GJ 3998

{{Starbox begin}}

{{Starbox observe

| epoch = J2000

| constell = Ophiuchus

| ra = {{RA|17|16|00.63687}}

| dec = {{DEC|+11|03|27.6158}}

| appmag_v = 10.83

}}

{{Starbox character

| type = main sequence

| class = M1V

| appmag_1 = {{val|7.634|0.021}}

| appmag_1_passband = J

| appmag_2 = {{val|7.020|0.029}}

| appmag_2_passband = H

| appmag_3 = {{val|6.816|0.016}}

| appmag_3_passband = K

| u-b = 1.183

| b-v = 1.510

| v-r = 0.970

}}

{{Starbox astrometry

| radial_v = {{val|-45.62|0.14}}

| prop_mo_ra = -137.435

| prop_mo_dec = -347.456

| pm_footnote =

| parallax = 55.0169

| p_error = 0.0287

| parallax_footnote =

| absmag_v = 9.58

}}

{{Starbox detail

| source =

| mass = {{val|0.52|0.05}}

| radius = {{val|0.50|0.05}}

| luminosity = {{val|0.041|0.008}}

| gravity = {{val|4.75|0.04}}

| temperature = {{val|3726|68}}

| metal_fe = {{val|−0.13|0.09}}

| rotation = {{val|30.2|0.3|ul=d}}

| rotational_velocity = {{val|0.93|0.55}}

| age_gyr = {{val|8.38|4.06}}

}}

{{Starbox catalog

| names = {{odlist | BD=+11 3149 | G=139-23 | GJ=3998 | HIP=84460 | L=1205-67 | LTT=15111 | TYC=982-121-1}}

}}

{{Starbox reference

| Simbad = GJ+3998

| NSTED = GJ-3998

}}

{{Starbox end}}

GJ 3998 is a red dwarf star located {{convert|59.3|ly|pc|lk=on|abbr=off}} away in the constellation Ophiuchus. It has about half the mass and radius of the Sun, and only 4% of its luminosity. Its rotation period is 30 days.

GJ 3998 hosts a system of three known planets, all super-Earth-mass planets detected by the radial velocity method. The outermost planet, with a minimum mass about six times the mass of Earth, orbits within the optimistic habitable zone. The star rotates with an inclination of >30° to the plane of the sky; if the planetary orbits are coplanar with the star, their true masses are at most twice their minimum masses.

The two inner planets were found in 2016, but were questioned by a 2022 study, which argued that the radial velocity signals may instead be due to intrinsic stellar activity. The third planet was found by a 2025 follow-up study by the original discovery team, who did a series of tests on stellar activity signals that they believe validate all three planets.

{{Orbitbox planet begin

| table_ref =

}}

{{Orbitbox planet

| exoplanet = b

| mass_earth = {{val|2.50|0.30|0.29|p=≥}}

| radius_earth =

| semimajor = {{val|0.030|0.001}}

| period = {{val|2.65033|0.00022|0.00019}}

| eccentricity = 0

| inclination =

}}

{{Orbitbox planet

| exoplanet = c

| mass_earth = {{val|6.82|0.78|0.75|p=≥}}

| radius_earth =

| semimajor = {{val|0.090|0.003}}

| period = {{val|13.727|0.003|0.004}}

| eccentricity = 0

| inclination =

}}

{{Orbitbox planet

| exoplanet = d

| mass_earth = {{val|6.07|1.00|0.96|p=≥}}

| radius_earth =

| semimajor = {{val|0.189|0.006}}

| period = {{val|41.78|0.05}}

| eccentricity = 0

| inclination =

}}

{{Orbitbox end}}