CI Tauri is a young star, about 2 million years old, located approximately away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign ** Vṛṣabha, in vedic astrology * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological ch ...

. It is still accreting material from a

debris disk A debris disk (American English), or debris disc ( Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris ...

at an unsteady pace, possibly modulated by the eccentric orbital motion of an inner planet. The spectral signatures of compounds of

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

were detected from the disk. The magnetic field on the surface of CI Tauri, equal to 0.22 T, is close to average for

T Tauri T Tauri is a Trinary star, trinary variable star in the constellation Taurus (constellation), Taurus, the prototype of the T Tauri stars. It was discovered in October 1852 by John Russell Hind. T Tauri appears from Earth amongst the Hya ...

stars.

Planetary system

CI Tauri hosts a

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

, and evidence for planets has been found via both

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

and disk morphology.

Radial velocity

CI Tauri displays several periodic

variations, including periods of 6.6 days, 9 days, and 25 days. The 9-day period was proposed to be due to a candidate massive planet on an eccentric orbit, CI Tauri b, in 2016. The discovery of CI Tauri b was notable because it is a

hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

, which are supposed to take a minimum of 10 million years to form, and are often thought to be too close to their parent stars to have formed there. The existence of this planet has been debated; in 2019, a detection of

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

attributed to the planet's atmosphere was announced, seemingly confirming it. However, a 2020 study found that the star rotates with a period of 9 days, and suggested that the radial velocity variations may be caused by the star's rotation rather than a planet. The carbon monoxide detection was attributed to magnetic interaction of the star with the circumstellar disk. Other studies have attributed the 6.6-day period to the stellar rotation and the 9-day period to the candidate planet. A 2024 study found evidence for a planetary origin of the 25-day radial velocity signal, while considering the 9-day signal to correspond to the stellar rotation and be caused by a

starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...

. This 25-day candidate planet would orbit CI Tauri at a distance of in a highly-eccentric orbit . The mass of this planet is estimated to be . While this is treated as a strong candidate and left undesignated by its discovery paper, the

NASA Exoplanet Archive The NASA Exoplanet Archive is an online astronomical exoplanet catalog and data service that collects and serves public data that support the search for and characterization of extra-solar planets (exoplanets) and their host stars. It is part of ...

lists it as a confirmed planet with the designation CI Tauri c.

Disk morphology

In 2018 the possible detection of three more planets, inferred by gaps in the

surrounding the star, was announced. Using the

Atacama Large Millimeter Array The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The ar ...

(ALMA) to look for 'siblings' of CI Tauri b, a team of researchers detected three distinct gaps in the protoplanetary disk which their theoretical modelling suggests are caused by three other planets. The two outer planets are believed to be about the mass of

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

, while the inner planet's mass is around the same as Jupiter. Two of the new planets are similarly located to those inferred in the HL Tauri protoplanetary disk. Another 2018 study also found evidence for the outermost of these planets at around 100 AU, estimating a mass of 0.25-0.8 times that of Jupiter. If this discovery is confirmed this would be the most massive collection of

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

s ever detected at this age with its four planets spanning a factor of a thousand in orbital radius. The gaps are visible in wideband photography, but not in the gas spectral lines. These "gaps" may be lower-temperature shadows of dust in the inner disk cast on outer parts rather than true gaps carved by planets.

References

{{DEFAULTSORT:CI Tauri Taurus (constellation) T Tauri stars J04335200+2250301 Planetary systems with one confirmed planet Tauri, CI Circumstellar disks