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Ross 128 b

Coordinates:Sky map11h47m44.4s,+00° 48′ 16″
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Ross 128 b
Artist's impression of the planet Ross 128 b, with the star Ross 128 in the background.
Discovery
Discovered byXavier Bonfils
Discovery dateNovember 15, 2017
Radial velocity
Orbital characteristics
Apastron0.0511 (± 0.0031)AU
Periastron0.0475 (± 0.0031)AU
0.0496 (± 0.0017)AU
Eccentricity0.036 (± 0.092)
9.8658 (± 0.0070)d
StarRoss 128
Physical characteristics
1.6+1.1
−0.65[1]R🜨
Mass1.8+0.56
−0.43[1]ME
Temperature213–301 K (−60–28 °C; −76–82 °F)

Ross 128 bis a confirmed Earth-sizedexoplanet,likely rocky, that is orbiting within the innerhabitable zoneof thered dwarfstarRoss 128,at a distance of around 11light-yearsfrom Earth.[2]The exoplanet was found using a decade's worth of radial velocity data using theEuropean Southern Observatory'sHARPSspectrograph(High Accuracy Radial velocity Planet Searcher) at theLa Silla Observatoryin Chile. Ross 128 b is the nearest exoplanet around a quietred dwarf,and is considered one of the best candidates forhabitability.The planet is only 35% more massive thanEarth,receives only 38% more starlight, and is expected to be a temperature suitable for liquid water to exist on the surface, if it has an atmosphere.[3]

The planet does nottransititshost star,which historically made atmospheric characterization very difficult, but this has become possible with the construction of larger telescopes like theJames Webb Space Telescope.[3]

Physical characteristics

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Mass, radius, and temperature

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Due to it being discovered by theradial velocitymethod,[4]the only known physical parameter for Ross 128 b is its minimum possible mass. The planet is at least 1.35ME,or 1.35 times the mass of Earth (about8.06×1024kg). This is slightly more massive than the similar and nearbyProxima Centauri b,with a minimum mass of 1.27ME.The low mass of Ross 128 b implies that it is most likely arockyEarth-sized planet with a solid surface. However, its radius, and therefore its density, is not known as no transits of this planet have been observed. Ross 128 b would be 0.5R🜨(Earth radii) for a pure-iron composition and 3.0R🜨for a pure hydrogen-helium composition, both implausible extremes. For a more plausible Earth-like composition, the planet would need to be about 1.10R🜨- i.e., 1.1 times the radius of Earth (approximately7008 km). With that radius, Ross 128 b would be slightly denser than Earth, due to how a rocky planet would become more compact as it increases in size. It would give the planet a gravitational pull around10.945 m/s2,or about 1.12 times that of Earth.[3]

Ross 128 b is calculated to have a temperature similar to that of Earth and potentially conducive to thedevelopment of life.[4]The discovery team modelled the planet's potential equilibrium temperature usingalbedosof 0.100, 0.367, and 0.750. Albedo is the portion of the light that is reflected instead of absorbed by a celestial object. With these three albedo parameters, Ross 128 b would have a Teqof either 294 K (21 °C; 70 °F), 269 K (−4 °C; 25 °F), or 213 K (−60 °C; −76 °F). For an Earth-like albedo of 0.3, the planet would have an equilibrium temperature of 280 K (7 °C; 44 °F), about 8 Kelvins lower than Earth's average temperature.[4]The actual temperature of Ross 128 b depends on yet-unknown atmospheric parameters, if it has an atmosphere.[3]

Host star

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Main article:Ross 128
Artist's impression of Ross 128 b along with its red dwarf parent star

Ross 128 b orbits the smallred dwarfstar known as Ross 128. The star is 17% the mass and 20% the radius of that of the Sun. It has a temperature of3192 K,a luminosity of 0.00362L☉,and an age of9.45±0.60billion years.For comparison, the Sun has a temperature of5772 Kand age of4.5billion years,making Ross 128 half the temperature and over twice the age. The star is only 11.03 light-years away, making it one of the 20 closest stars known.

In 2018, astronomers, based on near-infrared, high-resolution spectra (APOGEE Spectra), determined the chemical abundances of several elements (C, O, Mg, Al, K, Ca, Ti, and Fe) present in Ross 128, finding that the star has near solar metallicity.[5][6]

Orbit

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Ross 128 b is a closely orbiting planet, with a year (orbital period) lasting about 9.9 days.[3][4]Itssemi-major axisis 0.0496AU(7.42 million km). According to some models of the planet's orbit, its orbit is quite circular, with an eccentricity of around 0.03, but also with a large error range as well. However, if all the orbital models are brought together then the eccentricity is higher at about 0.116, and again this is subject to a large error range. Compared to the Earth's average distance from the Sun of 149 million km, Ross 128 b orbits 20 times closer. At that close distance from its host star, the planet is most likelytidally locked,meaning that one side of the planet would have eternal daylight and the other would be in darkness.[7][8]

Habitability

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Main article:Habitability of red dwarf systems

Stellar flux properties

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Ross 128 b is not confirmed to be orbiting exactly within thehabitable zone.It appears to reside within the inner edge, as it receives approximately 38% moresunlightthanEarth.Thehabitable zoneis defined as the region around astarwhere temperatures are just right for aplanetwith a thick enoughatmosphereto support liquidwater,a key ingredient in the development oflifeas we know it. With its moderately highstellar flux,Ross 128 b is likely more prone towaterloss, mainly on the side directly facing thestar.However, an Earth-likeatmosphere,assuming one exists, would be able to distribute theenergyreceived from thestararound theplanetand allow more areas to potentially hold liquidwater.[9]In addition, study authorXavier Bonfilsnoted the possibility of significantcloudcover on the star-facing side, which would block out much incoming stellarenergyand help keep theplanetcool.

Solar flare potential

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Theplanetis considered one of the mostEarth-like worldsever found in relation to itstemperature,size and rather quiet hoststar.[4]Ross 128 b is very close in mass toEarth,only about 35% more massive, and is likely around 10% larger in radius.Gravityon the planet would be only slightly higher. Also, its host star Ross 128 is an evolved star with a stable stellar activity.[4]Manyred dwarfslikeProxima CentauriandTRAPPIST-1are prone to releasing potentially deadlyflarescaused by powerfulmagnetic fields.Billionsof years of exposure to these flares can potentially strip aplanetof itsatmosphereand render it sterile with possibly dangerous amounts of radiation. While Ross 128 is known to produce such flares, they are currently much less common and less powerful than those of the previously mentioned stars.

Atmospheric potential

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As of 2017, it is not yet possible to determine if Ross 128 b has anatmospherebecause it does nottransitthe star.[4]However, theJames Webb Space Telescopeand upcoming massiveground-based telescopes,like theThirty Meter Telescopeand theEuropean Extremely Large Telescope,could analyze the atmosphere of Ross 128 b if it has an atmosphere without the need of transit. This would enablescientiststo findbiosignaturesin the planet's atmosphere, which arechemicalslikeoxygen,ozone,andmethanethat are created by knownbiological processes.

See also

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References

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  1. ^abTasker, Elizabeth J.;Laneuville, Matthieu; Guttenberg, Nicholas (7 January 2020)."Estimating Planetary Mass with Deep Learning".The Astronomical Journal.159(2): 41.arXiv:1911.11035.Bibcode:2020AJ....159...41T.doi:10.3847/1538-3881/ab5b9e.ISSN1538-3881.S2CID208267900.
  2. ^Newfound Earth-like exoplanet a good spot to hunt for aliens.Eric Mack,CBS News.15 November 2017.
  3. ^abcdeBonfils, Xavier (2017). "A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs".Astronomy and Astrophysics.613:A25.arXiv:1711.06177.Bibcode:2018A&A...613A..25B.doi:10.1051/0004-6361/201731973.S2CID37148632.
  4. ^abcdefgA potentially habitable planet has been discovered just 11 light-years awayArchived2018-02-21 at theWayback Machine.John Wenz,Astronomy Magazine.15 November 2017.
  5. ^Suoto, Diogo; et al. (13 June 2018)."Stellar and Planetary Characterization of the Ross 128 Exoplanetary System from APOGEE Spectra".The Astrophysical Journal Letters.860(1): L15.arXiv:1805.11633.Bibcode:2018ApJ...860L..15S.doi:10.3847/2041-8213/aac896.S2CID89612773.
  6. ^Staff (10 July 2018)."Rocky planet neighbor looks familiar, but is not Earth's twin - Detailed chemical abundances of the Ross 128 help us understand its exoplanet Ross 128 b".Eurekalert!.Retrieved11 July2018.
  7. ^Nearby Earth-sized Alien World Orbits 'Quiet' Star, Boosting Habitable Potential.Ian O'Neill,How Stuff Works.15 November 2017. Quote:"Tidal lock[ing] is expected for Ross 128 b," says Nicola Astudillo-Defra, who works at the Geneva Observatory, University of Geneva in Switzerland, and is co-author of the study.
  8. ^Ross 128.Sol Station.November 2017.
  9. ^Newly discovered nearby planet could support life.Ashley Strickland,CNN News.15 November 2017.
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