| Discovery | |
|---|---|
| Discovered by | Butler,Marcy et al. |
| Discovery site | California and Carnegie Planet Search  USA |
| Discovery date | April 15, 1999 |
| Radial velocity | |
| Orbital characteristics | |
| Apastron | ~478Gm |
| Periastron | ~282Gm |
| ~380Gm | |
| Eccentricity | 0.299 ± 0.072[1] |
| 1,276.46 ± 0.57[1]d ~3.49626[1]y | |
| Inclination | 23.758 ± 1.316[2] |
| 4.073 ± 3.301[2] | |
| 2,450,059 ± 3.495[2] | |
| 252.991 ± 1.311[2] | |
| Semi-amplitude | 68.14 ± 0.45[1] |
| Star | Upsilon Andromedae A |
| Physical characteristics | |
| ~1.02RJ | |
| Mass | 10.25+0.7 −3.3[2]MJ |
| Temperature | 218 K (−55 °C; −67 °F) |
Upsilon Andromedae d (υ Andromedae d, abbreviatedUpsilon And d,υ And d), formally namedMajriti/mædʒˈraɪti/, is asuper-Jupiterexoplanet orbiting within thehabitable zone of theSun-like starUpsilon Andromedae A, approximately 44light-years (13.5parsecs, or nearly 416.3 trillionkm) away fromEarth in the constellation ofAndromeda. Its discovery made it the firstmultiplanetary system to be discovered around amain-sequence star, and the first such system known in amultiple star system. The exoplanet was found by using theradial velocity method, where periodicDoppler shifts ofspectral lines of the host star suggest an orbiting object.
In July 2014 theInternational Astronomical Union launchedNameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[3] The process involved public nomination and voting for the new names.[4] In December 2015, the IAU announced the planet would be named "Majriti".[5] The winning name was submitted by the Vega Astronomy Club ofMorocco, honoring the 10th-century scientistMaslama al-Majriti.[6]
Upsilon Andromedae d is asuper-Jupiter, an exoplanet that has amass larger than that of the planetJupiter. It has a temperature of 218 K (−55 °C; −67 °F).[7] It has a mass of 10.25MJ[2] and a likely radius of around 1.02RJ based on its mass.[citation needed]
The planet orbits a (F-type)star named Upsilon Andromedae A. The star has a mass of 1.27M☉ and a radius of around 1.48R☉. It has a temperature of 6,074K and is 3.12 billion years old. In comparison, the Sun is about 4.6 billion years old[8] and has a temperature of 5,778 K.[9] The star is slightly metal-rich, with ametallicity ([Fe/H]) of 0.09, or about 123% of the solar amount. Its luminosity (L☉) is 3.57 times that of the Sun.
The star'sapparent magnitude, or how bright it appears from Earth's perspective, is 4.09. Therefore, Upsilon Andromedae can be seen with the naked eye.
Upsilon Andromedae d orbits its star nearly every 3.5 years (about 1,276 days) in aneccentric orbit, more eccentric than that of any of the known planets in theSolar System.[10] To explain the planet's orbital eccentricity, some have proposed a close encounter with a now-lost outer planet of Upsilon Andromedae A. The encounter would have moved planet "d" into an eccentric orbit closer to the star and ejected the outer planet.[11][12]
While Upsilon Andromedae d is likely a gas giant and therefore uninhabitable, it may have a moon or moons that are habitable.
The planet lies in the habitable zone of Upsilon Andromedae A as defined both by the ability for an Earthlike world to retainliquid water at its surface and based on the amount ofultraviolet radiation received from the star.[13]
For a stable orbit, the ratio between a moon'sorbital periodPs around its primary and that of the primary (planet) around its starPp must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.[14][15] Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet orbrown dwarf that orbits 1AU from a Sun-like star.[16] In the case of Upsilon Andromedae d, the orbital period would have to be no greater than 120 days (around 4 months) in order to have a stable orbit.
Upsilon Andromedae d was detected by measuring variations in its star'sradial velocity as a result of the planet'sgravity. This was done by making precise measurements of theDoppler shift of thespectrum of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, thehot JupiterUpsilon Andromedae b; however, by 1999, it was clear that the inner planet could not explain the velocity curve.
In 1999, astronomers at bothSan Francisco State University and theHarvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data.[17] The two new planets were designatedUpsilon Andromedae c and Upsilon Andromedae d.
Preliminaryastrometric measurements suggest the orbit of Upsilon Andromedae d may be inclined at 155.5° to the plane of the sky.[18] However, these measurements were later proved useful only for upper limits,[19] and contradict even the inner planet υ And b's inclination of >30°. The mutual inclination between c and d meanwhile is 29.9 degrees.[2] The true inclination of Upsilon Andromedae d was determined as 23.8° after combined results were measured from theHubble Space Telescope and radial velocity measurements.[2]
When it was discovered, a limitation of the radial velocity method used to detect Upsilon Andromedae d is that the orbital inclination is unknown, and only a lower limit on the planet'smass can be obtained, which was estimated to be about 4.1 times as massive as Jupiter. However, by combining radial velocity measurements from ground-based telescopes with astrometric data from theHubble Space Telescope, astronomers have determined the orbital inclination as well as the actualmass of the planet, which is about 10.25 times the mass ofJupiter.[2]
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