YZ Ceti is a
red dwarfstar in the
constellationCetus. Although it is relatively close to the
Sun at just 12
light years, this star cannot be seen with the naked eye. It is classified as a
flare star that undergoes intermittent fluctuations in
luminosity. YZ Ceti is about 13 percent the mass of the Sun and 17% of its radius.
This star is unusually close to
Tau Ceti, a star of
spectral class G8. The two are only about 1.6 light years apart, a little more than a third of the distance from the Sun to the Solar System's nearest neighbor,
YZ Ceti is a
variable star designation: the star shows occasional rapid and brief increases in brightness, sometimes reaching magnitude 12.03, caused by eruptions from the surface. This type of variable star is known as a
UV Ceti star after its first member, or more colloquially as a
YZ Ceti also shows small periodic variations in brightness caused by starspots or chromospheric features moving as the star rotates. This class of variable stars are known as
BY Draconis variables. The periodic variations allow the rotational period of the star to be measured at 68.3 days, although modelling of its planetary system gives a rotational period for the star of 83 days.
On 10 August 2017 three planets were announced to have been discovered around YZ Ceti and a possible fourth sub-Earth planet candidate, still needing confirmation, with 0.472±0.096 Earth masses at an orbital period of 1.04 days. The orbits of the three confirmed planets were determined to be too close to YZ Ceti to be within the star's habitable zone, with equilibrium temperatures ranging from 347–491 K (74–218 °C; 165–424 °F), 299–423 K (26–150 °C; 79–302 °F), and 260–368 K (−13–95 °C; 8–203 °F) for planets b, c, and d, respectively.
An August 2018 study reexamined the discovery measurements, confirming the orbit of YZ Ceti d, but finding a possibly marginally longer orbital period of YZ Ceti b of 2.02 days rather than 1.97 days, and additionally finding that YZ Ceti c probably orbits in only 0.75 days rather than 3.06 days. If the latter is true, YZ Ceti c would have a mass of only 0.58 Earth masses and a roughly 10% chance of transiting YZ Ceti. However, a 2020 study did not support the latter conclusion, finding the 0.75-day period to be an alias of the true 3.06-day period. It also did not find evidence for the fourth candidate planet.
A 2023 study detected bursts of radiation in
radio wavelengths from YZ Ceti, which may be associated with interaction of the innermost planet, YZ Ceti b, with the star.
abWatson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47.
^Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1.
abcJayasinghe, T; Stanek, K. Z; Kochanek, C. S; Holoien, T. W.-S; Shields, J. V; Thompson, T. A; Shappee, B. J; Prieto, J. L; Dong, Subo (2017). "ASAS-SN V-band Light Curve of Multi-Planet M-dwarf Host YZ Cet Reveals a Rotation Period of 68 Days". The Astronomer's Telegram. 0643: 1.