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New Planets from Old Data

We rightly celebrate exoplanet discoveries from dedicated space missions like TESS (Transiting Exoplanet Survey Satellite), watching the work go from initial concept to first light in space and early results. But let’s not forget the growing usefulness of older data, tapped and analyzed in new ways to reveal hidden gems. Thus recent work out of the Carnegie Institution for Science, where Fabo Feng and Paul Butler have mined the archives of the Ultraviolet and Visual Echelle Spectrograph survey of 33 nearby red dwarf stars, a project operational from 2000 to 2007.

The duo have uncovered five newly discovered exoplanets and eight more candidates, all found orbiting nearby red dwarf stars. Two of these are conceivably in the habitable zone, putting nearby stars GJ180 and GJ229A into position as potential targets for next-generation instruments. Both of these stars host super-Earths (7.5 and 7.9 times the mass of Earth), with orbital periods of 106 and 122 days respectively. Like the other planets unveiled in the discovery paper in The Astrophysical Journal Supplement Series, these worlds were all found using radial velocity methods, uniquely powerful when deployed on low-mass red dwarfs.

Temperate super-Earths are interesting in their own right, but one of these has a particular claim to our attention, as lead author Feng explains:

“Many planets that orbit red dwarfs in the habitable zone are tidally locked, meaning that the period at which they spin around their axes is the same as the period at which they orbit their host star. This is similar to how our Moon is tidally locked to Earth, meaning that we only ever see one side of it from here. As a result, these exoplanets [have] a very cold permanent night on one side and very hot permanent day on the other—not good for habitability. GJ180d is the nearest temperate super-Earth to us that is not tidally locked to its star, which probably boosts its likelihood of being able to host and sustain life.”

But GJ229Ac is also intriguing, a possibly temperate super-Earth in a system where the host star has a brown dwarf companion. That object, GJ229B, was one of the first brown dwarfs to be imaged, making this system an interesting testbed for planet formation models. We also have a Neptune-class planet orbiting GJ433 well out of the habitable zone, far enough from its star that the authors see it as a realistic candidate for future direct imaging. The planet is the coldest Neptune-like world we’ve yet found around another star, and also the nearest to Earth.

Image: Artist’s concept of GJ229Ac, the nearest temperate super-Earth to us that is in a system in which the host star has a brown dwarf companion. Credit: Robin Dienel, courtesy of the Carnegie Institution for Science.

Efforts like this don’t stop with a single dataset, but rely on multiple follow-ups to increase the fidelity of the data. Thus Feng and Butler used the Planet Finder Spectrograph at Las Campanas (Chile), ESO’s HARPS spectrograph (High Accuracy Radial Velocity Planet Searcher) at La Silla, and HIRES (High Resolution Echelle Spectrometer) at the Keck Observatory in a combination that, in Butler’s words, “increases the number of observations and the time baseline, and minimizes instrumental biases.”

I think Feng and Butler are right to emphasize the utility of the UVES data. From the paper:

The most important observation in a precision velocity data set is the first observation because observers cannot go back in time. For most of the stars in the UVES M Dwarf program, these are the first observations taken with state-of-the-art precision. This data set is all the more remarkable for focusing on some [of] the nearest stars, and the stars most likely to harbor detectable potentially habitable planets. These observations will continue to be important in finding and constraining planets around these stars for decades to come. We do not expect this to be the final word on this remarkable data set. We look forward to future researchers reanalyzing this data set with a superior Doppler reduction package, and producing the surprises that emerge from better measurement precision.

All of which emphasizes how creative we are learning to be with the data that in recent decades have been cascading in quantity, quality and importance. Nice work by the UVES M Dwarf team. As the paper goes on to say: “Starting back in the infancy of precision velocity measurements, they boldly went straight to the heart of the most interesting and challenging problem, finding potentially habitable planets around the nearest stars.”

And kudos to Feng and Butler for dedicating their paper to Carnegie astronomer and system manager Sandy Keiser, who died suddenly in 2017 during the analysis of the data from which these results emerged, but not before she produced work critical to this paper.

The paper is Butler et al., “A Reanalysis of the UVES M Dwarf Planet Search Program,” Astronomical Journal Vol. 158, No. 6 (2 December 2019). Abstract.

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{ 13 comments… add one }
  • Ashley.Baldwin January 15, 2020, 11:04

    The Gliese 229A system is one we are going to hear a lot about over the next decade – and see too hopefully . At just 19 light years distant both planets should have sufficient angular separation from their parent M2 dwarf star to be imaged by the E-ELT.

    229Ab with a mass of circa 32Me should also be just large enough and near enough to be picked up by Gaia and have its mass and orbital parameters determined to a previously unknown level of precision. If the system is coplanar that should provide the ‘i’ of the RV determined ‘msini’ of 229c – and an accurate figure obtained for it’s mass too.

    If the E-ELT comes equipped with the HIRES spectrograph and an integral field unit as a phase A instrument , its combination with the METIS polarimetric imager should provide ultra high res spectra of perfect target 229c at the least via the nascent but cutting edge ‘high dispersion imaging ‘ technique. A technique that still needs perfecting and what better target ? It should be a prime target for WFIRST too. Gaia, ELT and WFIRST is some triangulation.

    As I’ve said before, I reckon that this planet will become for some time the most studied and most understood planet outside of the solar system.

    Needs a proper name.

  • Ulrich Steffen January 15, 2020, 13:28

    Very interesting discovery. But it would be important to know if GJ180 and GJ229A are flare stars (most – but not all – spectral type M stars are flare stars). If so, it would be very questionable whether life could develop on the newly discovered planets in the “habitable zones” around their host stars. It would be better to focus more on exoplanets orbiting around spectral class K stars, which are usually much less problematic with regard to flares.

  • andy January 15, 2020, 15:18

    Really, they’re still doing nice rocky/watery landscapes as their visual for a planet with a minimum mass of over 7 Earths? Despite what we’ve learned about transitions between rocky and volatile-rich planets in the Earth–Uranus gap? Honestly, I’m not entirely surprised but I’m still disappointed this is still going on.

    The astrometric orbit of the brown dwarf GJ 229 B has been determined by Brandt et al. (2019), who also found that the object belongs to a growing class of over-massive T-dwarfs (this category also includes Epsilon Indi Ba and Bb). The inclination of the GJ 229 B orbit was found to be close to 13°, with the 95.4% confidence interval ranging from 1°-41°. If the GJ 229 A planets are coplanar with the brown dwarf (admittedly not a given), their masses are going to be substantially higher than the minimum: at 13° the mass of planet c ends up as 32 Earth masses, and even at 41° it would be an 11 Earth masses.

    The planets of GJ 229 A are at best sub-Neptunes, they may well be sub-Saturns.

    • Frank January 15, 2020, 16:23

      I agree – these are warm sub-Neptunes. The term super-Earth is over used and abused.

    • Enzo January 15, 2020, 17:37

      Yes, we have no earths :-)

      Paraphrasing the better known “yes, we have no neutrons” that makes fun of cold fusion.

  • Michael Fidler January 15, 2020, 17:39

    Here is the latest update: Search for Nearby Earth Analogs. II. Detection of Five New Planets, Eight Planet Candidates, and Confirmation of Three Planets around Nine Nearby M Dwarf.
    https://arxiv.org/abs/2001.02577

    For the last week I been trying to find info on GJ 173 without much luck can anyone point me in the right direction, my GPS doesn’t seem to be working! 🙂

    • Enzo January 15, 2020, 18:20
    • Michael Fidler January 16, 2020, 11:15

      We need an app that cross references the stars names or ID’s since most have 20 different ones.
      GJ 173:

      LP 715-52 HIP 21556 PLX 1026 UBV M 5319
      BD-11 916 Karmn J04376-110 PLX 1026.00 UCAC4 395-006371
      GCRV 2717 LTT 2050 PM J04376-1102 WEB 4138
      GEN# -0.01100916 2MASS J04374188-1102198 PPM [RHG95] 804
      GJ 173 MCC 106 StKM 2-373 Gaia DR2 3184351876391975808
      HIC 21556 NLTT 13657 TYC 5324-581-1 Gaia DR1 3184351872093838592

  • Michael Fidler January 15, 2020, 18:00

    Proxima Centauri, the sun’s nearest neighbor, may host a 2nd alien planet. Meet Proxima c.
    15 January 2020

    https://www.space.com/amp/proxima-centuri-candidate-alien-planet-proxima-c.html
    More new planets from old data!
    This large superearth could be the most common habitual planet in our Galaxy. These large well heated oceans in such world’s could evolve a completely alien civilizations compared to ours. Being right on our doorstep should make it easy to see how they have evolved. I wonder if this is the object that ALMA picked up? https://astrobites.org/2017/11/16/proxima-centauri-sports-a-fancy-dust-ring/

    • Michael Fidler January 15, 2020, 23:04

      The Curious Case of Proxima C
      Astronomers continue to gather evidence for a second world around the sun’s nearest neighboring star.

      Very good write up on several other results not mentioned in the other reports.

      https://www.scientificamerican.com/article/the-curious-case-of-proxima-c/

      RESEARCH ARTICLE PLANETARY SCIENCE
      A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5 AU
      Mario Damasso1,*, Fabio Del Sordo2,3,*, Guillem Anglada-Escudé4, Paolo Giacobbe1, Alessandro Sozzetti1, Alessandro Morbidelli5, Grzegorz Pojmanski6, Domenico Barbato1,7, R. Paul Butler8, Hugh R. A. Jones9, Franz-Josef Hambsch10, James S. Jenkins11, María José López-González12, Nicolás Morales12, Pablo A. Peña Rojas11, Cristina Rodríguez-López12, Eloy Rodríguez12, Pedro J. Amado12, Guillem Anglada12, Fabo Feng8

      Science Advances 15 Jan 2020:z

      https://advances.sciencemag.org/content/6/3/eaax7467

  • Spaceman January 19, 2020, 20:49

    What is the implied planet occurrence rate based on this new planets from old data study??

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