Sub-Earth

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Comparing the size of Earth, Mars, and exoplanets of Kepler-20 and Kepler-42. Comparing the size of Earth, Mars, and exoplanets of Kepler-20 and Kepler-42.jpg
Comparing the size of Earth, Mars, and exoplanets of Kepler-20 and Kepler-42.

A sub-Earth is a planet "substantially less massive" than Earth and Venus. [1] In the Solar System, this category includes Mercury and Mars. Sub-Earth exoplanets are among the most difficult type to detect because their small sizes and masses produce the weakest signal. Despite the difficulty, one of the first exoplanets found was a sub-Earth around a millisecond pulsar PSR B1257+12. The smallest known is WD 1145+017 b with a size of 0.15 Earth radii, or somewhat smaller than Pluto. However, WD 1145+017 b is not massive enough to qualify as a sub-Earth classical planet and is instead defined as a minor, or dwarf, planet. [2] It is orbiting within a thick cloud of dust and gas as chunks of itself continually break off to then spiral in towards the star, and within around 5,000 years it will have more-or-less disintegrated. [3]

The Kepler space telescope opened up a new realm of sub-Earth discoveries. On January 10, 2012, Kepler discovered the first three sub-Earths around an ordinary star, Kepler-42. As of June 2014, Kepler has 45 confirmed planets that are smaller than Earth, with 17 of them being smaller than 0.8 R. In addition, there are over 310 planet candidates with an estimated radius of <1 R, with 135 of them being smaller than 0.8 R. [1] [4]

There is suspected to be a sub-Earth orbiting Proxima Centauri, the closest star to the Sun. [5] The mass of Proxima d is believed to be between that of Mars and Venus. [6]

Sub-Earths commonly lack substantial atmospheres because of their low gravity and weak magnetic fields, allowing stellar radiation to wear away their atmospheres. [1] Due to their small sizes, and unless there are significant tidal forces when orbiting close to the parent star, sub-Earths also have short periods of geologic activity.

Related Research Articles

<span class="mw-page-title-main">Super-Earth</span> Type of exoplanet

A Super-Earth is a type of exoplanet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

<span class="mw-page-title-main">Discoveries of exoplanets</span> Detecting planets located outside the Solar System

An exoplanet is a planet located outside the Solar System. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such until 2016; no planet discovery has yet come from that evidence. What turned out to be the first detection of an exoplanet was published among a list of possible candidates in 1988, though not confirmed until 2003. The first confirmed detection came in 1992, with the discovery of terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method. As of 1 July 2024, there are 6,660 confirmed exoplanets in 4,868 planetary systems, with 995 systems having more than one planet. This is a list of the most notable discoveries.

Kepler-1520 is a K-type main-sequence star located in the constellation Cygnus. The star is particularly important, as measurements taken by the Kepler spacecraft indicate that the variations in the star's light curve cover a range from about 0.2% to 1.3% of the star's light being blocked. This indicates that there may be a rapidly disintegrating planet, a prediction not yet conclusively confirmed, in orbit around the star, losing mass at a rate of 1 Earth mass every billion years. The planet itself is about 0.1 Earth masses, or just twice the mass of Mercury, and is expected to disintegrate in about 100-200 million years. The planet orbits its star in just 15.7 hours, at a distance only two stellar diameters away from the star's surface, and has an estimated effective temperature of about 2255 K. The orbital period of the planet is one of the shortest ever detected in the history of the extrasolar planet search. In 2016, the planet was confirmed as part of a data release by the Kepler spacecraft.

WD 1145+017 is a white dwarf approximately 476 light-years from Earth in the constellation of Virgo. It is the first white dwarf to be observed with a transiting minor planet orbiting it.

<span class="mw-page-title-main">Kepler-1520b</span> Exoplanet orbiting the star Kepler 1520

Kepler-1520b, is a confirmed exoplanet orbiting the K-type main sequence star Kepler-1520. It is located about 2,020 light-years away from Earth in the constellation of Cygnus. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. The planet was previously proposed in 2012 when reports of its host star recorded drops in its luminosity varying from 0.2% to 1.3%, which indicated a possible planetary companion rapidly disintegrating. In 2015, the planetary nature of the cause of the dips was finally verified. It is expected to disintegrate in about 40–400 million years.

<span class="mw-page-title-main">Proxima Centauri b</span> Terrestrial planet orbiting Proxima Centauri

Proxima Centauri b, sometimes referred to as Alpha Centauri Cb, is an exoplanet orbiting within the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of the larger triple star system Alpha Centauri. It is about 4.2 light-years from Earth in the constellation Centaurus, making it and Proxima d, along with the currently disputed Proxima c, the closest known exoplanets to the Solar System.

<span class="mw-page-title-main">WD 1145+017 b</span> Exoplanetary object orbiting around WD 1145+017

WD 1145+017 b, is a confirmed exoasteroid or minor planet orbiting around and being vaporized by the white dwarf star WD 1145+017, likely one of multiple such objects around this star. It was discovered by NASA's Kepler spacecraft on its "Second Light" mission. It is located about 476 light-years away from Earth in the constellation of Virgo. The object was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

<span class="mw-page-title-main">Disrupted planet</span> Planet or related being destroyed by a passing object

In astronomy, a disrupted planet is a planet or exoplanet or, perhaps on a somewhat smaller scale, a planetary-mass object, planetesimal, moon, exomoon or asteroid that has been disrupted or destroyed by a nearby or passing astronomical body or object such as a star. Necroplanetology is the related study of such a process.

<span class="mw-page-title-main">Neptunian desert</span> Stellar region without planets equivalent to or above Neptune

The Neptunian desert or sub-Jovian desert is broadly defined as the region close to a star (period < 2–4 days) where no Neptune-sized (> 0.1 MJ) exoplanets are found. This zone receives strong irradiation from the star, meaning the planets cannot retain their gaseous atmospheres: They evaporate, leaving just a rocky core.

TOI-700 is a red dwarf 101.4 light-years away from Earth located in the Dorado constellation that hosts TOI-700 d, the first Earth-sized exoplanet in the habitable zone discovered by the Transiting Exoplanet Survey Satellite (TESS).

<span class="mw-page-title-main">TOI-700 d</span> Goldilocks terrestrial planet orbiting TOI-700

TOI-700 d is a near-Earth-sized exoplanet, likely rocky, orbiting within the habitable zone of the red dwarf TOI-700, the outermost planet within the system. It is located roughly 101.4 light-years (31.1 pc) away from Earth in the constellation of Dorado. The exoplanet is the first Earth-sized exoplanet in the habitable zone discovered by the Transiting Exoplanet Survey Satellite (TESS).

<span class="mw-page-title-main">Kepler-1649c</span> Earth-size exoplanet orbiting Kepler-1649

Kepler-1649c is an Earth-sized exoplanet, likely rocky, orbiting within the habitable zone of the red dwarf star Kepler-1649, the outermost planet of the planetary system discovered by Kepler’s space telescope. It is located about 301 light-years (92 pc) away from Earth, in the constellation of Cygnus.

<span class="mw-page-title-main">WD 1856+534</span> White dwarf located in the constellation Draco

WD 1856+534 is a white dwarf located in the constellation of Draco. At a distance of about 25 parsecs (80 ly) from Earth, it is the outer component of a visual triple star system consisting of an inner pair of red dwarf stars, named G 229-20. The white dwarf displays a featureless absorption spectrum, lacking strong optical absorption or emission features in its atmosphere. It has an effective temperature of 4,700 K, corresponding to an age of approximately 5.8 billion years. WD 1856+534 is approximately half as massive as the Sun, while its radius is much smaller, being 40% larger than Earth.

<span class="mw-page-title-main">Proxima Centauri d</span> Sub-Earth candidate orbiting Proxima Centauri

Proxima Centauri d is an exoplanet orbiting the red dwarf star Proxima Centauri, the closest star to the Sun and part of the Alpha Centauri triple star system. Together with two other planets in the Proxima Centauri system, it is the closest known exoplanet to the Solar System, located approximately 4.2 light-years away in the constellation of Centaurus. The first signs of the exoplanet emerged as a weak 5.15-day signal in radial velocity data taken from the Very Large Telescope during a 2020 study on Proxima b's mass. This signal was formally proposed to be a candidate exoplanet by Faria et al. in a follow-up paper published in February 2022.

References

  1. 1 2 3 Sinukoff, E.; Fulton, B.; Scuderi, L.; Gaidos, E. (2013-08-28). "Below One Earth Mass: The Detection, Formation, and Properties of Subterrestrial Worlds". Space Science Reviews. 180 (1–4): 71–99. arXiv: 1308.6308 . Bibcode:2013SSRv..180...71S. doi:10.1007/s11214-013-0019-1. S2CID   255071638.
  2. Vanderburg, Andrew; John Asher Johnson; Rappaport, Saul; Bieryla, Allyson; et al. (2015). "A disintegrating minor planet transiting a white dwarf". Nature. 526 (7574): 546–549. arXiv: 1510.06387 . Bibcode:2015Natur.526..546V. doi:10.1038/nature15527. PMID   26490620. S2CID   4451207.
  3. Rappaport, S.; Gary, B. L.; Kaye, T.; Vanderburg, A.; Croll, B.; Benni, P.; Foote, J. (June 2016). "Drifting asteroid fragments around WD 1145+017". Monthly Notices of the Royal Astronomical Society. 458 (4): 3904–3917. arXiv: 1602.00740 . Bibcode:2016MNRAS.458.3904R. doi: 10.1093/mnras/stw612 .
  4. NASA Exoplanet Archive
  5. Extrasolar Planets Encyclopaedia
  6. Faria, J. P.; Suárez Mascareño, A.; Figueira, P.; Silva, A.M.; et al. (February 2022). "A candidate short-period sub-Earth orbiting Proxima Centauri". Astronomy and Astrophysics. 658: A115. arXiv: 2202.05188 . Bibcode:2022A&A...658A.115F. doi: 10.1051/0004-6361/202142337 .