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A Super-Earth Orbiting Barnard’s Star

The detection of a planet around Barnard’s Star really hits home for me. No, this isn’t a habitable world, but the whole topic of planets around this star has resonance for those of us who remember the earliest days of exoplanet study, which could be extended back to Peter van de Kamp’s work at Swarthmore’s Sproul Observatory in Pennsylvania. The astronomer thought he had found evidence for a 1.6 Jupiter mass planet in a 4.4 AU orbit there, based on what he interpreted as telltale wobbles in photographic plates of the star taken between 1916 and 1962.

This work, ending in the early 1970s, turned out to be the result of errors in the instrument van de Kamp was using, but the buzz about possible planets around Barnard’s Star had been sufficient to create a small crest of enthusiasm for exoplanet studies in general. The British Interplanetary Society saw in Barnard’s Star a target worth investigating, and designed their Daedalus star probe around a mission there. In any case, van de Kamp’s assumption that planetary systems were common has been proven out, and now we do have a planet around this star, though not the one that the Swarthmore researcher thought he had found.

What Guillem Anglada-Escudé (Queen Mary University, London) and Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain) have uncovered is a super-Earth in an orbit near the star’s snowline. From the paper in Nature:

Here we report that the combination of numerous measurements from high-precision radial velocity instruments reveals the presence of a low-amplitude but significant periodic signal at 233 days. Independent photometric and spectroscopic monitoring, as well as the analysis of instrumental systematic effects, show that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard’s star is a cold super-Earth with a minimum mass of 3.2 Earth masses orbiting near its snow-line.

Image: An artist’s impression of the surface of Barnard’s Star b. Credit: ESO – M. Kornmesser. Licence: Creative Commons with Attribution, https://creativecommons.org/licenses/by/4.0/

Barnard’s Star b thus becomes the second closest known exoplanet to Earth (although bear in mind that the search for planets around Centauri A and B continues, as does examination of Proxima Centauri for other planets beyond Proxima b). The snow-line at Barnard’s Star, where volatiles like water can condense into solids, is close to the planet’s orbit at 0.4 AU, a reminder that the host is a red dwarf that provides but 2% of the energy the Earth receives from the Sun. The scientists believe the temperature of Barnard’s Star b would be in the range of -150 ℃.

The new planet’s position in relation to the snow-line is itself interesting, as the paper notes:

The candidate planet Barnard’s star b lies almost exactly at the expected position of the snow-line of the system, located at about 0.4 au. It has long been suggested that this region might provide a favourable location for forming planets, with super-Earths being the most common planets formed around low-mass stars. Recent models incorporating dust coagulation, radial drift, and planetesimal formation via the streaming instability support this idea . Although this has yet to be shown to be part of a general trend, observational evidence would significantly constrain theories of planetary migration.

The authors point out that the Barnard’s Star work “…pushes the limits of the radial velocity technique into a new regime of parameter space,” comprising our ability to detect super-Earths in much wider orbits than ever before. Until now, such a detection would have been a matter for gravitational microlensing, with the attendant problem that such studies are inherently one-off affairs, depending on chance celestial alignments. Now we learn of a serious leap forward for radial velocity studies, one that highlights what a tricky catch this was.

Consider the range of instruments involved, among them the European Southern Observatory’s HARPS (High Accuracy Radial velocity Planet Searcher) and UVES (Ultraviolet and Visual Echelle Spectrograph) spectrographs. Says Anglada Escudé:

“HARPS played a vital part in this project. We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities. The combination of instruments was key to allowing us to cross-check our result.”

All told, data from seven different instruments were put into play, a total of 771 measurements covering 18 years in a collaboration organized by the Red Dots project, which searches for terrestrial planets in warm orbits around the red-dwarf stars closest to the Sun. It was the Red Dots collaboration that was responsible for the discovery of Proxima Centauri b in 2016.

In addition to HARPS and UVES, the work included data from HIRES (High Resolution Echelle Spectrograph) at the Keck 10-meter telescope; PFS (Planet Finder Spectrograph) at the Carnegie’s Magellan 6.5-m telescope; APF (Automated Planet Finder) at the 2.4-m telescope at Lick Observatory; and CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs) at the Calar Alto Observatory. Further observations were made with the 90-cm telescope at Sierra Nevada Observatory, the 40-cm robotic telescope at SPACEOBS (San Pedro de Atacama Celestial Explorations), and the 80-cm Joan Oró Telescope of the Montsec Astronomical Observatory (OAdM).

I don’t usually list every last instrument used in a particular detection, but I did so here because it’s a measure of what it took to find a planet of this size in a relatively cool orbit. Consider this: The data show that Barnard’s star is approaching and moving away from us at about 1.2 m/s, which is roughly the speed I make when out for my morning walk. This tiny motion detected through Doppler methods is at the heart of the new planet’s detection. The researchers note that further observations are still necessary and are underway:

“After a very careful analysis, we are over 99% confident that the planet is there, since this is the model that best fits our observations,” says Ignasi Ribas. “However, we must remain cautious and collect more data to nail the case in the future, because natural variations of the stellar brightness resulting from starspots can produce similar effects to the ones detected.”

Image: Graphic representation of the relative distances to the nearest stars from the Sun. Barnard’s star is the second closest star system, and the nearest single star to us. Credit: IEEC/Science-Wave – Guillem Ramisa Licence: Creative Commons with Attribution, https://creativecommons.org/licenses/by/4.0/

Barnard’s Star is surely in our future if we reach the stage of sending instrumented probes to other stellar systems. At 6 light years, it is our closest target after the Alpha Centauri stars, and has been famous since its 1916 discovery for its remarkable proper motion of 10.3 arcseconds per year relative to the Sun. What that means is that from our perspective on Earth, this star moves faster against the background stars than any other, covering a distance equivalent to the Moon’s diameter across the sky every 180 years. In comparison to younger M-dwarfs, it is relatively quiet in terms of flare activity. Thought to be about twice the age of our Sun, it’s a reminder of our own star’s position among many stars much older than our Solar System.

The paper is Ribas, Anglada Escudé et al., “A super-Earth planet candidate orbiting at the snow-line of Barnard’s star,” Nature 15 November 2018.

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{ 67 comments… add one }
  • ljk November 14, 2018, 14:48

    Quoting from the main article:

    “In comparison to younger M-dwarfs, it is relatively quiet in terms of flare activity.”

    According to the Wikipedia entry on Barnard’s Star:

    https://en.wikipedia.org/wiki/Barnard%27s_Star

    In 1998 a stellar flare on Barnard’s Star was detected based on changes in the spectral emissions on July 17 during an unrelated search for variations in the proper motion. Four years passed before the flare was fully analyzed, at which point it was suggested that the flare’s temperature was 8000 K, more than twice the normal temperature of the star.[48] Given the essentially random nature of flares, Diane Paulson, one of the authors of that study, noted that “the star would be fantastic for amateurs to observe”.[21]

    • jonW November 14, 2018, 21:45

      Hey those massive flares are great news, they will thaw out a planet at the snow line so the temperature ends up juuuuust right!

      • Michael November 15, 2018, 12:45

        More like blind you, scramble your DNA and then leaving you to freeze to death. However saying that the mass is at the minimum so it could still be a warmish if you can swim mini Neptune.

  • ljk November 14, 2018, 14:52
  • Antonio November 14, 2018, 14:55

    Nice! One more destination for near future probes!

  • Ashley Baldwin November 14, 2018, 15:19

    And with a projected angular separation of about 220 mas , well within the latest performance projections of the CGI on WFIRST. With a likely mass around 4Me it falls in that grey area between terrestrial planets and mini Neptunes. Well outside the conventional habitable zone ( receiving a stellar flux mid way betwen that of Jupiter and Saturn ) it may have just enough mass to retain a thin but heat retaining H/He envelope without reaching the crushing atmospheric pressures of a mini Neptune . This planet could yet turn out to be one of Sara Seager’s hypothetical uber greenhouse effect extended habitable zone planets . Well worth a look.

    • Thomas W. Hair November 15, 2018, 0:38

      Excellent point on a fine detail I had not noticed, thank you Ashley.

    • Harry R Ray November 15, 2018, 11:20

      I just found out that if the planet does exist, the upper limit to its mass is 8 Earth masses, because, otherwise; HST would have detected it with its fine guidance sensor over 20 years of observations.

  • Ashley Baldwin November 14, 2018, 15:31

    And with an angular separation of about 220 mas , well within the projected capability of the CGI on WFIRST.

    Well outside the conventional habitable zone ( receiving a stellar flux between that of Jupiter and Saturn ) with a likely mass of 4 Me it sits within Rogers, Chen & Kipping’s “grey zone” betwen terrestrial and mini Neptune planets. It’s mass might be just enough to retain a thin “primitive” H/He atmospheric blanket without ever reaching the crushing pressures of a true mini Neptune. If so this is potentially exciting as it might represent the first of Sara Seager’s hypothetical uber greenhouse effect extended hab zone planets capable of sustaining some sort of exotic life. Well worth a look.

    • ljk November 15, 2018, 10:32

      Not all alien planet hunters are convinced yet. A quote from the article linked below:

      https://www.scientificamerican.com/article/a-frozen-super-earth-may-orbit-barnards-star/

      “In light of the troubled history of planet claims for this star, the authors are very brave to stick their necks out like this,” says Ignas Snellen, an astronomer at Leiden University in the Netherlands who did not take part in the research. “These are very difficult measurements!”

      So difficult, in fact, that some experts remain unconvinced. “Since there are planets everywhere, I suppose that there must be planets around Barnard’s Star,” says Debra Fischer, an astronomer and veteran planet hunter at Yale University who was not involved with the putative discovery. “There may even be one a few times the Earth’s mass with a period of 233 days. But this analysis doesn’t provide strong enough support, in my opinion.”

      • RAS November 15, 2018, 17:07

        It strikes me as somewhat disingenuous to describe the people involved in this as sticking their necks out considering the length of time the data was collected over and the number of observatories involved.

      • Ashley Baldwin November 16, 2018, 12:04

        The caution is understandable and in no way detracts from the hard work that went into this . I don’t think it’s Barnard’s b so much as M dwarf planets as a whole. They present unique difficulties. Such discoveries have been challenged before and successfully. Think Kapeteyn’s b.

        The RV changes so far out from such a low mass will be extremely small for what is a relatively small planet . The confounding background stellar noise will be substantial from a star with an active photosphere as in this instance .

        As was done for Proxima b , the best way of negating stellar noise systematic errors in such stars is to first accurately model the photospheric activity with extended ( nee continuous ) ground based spectrophotometry.

        Jason Wright at Penn State in particular has a track record of applying ultimate rigour to RV process and confirmation from his team after a review of all the old and new data would seal the discovery.

        Either way confirmation is needed.

  • andy November 14, 2018, 15:42

    Barnard’s Star? Watch out for Vogon Constructor Fleets while navigating the local roundabouts.

    • Ashley Baldwin November 14, 2018, 19:53

      Don’t Panic.

      • Harry R Ray November 15, 2018, 10:29

        Panic! `Oumuamua was their survey mission. lol(I hope).

        • Michael November 15, 2018, 12:49

          Worse it was the final demolition notice !

          Que, Mr Arthur Dent…

          • Ashley Baldwin November 15, 2018, 16:26

            Now that’s why we need to discover planets around Alpha Centauri . That’s were the local intergalactic highway planning office is after all. Would help avoid a whole lot of unnecessary travel and Deep Thought.

            • andy November 15, 2018, 20:09

              “What do you mean you’ve never been to Alpha Centauri? Oh, for heaven’s sake, mankind, it’s only four light years away, you know. I’m sorry, but if you can’t be bothered to take an interest in local affairs, that’s your own lookout.”

              • ljk November 16, 2018, 12:21

                We Earthbound creatures automatically assume life works from a planet. For all we know the planning office could be located aboard a giant free-floating space station or space city circling one of the Alpha Centauri suns.

                The interstellar-savy Vogons probably did not feel the need to have to explain this being so used to existing in a galaxy-spanning culture.

                • andy November 16, 2018, 14:34

                  This raises the question of whether or not the custom planets built by the Magratheans count as space habitats…

                  • Ashley Baldwin November 17, 2018, 6:21

                    Hold you horses ! Don’t be so Slartibart-fast . We don’t want to end up in the total perspective vortex.

        • Ashley Baldwin November 15, 2018, 16:23

          “Ou-Rama” as in rendezvous with ?

  • Laintal November 14, 2018, 15:44

    I just heard this announcement on the news this morning along with an interview with an Astronomer and I was hoping you would have done a post for us to all read.

    Now to catch up on this one.

  • Coacervate Droplet November 14, 2018, 15:47

    I remember the van de Kamp ‘discovery’ very well. I was building a “Mars Snooper” at the time and stealing pop bottles to cash in for a package of B84 engines.

    One question I’ve always had is about transits… why did it take so long to implement that technique? It seems to me that a light meter with enough sensitivity to detect a transit would have existed ca. 1970’s

    • Bruce D. Mayfield November 15, 2018, 13:26

      In Barnard’s system there are no transits, as will be true for most planetary systems. For the RV method of detection a long series of spectra must be accumulated. For a planet with a 233 day orbit it would take years to accumulate enough data.

      • ljk November 15, 2018, 15:37

        Are any of Van de Kamp’s decades of data of any use in this regard? Could modern techniques weed out the errors to find some real exoplanet data?

        • Bruce D. Mayfield November 16, 2018, 0:37

          I’d doubt it because the data required is spectra fine enough to pin down the redshift/blueshift changes to an accuracy of 1 m/s. If such detailed older data was available I’m sure the team would have used it if it was up to par, but in RV studies using very noisy data could be worse than no data because it would hide the real signal.

        • Ashley Baldwin November 16, 2018, 12:15

          Unfortunately not. There were marked instrument systematic errors that did for his many astrometric planets.

          Even before one considers that ground based astrometry has unavoidable limits , the more so fifty years ago . Even Gaia is likely to be insufficiently sensitive to constrain Barnard’s b even at under 6 light years distance . It should however be able to pick up a Neptune mass planet at 5 AU though – if the signal picked up by Ribas’ team is real – especially if it’s mission extends to nine years or so.

          Returning to PVdK , if I recall, one of the systematic errors arose from his telescope undergoing a major upgrade/ refurbishment during the observation period.

      • Coacervate Droplet November 16, 2018, 11:05

        I was asking without specific regard to Barnard’s Star.

    • ljk November 15, 2018, 15:36

      Please do tell us more about this Mars Snooper and rocket engines that can be bought with soda bottle change! And you bring up a very good question about detecting exoplanet transits decades before they were which I hope someone can answer.

      • jonW November 15, 2018, 21:32

        Presumably, like >95% of systems, the plane in which Barnard’s Star revolves and any planets orbit is not edge-on to us, so transits cannot be observed from our location. I believe this is why the transit method will never be sufficient to rule out the existence of exoplanets.

      • Coacervate Droplet November 16, 2018, 11:14

        http://archive.rocketreviews.com/reviews/all/hh_super_mars_snooper.shtml

        “She’s fully automated. A chimpanzee and two trainees can run her.”
        -Scotty

        • ljk November 16, 2018, 12:27

          Ah, thank you. My idea on what that Mars Snooper could be is totally at odds with the reality. :^)

  • Robert November 14, 2018, 15:51

    This planet needs some serious greenhouse gasses. I wonder if that would even be in the realm of possibility to warm it up over time?

    • Ashley Baldwin November 14, 2018, 20:07

      A thin hydrogen /helium envelope would do it . Not enough to create a crushing mini Neptune atmosphere , but hydrogen is a potent greenhouse gas and this planet might have just the “goldilocks” mass at around 4Me to retain enough to warm it up sufficiently to sustain liquid ,water even so far out. Yet at Atmospheric pressures still conducive to life even. See my post above.

  • Andrew LePage November 14, 2018, 16:18

    What great news that after all these decades we seem to have finally found a planet orbiting Barnard’s Star!!! For those interested in the history of Barnard’s Star planet searches up to 2015, feel free to check out the following summary:

    https://www.drewexmachina.com/2015/04/23/search-for-planets/

  • Wojciech J November 14, 2018, 16:29

    Brilliant news, I wonder if geological activity and atmosphere could result in revised temperature of the planet.
    Can’t wait for new observations by telescopes we should get in 20’s

  • P November 14, 2018, 17:14

    From the discovery paper:
    “…at some marginally significant signals may be present in the
    residuals of the two signal model (e.g., at 81 d), but current evidence is inconclusive, We can, however, set stringent limits on the exoplanet detectability in close-in orbits around Barnard’s star. Our analysis is sensitive to planets with minimum masses 0.7 and 1.2 Earth masses at respective orbital periods of 10 and 40 days, which correspond to the inner and outer optimistic habitable zone limits…”
    Fair enough, plenty of discovery space left interior to Barnard b at lower masses then. Keep taking measurements and hope that Gaia turns up something.

    In the meantime well done Red Dots! Wolf 359 next! Does anyone know if they are observing the Luhman twins, or are they just too faint for RV?

    P

  • Laintal November 14, 2018, 18:12

    I’m just about to have a read of the paper on the ESO website

    ESO – Press release
    https://www.eso.org/public/news/eso1837/

    Here is the paper
    https://www.eso.org/public/archives/releases/sciencepapers/eso1837/eso1837a.pdf

  • Ashley Baldwin November 14, 2018, 20:22

    It’s impossible to overstate the importance of this discovery. And not just in terms of Barnard b itself. To measure the change in radial velocity required to pluck out such a ” small ” planet , at 0.4 AU from a tiny 0.14 Msun star ( and an active red dwarf too) is an incredible achievement . Red Dot are certainly perfecting their method . It opens the gates to looking for similar planets in wider orbits around lots of other neighbouring stars , frequently more interesting examples too. Especially with many such searches upcoming . Kepler may be dead but TESS is getting the necessary RV backup it was designed for .

    In terms of other neighbouring stars I would like to see the 8.3 light year distant Lalande 21185 targeted now. It is over an order of magnitude brighter than Barnard’s star . Itnis over three times more massive too , so will offer larger RV signals out to tenths of AUs and has a potential conventional hab zone out as far as 0.3 AU. Like Barnard’s star it also has loads of preexisting RV data and one close in Super Earth discovered already at 0.06 AU. Relative low metallicity and the absence of a Jupiter mass analogue of any type suggests it may have a retinue of smaller planets as described in the last Centauri Dreans post . Unlike most nearby red dwarfs it is old AND quiescent so a terrestrial planet around 0.25 AU out should be “easier” to pick out than Barnard b , yet well within its stellar hab zone.

  • Michael C. Fidler November 14, 2018, 20:47
    • Michael C. Fidler November 15, 2018, 10:17

      Prospects for detecting the astrometric signature of Barnard’s Star b.

      “A low-amplitude periodic signal in the radial-velocity (RV) time-series of Barnard’s Star was recently attributed to a planetary companion with a minimum mass of ∼3.2 M⊕ at an orbital period of ∼233 days. The proximity of Barnard’s Star to the Sun raises the question whether the true mass of the planet can be constrained by accurate astrometric measurements. We review the astrometric capabilities and limitations of current and upcoming astrometric instruments. By combining the assumption of an isotropic probability distribution of the orbital orientation with the RV analysis results, we calculate the probability distribution function of the planet’s astrometric signature. We conclude that there is a probability of only ∼1% that Gaia observations will detect it. Observations with the Hubble Space Telescope (HST) may increase the detection probability to ∼10%. In case of no detection, the implied mass upper limit with HST observations would be ∼8 M⊕, which will place the planet in the super-Earth mass range. In the next decade, observations with the Wide-Field Infrared Space Telescope (WFIRST) may increase the prospects of measuring the planet’s true mass to ∼99%.”

      https://arxiv.org/abs/1811.05920

  • Charley November 15, 2018, 1:51

    While is way, way too early to get into this type of speculation, it still seems necessary to ask a question about this new planet (if were actually sure it exists). If, this thing has properties, which would make a voyage to the star system worthwhile, is there even the remotest possibility that if we get a voyage down to a 40-50 year timeline that we can in any way shape or form be able to achieve an orbit about the star, such that the planet can be examined in a close manner rather than a quick flyby?

    It seems if you’re going to spend the money and the manpower to do something to go and investigate it, you want to investigate a little bit more than about 30 seconds as it flies through the star system…

  • AlexT November 15, 2018, 3:59

    Every new planet that is found in our close neighbourhood – in reality is bad news for the Drake equation and SETI :-) (Accounting Fermi paradox)…

    • hiro November 15, 2018, 16:45

      Not every-planet is equal.

      • AlexT November 17, 2018, 4:19

        I am sure every new found planet automatically correct Drake’s equation, it is not so important the exact planet classification, especially accounting some huge uncertainty in present exoplanet search methods.

  • Al Jackson November 15, 2018, 9:19

    I wrote Peter van de Kamp when I was a junior at university in 1963 about Barnard’s ‘planet’ plus a question about double stars. I don’t quite know what possessed me at 23 to write that letter, except at the time I was interested in SETI (a new topic than!) . I think I asked about both the hypothetical planet and also mentioned, because he had done double star work, a question about the computation of double star orbits. His reply was encouraging but brief. I did not expect him sending reprints about computing double star orbits, which I tried to code in Fortran, the first time I ever did a long code, as I remember it was too hard to debug when using punched cards.

  • Harry R Ray November 15, 2018, 10:42

    Yesterday’s Twitter announcement was the non-embargoed Nature article. Today the embargoed article will be revealed concerning Ross 154, a true Proxima Centauri analog(not a twin, because it is a bit more luminous, but its flaring activity is on a par with Proxima Centauri’s). Because it is embargoed, I surmise a possible Proxima b twin. We’ll just have to wait and see.

  • ljk November 15, 2018, 14:13

    The enduring mystique of Barnard’s Star

    By Larry Sessions in Astronomy Essentials | November 14, 2018

    Sometimes called Barnard’s Runaway Star, it’s one of the best known stars in the history of astronomy and in popular culture.

    https://earthsky.org/astronomy-essentials/barnards-star-closest-stars-famous-stars

  • ljk November 15, 2018, 14:29

    When we do explore Barnard’s Star b directly, perhaps we can use Russia’s new plan for an interstellar vessel:

    http://www.pravdareport.com/news/science/tech/13-11-2018/141982-interstellar_spaceship-0/

    Which has already been pointed out as looking awfully familiar:

    http://nasawatch.com/archives/2018/11/russias-new-sta.html

    This is not a bad thing, because the starship seen in Avatar, as brief as it was, is incredibly scientifically accurate – especially for a Hollywood starship and one that was not even the focus of the film!

    http://www.projectrho.com/public_html/rocket/slowerlight.php#id–Go_Fast–Starships–Avatar_ISV_Venture_Star

    So why not use a design that works? Of course now the question is, will it ever be built?

    • Michael C. Fidler November 16, 2018, 9:37

      Actually, what was really interesting was the radiator system, which was successfully tested.

      “One of the engineering challenges that must be solved to create such a system is dealing with a lot of waste heat. Since the spacecraft operates in vacuum, the heat needs to be radiated into space, rather than carried away by large amounts of water, as is the case with regular nuclear power plants.

      Regular radiators for spacecraft are basically long tubes mounted outside, through which the coolant flows until its temperature drops down enough. But this approach turned out to be too bulky for the YaEDU, and also vulnerable to micrometeorites – a serious threat during missions that the system is designed for.

      So, instead Russian engineers created a liquid droplet radiator. This device generates a stream of droplets that collectively have a very large surface and can radiate a lot of heat into space. The droplets are then collected and pumped back into the system.

      The report, cited by RIA Novosti, states that the Keldysh Research Center, a leading Russian space lab, has “created and tested prototypes of droplet generator and elements of the collector… completed testing of a prototype liquid droplet radiator.”
      https://cdni.rt.com/files/2018.10/article/5bd6c849dda4c895258b456b.jpeg

      https://cdni.rt.com/files/2018.10/original/5bd6c87dfc7e93272d8b4628.jpeg

      https://www.rt.com/news/442521-nuclear-propulsion-system-russia/

    • AlexT November 17, 2018, 9:23

      I am pretty sure that Russia in it’s present state is unable to build anything, maximum that is still possible in Russia – to produce brave fake news, absolutely disconnected from reality.

      • Michael C. Fidler November 18, 2018, 9:56

        That’s what they said before Pearl Harbor and the radar operators did not believe their scopes. The N1 was not fake news and it’s the idea that counts – “created and tested prototypes of droplet generator and elements of the collector… completed testing of a prototype liquid droplet radiator.” We would probably be still trying to reach the Moon if Russia had not designed the N1 long before there were any plans for the Saturn 5.

  • wdk November 15, 2018, 19:51

    This website seems to have an upbeat “breaking news” story about every other day. Once you take a dip, it’s hard to stay out. Much less ignore. Is it that Centauri Dreams finds all the pearls in the shells or we are living in exciting times?

    The Barnard’s Star story has had its ups and downs too. I remember back about high school that the argument for exoplanets almost entirely rested on what was eked out of Sproul Observatory over decades. Then in the 1970s, while studying stars in an astronomy class, the lecturer happened to note that the maintenance work on the instruments there had introduced a bias or systematic error. At that point, exoplanets returned to the realm of a quest for something like the Abominable Snowman.

    Still, there is another lesson to be drawn from spectroscopic binaries, whether stars, brown dwarfs or planets. The radial velocity elements are tough enough to discern in this case, true. But in addition, terms such as likely planetary mass should be defined. I you define the line of sight from Earth to Barnard’s star as inclination zero if it is in the Barnard b’s orbital plane, then the doppler radial component observed VRdoppler = VR cos i, the actual radial component. If not, then the radial component is a fraction.
    The “most likely” radial component would be halfway between zero and 90 degrees inclination, but I think the higher inclinations would also get harder to observe. But say it is 45 degrees. Then the mass would be 1.414 higher than the minimum mass of zero degrees. And were it zero degrees inclination, we should have caught a transit.

    So should we anticipate a 6 earth mass planet in this case? Or based on
    a typical inclination, we might get something less massive than x 4?

    • Paul Gilster November 15, 2018, 20:35

      Exciting times indeed, wdk, and very pleased to have you with us to discuss them!

    • Bruce D. Mayfield November 16, 2018, 15:05

      We are living in exciting times wrk, and I second your thanks for this site.
      We’re living through the dawn of a kind of golden age of exo-planetary discovery, and it is nice to have go to place that brings it all together.

      Good points about mass uncertainty due to to unknown orbital inclination. But, while it’s right that the rough average of all planetary inclinations will be 45 degrees, that won’t be even close to the average of all RV detected systems’ i values. Systems with large inclinations aren’t detectable (by RV) at all, so the fact that Bernard b was detectable suggests an i much closer to zero than to 90 degrees. Therefore my guess would be that it is < 4 Earths in mass, and if over 4, not much over.

      • Paul Gilster November 16, 2018, 17:40

        A golden age indeed. It’s extraordinary how lucky we are to be living through this early explosion of knowledge about exoplanets. We’ll be telling stories to our grandkids.

  • ljk November 16, 2018, 12:35

    Two free-range planets found roaming the Milky Way in solitude

    If confirmed, the newly discovered worlds lend credence to the belief that rogue planets are quite common throughout the Milky Way.

    By Jake Parks | Published: Thursday, November 15, 2018

    http://www.astronomy.com/news/2018/11/rogue-one-and-two

    There may be exoplanets much closer to our Sol system than Alpha Centauri, now that we know rogue worlds are real. A sample of another star system coming to us, or at least relatively close.

  • Dave Moore November 16, 2018, 15:24

    Is there knowledge of Barnard’s Star axial tilt relative to our line of sight?
    Chances are that the system will be approximately co-planar with the star’s equator, and this would give us a better idea of the mass constraints of both Barnard b and any postulated planets interior to it.

  • Harry R Ray December 10, 2018, 20:16

    A new economical(!?) way we can GET to Barnard’s Star. “Spacecraft With Interstellar Medium Momentum Exchange Reactions: The potential and limitations of propelantless interstellar travel.” by Drew Bisban. This kind of sounds like a simpler, lower acceleration version of a Bussard Ramscoop, but using an electric field instead of a magnetic field.

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