K2-3d
{{Short description|Mini-Neptune orbiting K2-3}}
{{Infobox planet
| name = K2-3d
| image = Exoplanet Size Comparison K2-3d.png
| caption = Size comparison between the
Earth and K2-3d.
| discovery_site = Kepler Space Observatory
| discovered = 2015
| discovery_method = Transit
| apsis = astron
| semimajor = {{val|0.2014|0.0034|0.0033|ul=AU}}
| eccentricity = {{val|0.091|0.120|0.064}}
| period = {{val|44.55603|0.00013|0.00012|ul=d}}
| inclination = {{val|89.788|0.033|0.029|u=deg}}
| semi-amplitude = {{val|p=<|0.39|ul=m/s}}
| star = K2-3
| mean_radius = {{val|1.458|0.056|0.051|ul=Earth radius}}
| mass = {{val|p=<|1.6|ul=Earth mass}}
| density = {{val|p=<|2.1|ul=g/cm3}}
| surface_grav =
| single_temperature = {{val|305.2|3.1|3.2|ul=K}} ({{convert|305.2|K|C F|disp=out}}, equilibrium)
}}
K2-3d, also known as EPIC 201367065 d, is a confirmed exoplanet of probable mini-Neptune
type orbiting the red dwarf star K2-3, and the outermost of three such planets discovered in the system. It is located {{convert|143|ly|pc|lk=on|abbr=off}} away from Earth in the constellation of Leo.{{cite web|url=https://exoplanet.eu/catalog/k2_3_d--2363/|work=Extrasolar Planets Encyclopaedia|title=The Extrasolar Planet Encyclopaedia — K2-3 d}} 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. It was the first planet in the Kepler "Second Light" mission to receive the letter "d" designation for a planet. Its discovery was announced in January 2015.
Characteristics
=Mass, radius, density and temperature=
K2-3d is a super-Earth or a mini-Neptune, meaning it has a mass and radius bigger than Earth's, but smaller than that of the ice giants Uranus and Neptune. It has an equilibrium temperature of {{convert|305|K|C F}} and a radius of 1.5 to 1.6 {{Earth radius}}. The planet is likely to be a mini-Neptune, with no solid surface.{{cite news|url=https://astrobites.org/2014/07/31/most-1-6-earth-radius-planets-are-not-rocky/|title=Most 1.6 Earth-radius planets are not rocky|newspaper=Astrobites |date=31 July 2014|last1=Angus |first1=Ruth }} While originally estimated to have a very high density, later analysis of HARPS data in 2018 constrained the mass to less than 4 {{Earth mass}} to a 1σ confidence, and by 2023 this upper limit has been reduced to 2 {{Earth mass}}. This corresponds to a relatively low density, similar to that of Neptune, suggesting a very large volatile layer and significantly reducing the potential habitability of the world.
=Host Star=
{{main|K2-3}}
The planet orbits a (M-type) red dwarf star named K2-3, orbited by a total of three known planets, of which K2-3d has the longest orbital period. The star has a mass of 0.60 {{solar mass}} and a radius of 0.56 {{solar radius}}. It has a temperature of 3896 K and is about 1 billion years old. In comparison, the Sun is 4.6 billion years old{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008 |publisher=Universe Today |access-date=19 February 2011}} and has a surface temperature of 5778 K.{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=15 September 2008 |publisher=Universe Today |access-date=19 February 2011}}
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 12.168. Therefore, it is too dim to be seen with the naked eye.
=Orbital statistics=
Habitability
The planet orbits on the edge of the inner (empirical) habitable zone, a region where, with the proper atmospheric properties and pressure, liquid water may exist on the surface of the planet. However, it is very likely tidally locked to its star, with one side facing towards its star in scorching heat, and the opposite side in bitter darkness.{{cite web|title=K2-3 d (M-Warm Terran)|website=phl.upr.edu|url=http://www.hpcf.upr.edu/~abel/phl/hec_plots/hec_orbit/hec_orbit_K2-3_d.png|archive-url=https://web.archive.org/web/20190809080625/http://www.hpcf.upr.edu/~abel/phl/hec_plots/hec_orbit/hec_orbit_K2-3_d.png|date=July 2018|archive-date=9 August 2019|access-date=30 June 2024}} Despite this, there is an area – the terminator line – where the surface temperatures may be comfortable enough to support liquid water. However, given that most models of the habitable zone parameters put K2-3d slightly beyond the inner edge of the habitable zone, it is likely to be too hot even at the terminator line and thus not habitable at all. Also, the stellar flux for the planet is an abnormally high 1.4 times that of Earth, which could result in surface temperatures of up to {{convert|400–500|K|C F}} because of a runaway greenhouse effect.
Discovery
The planet, along with the other two known planets in the K2-3 system, was announced in early January 2015 as part of the first results from the second mission of the Kepler spacecraft. With this, it was the first multiplanetary system of the mission as well.
See also
References
{{reflist|refs=
| url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=K2-3+d&type=CONFIRMED_PLANET
| title=K2-3 d CONFIRMED PLANET OVERVIEW PAGE
| work=NASA Exoplanet Archive
| access-date=2015-10-17
}}
{{cite journal |last1=Bonomo |first1=A. S. |last2=Dumusque |first2=X. |display-authors=etal |date=April 2023 |title=Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems |journal=Astronomy & Astrophysics |volume= |issue= |pages= |doi= 10.1051/0004-6361/202346211|arxiv=2304.05773|s2cid=258078829 }}
}}
{{K2-3}}
{{2015 in space}}
{{Sky|11|29|20.39|-|01|27|17.2}}
Category:Exoplanets discovered in 2015
Category:Transiting exoplanets