Astronomers Find Tantalizing Hints of a Potentially Habitable Exoplanet

Article written: 8 Nov , 2012
Updated: 23 Dec , 2015

Dwarf star HD 40307 is now thought to host at least 6 exoplanet candidates… one of them well within its habitable zone. (G. Anglada/Celestia)

Located 43 light-years away in the southern constellation Pictor, the orange-colored dwarf star HD 40307 has previously been found to hold three “super-Earth” exoplanets in close orbit. Now, a team of researchers poring over data from ESO’s HARPS planet-hunting instrument are suggesting that there are likely at least six super-Earth exoplanets orbiting HD 40307 — with one of them appearing to be tucked neatly into the star’s water-friendly “Goldilocks” zone.

HARPS (High Accuracy Radial velocity Planet Searcher) on ESO’s La Silla 3.6m telescope is a dedicated exoplanet hunter, able to detect the oh-so-slight wobble of a star caused by the gravitational tug of orbiting planets. Led by Mikko Tuomi of the UK’s University of Hertfordshire Centre for Astrophysics Research, a team of researchers reviewed publicly-available data from HARPS and has identified what seems to be three new exoplanets in the HD 40307 systems. The candidates, designated with the letters e, f, and g, all appear to be “super Earth” worlds… but the last one, HD 40307 g, is what’s getting people excited, as the team has calculated it to be orbiting well within the region where liquid water could exist on its surface — this particular star’s habitable zone.

In addition, HD 40307 g is located far enough away from its star to likely not be tidally locked, according to the team’s paper. This means it wouldn’t have one side subject to constant heat and radiation while its other “far side” remains cold and dark, thus avoiding the intense variations in global climate, weather and winds that would come as a result.

“The star HD 40307, is a perfectly quiet old dwarf star, so there is no reason why such a planet could not sustain an Earth-like climate.”
– Guillem Anglada-Escudé, co-author.

“If the signal corresponding to HD 40307 g is a genuine Doppler signal of planetary origin, this candidate planet might be capable of supporting liquid water on its surface according to the current definition of the liquid water habitable zone around a star and is not likely to suffer from tidal locking.” (Tuomi et al.)

If HD 40307 g is indeed confirmed, it may very well get onto the official short list of potentially habitable worlds outside our Solar System — although those others are quite a bit closer to the mass of our own planet.

UPDATE: HD 40307 g has been added to the Planetary Habitability Laboratory’s Habitable Exoplanets Catalog, maintained by the PHL at the University of Puerto Rico at Arecibo. It’s now in 4th place of top exoplanets of interest based on similarity to Earth. According to Professor Abel Mendez Torres of the PHL, “Average temperatures might be near 9°C (48°F) assuming a similar scaled-up terrestrial atmosphere. It might also experience strong seasonal surface temperature shifts between -17° to 52°C (1.4°  to  126°F) due to its orbital eccentricity. Nevertheless, these extremes are tolerable by most complex life, as we know it.” (Read more here.)

While the other planetary candidates in the HD 40307 system are positioned much more closely to the star, with b, c, d, and e within or at the equivalent orbital distance of Mercury, g appears to be in the star’s liquid-water habitable zone, orbiting at 0.6 AU in an approximately 200-day-long orbit. At this distance the estimated 7-Earth-mass exoplanet receives around 62-67% of the radiation that Earth gets from the Sun.

Representation of the liquid water habitable zone around HD 40307 compared to our Solar System (Tuomi et al., from the team’s paper.)

Although news like this is exciting, as we’re always eagerly anticipating the announcement of a true, terrestrial Earthlike world that could be host to life as we know it, it’s important to remember that HD 40307 g is still a candidate — more observations are needed to not only confirm its existence but also to find out exactly what kind of planet it may be.

“A more detailed characterization of this candidate is very unlikely using ground based studies because it is very unlikely [sic] to transit the star, and a direct imaging mission seems the most promising way of learning more about its possible atmosphere and life-hosting capabilities,” the team reports.

Read: How Well Can Astronomers Study Exoplanet Atmospheres?

Still, just finding potential Earth-sized worlds in a system like HD 40307’s is a big deal for planetary scientists. This system is not like ours, yet somewhat similar planets have still formed… that in itself is a clue to what else may be out there.

“The planetary system around HD 40307 has an architecture radically different from that of the solar system… which indicates that a wide variety of formation histories might allow the emergence of roughly Earth-mass objects in the habitable zones of stars.”

The team’s paper will be published in the journal Astronomy & Astrophysics.

Another researcher on the team, Guillem Anglada-Escudé of Germany’s Universität Göttingen, assembled this tour of the HD 40307 system (not including g) via Celestia.

Inset image: current potentially habitable exoplanets. Credit: PHL @ UPR Arecibo.

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46 Responses

  1. newSteveZodiac says

    Even assuming a VASIMR engine with a very large propellant tank, a monster ice shield and .99C capability I wonder if we will ever be able to contemplate a 100 year spacecraft mission – 150 years unless we can crack FTL comms

    • Zoutsteen from Holland says

      Maybe it will make you feel happy to know that the limitation of FTL is based on the assumption of the maximum speed of electromagnectic propulsion, which is the speed of light.
      That means, its in theory possible that a different means of acceleration might improve the maximum attainable speed, as long as it doesn’t boil down to EM’s domain. Example: manipulation of the Higgsfield would be an option. No idea how you can project one though. Especially if you can imagine that it takes an Earth mass to give 1g.

      • Olaf2 says

        Is this the new New Age pseudo science hype?

        Manipulate the higgs field and we can have FTL?

        Light speed has nothing to do with light or EM.

      • Zoutsteen from Holland says

        try going back to basics: mechanical stone thrower gives reaction opposite direction. The curve for energy transfer into speed is the same.
        If we used the LHC as propulsion, the curve would be the same.
        The limitation really is nothing more than basic Newtonian physics.
        => Hence the dream of particles that might go faster than the speed of light … just for the same Newtonian action is reaction accelaration.
        Nothing new age. Its a long time known limitation.

      • Olaf2 says

        Yep New Age pseudo science.

      • Zoutsteen from Holland says

        If you would have said that a ship cannot project a field in front of it due to information speed limitations, than you would at least have a point.

        Now, you are just being a mechanical rock thrower.Don’t throw rocks, ,throw information and you would have known its limitatios … and that it is possible with a projected gravity field to bypass that limitation easily.

      • Olaf2 says

        Look neutrino’s failed to deliver the FLT promised the crackpots jumped on to, now it is the Higgs field? I am sorry but the Higgs field is not going to give you FTL.

      • The neutrino thing wasn’t posited by crackpots. Actual physicists (some of the best) at CERN announced that they got data that seemed to suggest this and the news media took over and made it seem like it was being tauted as actual when the jury was still WAY out. They then followed the scientific method and tried to reproduce the effect and after a time realized that there was a flaw in some GPS cabling. If you’re going to criticize at least get the full story rather than making stuff up to fill in the gaps of your information… (PS: It’s, “neutrinos” plural, not “neutrino’s” possessive”)

      • Olaf2 says

        Yes the scientist did what they had to do. Produce a paper.

        I was commenting on the fact that the crackpots and New Agers ran with it and created crazy claims out of this. And what I now see is that they replaced the word neutrino with higgs field as their new pet quackery.

      • oops…. read wrong. sry. >.<

      • Zoutsteen from Holland says

        Think blackholes and Schwarzschilds 😉

      • Torbjörn Larsson says

        “GPS cabling”. It was in the timing chain, a loose optical connector (so triggering on a distorted flank of a weakened signal) and a faulty oscillator, who partly concealed each other’s systematic errors.

        It wasn’t the GPS distance measurement, which was one GPS application. I can’t remember if it was within the GPS time stamp loop synchronizing transmitter accelerator with receiver detector, but I suspect not. It should be in the timing leading up to that comparison.

        So, on GPS technology in a rundabout way perhaps.

      • Zoutsteen from Holland says

        actualy, the scientists knew something was wrong and asked the general scientists for assistance in solving the problem.
        It was the general public that jumped the conclusion and a few “enthousiastic scientists”. And it was great reading the alternatives to explain how it might be possible and it kickstarted also a discussion about FTL.
        But it was only the public hunger that made FTL stories more prominent than its actual worth. Same here … there is a beautiful planet we all would like to see close up. And its not going to happen, unless … !!! 🙂

      • lcrowell says

        Information propagates at the speed of light or less. The nonlocal physics of quantum mechanics does involve spacelike connections, but there are no-signaling rules with such entanglements. Unfortunately we appear to be stuck at speeds equal to (for massless particles and fields) or slower than light.

        There is of course the Alcubierre warp drive. This is a solution to the Einstein field equations that compresses a region of space in the forward direction and expands it in the trailing direction. If the compression is say 10, then the effective distance traveled in the frame of this system is 1/10th that of ordinary distance. The result is this can move faster than light.

        However, there is a hitch. This requires that the stress-energy of the field that is the source of this curvature be negative. This means the field as a quantum system has no minimal quantum energy level. So the field can cascade down an infinite ladder of ever lower energy states and produce an arbitrary amount of radiation. That’s bad, really bad. So these types of solutions are not regarded as likely physically real. There is though no proof to this effect.


      • Zoutsteen from Holland says

        of coarse, the information speed limitation to compress space in front of the ship still stands! But in an LHC like setup, you can decide ahead of the “test subject” where the field exists, by creating space compressors along the tube. That way you bypass the information speed cap.

      • lcrowell says

        The LHC is no more going to allow us to warp spacetime, even in small or particle test situations, than could the caravels of the 16th century fly to the moon. There may be some correspondences between the QCD gauge field-particle called a gluon and the graviton, but evidence for this will amount to tiny amplitudes and evidence from “missing momentum.”

        The difficulties with the Alcubierre warp drive and other exotic solutions of the Einstein field equations, wormholes, Kraznikov tubes and so forth, lie at the foundations of physics. The source of the spacetime curvature as a quantum field is pathological. It is then not likely that these solutions are physical. In addition if nature permits these to exist then time travel is possible. To be honest I don’t think these things exist, and if they do they exist they do so on scales smaller than the scale of superstrings ~ 10^{-31}cm.


      • Ivan B says

        Basics? Ok, Basically the faster you move through space (approaching speed of light), the harder it becomes to accelerate further due to relativistic effects. This limitation has nothing to do with ‘Newtonian physics’, and you can’t apply 300+ year old physics to something like this

      • Santa says

        It doesn’t matter where you get propulsion from. Reaction mass is reaction mass.

      • lcrowell says

        Olaf2 is basically right. The speed of light has to do with the structure of spacetime. Spacetime in any coordinate basis has a projective subspace of lines with zero length that pass through a point or the origin of that coordinate system. These are null paths that massless particles follow. In a spatial coordinate system these massless particles travel at the same speed, which we call the speed of light. This is a fundamental invariant, which is not violated by ordinary means. If you could reach the interior of a black hole and play around with the singularity that might be something else.

        At 43 light years this is at the outer range of what we might be able to accomplish with sending a probe on a photon sail. This would be a 100+ year mission, and those who send it out are not likely to live to see the results. A photon sail, which is pushed along by collimated photons from a Fresnel lens in space that directs solar light, could in principle reach ? = 1.5 or about .75c. This means it would take about 70 years for the probe to reach the star, considering acceleration etc, and another 43 years for a signal to return.


      • Kawarthajon says

        Ok, I understand that travelling there would be tough for humans and even robots – to get something that would work for over 100 years would be a real challenge.

        What about communication if someone (something?) was living there and intelligent? Do we have equipment powerful enough to send a recognizable/intelligible message that far? I know it is close in cosmic terms, but it is still pretty far. If we beamed a strong radio message out their way, would it survive and be concentrated enough for anyone to pick up – or vice versa if they did that to us? What about regular radio messages, like tv/radio/satellite transmissions? Would they be intelligible at that distance?

        Wouldn’t it be cool if something intelligent was there and we could beam photos/information back and forth, instead of having to travel the distance ourselves? I know it would be a very slow process, involving multiple generations, like a really bad, long-distance telephone connection, but it would save money and time to be able to do it this way.

      • lcrowell says

        Sending a signal to this planet is not unreasonable. However, I think the probabilities anyone is listening in are nearly infinitesimal. However, the cost of doing that is very small compared to sending a probe there.

        Sending a probe to this planet would be a huge challenge. It would also be a multi-generation space mission or experiment. However, if science and technology proceeds through this century it is plausible that we may be able to send an array of probes to nearby stars, where HD 40307 is at the extreme practical limit for such space missions. Maybe people at the end of the 22nd century will get a close up look at this planet.


      • Kawarthajon says

        Hypothetically, assuming that there is someone listening, would the radio signal be clear enough to be intelligible to the recipients when sent across that distance?

      • lcrowell says

        I would have to do some calculations. The one problem is that interstellar space is filled with a diffuse ionized gas, mostly hydrogen making protons and electrons. Electromagnetic radiation propagating through this causes these charged particles to move, which in turn causes them to radiate energy in all directions. The signal is attenuated faster than 1/r^2. For this reason our radio and TV broadcasts probably do not have much signal beyond about 10 light years. A directed signal would put more EM energy in a selected direction and might be able to reach this far.


      • lcrowell says

        Given the roil the BBC is in right now I suppose this is a minor issue. I suppose they are prevented from receiving signals from other transmitting facilities. The probabilities of receiving a signal are very small in my opinion.


  2. Helm, set a course for HD 40307 g. Maximum Warp!

  3. It is worth remembering that if a space craft can get close to the speed of light, and that is a big if, time slows w a y down. A space craft capable of extended 1g acceleration could reach alpha centauri in 6 years, many more stars in 10 years, and the center of the galaxy in about 20 years. Shipboard time. Much more time would pass for those that were not on the ship and many people might think no one would volunteer for that trip – wanna bet? Of course, a constant 1g acceleration is not on the horizon but it doesn’t violate the ‘nothing goes faster than light’ rule.

    • Member
      Aqua4U says

      Key words here are “shipboard time”…

    • Frankhy says

      It is also worth considering that by the time we are able to construct near lightspeed spacecraft (unlikely to happen this century), we are very likely to have solved human ageing long ago, even by much more conservate estimates than what the likes of Aubrey de Grey use, to extend lifespan at the very least into the several hundreds of years if not “infinite”. If you are able to live many hundreds of years, spending 100 of those years on an interstellar roundtrip may seem a lot less discouraging than it does to us 20th century borns.

  4. Lord Haw-Haw. says

    Thank you Jason for providing the links to the relevant Paper, an article on HD40307g was published in the “Daily Telegraph” a short while ago in which the author mentioned the Paper had been published in the Astronomy & Astrophysical journal, despite an extensive search of the website there is currently no trace of it, as you correctly note Jason it *will* be published as the submitted Paper has today’s date on same.

  5. Torbjörn Larsson says

    I am general skeptical to the idea that tidal lock is a serious impediment for habitability. But it is an often promoted hypothesis.

    Hence it is nice to see that not only do we observe non-tidal locked habitables around red dwarfs, but the current ratio of non-locked to possibly locked red dwarf (M star) habitables is ~ 20 %. (One of the Gliese habitables in The Habitable Exoplanet Catalog is a K star.)

    The statistics is meager. However, it is already pretty safe to note that since M stars are the most common stars and are expected to have many terrestrials (see the current HEC statistics), this means many by all acceptable (“certified”) habitables around M stars.

    • Per tidally locked super Earths, I can imagine some sort of an exotic, if not really windy ecosphere existing in the permanent terminator ring…

      • Torbjörn Larsson says

        Yes. Other pathways is that the dense atmosphere of superEarths would disperse heat evenly enough as some models have shown, or that we have at least crustal habitability in a larger band around such treminator rings.

    • Not sure where the non-tidal locked info comes from. Were a planet not tidally locked while deep in the gravity well of a star, the tides would be huge. Really huge.

      • Torbjörn Larsson says

        The paper refers to other papers (Kasting among them), so it would take a while to see if it bears up.

        Tides on the other hand are, ironically, considered beneficial in many scenarios of chemical evolution (say, the protein cycle which needs periodical drying out of the cycle members while it builds peptide chains) and land establishment (tidal zones providing early coastal nutrients).

  6. It’s an interesting discovery, like the others: Gliese, HD, Kepler, etc… but the real truth, is that we can’t travel those distances. It’s simply out of the question. Even traveling at light speed, it’s a 43 years trip (one-way), 86 years round-trip.

  7. Daniel Selby says

    I feel very lucky when I read about all of this. Being born on Earth and in one of the greatest countries on Earth the United States of America. It is like hitting the lottery every day of my life.

  8. Mike says

    My SETI searches now seem more worthwhile 🙂

  9. freddy verhelst says

    If intellectual they are lucky having a star with appr. the mass of 0.72 the mass of the sun. it will give them continuous constant energy for several tens of billions of years

  10. Member
    StockportJambo says

    Human beings can’t usefully handle more than 5 Gs, so what would 7 Gs be like? You wouldn’t be able to walk around on the surface that’s for sure!

    • Erx says

      7 x the mass of earth doesn’t mean the G’s you feel when standing on the planet is 7 x greater, there is a formula to calculate it, but it is much less, consider the gravity of the sides which pull you side to side but you don’t feel it because they cancel each other out on any round shaped object. If the planet was the size of a basketball AND was 7 x heavier than earth, then yes, you’d feel all 7 G’s because all of it is used to pull on you, but because it’s larger, not all is used to pull on you. And if the size is 7 x greater, then that’s an entirely different story, due to density variations of planet etc. But the g force you feel is probably about 2.5 G’s.

  11. Prism2Spectrum says

    An Orange-Dwarf Star, with six heavy-weight super-“Earths”, four “in close orbit”. One elliptically orbits in the Habitable Zone of liquid. Yet you have four husky worlds orbing inwards, around Mercury distance. So g, in the Goldilocks zone, may be free, but how “livable” is it, subject to tidal forces from inward star-huddling brothers (if not negligible)? How orbitally stable is it in that band of life possibility? Is its crustal surface (an entire set of assumptions necessary here as well), is it subject to violent upheavals, from sibling stresses and tension?

    From faintest Doppler-shift detection, in light of star-type, some reasonable deductions, but I wonder if maybe too many assumptions. For example, does it have an “atmosphere”? ________________________________

    “The planetary system around HD 40307 has an architecture radically different from that of the solar system… which indicates that a wide variety of formation histories might allow the emergence of roughly Earth-mass objects in the habitable zones of stars.” _______________________________________________________

    Far from me to ask, but does this take into account a System running down, like a clock of time? Migration from a more reasonably spaced family formation of youth? This bazaar-tendency to crowd-in around the burning fire of alien suns is not encouraging.

    • Frankhy says

      Pretty much all of the “potentially habitable candidates” seem to be mostly bodies that have managed to clear the first one or two hurdles out of a million hurdles race, as far as intelligent life goes. The whole “habitable” concept is extremely loosely defined. Do we mean a bacteria can live there? Fungi? Multicellular life? “Animals”? Sentient beings? Or just that it is a viable candidate for humans colonizing it after some terraforming? Pretty big difference. For bacteria, you may perhaps only need to be in the Goldilocks zone, but our knowledge of the origins of early life even here on Earth is so patchy that it is little more than guesswork when transplanted to extrasolar systems.

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