full investigation of the entire system to staple down as much information as possible with current technology.
In the paper, they state that “we assume the inclination will be measured with ground-based high-resolution optical spectroscopy to a precision of about 1 deg.” That sounds reasonable, but there of course will be an intense competition for the first image of this planet, and I expect them to be obtained in due course.
What really BURNS me is if The Planet Finder interferomic mission had NOT been CANCELED we would ALREADY HAVE ONE! PRD would be merely CONFIRMING THE MASS!
Paul, it is NOT 1.6Me that is the generally accepted cut-off point, it is 1.6Re(radius, NOT mass). What IS a bit disconcerting is the recent paper by Kipping and Chen, stating that an ever accelerating TRANSITION from terrestrial to Neptunian STARTS at 2Me. The generally accepted MOST LIKELY mass is around 30% greater than the minimum mass, or approximately 1.7Me. In the LIKELY(98.5%)scenario of NO transits, if JWST can get detailed phase curve data, they should then have a good ESTIMATE of the angle of inclination of the orbit, and then we will know pretty much for sure.
Absolutely right, of course, and I’ve corrected the original. Asleep at the switch this morning…
DJ Caplan. I suspect that until the technology is perfected, and because of timescales, the Alpha Centauri system will be the first to be visited regardless.
It is the nearest and being a multiple star system is interesting from that perspective alone.
There is circumstantial evidence of planets for both A Cen A and A Cen B, these should be confirmed or refuted in the coming years. Any planets in the primary system make a visit even more scientifically interesting.
Absolutely. And the technology for that does exist already. Not only exists but at reasonable cost. ACEsat. Capable of high contrast imaging any planets in the Hab zones of Alpha Centauri A and B and rudimentary spectroscopy for less than that of a Nasa small Explorer programme budget ( $120 million) . Not successful but later guises allow imaging of the system for just $25 million with the Cubesat based 0.25m Centaur telescope .
The common denominator for ALL these exoplanet characterising techniques is plain for all to see:
Bespoke and dedicated .
Hopefully the discovery of Proxima b will highlight this. Decadel is tasked to looking for the follow up telescope to WFIRST/Hubble , but maybe it should be telescopes .
JWST has done the footwork for deployable telescopes and improvements in sensor technology should allow visible to 12 micron observation without expensive cryogenic cooling . Spectrograph technology has also benefitted from JWST with NIRSpec, MIRI and MRS. WFIRST has driven coronagraph technology .
Coronagraphs work best on unobstructed off axis , monolithic ( non segmented ) telescopes, the mirrors for which can easily be converted from ground based ULE mirrors. The less potent the coronagraph , the better it’s crucial stability and see of use and the lower its cost. Hence 1e8 ACEsat. Not enough to image terrestrial planets in Hab zones of stars like Alpha Centauri , but with modern sophisticated post processing of images like Orbital Differential Imaging which plots a prospective planets orbit by taking thousands of images over the course of its potential orbit and excludes interference signals as they wont possess classic Keplerian positions . Increases image contrast by up to 1000 times which with the 1e8 provided by the coronagraph takes it up to 1e11. More than enough for a terrestrial hab zone planet.
The drawback? For the Alpha Centauri Sun like stars the time required to plot out perspective orbits is years so requires that length of time to calculate . Fine if you have the dedicated telescope time to do this rather than shared with countless other equally deserving projects on a limited number of telescopes , especially in space .
So if established technology exists , rather than one colossal but development requiring telescope after WFIRST, why not have two big but smaller ? Why build a stretch goal 16m scope when thinks to extreme adaptive optics there will be top resolution from the 30m plus ELTs? JWST cost $8.5 million and overspent hugely , but because it was driving forward multiple new technologies simultaneously . Expensive but incredibly successful in that goal , it has laid the groundwork for a unique future of big but cost effective scopes . WFIRST pre-formulation and other telescopes have simultaneously driven coronagraph and sensor development .( driving down the cost of the latter significantly too)
Build a big ,deployable , wide field telescope based around JWST but not cryogenically cooled and with a bandwidth from U.V ( mirror coating only ) to 12 microns ( HgCdTe sensors) . Multi purpose and a 12m aperture still guarantees great resolution but easily launched within current or imminent EELVs . No new technology required or major development needs so no danger of uncontrollable “mission creep” in costs.
Also a separate 4.5-6m monolithic coronagraph dedicated exoplanet scope . Similar potency coronagraph to ACEsat ( 1e8) , though bigger for the larger scope but with reduced costs still as opposed to 1e10 version. The top up contrast provided by post processing including ODI and the lower potency coronagraph reducing stability requirements . As dedicated to nothing else it has the months required to do this. Utilises established spectroscopic technology as the 12m scope. Could even use the second hand mirror of decommissioned ground scope no longer needed ( afforded) as the ELTs come on line. Easily big enough to resolve habitable zone planets within fifty light years or more .
Both telescopes could be fitted with next generation ion thrusters to allow return to LEO for easy and safe servicing to prolongue useful decades long life . They could cross cover whilst one is being serviced and work in tandem for exceptional targets . Together they would produce a huge science return .
Both could be star shade adopted should the need arise. ( could this later be modified to help create a interferometer ?)
Two is better than one.
Costs for both telescopes could be amortised over years to avoid big peaks of spending. Instrument upgrades could be facilitated through module design. Extremely high resolution provided by ELTs alone and in conjunction.
Yes, the HDST is a popular item on many astrophysicists wish lists. Seems like a logical interim step preceeding an era of large interferometric space telescopes.
The limiting factor as always will likely be the OMB. Fantasy break: Until such point as a completely AI driven manufacturing sector is established which will free us from the age old traditional financing strictures.
OBM
The way to win over the OBM with any future telescope development is to design scopes that only use already proven technology , just scaled up within reason. Highly capable telescopes and related instrumentation are now readily available with extensive heritage rather than untried cutting edge technology. No new ideas that require the Long term maintenance of a highly skilled research/engineering team (which all so added to the cost of JWST).
Both JWST and WFIRST will have driven things on immeasurably by the end of the next decade. So it should be much easier to accurately predict telescope cost (better costing model will have been produced too thanks to JWST) and thus ease the burden by spreading it over time . Two telescopes may be more expensive than one , but the other lesson learned from JWST is to make your design modular so that service and upgrade are an option when required giving extended lifespans up to fifty years .( Hubble is over 25 years old and no one is saying it is past it, indeed it remains at the forefront of astrophysics research, including exoplanet science ) . That saves costs by not having to go for a complete rebuild every twenty years. Is a 12m LUVOIR telescope with updated , new instrumentation going to be redundant in twenty years? The same for a 6m HabEX scope .I think not. How old is the Hale telescope ?
Any large space telescopes could be equipped with increasingly potent ion drives and solar arrays to allow return to Earth/Moon Lagrange point for easy service or even all the way back to LEO . The return of manned space flight with cheaper launchers will help if robotic servicing is delayed .
This may be very important as it allows the scope to be positioned in an orbit that would be fuel costly using chemical engines. For large scopes, the X-37B in testing a new Xenon ion drive. There are also much smaller ion drives suitable for small scopes and the new cheap, micro, ion drive developed at MIT for use in cube sat sized telescopes/imagers.
Ion drives were first used in 1999 and are rapidly becoming mainstream. Solar sails are even more recent, and I’m hoping StarShot will push beamed sail technology to the forefront of fast propulsion technologies so that deep space probes will generate results quickly, rather than waiting many years.
Nasa recently signed a contract with AeroJet Rocketdyne to begin production of the 13 KW Hall thruster . Twice as powerful as the NEXT drive it supersedes and with massive improvements in solar cell technology , easily powered by modestly sized arrays in the vicinity of Earth and the various local Sun/Moon /Earth Lagrange points . Importantly without adding to vibration during telescope imaging . Large enough to return the scope even to LEO for servicing if deemed too risky in deep space for manned missions or until robotic technology can handle it.
Is this an overly restrictive assumption? Europa has no atmosphere, yet it has an ice covered subsurface ocean. So does a thermal redistribution signal of a atmosphereless rocky world rule out a permanently frozen over ocean on its darkside? IOW, will such an ocean fail to form and be stable under conditions where the atmosphere is ripped away from the sunlit hemisphere?
If the idea of ocean vent origin of life is correct, a rocky world with such an icebound ocean could have active vents with chemotrophic life, rather than terrestrial aerobic life. Such life would be of immense interest to biologists, even if it disappoints the general public.
Arguments about the problem of x-rays on life again seems to assume surface living organisms. x-rays are rapidly blocked by rock and even water. This seems to suggest to me that even terrestrial life could survive behind the terminator. It may also be fine in the deep ocean on the sunlit hemisphere, assuming that an ocean is stable and not lost to evaporation and photolysis.
I must strongly second Alex Tolley here.
Scenarios for an being earth-like Proxima b all seem to have a range of prerequisites (for example in this paper, http://arxiv.org/abs/1608.06919 , it needs both a starting hydrogen envelop AND several “Earths-worth” of water, to end up as an evaporated core). However, if it has undersea geothermal vents, and ice cover, we should (one hopes) be good to go.
Tangentially, perhaps just beyond a red dwarf’s snowline should also be considered for quasi-HZ worlds. If water worlds can retain their surface ice around such stars, then there is a possible path from vent-life to surface/near surface life. This paper covers coral bioflorescence to mediate the effects of our sun’s UV: https://t.co/XwZu6Y3lfj , and suggests similar adaptation at Proxima b.
Assuming such, then “deep-sea” chemotrophs could produce visible light during flares – that phototrophs could use. You could see a “race to the surface” as creatures start literally evolving their way upwards, developing better bioflorescence and photosynthesis.
It is possible to see if an exoplanet has an ocean by imaging reflected light, so called “Ocean glint”. Unfortunately JWST’s coronagraphs don’t allow anything like the 1e8 contrast to image this but the ELTs will especially if their first spectrums of Proxima b show high H2O absorption peaks in the right place .
Well, typically when scientists use the term “habitable planet”, they are talking about “habitable” in the Earth-like sense where the surface conditions can support the presence of liquid water leading to the possibility of life as we know it. But “habitable planets” by this normally implied definition are probably just a subset of all the worlds which could host biocompatible environments (not to mention the totally open question of conditions required to support life as we do NOT know it). Scientists need to start their search somewhere and starting with worlds which are most similar to the Earth (where we know for a fact that life exists) is the logical first step. This does not preclude searching for other types of worlds which may also support life but it is difficult to set any meaningful search criteria when the question about there being life on Europa, Enceladus, Mars or any number of other worlds in our own solar system is still very speculative.
I appreciate that it usually means planets where liquid water can exist on the surface. Which is fine when the planet rotates and heat is distributed. Added comp.lications when the HZ changes with the stars evolution. With tidally locked planets, the planet may only be able to maintain liquid water near the terminator. Obviously this requires an atmosphere otherwise the water will sublime and decompose, so another constraint. Icy moons with subsurface oceans have been excluded, rightly IMO, as we have no evidence that life can evolve on such worlds. However, it is different when the world is within the HZ, but loses its primordial atmosphere, yet retains a condition where water can remain near the surface, protected by an ice cover. It is analogous to Lake Vostok in Antarctica. This seems to be a more ambiguous situation, perhaps a bit more “out of the box” than the usual thinking on this in astrobiology.
If there was no atmosphere the combined low ,zero pressure and low temperatures would cause any liquid water to boil off immediately . Even any temporary surface water ice is lost through sublimation on low pressure , cold Mars .
Ashley, I think we must be using different models here. We know that water ice can exist in zero atmospheric pressure at 1 AU because we have some existence proof of ice in cold traps at the lunar poles. At Mars’ distance, we have subsurface ice with very low atmospheric pressure.
Given that Proxima b is tidally locked, and that the atmosphere has been stripped to prevent heat transfer, we have a cold trap in te hemisphere away from the sun. If the ocean freezes while there is an atmosphere, then the atmosphere is lost, I see no reason why the cold wouldn’t prevent the ice from sublimating. It would require heat transfer around the planet, or sufficient internal heat to allow this. However, given we know that this is possible in our outer solar system and that ice is possible in cold traps on the Moon and Mercury in the inner solar system, I do not see how you can be certain that such conditions are not possible on Proxima b. Unlikely perhaps, but not impossible.
Fair comment. I was thinking very much terms of Mars and the suggestion that small amounts of liquid water can exist at very low lying areas near the equator during periods of above freezing temperatures before evaporating off along with small areas of exposed subsurface water ice uncovered by rovers . Clearly larger areas of frozen water exist on the surface of many solar system bodies .
As far as Proximal b I’m sure the same applies . Like everyone it would be great to think there is enough atmosphere and warmth to allow even liquid oceans . My feeling is the big issue is as to whether it has an atmosphere at all . If so I’m convinced by the scientific arguments for the heat transfer by either wind or/and ocean currents of tidally locked planets from Light to dark side, establishing an equilibrium and preventing the dark side atmosphere freezing off.
Hi
It is generally taken for granted that this planet is tidally locked ,but I wander if the magnetic field of Proxima ,probably much stronger than the one we have at the earth orbit , could not make the planet spin and fight tidal effects ?
Well , I had to ask , even if it makes me seem stupid !
And other question : Could it be possible to listen to this star (and others ) with a radio-telescope and try to find something analog to Jupiter decametric radio emissions ? Yes the magentic field again ; but also a way to detect planets . Think the way we can detect Io from its signature in the radio emissions !
End of brain storming
I read a paper by a Berkeley Grad student a while back speculating on methods to detect exoplanet magnetic fields. It involved searching for cyclotron radiation resultant from stellar wind interacting with extant planetary magnetic fields. A difficult undertaking due to the expected weakness of the emissions. A large CME on the scale of the Carrington Event was seen as probably necessary in order to generate a detectable level of flux. And since the Earth’s ionosphere swallows radio waves in the frequency range expected, the author proposed a lunar based detector. All in all a good read, but…
Found it: https://people.eecs.berkeley.edu/~stevo.bailey/documents/exofields_report.pdf
A lunar radio telescope concept is currently under consideration by the Chinese Space Agency . Allegedly for just these reasons .
A low frequency lunar array concept was also worked on by the a team at University of Colorado. However, its deployment and operation come with a gigantic price tag. If you’re interested: http://lunar.colorado.edu/lowfreq/
The same conclusion reached by most Chinese scientists I think. Good , but cost doesn’t justify gain over either large Earth based scopes (especially with interferometers burgeoning all the time ) or space based.
I doubt a planetary magnetic field would be strong enough to significantly alter rotation, or be easily detected against the noise of its star. This is especially true of a terrestrial, non-gas-giant planet. Others can correct me if I’m wrong.
With that said, the presence of a magnetosphere is a very important factor for habitability.
Wow, this gives me butterflies in my stomach (fjärilar i magen). Makes me wish I had a science degree, but I got the art/abstract-gene instead :)
Would love for some remnants of alien architechture found in the Alpha Centauri system within my lifetime.. – well I can at least dream about it..
If we are the first…are we not obliged to build the alien architecture that others might discover it.
Yes, that of course should be our goal.
Then unmanned probes designed to go to other stars and making use of solar hydrogen three dee print shipyards from protons in other solar systems (designed to build more probes to send to other stars).
Life on PCb…..
First of all we need to move away from Earth centric thoughts. It is highly unlikely that nature has used a single model or chemical path to the creation of life, so for me the presence of water is niether here nor there.
In the case of PCb we have a world that has the potential to host liquid water, but the coditions for liquid water are varied and many fold. Temperature and atmospheric pressure are key. Having a world warm enough for water is one thing, but the pressure at the surface needs to exceed around 0.45 bar for water to remain liquid, too low a pressure and its boiling point decreases dramatically and sublimation occurs rapidly.
The other factor is the atmosphere…its chemical composition is key here, if this planet was heated sufficiently by the star then it may be a large Venus rather than Earth, it may have a super dence atmosphere that cloaks the surface and bakes it due to the greenhouse effect, or it could be a more N2 base atmosphere which then changes the ball game dramatically due to surface pressure, overall surface temperature as well as many other features.
If PCb is not tidally locked then the chances of a thick atmosphere increase as gravitational tides in the planet are likely to stoke the fires in the form of volcanic outgasing.
However, we can all speculate till the cows come home, but until we can fully investigate this nearest of exoplanets, everything is largely speculation, pure and simple.
As to the likelihood that nature has taken the same path: it’s probably safe to say that the path to life on Earth could be replicated- on another Earth-like planet. Certainly the fact that life on Earth appears to have been initiated by a single event, and- I’m on shaky ground here- it appears to have been initiated only once-it is also possible that other similar planets have a low likelihood of developing pesky apes.
Detailed astrometry and RV spectroscopy over more than a decade have already ruled out Jupiter ( and Saturn) mass planets within several hundred AU of Proxima . Both observations and simulation evidence suggests that gas giants will be rare around M dwarfs . Anything much nearer to the star would be drowned out by the star ‘s background activity .
In terms of rotation, it’s the spin of the planet that drives a dynamo based magnetic field rather than the other way round . In terms of resisting tidal locking ,thick planetary atmospheres have been simulated as being able to around M dwarfs . If Proxima b had a high initial orbital eccentricity ( if perhaps it migrated in from further out )then it could be in either 3:2 orbital resonance ( like Mercury ) or even a 2:1 .
I have been trying to figure if a planet that is tidally locked could rotate on an axis with the pole pointing toward the star? This would be similar to Uranus, but the gyroscopic effect would tend to keep the pole pointing in one direction, like the earth north pole pointing toward Polaris. Then in that case Proxima B would also rotate in an 11.2 day period and whatever the rotation would be, let’s say 20 hours. Would that keep it from being tidally locked? The other question is why would it be sideways, could the strong magnetic field from Proxima Centauri do that? We only have examples of tidal locking on moons and planets (Mercury and Venus) with little or no magnetic field and none have their poles sideways. Mercury and Venus are also locked to Earth’s orbital period and guess who has a high magnetic field! Some food for thought – all the planets that have high rotation rates also have large magnetic fields, so could there be a simple connection? Which came first? How do we know if the magnetic field is not involved with a larger active planets (Jupiter and Io) that have a molten iron core. Cutting thru Proxima Centauri magnetic field and Proxima B’s field generating its rotation.
My understanding is that Earth doesn’t have any orbital resonance with Mercury and Venus . We wouldn’t likely be here if it did . Mercury has a high orbital eccentricity ( 0.2) and it’s probably this that led to it being in a 3:2 resonant orbit rather than truly tidally locked. Resonances as high as 2:1 are possible and initial inclination of the planetary orbit to the plane of the ecliptic can indeed also contribute to this .
Venus isn’t tidally locked. It’s slow rotation is probably related to its dense atmosphere . Atmospheric resistance to tidal locking ( with even quite modest atmospheres let alone Venus’ 90 bar ) has been described by Leconte ( 2015) even in the close in planets of M dwarf systems .
Mars has little or no magnetic field and its rotation rate is nearly identical to Earth’s . Unfortunately it’s too small to have retained its heat of formation or a large enough radio nucleotide content to maintain the molten outer core the movement of which is believed to be pivotal in the dynamo production of a magnetic field as a planet rotates .
Juno is currently investigating Jupiter’s magnetic field so we should know soon. It currently believed to be due to electrical conduction a large liquid hydrogen based mantle caused by the enormous pressures within the planet. Any solid core ( still not proven and also under investigation by Juno) even if metallic would be so compressed by the incredible pressures at Jupiter’s core that however hot it couldn’t become liquid to allow creation of a field. This core compression is likely to be a big issue with rocky exoplanets substantially larger than Earth .
Io potentially has a liquid core due to its proximity to Jupiter and the massive energy released internally by complex tidal forces arising due to gravitational interaction between Jupiter and Io , Europa and Ganymede the three of which in turn are in a 4:2:1 orbital resonance .
Ironically icy Ganymede has a magnetic field which is believed to be cure to circulation of a sub surface briny ( electrolyte ) ocean.
Both planets show the same face to us.
From Wikipedia:
Spin–orbit resonance of Mercury:
After one orbit, Mercury has rotated 1.5 times, so after two complete orbits the same hemisphere is again illuminated. For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping the same face directed towards the Sun, in the same way that the same side of the Moon always faces Earth. Radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun; the eccentricity of Mercury’s orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly still in Mercury’s sky.[91]
The original reason astronomers thought it was synchronously locked was that, whenever Mercury was best placed for observation, it was always nearly at the same point in its 3:2 resonance, hence showing the same face. This is because, coincidentally, Mercury’s rotation period is almost exactly half of its synodic period with respect to Earth. Due to Mercury’s 3:2 spin–orbit resonance, a solar day (the length between two meridian transits of the Sun) lasts about 176 Earth days.[19] A sidereal day (the period of rotation) lasts about 58.7 Earth days.[19]
Venus:
The observed spin orbit resonance of Venus, whereby the same side on Venus faces the Earth at each inferior conjunction.
The paper recommends a detailed study of Proxima’s mid IR activity (and by default M dwarfs as a whole ) given most future phase and direct imaging by the JWST and ELTs is likely to take place in this wavelength which is currently poorly constrained and may help avoid the notorious activity seen generally at shorter wavelengths .
The ultra high res Doppler spectrograph ,ESPRESSO, “first light” later this year , is likely to initially be limited to observing quiet, low rotation M dwarfs in order to avoid disrupting stellar “noise” . Hopefully detailed IR observation will allow the creation of compensatory observation programmes .
Proxima’s discoverer- in- chief , Guillem Anglada- Escude , with others has been championing the need for creation of bespoke infrared Doppler spectrographs for some time .
In terms of heat transfer via phase observation from high resolution / high contrast imaging , this process is not new and has been used successfully before by Spitzer though for much easier close in gas giants.
Yes, I think this will be the first big test for ESPRESSO when she comes online.
That’s why the TRAPPIST and MOST Proxima Centauri observation runs are SO IMPORTANT, even if they do(did)NOT reveal any transits. An extensive database of the lower frequency near-continuous flares is IMPARITIVE for the modeling NECESSARY for the more sensitive ESPRESSO measurements!
i want to explore new planet especially promixa centauri b this new planet like i never seen soon i will be the first men to go on the planet promixa centauri b and other system plus exoplanet that why i want to be an astronaut just like in the sci-fi movies and show but this is reality my dream is promixa centauri thank you
I allways miss the major factors in articles about extra terrestrial life.
Despite the fact that mankind has found life on our planet on the most unexpected places (5km deep in hte ocean, near volcano outlets in extremely hot places) scientists keep telling us we need “rocky ground” breathable air etc etc.
Firstly: everybody forgets we (mankind) are running 250 miljoen years behind, due the the wipe-out of almost all life 250 mln years ago. So “others” might be way ahead of us.
Secondly: life can originate on the most unexpected places and atmosphere.
Shouldn’t we be using the different approach that life is everywhere untill proven otherwise?
“everybody forgets we (mankind) are running 250 miljoen years behind”
No. It can just as easily be argued that an extinction event accelerated species diversity and even intelligence by freeing up ecological space for more robust or adaptable creatures. When your house burns down it is a disaster, for you. For others it can mark a great opportunity. Life (and evolution) isn’t fair.
Evolutionary development rates and trajectories on other worlds will likely be highly diverse. A large number of variables play a role here.
Also, evolution is not by definition a linear process of ever increasing sophistication. Capabilities are gained and lost. For whatever reason, it took 4.5 billion years for the Earth to produce a technological species(assuming no undiscovered signs of predecessors in the rock strata ;) )
There was a very thought provoking article published on arXiv late this week that I think got a bit lost in the ongoing furore around Proxima b.
It addresses evolution of ” intelligence ” and links its to planetary habitability. As with all articles if this type its obviously open to debate but it’s the best of its kind I’ve seen yet. The author , Fergus Simpson of the University if Barcelona regularly publishes on this subject.
The article is :
“The longevity of habitable planets and the development of intelligent life “, Simpson 1/9 /2016 ( arxiv ) .
I suspect Paul may well run a piece on it at some point , so worth a crib ! An enjoyable and provoking read though whether you agree with it or not .
Yes, an interesting paper. I’m looking at it.
I would say that it only took 650 million years for us to develop, so how many billion year stable planets may be out there? So there was a 3 billion year void on this planet when no large animals developed mostly because of environmental problems. The real question is how many paradise planets are out there with intelligent aliens laying on the beach wondering why we have not figured it out yet.
The paper i cite above is available full text on arXiv and covers just these very issues. Nicely presented and a thought provoking read . Very much open to debate but covers the relationship between the length of planetary habitability and development of both complex and intelligent life.
Whilst gas giants have been ruled out in close orbits around all three AC stars, is it possible there are far-flung planetary mass objects bound to the system?
After all, if we hypothesise Proxima was formed along with A and B (admittedly this is not certain), it has ended up 150,000 AU from AB. So if Proxima could’ve been formed and flung out into a wide orbit why not gas giants?
15000 AU . If it is indeed gravitationally bound to Alpha Centauri A/B this might be the furthest way it will get in a high eccentricity elliptical orbit suggesting a much closer distance On occasion which is likely to disrupt any planets in wide orbits .
As to your speculation, Paul, on a mechanism to globally transfer heat on a tidally-locked planet: if an atmosphere exists, could one imagine very speedy global winds, driven largely by the temperature delta?
A tremendous upwelling of atmosphere could occur, driven by temperatures at different atmospheric levels; could this condition create large low-pressure cells (on the dark side, I’m thinking) that produce high ground level wind speeds?
Yes, I would think generating strong winds is inevitable in this situation, but maybe we have someone with some weather expertise who could jump in on this.
You’re spot on. There is a very nice little review going into detail on this :
“Life on a tidally locked planet ” , Singhal , arXiv 2014
And a somewhat more technical but still readable paper, referenced in the above :
“Climate instability on tidally locked planets ” Edwin Kite , Arxiv 2011
If life could exist on Earth 3.7 billion years ago, this does improve the chances for there being life on many other kinds of worlds, including ones we might currently consider hostile to organic creatures:
http://www.livescience.com/55950-worlds-oldest-fossils-found-in-greenland.html
To quote:
Both Kamber and Allwood also said the new findings have implications for the field of astrobiology and the search for evidence of past life on other planets — particularly on Mars.
Kamber said these potential clues about the very early emergence of life on Earth in the Hadean period supports his own recent research, published earlier this year, about the prospects for life in the water-filled craters caused by meteorite and comet impacts on the early Earth.
“I think the enclosed impact basins at the tail end of the bombardment at 3.8 [billion] to 3.85 billion years ago would have made great places for life to emerge from,” he said.
Allwood added that there is also clear evidence that, at the time the rocks at Isua were forming 3.7 billion years ago, conditions on Mars were similar to those on early Earth.
“[T]here were similar environments in bodies of water standing at the surface of Mars, offering a similar kind of environment to the ones that hosted the early evidence of life on Earth, at Isua and younger,” she said.
Until now, there had been a gap between the start of the fossil record on Earth and the youngest areas on Mars, where there was good evidence for standing bodies of water in the past.
“And you had to imagine that life could have arisen there before they dried up — but now at least we may have one example in the fossil record showing us that life can arise that quickly,” Allwood said.
@Navin Weeraratne I doubt that promixa will not have an atmosphere. It is at least as large as the Earth. Venus has a gravity close to the Earth and it still has an atmosphere over ninety times the Earths. Venus is thought by planetologists have thought it to have an atmosphere as high as 300 bars in the distant past since most of the water as in the form of steam. P. 223. Planetologists have thought that the solar wind removed most of the water over time.
Promixa b has thirty percent more mass than Earth and is at least as large as the Earth. Consequentily a large planet will have a large atmosphere. For a good greenhouse effect a lot of Co2 is not needed just a lot of pressure or many bars. P. 146. One bar equals Earth atmospheric pressure. Also a large planet might have a lot of volcanism. A tidally locked planet might have an increased volcanism due to unequal tidal forces on the planet like Jupiter’s closest moons. Some of the lost atmosphere can be replenished as on Venus which is thought to have over 100,000 volcanoes.
I expect to see a large atmosphere. It might be dominated by Co2, Co and So2. It might be planet with a greenhouse effect like Venus but not as hot with little liquid water and the oceans long evaporated. The big atmosphere of Venus still keeps its night side warm even though it has a retrograde rotation 243 days which is longer that it’s orbital period 225. I don’t think proxima b’s atmosphere makes it’s surface as nearly as hot as Venus but on the other hand the boiling point of water is higher than 212 F in a thicker atmosphere so it will be interesting to see what how much water is present in proxima b’s atmosphere if transit spectroscopy becomes available and eventually light polarization techniques which don’t need an occultation or star shade.
Source: The Scientific Exploration of Venus, Taylor, @2014
Perhaps now is the time for a lobby to be started to get funding to keep Hubble in operation longer. A robotic launch could attach a booster to put it into a higher orbit, failing that a service mission using a Soyuz capsule. To allow this technology to simply burn up in the atmosphere at this crucial stage is nothing short of negligence.
Of course it will be difficult and expensive, but a cheaper option that building a replacement and putting it into orbit. Hubble and Kepler have been viewed as “throw away” missions, yet some planning, financial support and foresight could see both serviced and maintained as scientific missions for years to come.
Kepler needs some fuel and new gyro’s, then the planet hunting can start again with avengeance, bit of planning and a new module could be added that would allow Kepler to change views and focus on other sections of the sky.
I am aware there are technical challenges to be overcome should we decide to take on these service missions, but these are less than the technical challenges in creating the missions in the first instance.
I agree. We could build a deep space space craft for servicing our space telescopes which our not in orbit around Earth. It could have three VASIMR engines, solar and nuclear power and we could fix a space telescope which breaks down anywhere in our solar system and use it also as an interplanetary exploration vehicle with a cargo bay for landing craft.
It could also tow space telescopes and place them in there proper orbits.