IRAS 04125+2902 b

Artist's impression of the IRAS 04125+2902 system.
Discovery [1]
Discovered by	Madyson Barber et al.
Discovery date	November 20, 2024
Detection method	Transit
Designations
Alternative names	TIDYE-1b
Orbital characteristics [1]
Semi-major axis	0.077+0.0069 −0.0100  AU
Orbital period (sidereal)	8.834978(28) days
Inclination	88.3 °+1.2 ° −1.6 °
Star	IRAS 04125+2902
Physical characteristics [1]
Mean radius	0.958+0.077 −0.075  RJ
Mass	<90 M🜨 (<0.3 MJ)
Temperature	854+59 −32  K

IRAS 04125+2902 b (TIDYE-1 b) is an extrasolar planet orbiting a young protostar. It is the youngest transiting exoplanet so far discovered, with an age of just three million years.

The planet has a mass less than 0.3 Jupiter masses (90 Earth masses) and a radius nearly equal to that of Jupiter, just 4% smaller, or the same as 10.7 Earth radii. ^[1] It is still enshrouded in an hydrogen envelope, and will shed its outer layers during its evolution, shrinking to a radius between two and four  R_🜨 and becoming either a super-Earth or a mini-Neptune. The planet's large radius and low mass make it a potential candidate for follow-up observations with the James Webb Space Telescope. ^[2]

It has a compact orbit around its host star, completing an orbit every just 8.8 days, and semi-major axis (mean separation from the star) is just 8% of the Earth-Sun distance ( astronomical unit). ^[1] Its short orbit and high mass mean that it likely formed at a larger distance and then migrated to inner regions, as regions so close to the host star don't have sufficient mass to form large planets. ^[2]

With an age of just three million years, IRAS 04125+2902 b is the youngest transiting exoplanet so far discovered, ^{[1] [2] [3]} and also one of the youngest exoplanets, only a couple of younger <13  M_J objects are listed in the NASA Exoplanet Archive. ^[4]

IRAS 04125+2902 b was detected using the transit method, which consists of observing small, regular dips in the brightness of the host star. These dips are planetary transits and happen when the planet passes through its host star as viewed from an observer. ^[5] Data from the Transiting Exoplanet Survey Satellite was analysed by the astronomer Madyson Barber and colleagues, allowing the planet detection. ^[6] Its discovery and confirmation was published on November 20, 2024, in the journal Nature. ^[1]

The planet has also the nickname TIDYE-1 b, derived from the TESS Investigation – Demographics of Young Exoplanets (TIDYE) project. ^[2]

IRAS 04125+2902

IRAS 04125+2902 (blue star in the middle) and its companion (yellow star below) Credit: Pan-STARRS & Meli_thev
Observation data Epoch J2000       Equinox J2000
Constellation	Taurus [7]
Right ascension	04h 15m 42.7871s [8]
Declination	+29° 09′ 59.832″ [8]
Apparent magnitude (V)	15.487±0.003 [9]
Characteristics
Evolutionary stage	Protostar [1]
Spectral type	M1.25±0.25 [9]
Variable type	T Tauri [10]
Astrometry
Radial velocity (Rv)	13.35±0.39 [8] km/s
Proper motion (μ)	RA: +21.811  mas/ yr [8] Dec.: −18.145  mas/ yr [8]
Parallax (π)	6.2474 ± 0.0270  mas [8]
Distance	522 ± 2  ly (160.1 ± 0.7  pc)
Details [1]
Primary
Mass	0.70±0.04  M☉
Radius	1.45±0.1  R☉
Luminosity	0.466±0.041  L☉
Temperature	4,080±95  K
Rotation	11.31±0.06  d
Rotational velocity (v sin i)	7.1±0.5 km/s
Age	3.3+0.6 −0.5  Myr
Companion
Mass	0.17±0.04  M☉
Radius	0.96±0.12  R☉
Luminosity	0.050±0.004  L☉
Temperature	2,830±90  K
Other designations
TIC 56658270, IRAS IRAS 04125+2902, 2MASS J04154278+2909597, WISE J041542.77+290959.5
Database references
SIMBAD	data

IRAS 04125+2902 is a M-type star and a T Tauri variable ^[10] located in the Taurus Molecular Cloud, 160 parsecs (520 light-years) from Earth. ^[6] This young protostar has 70% of the Sun's mass, ^[1] 1.5 times the Sun's radius and an effective temperature of 3,720  K (3,450 °C; 6,240 °F). ^[9] It is surrounded by a transitional disk, inclined at 30° relative to Earth, and has a wide companion at a projected distance of 635 astronomical units (9.50×10¹⁰ km). ^[1] The companion was discovered in 2009. It is 4 arcseconds distant from IRAS 04125+2902 and is called 2MASS J04154269+2909558. It does not show any infrared excess. ^[11] Gaia astrometry is similar between 2MASS J04154269+2909558 and IRAS 04125+2902. ^[8] A spectrum of the companion was taken in 2009 with the Hobby–Eberly Telescope and published in 2017, showing a spectral type of M6.5. ^[12]

The companions and the host star's equator are aligned, but the disk is not, and the reason for the misalignment of the disk is unclear. ^[1] It could be due to planetary migration in the past which misaligned the orbit of IRAS 04125+2902 b's orbit, but such an hypothesis requires the existence of another planet in the system, which has not been detected. Another hypothesis suggest that infalling material from the surrounding Taurus Molecular Cloud could be the cause of this misalignment, as those places are densely packed. ^[3]

A 2015 study found that the dust disk around the star is truncated, which could be caused by disk evolution or by an eccentric companion. It is unlikely that the wide companion is the responsible for the disk truncation, as its projected distance is much larger than the dust disk's outer limit, but given that the orbital eccentricity of the companion is unknown, this remains plausible. ^[9]

• V830 Tauri – Similar to IRAS 04125+2902 and has an unconfirmed planet