K2-38b

{{Infobox planet

| name = K2-38b

| discovery_ref =

| discovery_site = Kepler Space Observatory

| discovered = 2016

| discovery_method = Transit

| apsis = astron

| semimajor = 0.04994{{±|0.00048|0.00049}} AU

| eccentricity = 0.197{{±|0.067|0.060}}

| period = 4.01593 (± 0.0005){{cite web

| url=https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=K2-38+b&type=CONFIRMED_PLANET

| title=K2-38 b CONFIRMED PLANET OVERVIEW PAGE

| work=NASA Exoplanet Archive

| accessdate=2018-01-20

}} d

| inclination = 88.36 {{±|0.17|0.15}}

| star = K2-38

| mean_radius = 1.54{{±|0.14}}{{citation|arxiv=2007.01081|title=Characterization of the K2-38 planetary system|year=2020|doi=10.1051/0004-6361/202038187 |last1=Toledo-Padrón |first1=B. |last2=Lovis |first2=C. |last3=Suárez Mascareño |first3=A. |last4=Barros |first4=S. C. C. |last5=González Hernández |first5=J. I. |last6=Sozzetti |first6=A. |last7=Bouchy |first7=F. |last8=Zapatero Osorio |first8=M. R. |last9=Rebolo |first9=R. |last10=Cristiani |first10=S. |last11=Pepe |first11=F. A. |last12=Santos |first12=N. C. |last13=Sousa |first13=S. G. |last14=Tabernero |first14=H. M. |last15=Lillo-Box |first15=J. |last16=Bossini |first16=D. |last17=Adibekyan |first17=V. |last18=Allart |first18=R. |last19=Damasso |first19=M. |last20=d'Odorico |first20=V. |last21=Figueira |first21=P. |last22=Lavie |first22=B. |last23=Lo Curto |first23=G. |last24=Mehner |first24=A. |last25=Micela |first25=G. |last26=Modigliani |first26=A. |last27=Nunes |first27=N. J. |last28=Pallé |first28=E. |last29=Abreu |first29=M. |last30=Affolter |first30=M. |journal=Astronomy & Astrophysics |volume=641 |pages=A92 |s2cid=220302044 |display-authors=1 }} {{Earth radius|link=y}}

| mass = 7.3{{±|1.1|1.0}} {{Earth mass|sym=y|link=y}}

| density = 11.0{{±|5.8|3.7}} g cm⁻³

| surface_grav = 3.08{{±|1.2|0.74}} g

| single_temperature = {{convert|1266|K|C F}}

}}

K2-38b, also designated EPIC 204221263 b, is a massive rocky exoplanet closely orbiting a Sun-like star and is one of the densest planets ever found. Discovered in 2016 by Crossfield et al. and later characterized by Sinukoff et al., K2-38b is a rocky super-Earth about 55% larger than Earth (nearly 20,000 km wide) but about 12 times more massive (around 7.2*10^25 kg, a bit less than Uranus) indicating a composition rich in iron and an extremely high surface gravity. The planet is within K2 Campaign 2, in the constellation Scorpius.

Characteristics

=Mass, radius, and temperature=

K2-38b is a massive rocky exoplanet significantly larger and more massive than Earth. It has a radius of 1.55 {{Earth_radius}}, close to the 1.6 {{Earth_radius}} limit where planets would begin to accumulate thick hydrogen-helium atmospheres and become something similar to a Mini-Neptune. However, K2-38b is instead a very dense terrestrial planet. Initially it was believed planet is made almost entirely of iron, with a mass of about 12.0 {{Earth mass|sym=y}} and a density of about 17.5 g/cm³. This made it one of the densest exoplanets ever discovered. Measurement in 2020 have resulted in lower mass of 7.3{{±|1.1|1.0}} {{Earth mass|sym=y|link=y}}, and less extreme constraints on composition though.

=Orbit=

K2-38b has a very tight orbit around its host star. The planet takes just 4 days to complete a single orbit at a distance of about 0.05 AU. For comparison, Mercury orbits every 88 days at 0.38 AU from the Sun. The eccentricity of K2-38's orbit is slightly larger than that of Mars.

=Host star=

The parent star K2-38 is a G2 main-sequence star, similar to our own Sun. It is 1.10 {{Solar_radius}} and 1.07 {{Solar_mass}}, with a temperature of 5757 K and an unknown age. For comparison, the Sun has a temperature of 5778 K and is about 4.5 billion years old.

The visual magnitude of K2-38, or how bright it appears to the human eye, is 11.39. Therefore, it is far too dim to be seen without a telescope.

References

{{reflist|refs=

{{cite journal | title=Eleven Multiplanet Systems from K2 Campaigns 1 and 2 and the Masses of Two Hot Super-Earths | last1=Sinukoff | first1=Evan | last2=Howard | first2=Andrew W. | last3=Petigura | first3=Erik A. | last4=Schlieder | first4=Joshua E. | last5=Crossfield | first5=Ian J. M. | last6=Ciardi | first6=David R. | last7=Fulton | first7=Benjamin J. | last8=Isaacson | first8=Howard | last9=Aller | first9=Kimberly M. | last10=Baranec | first10=Christoph | last11=Beichman | first11=Charles A. | last12=Hansen | first12=Brad M. S. | last13=Knutson | first13=Heather A. | last14=Law | first14=Nicholas M. | last15=Liu | first15=Michael C. | last16=Riddle | first16=Reed | last17=Dressing | first17=Courtney D. | display-authors=1 | journal=The Astrophysical Journal | volume=827 | issue=1 | at=78 | year=2016 | arxiv=1511.09213 | bibcode=2016ApJ...827...78S | doi=10.3847/0004-637X/827/1/78 | doi-access=free }}

}}{{2016 in space}}{{Scorpius}}

Category:Exoplanets discovered in 2016

Category:Exoplanets discovered by K2

Category:Transiting exoplanets