HIP 11915

HIP 11915 is a G-type main-sequence star located about 170 light-years from Earth in the constellation Cetus. It is best known for its characteristics, which are very similar to those of the Sun, including the mass, radius, temperature, metallicity and age, which means that it is almost a solar twin, being just 500 million years younger than the Sun and with a lower metallicity.^[a] It is also known for its planetary companion, HIP 11915 b, which has a mass and orbital distance very similar to that of Jupiter, but probably with a slightly higher orbital eccentricity.

HIP 11915

Observation data Epoch J2000      Equinox J2000
Constellation	Cetus
Right ascension	02h 33m 49.026s[1]
Declination	–19° 36′ 42.500″[1]
Apparent magnitude (V)	8.58[2]
Characteristics
Evolutionary stage	Main sequence
Spectral type	G5V[2]
Astrometry
Radial velocity (Rv)	14.45±0.14[3] km/s
Proper motion (μ)	RA: +223.559 mas/yr[3] Dec.: +35.513 mas/yr[3]
Parallax (π)	18.6292±0.0224 mas[3]
Distance	175.1 ± 0.2 ly (53.68 ± 0.06 pc)
Absolute magnitude (MV)	4.83[4]
Details
Mass	0.991±0.003[5] M☉
Radius	0.974±0.001[3] R☉
Luminosity	1.0+0.13 −0.12[6] L☉
Surface gravity (log g)	4.47±0.008[5] cgs
Temperature	5773±2[5] K
Metallicity [Fe/H]	−0.057±0.003[5] dex
Rotational velocity (v sin i)	0.99 ± 0.15 km/s
Age	3.87±0.39[5] Gyr
Other designations
HD 16008, HIP 11915, SAO 148468, BD-20°481[1]
Database references
SIMBAD	data

This star is entry number 11915 in the Hipparcos Catalogue. The star is located at 02:33:49.02495 right ascension, −19° 36' 42.5032" dec.^[1][9] Too faint to be seen with the unaided eye, the star can be spotted with good binoculars.^[9]

Stellar characteristics

HIP 11915 is a G-type main sequence star that is just about the same mass of and likely 101% the radius of the Sun. It has a temperature of 5760 K and is 4.16 billion years old,^[2][10] nearly 500 million years younger than the Sun, which is about 4.6 billion years old^[11] and has a temperature of 5778 K.^[12]

The star is slightly poor in metals, with a metallicity ([Fe/H]) of about −0.059, or about 87% of the amount of iron and other heavier metals found in the Sun.^[10] Given the similar properties of the Sun, HIP 11915's luminosity is likely close to the same as the Sun (give or take about 10% in uncertainty).

Planetary system

The HIP 11915 planetary system^[2]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.99 ± 0.06 MJ	4.8 ± .01	3830.0 ± 150	0.1 ± 0.07	—	~1 RJ

The system contains a gas giant, HIP 11915 b, with a mass and orbit very similar to that of Jupiter, located at approximately the same distance from its star. The discovery of HIP 11915 b is significant, because it is the first, and to date only, distant planetary system found that may be somewhat like the Solar System.^[13] The radial velocity data also indicates that there is no large gas giant in this system with an orbital period of less than 1000 days. This means that there could be one or more terrestrial planets in the inner parts of the system, and the possibility of a habitable Earth-like planet.

This new discovery was made at the La Silla Observatory in Chile, using the High Accuracy Radial Velocity Planet Searcher instrument mounted on the European Southern Observatory's 3.6-meter telescope.^[14][15]

According to Jorge Meléndez, who led the University of São Paulo, Brazil team that discovered HIP 11915 b, "the quest for an Earth 2.0, and for a complete Solar System 2.0, is one of the most exciting endeavors in astronomy".^[16]

Comparison to the Sun

This chart compares the properties of the Sun to HIP 11915.

Identifier	J2000 Coordinates		Distance (ly)	Stellar Class	Mass (M☉)	Radius (R☉)	Temperature (K)	Metallicity (dex)	Age (Gyr)	Notes
	Right ascension	Declination
Sun	—	—	0.00	G2V	1	1	5,778	+0.00	4.6	[8]
HIP 11915 [17]	02h 33m 49.02s	−19° 36′ 42.5″	190	G5V	0.99	1.01	5,760	−0.059	4.1	[18]

Footnotes

1. An exact solar twin would be a G2V star with a 5778 K temperature, be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation.^[7][8]