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Gliese 514 Exoplanet System

Eccentric super-Earth moving in and out of the habitable zone //

Gliese 514 (Gl 514) is a real exoplanet system located 24.85 light-years away in the constellation Virgo. It consists of a solitary star and one known planet. The star Gl 514 is a high-end red dwarf with 0.51 solar masses and 0.5 solar radii. It has an M0.5V–M1.0V spectral type, surface temperature of 3714 K (3441 °C) and luminosity 4.3% that of the Sun. The system is likely at least 800 million years old. One source estimates a much higher 8.25 billion years but also notes significant limitations in their method, so this number may not be reliable.

In 2022, analysis of data spanning 25 years led to the discovery of Gl 514 b—a planet around Gl 514 with a minimum mass 5.2 times that of Earth. This super-Earth orbits its star every 140.43 days at an average distance of 0.422 AU. Unusually, its path is highly elliptical with an eccentricity value of 0.45. This is the highest of any low-mass planet around red dwarfs in our stellar neighbourhood. Consequently, Gl 514 b skirts by the inner edge of Gl 514’s habitable zone at its closest before travelling back out into the colder fringes of the system. It is currently unclear how the planet ended up in such a predicament. A common thought might be that the gravitational pull from a nearby gas giant is to blame, but further analysis has ruled out any such object within several tens of AU.

Gl 514 b’s orbit means that it spends only 34% of the time in the habitable zone, prompting interest in using it as a case study to investigate the habitability of eccentric super-Earths. Does it undergo extreme cycles of freezing and thawing? Or could it buffer these temperature swings with a thick atmosphere and oceans? Such questions are speculative for now as we wait for more data on this unique planet. As very few low-mass planets are known to exist in the habitable zone of high-end red dwarfs—only K2-3 d and GJ 229 A c are close analogues—Gl 514 b is a valuable addition to this sample.

In this simulation, features of the Gl 514 system are replicated from existing data wherever possible or inferred in cases of knowledge gaps:

• Determining the physical characteristics of Gl 514 b is difficult because we do not yet know its radius. At ~5 Earth masses, it could either be rocky or, if it has a thick gaseous envelope, a mini-Neptune. That being said, most sources refer to the planet as a super-Earth, so I've imagined Gl 514 b as a temperate lacustrine super-Terra with 1.59 Earth radii.
  
• The surface of Gl 514 b is dominated by tremendous massifs, valleys and deep lakes. The higher gravity of such super-Earths would normally hinder mountain growth, but its eccentric orbit induces tidal forces that promote tectonics and volcanism, leading to the formation of these behemoths.
  
• The planet’s average temperature is a chilly 252 K (-21 °C). This is a fair bit colder than Earth but values above 250 K are still considered “temperate”. Its climate is relatively stable despite its elliptical orbit thanks to a substantial atmosphere, though a great proportion of the surface is still locked under snow and ice.
  
• Close-in planets can become tidally locked with one side always facing their star, but because Gl 514 b's orbit is eccentric, this is unlikely to be the case. Instead, I've imagined that it experiences a 5:2 spin-orbit resonance, meaning that it rotates five times for every two orbits completed. This creates an interesting phenomenon where its star would at times appear motionless or even move backwards in the sky. The result is two "hotspots" on the planet that receive more stellar energy, leading to higher local temperatures up to ~303 K (30 °C). One might entertain the thought of settlers or alien life huddling around these pockets for warmth and light.

LHS 352, IRAS 13275+1038, PM J13299+1022, USNO-B1.0 1003-00216029, AG+10 1630, JP11 45, PPM 129864, VVO 5, AKARI-IRC-V1 J1330002+102230, Karmn J13299+102, Ross 490, WEB 11651, AP J13295979+1022376, LFT 1012, RX J1329.9+1022, WISEA J133000.58+102226.4, ASCC 955736, LSPM J1329+1022, 1RXS J132958.5+102252, Zkh 200, BD+11 2576, LTT 13925, StKM 2-947, [FS2003] 0673, Ci 20 782, 2MASS J13295979+1022376, TIC 404519959, [RHG95] 2123, GCRV 8008, MCC 143, TYC 895-317-1, [ZEH2003] RX J1329.9+1022 2, GEN# +0.01102576, NLTT 34287, UBV 12123, Gaia DR2 3738099879558957952, G 63-34, 8pc 131.12, UBV 12139, Gaia DR3 3738099879558957952, GJ 514, PLX 3079, UBV M 489, HIC 65859, PLX 3079.00, UCAC2 35403307, HIP 65859, PM 13275+1039, UCAC4 502-056873

• Damasso, M., Perger, M., Almenara, J.M., Nardiello, D., Pérez-Torres, M., Sozzetti, A., Hara, N.C., Quirrenbach, A., Bonfils, X., Osorio, M.Z. and Astudillo-Defru, N., 2022. A quarter century of spectroscopic monitoring of the nearby M dwarf Gl 514-A super-Earth on an eccentric orbit moving in and out of the habitable zone. Astronomy & Astrophysics, 666, p.A187.
  
• Maldonado, J., Micela, G., Baratella, M., D’Orazi, V., Affer, L., Biazzo, K., Lanza, A.F., Maggio, A., Hernández, J.G., Perger, M. and Pinamonti, M., 2020. HADES RV programme with HARPS-N at TNG-XII. The abundance signature of M dwarf stars with planets. Astronomy & Astrophysics, 644, p.A68.