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Thread: Gliese 581g -- in the habitable zone (barely)

  1. #211
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    Looking back at several of the papers out over the last year either directly or indirectly addressing Gleise 581g, it is obvious that if nothing else the potential of this planet is spurring much interesting and intriguing consideration and study in regards to Goldilocks planets. While not comprehensive in coverage, the follow few are interesting, and I don't see that they have been mentioned in this thread yet.

    Habitable Planets: What Are We Learning from Kepler and Ground-Based Searches?
    http://www.earth.northwestern.edu/pe...asting.ast.pdf

    Super-Earths: A New Class of Planetary Bodies
    http://arxiv.org/PS_cache/arxiv/pdf/...108.0031v1.pdf

    Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone
    http://arxiv.org/ftp/arxiv/papers/1110/1110.4525.pdf

  2. #212
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    Seems the presentation has been canceled. Does anyone know why? What happened?

  3. #213
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    Quote Originally Posted by Bitula View Post
    Seems the presentation has been canceled. Does anyone know why? What happened?
    It was origninally scheduled for the ballroom and was apparently withdrawn and cancelled by the presenters, I did hear some unsubstantiated scuttlebutt about a week before the the conference, but nothing that is confirmable (or that even sounds likely to my knowledge of the people). I'll look into it a bit more and see if I can find anything reasonable to address the issue over the next couple of days.

    414.08. WITHDRAWN: GJ 581 Update: An Independent Re-analysis Of The HARPS Data Set
    Steven S. Vogt1, R. Butler2, E. R. Rivera1, N. Haghighipour3

  4. #214
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    As you probably know, Vogt et al (Im not sure though on his personal role here) has confirmed a new habitable (zone) planet: http://arxiv.org/abs/1202.0446, which is now at the top of the list of habitable candidates of all confirmed HZ planets.
    Note, it seems to be slightly heavier and warmer, but the interesting thing is this:
    "Combining HARPS 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported."
    Which to me indicates again that for detecting the signals combining the datasets is required and the method works fine.
    Note, yet, this planet is listed as CONFIRMED on exoplanet.eu! Methodology should have been similar, so I wouldn't dismiss 581 g this easily... (Though the cancelation of the presentation is a bit fishy...)

  5. #215
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    Quote Originally Posted by Bitula View Post
    As you probably know, Vogt et al (Im not sure though on his personal role here) has confirmed a new habitable (zone) planet: http://arxiv.org/abs/1202.0446, which is now at the top of the list of habitable candidates of all confirmed HZ planets.
    Note, it seems to be slightly heavier and warmer, but the interesting thing is this:
    "Combining HARPS 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported."
    Which to me indicates again that for detecting the signals combining the datasets is required and the method works fine.
    Note, yet, this planet is listed as CONFIRMED on exoplanet.eu! Methodology should have been similar, so I wouldn't dismiss 581 g this easily... (Though the cancelation of the presentation is a bit fishy...)
    You do realize that "Combining HARPS 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported," refers to GJ 667C, don't you?

    I wouldn't argue against combining datasets where possible and if the proper combining methodology is employed.

    Even though HARPS is probably the most precise astronomical spectrometer ever built,
    the Cross-Correlation Function (CCF) data analysis method that has been commonly used
    to analyze this data, is suboptimal in the sense that it does not exploit the full Doppler
    information in the stellar spectrum (Pepe et al. 2002). For this reason, instead of using the
    CCF RVs provided by the ESO archive, we use a least-square template-matching method
    to derive new RV measurements. Thanks to the instrumental stability and the excellent
    wavelength calibration provided by the HARPS-ESO data reduction software, the model
    required to match each observation to a high signal-to-noise-ratio (SNR) template only needs
    to include a Doppler offset and a multiplicative polynomial to correct for the flux variability
    across each echelle order. The template is obtained by co-adding all the spectra after a
    preliminary RV measurement is obtained using the highest SNR observation. The leastsquares
    matching technique has been used on HARPS data before. An example are the RV
    measurements on GJ 1214 (V=14.57) used to derive the mass of the transiting super-Earth
    reported in Charbonneau et al. (2009). The performance and description of our software
    tool, HARPS-TERRA (Template Enhanced Radial velocity Re-analysis Application) on a
    representative sample of stars can be found in Anglada-Escud´e & Butler (2012).
    We still need to insure to the best of our ability that the processes we use don't generate artifacts that may be interpreted as a signal. With regards to GJ667c, I feel good enough about the character of the signal, at this time, to accept and acknowledge this exoplanet's position and general characteristics. As for the GJ581 family we have to go by the best data available, if data updates indicate a need to revise our understandings, that is what we do.

  6. #216
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    Quote Originally Posted by Trakar View Post
    You do realize that "Combining HARPS 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported," refers to GJ 667C, don't you?
    Well sure, thats why it is important that we have a confirmed planet associated with their methodology, not just candidates.


    Quote Originally Posted by Trakar View Post
    We still need to insure to the best of our ability that the processes we use don't generate artifacts that may be interpreted as a signal.
    Cant outrule that, but seems in this case they may need to retract at least 5 planet candidates, which would be surprising...

  7. #217
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    Below article looks quite recent (2012 mid march):
    http://arxiv.org/pdf/1203.3140v1.pdf

    Some interesting positive excerpts:
    In panel (B), we have a similar situation but considering all planets in circular orbits. Now the wrms
    of the best-fit solution in the model with 4 planets is 2.17m/s and that of the model with 5 planets
    is 2.03m/s. In this case, the inclusion of the fifth planet (GJ581 g) means a real improvement and
    would support a conclusion positive concerning the existence of the planet GJ581 g.

    Forveille et al. 2011, using new observations, were not able to confirm the existence of the planets g and f. But, this statement could not be verified because the new data were not yet made available in public domain.
    In adition, we have that the analysis done by them did not include the V10 data set.

    The signal with the frequency of the alleged sixth planet - GJ581 f - was found, but it is in the thresh-
    old of confidence level.We cannot discard the hypotesis that the period of the sixth planet is produced
    by some complicated beating with the observation window of 1yr, once both are comparables.

    I wonder, though, why the original discovering team did not update their findings in a follow up paper including new datasets. I would have thought that is in their best interest. Here are some questions:
    1) Is the HIRES team still collecting measurements using their (or an other) telescope/spectrometer, or they just sit and wait for others to do that.
    2) Did HARPS publish only the original dataset so far? If so, why? Are the additional datasets secret?

  8. #218
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    Quote Originally Posted by Bitula View Post
    Below article looks quite recent (2012 mid march):
    http://arxiv.org/pdf/1203.3140v1.pdf
    Which journal has this paper been submitted to and when is publication anticipated?

    From paper:

    Conclusion
    From a purely statistical point of view, it is not incorrect to state the existence of GJ581 g. However, this can only be done by assuming that all planets are in circular orbits. The explanation of this fact is a well-known phenomenon, described in detail in Anglada-Escud´e et al. (2009, 2010) and Giuppone et al. (2009), happens when the periods are close to a commensurability relation (the period of GJ581 d is almost twice the period of GJ581 g). In this circumstance, the eccentricity of the external body will be overestimated and can hide totally the signal of the internal body. In this case, the analysis of the radial velocity measurements does not allow us to distinguish the signal of the putative fifth
    planet (GJ581 g) from an overestimated eccentricity of the orbit of GJ581 d. Additional tests were done, but we have not been able to verify the existence of the planet g when we consider the d with a fixed and low (≈ 0.1) but not zero eccentricity...
    So far, this paper seems to be more about "hoped for" potentialities than verifiable likelihoods. Interesting more in understanding the limitations of our astronomical techniques and methods than in the nature of the universe revealed,...at least for now.

  9. #219
    Quote Originally Posted by marsbug View Post
    For these purposes I would say Venus is Earthlike, as it orbits within the goldilocks zone and has close to one Earth mass. An alien using the same radial detection method as us could not easily distinguish between the two worlds- and in turn this shows that Venus is an example of the dangers of making conclusions about a world based on just orbit and mass.

    There is a great deal that we still don't understand about the formation of planetary systems. It is a long road from the protostar and protoplanetary disk, which initially share the same compostion, to an evolved star system with a stable configuration-a road that can leave any given object in a star system with a very different ratio of elements than its parent sun has. Mercurys iron content, for example, is not predictable from solar iron abundances- thats a result of mercurys specific history of giant impacts.

    Given this I think you're making a bit of a big leap by saying 581g is the denuded core of an ice giant. But its a reasonable guess given the very little we know so, ok: why does that make it not interesting? More specifically, (and I really have no idea about this) why does it preclude 581g being habitable?
    I would actually consider Venus to be sunward of the Habitable Zone and the Earth in the inner edge of the HZ. within 2 billion years as the Sun gets hotter CO2 levels will reach near 0, plant life will die, and the Earth's thermostat will stop functioning. Then the Moist Greenhouse begins and we end up like Venus.

    I suspect Venus is the normal fate of Earth-like planets that leave the HZ as their star brightens.

  10. #220
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    Quote Originally Posted by Bitula View Post
    Below article looks quite recent (2012 mid march):
    http://arxiv.org/pdf/1203.3140v1.pdf

    Some interesting positive excerpts:
    In panel (B), we have a similar situation but considering all planets in circular orbits. Now the wrms
    of the best-fit solution in the model with 4 planets is 2.17m/s and that of the model with 5 planets
    is 2.03m/s. In this case, the inclusion of the fifth planet (GJ581 g) means a real improvement and
    would support a conclusion positive concerning the existence of the planet GJ581 g.

    Forveille et al. 2011, using new observations, were not able to confirm the existence of the planets g and f. ...
    Another disconfirmation, this time by Makarov, Berghea, and Efroimsky.

  11. #221
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    Did we miss this?:
    http://arxiv.org/abs/1207.4515

    It seems finally Vogt reacts to critics and publishes a paper supporting his findings in light of the newer HARPS data sets. It's quite recent: Submitted on 18 Jul 2012. If you read CentauriDreams people are quite optimistic there about his findings. Now is it a "turnaround"? - not for me, I've always believed in this planet, just was very strange Vogt has been so silent for so long.

  12. #222
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    My point of view regarding Gliese system or any other system like that: until we developed some new technology to observe (aka, new telescopes), and new propulsion methods, we will never know precise data.

    For a moment, consider this: imagine -yes, just imagine- that we confirm that there's life (simple or complex) in Gliese 581g. The great question "are we alone?" is finally answered. OK... but, how do we plan to get there? or at least, send a probe? it's located "only" 20 light-years away... that's a very vast distance, impossible to cover with present technology. A message was sent to Gliese system... travelling at the speed of light, it will take 20 years to arrive! and the response? assuming that life might be able to respond... another 20 years at the speed of light... 40 years just to say "hello?" --- "yes, we received your message".... not feasible.

    A probe? forget about it, even travelling at the speed of light, too slow. So... what can we do? not much... and we are talking about the "closest" potentially exoplanet to harbor life.

    And, another thing that nobody seems to care, but for me, it's very important. Does anybody consider that life out there could be... hostile? Why do we always assume that extraterrestial life is more intelligent and peaceful? here on Earth, there are/was several evil forces, human beings that are considered by me like "black and evil force" (aka, Hitler, dictatorships, a murderers, etc), so... should we expect some kind of paralelism? could be there some evil/hostile life forms?

    So, without evidences, I'd like to consider both possibilities (peaceful and hostile life-forms). Of course everybody would like to find some beautiful, peaceful and innofensive life out there... but Aliens -in a sort way- or a much worse, unimaginable life-form might exist somewhere.

  13. #223
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    Quote Originally Posted by MRFTest View Post
    My point of view regarding Gliese system or any other system like that: until we developed some new technology to observe (aka, new telescopes), and new propulsion methods, we will never know precise data.

    For a moment, consider this: imagine -yes, just imagine- that we confirm that there's life (simple or complex) in Gliese 581g. The great question "are we alone?" is finally answered. OK... but, how do we plan to get there? or at least, send a probe? it's located "only" 20 light-years away... that's a very vast distance, impossible to cover with present technology. A message was sent to Gliese system... travelling at the speed of light, it will take 20 years to arrive! and the response? assuming that life might be able to respond... another 20 years at the speed of light... 40 years just to say "hello?" --- "yes, we received your message".... not feasible.
    Actually a radio signal intended for the Gliese 581 system has already been sent off, four years ago, by the Russian astronomer Alexander Zaitsev using a radar telescope in Ukraine. See the WP page: A message from Earth.

    Using a signal that travels at the speed of light might seem a slow way of exchanging messages with a planet 20 light-years away, but it is the faster method known to science.

    And, another thing that nobody seems to care, but for me, it's very important. Does anybody consider that life out there could be... hostile? Why do we always assume that extraterrestial life is more intelligent and peaceful? here on Earth, there are/was several evil forces, human beings that are considered by me like "black and evil force" (aka, Hitler, dictatorships, a murderers, etc), so... should we expect some kind of paralelism? could be there some evil/hostile life forms?
    Well, for instance Stephen Hawking has considered that other civilizations might be hostile, and so has David Brin. That is why the idea of sending out messages (METI) is a lot more controversial than just listening (SETI).

    So, without evidences, I'd like to consider both possibilities (peaceful and hostile life-forms). Of course everybody would like to find some beautiful, peaceful and innofensive life out there... but Aliens -in a sort way- or a much worse, unimaginable life-form might exist somewhere.
    I agree we should consider a range of possibilities... They might turn out to be a threat to us... For that matter, we might turn out to be a threat to them. How many species of life on our own planet have we wiped out already?

    It may turn out to be just as well, for them and us, that Gliese 581 isn't any closer...

  14. #224
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    Quote Originally Posted by Colin Robinson View Post
    Actually a radio signal intended for the Gliese 581 system has already been sent off, four years ago, by the Russian astronomer Alexander Zaitsev using a radar telescope in Ukraine. See the WP page: A message from Earth.

    I agree we should consider a range of possibilities... They might turn out to be a threat to us... For that matter, we might turn out to be a threat to them. How many species of life on our own planet have we wiped out already?

    It may turn out to be just as well, for them and us, that Gliese 581 isn't any closer...
    Yeah, I knew about the message that has been sent to Gliese system. But, it's a looong waiting-period to expect some kind of reply, which I highly doubt.

    And, as you say (and I was thinking about it): maybe the vastness of the Cosmos is in fact, a way of "protecting" one civilization from another... distances that are beyond of our understanding, maybe could be interpreted as an effective "barrier" for us to make contact, and vice-versa. Interesting, isn't it?
    Last edited by MRFTest; 2012-Oct-18 at 02:41 PM.

  15. #225
    Quote Originally Posted by TaylorS View Post
    I suspect Venus is the normal fate of Earth-like planets that leave the HZ as their star brightens.
    I partially agree with you. So, considering that scenario and that fact, we can say that Venus had life once. So, maybe Mars and Venus were the planets which harbored some kind of life millions of years ago. So... what kind of life did they have? did that life migrate to Earth? why can't we find some evidence of ancient harbored-life in Venus and Mars?

  16. #226
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    Quote Originally Posted by kzb View Post
    Can I point out that the star Gliese 581 has lower metallicity than the sun, M/H = -0.33. Yet here we have at least 6 planets, including at least 5 "rocky" planets, each of which exceed the mass of the Earth, the most massive terrestrial planet in our system.
    Are we sure these planets actually ARE rocky? Couldn't they also be gas balls -- gas non-giants, as it were?

  17. #227
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    An update for a popular thread some years ago: GJ 581, an M3.0V red dwarf, has been confirmed to have a multiplanet system with a Kuiper Belt. However, the number of planets is disputed.

    http://cdsads.u-strasbg.fr/abs/2019LPI....50.1634B
    https://www.hou.usra.edu/meetings/lpsc2019/pdf/1634.pdf (short paper)
    "Viability of Lithopanspermia Between Planets of Gleise 581"
    Broad, K. E.; Brock, L. S.; Melosh, H. J.
    50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1634
    By studying impact exchange within the Gleise 581 multiplanet system, we find that lithopanspermia is possible but different from that in our own solar system.

    https://arxiv.org/abs/1803.02832
    "Kuiper Belt Analogues in Nearby M-type Planet-host Systems"
    Grant M. Kennedy, et al. (Submitted on 7 Mar 2018)
    We present the results of a Herschel survey of 21 late-type stars that host planets discovered by the radial velocity technique. The aims were to discover new disks in these systems and to search for any correlation between planet presence and disk properties. In addition to the known disk around GJ 581, we report the discovery of two new disks, in the GJ 433 and GJ 649 systems. Our sample therefore yields a disk detection rate of 14%, higher than the detection rate of 1.2% among our control sample of DEBRIS M-type stars with 98% confidence. Further analysis however shows that the disk sensitivity in the control sample is about a factor of two lower in fractional luminosity than for our survey, lowering the significance of any correlation between planet presence and disk brightness below 98%. In terms of their specific architectures, the disk around GJ 433 lies at a radius somewhere between 1 and 30au. The disk around GJ 649 lies somewhere between 6 and 30au, but is marginally resolved and appears more consistent with an edge-on inclination. In both cases the disks probably lie well beyond where the known planets reside (0.06-1.1au), but the lack of radial velocity sensitivity at larger separations allows for unseen Saturn-mass planets to orbit out to ∼ 5au, and more massive planets beyond 5au. The layout of these M-type systems appears similar to Sun-like star + disk systems with low-mass planets.

    https://arxiv.org/abs/1710.01595
    "The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems"
    T. Trifonov, et al. (Submitted on 4 Oct 2017 (v1), last revised 30 Jan 2018 (this version, v3))
    Context: The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M-dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ15A, GJ176, GJ436, GJ536 and GJ1148) or are multiple planetary systems (GJ581 and GJ876).
    Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.
    Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems are fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.
    Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ15A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days.
    Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.

    QUOTE: GJ 581: This star has one of the most debated multiple planetary systems when it comes to the number of detected planets. The first planet GJ 581 b, was discovered by Bonfils et al. (2005) followed by Udry et al. (2007), who increased the planet count to three by discovering GJ 581 c and d. The planetary system suggested by Udry et al. (2007) consists of three planets with orbital periods of Periods = 5.4, 12.9 and 83.6 d and minimum masses of mass sin i = 15.7, 5.0 and 7.7 M-earth, respectively. Later, Mayor et al. (2009) revised the period of GJ 581 d to 66.8 d and discovered an additional 1.7-M-earth mass planet at 3.15 days named GJ 581 e. A simultaneous analysis of the HIRES and HARPS data for GJ 581 led Vogt et al. (2010) to increase the planet count to six by introducing GJ 581 f and g with Periods = 433 and 37 d, suggesting a very compact system where all six planets must have near-circular orbits. Since Vogt et al. (2010), a number of independent studies have disputed some of these discoveries. Forveille et al. (2011) and Tuomi (2011) strongly supported only four planetary companions, arguing against GJ 581 f and g. Baluev (2013) suggested that the impact of red noise on precise Doppler planet searches might lead to false positive detections and, therefore, even GJ 581 d might not be real. Robertson et al. (2014) corrected the available Doppler data for activity and also suggested that the signal of GJ 581 d might be an artifact of stellar activity. Finally, Hatzes (2016) showed an anti-correlation of the 66.8 d period with the H equivalent width to confirm that the signal of GJ 581 d is intrinsic to the star. To our knowledge, the currently confirmed planets orbiting the GJ 581 system are three (b, c, e), and in our analysis we will assume this number.

    [NOTE: This paper confirms planets e, b, and c only, disputing all others. GJ 581 c abuts the habitable zone.]

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