Ross 128 b

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Exoplanet
Ross 128 b

Artist's impression of the planet Ross 128b and the star it orbits

Artist's impression of the planet Ross 128b and the star it orbits
Constellation Virgin
Position
equinox : J2000.0
Right ascension 11h 47m 44.3974s
declination −0 ° 48 ′ 16.395 ″
Orbit data
Central star Ross 128
Major semi-axis 0.0496 AU
eccentricity 0.036
Period of circulation 9.8658 days
Further data
radius 0.5-3.0 earth radii
Minimum dimensions 1.35 earth masses
distance 3.381 pc
history
discovery Xavier Bonfils
Date of discovery 15th November 2017
Catalog names
FI Virginis b, FI Vir b, G 010-050 b, GCTP 2730 b, GJ 447 b

Ross 128 b is a confirmed, probably rocky exoplanet of Earth-like size orbiting in or near the habitable zone of the red dwarf Ross 128 . It is the second closest known potentially habitable exoplanet at a distance of about 11 light years ; only Proxima Centauri b is closer. The exoplanet was determined with the aid of the HARPS spectrograph ( radial velocity s-planet finder with high accuracy) at the La Silla Observatory in Chile using radial velocity data from a decade. Ross 128b is the closest exoplanet to orbiting a silent red dwarf and is widely recognized as one of the best candidates for habitability. The planet is about 35% more massive than Earth and receives about 38% more sunlight, so liquid water could exist there.

The planet does not pass its star from Earth, which will make atmospheric characterization difficult until larger telescopes like the Extremely Large Telescope provide new data.

Characteristics

Mass, radius, and temperature

Due to the discovery of the planet by the radial velocity method , the only known physical parameter for Ross 128 b is its minimum possible mass. The planet has a mass of at least 1.35 Earth masses (approx. 8.06 · 10 24 kg). This makes it a little more massive than Proxima Centauri b with a minimum mass of 1.27 ME. The small mass of Ross 128 b suggests that it is likely a rocky, earth-sized planet with a solid surface. However, the exact mass and radius are not known, as no transits of this planet are known, so the radius of Ross 128 b can only be derived mathematically: Ross 128 b can have a radius between 0.5 RE (earth radii) for a pure iron composition and 3.0 RE for a pure hydrogen-helium composition, but both are implausible extreme values. For a more plausible, Earth-like composition, the planet would have to have about 1.1 earth radii (thus about 7,008 km). With this radius, Ross 128 b would be a little denser than Earth, since a rocky planet becomes more compact with increasing size. It would give the planet a gravitational force of about 10,945 m / s², which is about 1.12 times the gravitational force on earth.

Ross 128b has a temperature similar to Earth and is a potential candidate for the evolution of life. The team of explorers modeled the planet's potential equilibrium temperature using an albedo of 0.100, 0.367, and 0.750. With these three albedo parameters, Ross 128 b would have an equilibrium temperature of either 294, 269, or 213 K. For an Earth-like albedo of 0.3, the planet would have an equilibrium temperature of 280 K (7 ° C), about 8 Kelvin lower than the average temperature the earth. The actual temperature of Ross 128 b depends on as yet unknown atmospheric parameters.

Orbit and rotation

The rotation of Ross 128 b takes about 9.9 earth days. Its semi-axis is 0.0496 AU, which means that the earth is more than 20 times farther away from the sun than Ross 128 b is from its central star. This corresponds to 7.38 million kilometers between Ross 128 b and the central star Ross 128, compared with a distance of 149 million kilometers between the sun and earth. The orbit of Ross 128 b is approximately circular with an eccentricity of about 0.036, although this value can only be estimated very roughly so far.

The planet is most likely linked to its star by a bound rotation , meaning that one side of the planet is always facing Ross 128. Thus, an orbit of Ross 128 b around its central star would also take about 9.9 Earth days, which by definition corresponds to the duration of rotation.

Star system

Ross 128 b orbits the M dwarf Ross 128. The star has 17% of the mass and 20% of the radius of the Sun. It has a temperature of 3,192 K, a luminosity of 0.000362 suns and an age of 9.45 ± 0.60 billion years. For comparison: the sun has a temperature of 5,778 K and an age of 4.5 billion years. This means that Ross 128 is about half as hot and twice as old. The star is 11.03 light years away, making it one of the 20 closest known stars .

Habitability

It is not confirmed that Ross 128b is in the habitable zone . It appears to be within the inner edge of this zone as it receives approximately 38% more sunlight than Earth. The habitable zone is defined as the region around a star in which the temperatures are suitable for the formation of a planet with a dense atmosphere . This favors the existence of liquid water, which in turn is a prerequisite for the development of life forms known to us. With its relatively high irradiance , Ross 128b is likely to be more prone to water loss, mainly on the side directly facing the star. An Earth-like atmosphere, however, would be possible if one assumed that the planet was able to distribute the energy received from the star around the planet, allowing more areas to contain liquid water. Additionally, study author Xavier Bonfils noted the possibility of significant cloud cover on the star-facing side, which could block a lot of incoming stellar energy and help keep the planet cool. It was calculated that the planet has an equilibrium temperature of at least 280 K, with an Earth Similarity Index (ESI) value of 0.86 - and thus the third highest of all known planets, together with GJ 3323 b .

If the planet is not in a bound rotation because of the thermal tides , it would be considered one of the most promising candidates for life found so far. Not only because of its Earth-like temperatures, but also because of its small size and its rather calm central star. In the event that the most likely theories are correct, Ross 128 b would be very close to Earth in mass and about 10% larger in radius. The force of gravity on the planet would be only slightly stronger than what one would feel when walking on the surface of the earth. In addition, the central star Ross 128 is an evolved star with limited stellar activity. Many red dwarfs like Proxima Centauri and Trappist-1 have a tendency to release potentially hostile flares caused by strong magnetic fields inside the star. These flares can gradually drag the atmosphere of a planet with them into space and also sterilize the planet with dangerous amounts of radiation. Although Ross 128 also produces such flares, they are much rarer and fainter than those of the other stars mentioned, which increases the likelihood of a stable, intact atmosphere, should Ross 128 have one.

So far it is not possible to determine whether Ross 128 b has an atmosphere and whether the existence of life is possible there, since it does not pass its central star from our line of sight. But upcoming missions like the James Webb Space Telescope and new ground telescopes like the Thirty Meter Telescope and the European Extremely Large Telescope could possibly help to analyze the atmosphere of Ross 128 b - if one exists. The goal would be to find biosignatures in the planet's atmosphere , which are chemicals like oxygen , ozone and methane , which are often created by biological processes.

See also

Web links

Commons : Ross 128 b  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c X. Bonfils, N. Astudillo-Defru, R. Diaz, J.-M. Almenara, T. Forveille, F. Bouchy, X. Delfosse, C. Lovis, M.Mayor, F. Murgas, F. Pepe, NC Santos, D. Segransan, S. Udry, A. Wunsche: A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs , Astronomy and Astrophysics .
  2. ↑ GJ 3323 b in The Extrasolar Planet Encyclopedia on exoplanet.eu, accessed on November 21, 2017