HD_63433_c

HD 63433 c

HD 63433 c

Mini-Neptune orbiting the Sun-like star HD 63433

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]

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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 ME, being situated between the masses of Uranus and Neptune, which are 14.54 and 17.15 ME 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]

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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

Main article: HD 63433

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]
    Capistrant, Benjamin K.; Soares-Furtado, Melinda; Vanderburg, Andrew; Jankowski, Alyssa; Mann, Andrew W.; Ross, Gabrielle; Srdoc, Gregor; Hinkel, Natalie R.; Becker, Juliette (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, arXiv:2401.04785, Bibcode:2024AJ....167...54C, doi:10.3847/1538-3881/ad1039
  2. [2]
    "Puffy Planets Lose Atmospheres, Become Super-Earths". hubblesite.org. February 3, 2022. Retrieved January 11, 2023.
  3. [3]
    Mallorquín, M.; Béjar, V. J. S.; Lodieu, N.; Osorio, M. R. Zapatero; Tabernero, H.; Mascareño, A. Suárez; Zechmeister, M.; Luque, R.; Pallé, E.; Montes, D. (2023-03-01). "Dynamical masses of two young transiting sub-Neptunes orbiting HD 63433". Astronomy & Astrophysics. 671: A163. arXiv:2303.15411. Bibcode:2023A&A...671A.163M. doi:10.1051/0004-6361/202245397. ISSN 0004-6361.
  4. [4]
    Mann, Andrew W.; Johnson, Marshall C.; Vanderburg, Andrew; Kraus, Adam L.; Rizzuto, Aaron C.; Wood, Mackenna L.; Bush, Jonathan L.; Rockcliffe, Keighley; Newton, Elisabeth R.; Latham, David W.; Mamajek, Eric E.; Zhou, George; Quinn, Samuel N.; Thao, Pa Chia; Benatti, Serena (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. arXiv:2005.00047. Bibcode:2020AJ....160..179M. doi:10.3847/1538-3881/abae64. ISSN 0004-6256.
  5. [5]
    "Neptune Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved January 18, 2024.
  6. [6]
    Zhang, Michael; Knutson, Heather A.; Wang, Lile; Dai, Fei; Santos, Leonardo A. dos; Fossati, Luca; Henry, Gregory W.; Ehrenreich, David; Alibert, Yann; Hoyer, Sergio; Wilson, Thomas G.; Bonfanti, Andrea (2022-02-01). "Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune". The Astronomical Journal. 163 (2): 68. arXiv:2106.05273. Bibcode:2022AJ....163...68Z. doi:10.3847/1538-3881/ac3f3b. ISSN 0004-6256.
  7. [7]
    "Puffy planets lose atmospheres, become super-Earths". phys.org. Retrieved 2024-01-11.
  8. [8]
    "Uranus Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved January 18, 2024.
  9. [9]
    "Facts About Earth - NASA Science". science.nasa.gov. Retrieved 2023-12-04.
  10. [10]
    "Mercury Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved January 18, 2023.
  11. [11]
    "HD 63433". Open Exoplanet Catalogue. Archived from the original on January 14, 2024. Retrieved January 14, 2024.
  12. [12]
    "HD 63433". simbad.cds.unistra.fr. Retrieved 2024-01-11.
  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. [N 1]
    Neptune is 3.883 times larger than Earth, and 17.15 times more massive.[5]
  2. [N 2]
    The radius of Neptune and Uranus are 3.883 R🜨[5] and 4.007 R🜨[8] respectively.
  3. [N 3]
    The density of Earth is 5.513 g/cm3.[9]
  4. [N 4]
    The densities of Neptune and Uranus are 1.638 g/cm3[5] and 1.27 g/cm3[8] respectively.
  5. [N 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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