Editing Upsilon Andromedae (section)

== Planetary system ==
[[Image:Upsilon Andromedae A System (NASA, ESA).jpg|thumb]]
{{OrbitboxPlanet begin
| name = Upsilon Andromedae A
| table_ref = <ref name=Ligi2012/>
}}
{{OrbitboxPlanet
| exoplanet = [[Upsilon Andromedae b|b (Saffar)]]
| mass = {{val|1.70|0.33|0.24}}<ref name=Pizkorz2017/>
| period = {{val|4.62|0.23}}
| semimajor = {{val|0.0594|0.0003}}<ref name="McArthur2010"/>
| eccentricity = {{val|0.022|0.007}}
| inclination = {{val|24|4}}<ref name=Pizkorz2017/>
| radius = 1.8<ref>{{Cite journal |last1=Deitrick |first1=Russell |last2=Barnes |first2=Rory |last3=McArthur |first3=Barbara |last4=Quinn |first4=Thomas R. |last5=Luger |first5=Rodrigo |last6=Antonsen |first6=Adrienne |last7=Benedict |first7=G. Fritz |date=2014-12-18 |title=The 3-dimensional architecture of the Upsilon Andromedae planetary system |journal=The Astrophysical Journal |volume=798 |issue=1 |pages=46 |doi=10.1088/0004-637X/798/1/46 |issn=1538-4357|arxiv=1411.1059 |bibcode=2015ApJ...798...46D }}</ref>
}}
{{OrbitboxPlanet
| exoplanet = [[Upsilon Andromedae c|c (Samh)]]
| mass = {{val|13.98|2.3|5.3}}<ref name="McArthur2010"/>
| period = {{val|241.26|0.64}}
| semimajor = {{val|0.829|0.043}}<ref name="McArthur2010"/>
| eccentricity = {{val|0.260|0.079}}
| inclination = 7.9 ± 1<ref name="McArthur2010"/>
}}
{{OrbitboxPlanet
| exoplanet = [[Upsilon Andromedae d|d (Majriti)]]
| mass = {{val|10.25|0.7|3.3}}<ref name="McArthur2010"/>
| period = {{val|1276.46|0.57|fmt=commas}}
| semimajor = {{val|2.530|0.014}}<ref name="McArthur2010"/>
| eccentricity = {{val|0.299|0.072}}
| inclination = 23.8 ± 1<ref name="McArthur2010"/>
| radius = 1.02{{citation needed|date=May 2024}}
}}
{{Orbitbox end}}

The innermost planet of the Upsilon Andromedae system was discovered in 1996 and announced in January 1997, together with the planet of [[Tau Boötis]] and the innermost planet of [[55 Cancri]].<ref name="Butler1997"/> The discovery was made by [[Geoffrey Marcy]] and [[R. Paul Butler]], both [[astronomer]]s at [[San Francisco State University]]. The planet, designated [[Upsilon Andromedae b]], was discovered by measuring changes in the star's [[radial velocity]] induced by the planet's [[gravity]]. Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. The planet appears to be responsible for enhanced activity in the [[chromosphere]] of its star.<ref>{{cite journal | title=Hot Jupiters and Hot Spots: The Short- and Long-term Chromospheric Activity on Stars with Giant Planets | display-authors=1 | last1=Shkolnik | first1=E. | last2=Walker | first2=G. A. H. | last3=Bohlender | first3=D. A. | last4=Gu | first4=P.-G. | last5=Kürster | first5=M. | journal=The Astrophysical Journal | volume=622 | issue=2 | date=2005 | pages=1075–1090 | doi=10.1086/428037 | bibcode=2005ApJ...622.1075S|arxiv = astro-ph/0411655 | s2cid=119356064 }}</ref>

[[File:Upsand.jpg|thumb|right|Artist's conception of the planets of Upsilon Andromedae]]
Even when the first planet was taken into account, there still remained significant residuals in the radial velocity measurements, and it was suggested there might be a second planet in orbit. In 1999, astronomers at both [[San Francisco State University]] and the [[Harvard-Smithsonian Center for Astrophysics]] independently concluded that a three-planet model best fit the data.<ref>{{cite journal | display-authors=1 | last1=Butler | first1=R. Paul | last2=Marcy | first2=Geoffrey W. | last3=Fischer | first3=Debra A. | last4=Brown | first4=Timothy M. | last5=Contos | first5=Adam R. | last6=Korzennik | first6=Sylvain G. | last7=Nisenson | first7=Peter | last8=Noyes | first8=Robert W. | title=Evidence for Multiple Companions to υ Andromedae | journal=The Astrophysical Journal | volume=526 | issue=2 | pages=916–927 | date=1999 | doi=10.1086/308035 | bibcode=1999ApJ...526..916B | doi-access=free }}</ref> The two outer planets were designated [[Upsilon Andromedae c]] and [[Upsilon Andromedae d]] in order of increasing distance from the star. Both of these planets are in more [[Orbital eccentricity|eccentric]] orbits than any of the planets in the Solar System (including [[Pluto]]).<ref name="Butler(2006)">{{cite journal | display-authors=1 |last1=Butler |first1=R. P. |last2=Wright |first2=J. T. |last3=Marcy |first3=G. W. |last4=Fischer |first4=D. A. |last5=Vogt |first5=S. S. |last6=Tinney |first6=C. G. |last7=Jones |first7=H. R. A. |last8=Carter |first8=B. D. |last9=Johnson |first9=J. A. |last10=McCarthy |first10=C. |last11=Penny |first11=A. J. | doi=10.1086/504701 | title=Catalog of Nearby Exoplanets | journal=The Astrophysical Journal | volume=646 | issue=1 | pages=505–522 | date=2006 | bibcode=2006ApJ...646..505B|arxiv = astro-ph/0607493 |s2cid=119067572 }} ([http://exoplanets.org/planets.shtml web version])</ref> Upsilon Andromedae d resides in the system's [[habitable zone]].<ref name="buccino"/>

The orbital parameters of this three-planet system have been fully determined. The system is not [[coplanar]], with each other or with the stellar rotation, as in our [[Solar System]].<ref name=McArthur2010/> Samh, planet c, has an orbit significantly inclined from those of the other two, and from the perspective of Earth is inclined by only about 8 degrees from the celestial sphere; when it was first discovered, it was thought to have a mass closer to only 2 Jupiter masses due to a comparatively small radial velocity signal. Simulations shows that the measured configuration of the planets produces indeed stable orbits for at least 100 million years, where planets ''b'' and ''d'' remain roughly coplanar. [[General relativity]] is expected to have strong effects on planet ''b'', because it orbits at a distance of just ~0.05 AU from the parent star. The [[apsis|apsides]] of planet ''c'' and ''d'', instead, oscillates with time;<ref name=Pizkorz2017/> the orbit of Upsilon Andromedae c thus returns to a nearly circular state every 9,000 years. The eccentricity of those planets may have arisen from a close encounter between the outer planet and a fourth planet, with the result that the third planet was ejected from the system or destroyed.<ref>{{cite journal | display-authors=1 | first1=Eric B. | last1=Ford | first2=Verene | last2=Lystad | first3=Frederic A. | last3=Rasio | title=Planet-planet scattering in the upsilon Andromedae system | journal=[[Nature (journal)|Nature]] | volume=434 | pages=873–876 | date=2005 | doi=10.1038/nature03427 | pmid=15829958 | issue=7035 | bibcode=2005Natur.434..873F | arxiv=astro-ph/0502441 | s2cid=4324250 }}</ref> Such a mechanism could have been triggered by perturbations on the orbit of the companion star, which arise from close encounters with other stars and from the tidal field of the [[Milky Way]].<ref>{{cite journal|last1=Kaib |first1=N.A. |last2=Raymond |first2=S.N.| last3=Duncan|first3=M.|title=Planetary system disruption by Galactic perturbations to wide binary stars|journal=[[Nature (journal)|Nature]]|volume=493|issue=7432|pages=381–384|date=January 2013|doi=10.1038/nature11780|pmid=23292514 |arxiv=1301.3145 |bibcode=2013Natur.493..381K|citeseerx=10.1.1.765.6816 |s2cid=4303714 }}</ref> The orbits of the two inner planets seems to be shaped by tidal interactions, while the evolution of ''c'' and ''d'' orbits is secular.<ref>{{cite journal | title=Extrasolar Planet Interactions | journal=Proceedings of the International Astronomical Union | volume=3 | pages=469–478 | arxiv=0801.3226v1 |date=2008 | last1=Barnes | first1=Rory | last2=Greenberg| first2=Richard | doi=10.1017/S1743921308016980 | bibcode=2008IAUS..249..469B | s2cid=17096607 }}</ref>

===Additional planets{{anchor|Upsilon Andromedae e}}===
Astronomers initially thought that a fourth planet in this system could not exist because it would have made the planetary system unstable and would have been ejected.<ref>{{cite journal | display-authors=1 | first1=Eric B. | last1=Ford | first2=Verene | last2=Lystad | first3=Frederic A. | last3=Rasio | title=Planet-planet scattering in the upsilon Andromedae system | journal=[[Nature (journal)|Nature]] | volume=434 | pages=873–876 | date=2005 | doi=10.1038/nature03427 | pmid=15829958 | issue=7035 | bibcode=2005Natur.434..873F | arxiv=astro-ph/0502441 | s2cid=119496437 }}</ref> But in 2007, an island region of stability was reported where a fourth planet could exist.<ref>{{cite journal | title=Extrasolar planet interactions | arxiv=0801.3226v1 |date=2008 | last1=Barnes | first1=Rory | last2=Greenberg| first2=Richard | journal=Proceedings of the International Astronomical Union | volume=3 | pages=469–478 | doi=10.1017/S1743921308016980 | bibcode=2008IAUS..249..469B | s2cid=17096607 }}</ref>

The existence of further planets too small or distant to detect has not been ruled out, though the presence of [[Jupiter mass|Jupiter-mass]] planets as close as 5 AU from Upsilon Andromedae A would make the system unstable.<ref>{{cite journal|last1=Lissauer |first1=J. |last2=Rivera |first2=E.|title=Stability analysis of the planetary system orbiting υ Andromedae. II. Simulations using new Lick observatory fits|journal=The Astrophysical Journal|volume=554|issue=2|pages=1141–1150|date=2001|doi=10.1086/321426|bibcode=2001ApJ...554.1141L|doi-access=free}}</ref> However, a potential fourth planet (Upsilon Andromedae e) was discovered in 2010. This planet seems to be in a 3:1 resonance with Upsilon Andromedae d.<ref name="Curiel2010"/> Subsequent studies in 2011 and 2014, while finding some evidence for a fourth planet, found large inconsistencies in the estimated orbital period of Upsilon Andromedae e depending on what dataset was used,<ref name="Tuomi2011"/> suggesting that the apparent planetary signal is more likely to be an instrumental artifact.<ref name="McArthur2014"/><ref name=Deitrick2014/>

If it exists, Upsilon Andromedae e would have a [[minimum mass]] slightly greater than [[Jupiter mass|Jupiter's]] and orbit at a similar distance as Jupiter from the Sun, at {{Val|5.2456|ul=AU}} compared to {{Val|5.2043|u=AU}} for Jupiter. Although only the [[minimum mass]] is determined since inclination is not yet known, its [[true mass]] might be much greater. It would take over a decade to orbit the star. At an eccentricity of 0.00536, the planet's orbit would be more circular than that of any of the planets in the [[Solar System]].<ref name="Curiel2010"/>

Upsilon Andromedae does not appear to have a [[circumstellar dust]] disk similar to the [[Kuiper belt]] in the Solar System.<ref>{{cite journal | last1=Trilling |first1=D. E. |last2=Brown |first2=R. H. |last3=Rivkin |first3=A. S. | title=Circumstellar dust disks around stars with known planetary companions | journal=The Astrophysical Journal | volume=529 | issue=1 | pages=499–505 | date=2000 | doi=10.1086/308280 | bibcode=2000ApJ...529..499T|s2cid=121999545 }}</ref> This may be the result of perturbations from the companion star removing material from the outer regions of the Upsilon Andromedae A system.<ref name="lowrance"/>