Astronomy:K2-32

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K2-32 is a G9-type main sequence star slightly smaller and less massive than the sun.[1] Four confirmed transiting exoplanets are known to orbit this star.[2] A study of atmospheric escape from the planet K2-32b caused by high-energy stellar irradiation indicates that the star has always been a very slow rotator.[3]

Planetary system

Discovery

The star K2-32 was initially found to have three transiting planet candidates by Andrew Vanderburg and collaborators in 2016.[4] The innermost planet candidate, at that time, K2-32b was confirmed using radial velocity measurements made with the Keck telescope.[1] Confirmation of planets c and d was made by Sinukoff et al. using adaptive optics imaging and computer analysis to eliminate possible false positives.[5]

The Earth-sized planet K2-32e was discovered and validated by René Heller and team in 2019.[2][6]

Transit light curves of all four planets orbiting the star K2-32.[2]

Characteristics

With periods of 4.34, 8.99, 20.66 and 31.71 days the four planets orbits are very close to a 1:2:5:7 orbital resonance chain. The densities of planets b, c, and d are between those of Saturn and Neptune, which suggests large and massive atmospheres. The planet K2-32e with a radius almost identical to that of the Earth is almost certainly a terrestrial planet.[2] All four planets are well inside even the optimistic inner boundary of the habitable zone located at 0.58 astronomical units.[7]

Planetary system of the star K2-32 showing planetary radii and orbital resonances.[2]
The K2-32 planetary system[2][8][9]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
e 2.1+1.3−1.1 M⊕ 0.04899+0.00041−0.00038 4.34934±0.00039 0.043+0.048−0.030 89.0±0.7° 1.212+0.052−0.046 R⊕
b 15.0+1.8−1.7 M⊕ 0.07950+0.00066−0.00062 8.992±0.00008 0.03+0.032−0.02 89.0+0.5−0.3° 5.299±0.191 R⊕
c 8.1±2.4 M⊕ 0.13843+0.00115−0.00108 20.66093+0.00080−0.00079 0.049+0.046−0.035 89.4+0.3−0.2° 2.134+0.123−0.102 R⊕
d 6.7±2.5 M⊕ 0.18422+0.00152−0.00144 31.71701+0.00101−0.00096 0.05+0.053−0.035 89.4±0.1° 3.484+0.112−0.129 R⊕

References

  1. ↑ 1.0 1.1 Dai, Fei et al. (2016). "Doppler Monitoring of Five K2 Transiting Planetary Systems". The Astrophysical Journal 823 (2). doi:10.3847/0004-637X/823/2/115. Bibcode: 2016ApJ...823..115D. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Heller, René; Rodenbeck, Kai; Hippke, Michael (2019). "Transit least-squares survey. I. Discovery and validation of an Earth-sized planet in the four-planet system K2-32 near the 1:2:5:7 resonance". Astronomy and Astrophysics 625. doi:10.1051/0004-6361/201935276. Bibcode: 2019A&A...625A..31H. https://www.aanda.org/articles/aa/full_html/2019/05/aa35276-19/aa35276-19.html. 
  3. ↑ Kubyshkina, D. et al. (2019). "Close-in Sub-Neptunes Reveal the Past Rotation History of Their Host Stars: Atmospheric Evolution of Planets in the HD 3167 and K2-32 Planetary Systems". The Astrophysical Journal 879 (1). doi:10.3847/1538-4357/ab1e42. Bibcode: 2019ApJ...879...26K. 
  4. ↑ Vanderburg, Andrew et al. (2016). "Planetary Candidates from the First Year of the K2 Mission". The Astrophysical Journal Supplement Series 222 (1). doi:10.3847/0067-0049/222/1/14. Bibcode: 2016ApJS..222...14V. 
  5. ↑ Sinukoff, Evan et al. (2016). "Eleven Multiplanet Systems From K2 Campaigns 1 and 2 and the Masses of Two Hot Super-Earths". The Astrophysical Journal 827 (1). doi:10.3847/0004-637X/827/1/78. Bibcode: 2016ApJ...827...78S. 
  6. ↑ "Astronomers Discover 18 New Small Exoplanets in Kepler Data" (Press release). Sci-News.com. 2019-05-28. Retrieved 2019-09-27.
  7. ↑ Wittenmyer, Robert A. et al. (2018). "The K2-HERMES Survey. I. Planet-candidate Properties from K2 Campaigns 1–3". The Astronomical Journal 155 (2). doi:10.3847/1538-3881/aaa3e4. Bibcode: 2018AJ....155...84W. 
  8. ↑ Petigura, Erik A. et al. (2017). "Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes". The Astronomical Journal 153 (4). doi:10.3847/1538-3881/aa5ea5. Bibcode: 2017AJ....153..142P. 
  9. ↑ Lillo-Box, J. et al. (2020). "Masses for the seven planets in K2-32 and K2-233". Astronomy & Astrophysics 640. doi:10.1051/0004-6361/202037896. Bibcode: 2020A&A...640A..48L. 

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