Astronomy:HD 63433 c

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Short description: Mini-Neptune orbiting the Sun-like star HD 63433
HD 63433 c
Discovery
Discovered byMann et al. (THYME)[1]
Discovery date30 April 2020[1]
Transit[2]
Designations
TOI-1726 c, BD+27 1490 c, HIP 38228 c, V377 Geminorum c
Orbital characteristics[1]
0.1448+0.0073
−0.0077 astronomical unit|AU
Eccentricity0.21+0.33
−0.14
Orbital period20.54 days
Inclination89.28°+0.4°
−0.22°
StarHD 63433
Physical characteristics[3]
Mean radius2.692±0.108 R⊕
Mass15.54±3.86 M⊕
Mean density4.6±1.3 g/cm3
PhysicsTeq: 540+10
−9[lower-alpha 1] — 679+13
−11 K [lower-alpha 2]


HD 63433 c (TOI-1726 c) is a mini-Neptune exoplanet orbiting the Sun-like star HD 63433.[4] It is the outermost planet in its planetary system, being located 0.1448 astronomical units (21,660,000 km) from its star, and completing one orbit every 21 days.[1] Despite being the outermost planet in the system, it is still located close to its star, meaning that its temperature is hot, being estimated between 267 and 406 °C.[3] HD 63433 c is about 2.7 times larger than Earth and 15.5 times more massive,[3] but still smaller and less massive than Neptune.[note 1] In 2022, a study showed that its atmosphere, made up of hydrogen, is being evaporated by the strong radiation from its star, causing it to slowly turn into a super-Earth planet.[6][7]

Characteristics

HD 63433 c is classified as a mini-Neptune planet,[6] a class of planets that are smaller than Neptune but still have an atmosphere of hydrogen and/or helium, just like Neptune.[6] According to theoretical models, its composition is mainly of silicate and water, surrounded by a gaseous envelope that makes up about 2% of the planet.[3] HD 63433 c is 2.7 times larger than Earth, but still 1/3 smaller than the Solar System's ice giants, Neptune and Uranus.[3][note 2] Its mass is about 15.5 M⊕, being situated between the masses of Uranus and Neptune, which are 14.54 and 17.15 M⊕ respectively.[5][8] The density of HD 63433 c is calculated at 4.6 g/cm3,[3] slightly lower than Earth's,[note 3] but higher than the densities of Neptune and Uranus.[note 4] The age of the planet is estimated at 400 million years.[4]

It is the outermost planet in its planetary system, orbiting its star at a distance of 0.145 astronomical units (21,700,000 km), with an orbital period of 21 days.[1] Despite being the outermost planet, its distance is about 37% of Mercury's distance from the Sun,[lower-alpha 3] in addition to having a high temperature, estimated between 267 and 406 degrees Celsius.[3][lower-alpha 4]

Size comparison
Neptune HD 63433 c
Neptune Exoplanet

The discovery of HD 63433 c, as well as all planets orbiting HD 63433, is part of a project called TESS Hunt for Young and Maturing Exoplanets (THYME), whose objective is to discover transiting exoplanets in stellar associations, moving groups and open clusters.[4][1] It was discovered in 2020 by Mann et al., using the Transiting Exoplanet Survey Satellite (TESS), together with HD 63433 b.[11] Both planets were discovered through the transit method.[11]

Evaporating atmosphere

In 2022, a study led by Michael Zhang observed two mini-Neptunes from distinct planetary systems: HD 63433 c, using the Hubble Space Telescope, and TOI-560.01, using the W. M. Keck Observatory.[7] This study revealed that the atmospheres of the two planets – made up mainly of hydrogen (HD 63433 c) and helium (TOI-560.01) – are evaporating and transforming them into super-Earths, as the strong radiation of their host stars is slowly stripping away their puffy atmospheres, causing them to escape into space, like a hot air balloon.[7][2] In HD 63433 c in particular, these gases are escaping at a speed of 50 km/s, and forming a gas cocoon 12 times larger than the planet itself.[7]

The same effect was not identified on the sibling planet HD 63433 b, which could indicate that it has already lost its primordial atmosphere.[7]

Host star

The host star of HD 63433 c is HD 63433, a G-type main-sequence star that is located 73 light-years from Earth in the constellation Gemini.[4][note 5] The properties of this star, such as its radius (0.912 R☉) and its mass (0.99 M☉) are very similar to those of the Sun, which makes it classified as a Solar analog.[4] The star is part of the Ursa Major moving group, allowing its age to be estimated at 414±23 million years.[4] There are other exoplanets orbiting this star, HD 63433 b, also a mini-Neptune, and HD 63433 d, an Earth-sized planet.[1]

See also

Notes and references

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Capistrant, Benjamin K.; Soares-Furtado, Melinda; Vanderburg, Andrew; Jankowski, Alyssa; Mann, Andrew W.; Ross, Gabrielle; Srdoc, Gregor; Hinkel, Natalie R. et al. (2024-01-09), "TESS Hunt for Young and Maturing Exoplanets (THYME) XI: An Earth-sized Planet Orbiting a Nearby, Solar-like Host in the 400Myr Ursa Major Moving Group", The Astronomical Journal 167 (2): 54, doi:10.3847/1538-3881/ad1039, Bibcode: 2024AJ....167...54C 
  2. ↑ 2.0 2.1 "Puffy Planets Lose Atmospheres, Become Super-Earths". February 3, 2022. https://hubblesite.org/contents/news-releases/2022/news-2022-009. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Mallorquín, M.; Béjar, V. J. S.; Lodieu, N.; Osorio, M. R. Zapatero; Tabernero, H.; Mascareño, A. Suárez; Zechmeister, M.; Luque, R. et al. (2023-03-01). "Dynamical masses of two young transiting sub-Neptunes orbiting HD 63433" (in en). Astronomy & Astrophysics 671: A163. doi:10.1051/0004-6361/202245397. ISSN 0004-6361. Bibcode: 2023A&A...671A.163M. https://www.aanda.org/articles/aa/abs/2023/03/aa45397-22/aa45397-22.html. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Mann, Andrew W.; Johnson, Marshall C.; Vanderburg, Andrew; Kraus, Adam L.; Rizzuto, Aaron C.; Wood, Mackenna L.; Bush, Jonathan L.; Rockcliffe, Keighley et al. (2020-10-01). "TESS Hunt for Young and Maturing Exoplanets (THYME). III. A Two-planet System in the 400 Myr Ursa Major Group". The Astronomical Journal 160 (4): 179. doi:10.3847/1538-3881/abae64. ISSN 0004-6256. Bibcode: 2020AJ....160..179M. 
  5. ↑ 5.0 5.1 5.2 5.3 "Neptune Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html. 
  6. ↑ 6.0 6.1 6.2 Zhang, Michael; Knutson, Heather A.; Wang, Lile; Dai, Fei; Santos, Leonardo A. dos; Fossati, Luca; Henry, Gregory W.; Ehrenreich, David et al. (2022-02-01). "Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune". The Astronomical Journal 163 (2): 68. doi:10.3847/1538-3881/ac3f3b. ISSN 0004-6256. Bibcode: 2022AJ....163...68Z. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 "Puffy planets lose atmospheres, become super-Earths" (in en). https://phys.org/news/2022-02-puffy-planets-atmospheres-super-earths.html. 
  8. ↑ 8.0 8.1 8.2 "Uranus Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html. 
  9. ↑ "Facts About Earth - NASA Science" (in en). https://science.nasa.gov/earth/facts/. 
  10. ↑ "Mercury Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html. 
  11. ↑ 11.0 11.1 "HD 63433". https://www.openexoplanetcatalogue.com/planet/HD%2063433%20c/. 
  12. ↑ "HD 63433". https://simbad.cds.unistra.fr/mobile/object.html?object_name=HD%2063433. 
  1. ↑ Assuming an albedo of 0.6
  2. ↑ Assuming an albedo of 0
  3. ↑ The distance of Mercury to the Sun is 0.387 AU.[10]
  4. ↑ Assuming albedos of 0.6 and 0 respectively.
  1. ↑ Neptune is 3.883 times larger than Earth, and 17.15 times more massive.[5]
  2. ↑ The radius of Neptune and Uranus are 3.883 R⊕[5] and 4.007 R⊕[8] respectively.
  3. ↑ The density of Earth is 5.513 g/cm3.[9]
  4. ↑ The densities of Neptune and Uranus are 1.638 g/cm3[5] and 1.27 g/cm3[8] respectively.
  5. ↑ Obtained with a right ascension of  07h 49m 55.06s and a declination of 27° 21′ 47.5″[12] on this website.



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