 Artist's impression of HD 63433 d as compared with Earth | |
| Discovery | |
|---|---|
| Discovered by | Capistrant, Soares-Furtado et al. (THYME)[1] |
| Discovery date | 10 January 2024[1] |
| Transit[2] | |
| Designations | |
| TOI-1726 d, BD+27 1490 d, HIP 38228 d, V377 Geminorum d | |
| Orbital characteristics[1] | |
| 0.0503+0.0025 −0.0027 AU | |
| Eccentricity | 0.16+0.36 −0.12 |
| 4.20975+0.000012 −0.000023 d | |
| Inclination | 88.73°+0.85° −1.06° |
| Star | HD 63433 |
| Physical characteristics[1] | |
| 1.073+0.046 −0.044 R🜨 | |
| Temperature | 1040±40 K(767 ± 40°C) (mean),[a], 1,530 K (1,260 °C) (daytime)[b] |
HD 63433 d (TOI-1726 d) is a confirmedexoplanet orbitingHD 63433, aSun-like star located 73light-years away in the constellationGemini.[3] Its radius is measured at around 1.1 R🜨, which makes it similar to the Earth in size.[1] It was the third (and most recent) exoplanet to be discovered in orbit around this star; the other two,HD 63433 b andc, were discovered in 2020.[1][4] Orbiting its star at a distance of 0.0503astronomical units (7,520,000 km), HD 63433 d is the innermost planet orbiting HD 63433, and completes an orbit around it just every 4 days.[1] Due to the proximity of its star, the planet is scorching hot, having a temperature estimated at 1260 °C at daytime.[4][1] The proximity of its star also causes it to betidally locked.[4][5]
Having a radius of1.073 R🜨 (~6,845 km), it is roughly the size of Earth, but its mass is still unknown.[1] HD 63433 d is the innermost planet in the system, orbiting its star at a distance of 0.0503astronomical units (7,520,000 km) and completing oneorbital period around it every 4 days and 5 hours.[1] The proximity of its star causes HD 63433 d to be scorching hot, having a daytime temperature estimated at 1,260 °C (2,300 °F),[1][b] which is similar to otherlava planets such asKepler-10b andCoRoT-7b,[5][3] and hot enough to melt allminerals on its surface.[6] In addition, the planet istidally locked, meaning that one side of the planet always faces its star, while the other side always faces away from it, and it possibly lacks a substantialatmosphere.[4][5][7] Tidal locking also happens with theMoon, which has one side always facingEarth.[4]
It is believed that its dayside, always facing its star due totidal locking, is completely molten and dominated bylava,[8][5] in addition to possibly havingvolcanic activity.[9][10] Meanwhile, the night side of the planet could be as cold asPluto, having glaciers of frozennitrogen, depending on its composition.[11]
With an age estimated at 414 million years, it is the smallest known exoplanet less than 500 million years old, and the nearest Earth-sized planet this young.[1][5][9]
The small size, young age and the proximity of its star make HD 63433 an interesting planet for further exploration.[5] According to the HD 63433 d discovery team, this planet and another youngterrestrial planets are critical test beds to constrain the current theories ofplanetary formation and evolution.[5][1][12] The study of HD 63433 d could produce valuable information about the formation and evolution of Earth-sized planets.[10]
The planet was discovered by a team of scientists led by Benjamin Capistrant and Melinda Soares-Furtado after analyzing atransit observation made by theTransiting Exoplanet Survey Satellite (TESS). The team took the data and removed the transit signals of the other planets, thus revealing an additional transit signal that reappeared every 4.2 days.[1][5][7] Later investigations validated that this transit signal was from a third planet around the starHD 63433.[5][7] The discovery was announced on January 10, 2023, inThe Astrophysical Journal.[4][11]
The discovery of HD 63433 d is part of a project calledTESS Hunt for Young and Maturing Exoplanets (THYME), which seeks to discover youngtransiting exoplanets inmoving groups,stellar associations andopen clusters.[1]
The host star of HD 63433 d isHD 63433, aG-type main-sequence star which is located 73light-years away in theGemini constellation.[3] Having a radius 91% similar to that of the Sun, and a mass 99% similar, HD 63433 has properties very similar to those of theSun, being classified as asolar analog.[13] With anapparent magnitude of 6.9, the star cannot be been with thenaked eye, but can be with asmall telescope[14] orbinoculars.[15] HD 63433 is part of theUrsa Major moving group, which makes its age estimated at 414 million years.[13] Other stars located in this group includeAlioth andMizar, located in theBig Dipper.
HD 63433 also hosts two other exoplanets:HD 63433 b andc, twomini-Neptune planets discovered in 2020 by Mann et al.[13]