View source for WASP-17b

{{Short description|Hot-Jupiter exoplanet in the orbit of the star WASP-17}}
{{good article}}
{{Infobox planet
| name = WASP-17b / Ditsö̀
| image = WASP-17b.jpg
| caption = Artist impression of Ditsö̀
<!-- DISCOVERY           -->
| discovery_ref = <ref name="Anderson2010"/>
| discoverer = David R. Anderson ''et al''
| discovered = 11 August 2009
| discovery_method = [[Methods of detecting exoplanets#Transit photometry|Transit]] (including secondary eclipse)
<!-- DESIGNATIONS        -->
<!-- ORBITAL             -->
| orbit_ref = <ref name="Bonomo2017"/>
| apsis = astron
| semimajor = {{val|0.05151|0.00035|ul=AU}}
| eccentricity = <0.020
| period = {{val|3.7354845|0.0000019|ul=d}}
| inclination = {{val|86.83|0.68|0.53|u=deg}}
| arg_peri = −70{{citation needed|date=October 2023}}
| semi-amplitude = {{val|56.0|4.1|4.0|ul=m/s}}
| star = [[WASP-17]]
<!-- PHYS CHARS          -->
| physical_ref = <ref name="Bonomo2017"/>
| mean_radius = {{val|1.991|0.081|ul=Jupiter radius}}
| mass = {{val|0.512|0.037|ul=Jupiter mass}}
| density = {{val|0.080|0.013|0.011|ul=g/cm3}}
| single_temperature = {{val|1550|170|200|ul=K|fmt=commas}}<ref name="AandA2018"/>
<!-- ATMOSPHERE          -->
<!-- NOTES               -->
}}
'''WASP-17b''', officially named '''Ditsö̀'''{{Pronunciation needed|date=November 2024}}, is an [[exoplanet]] in the [[constellation]] [[Scorpius]] that is orbiting the [[star]] [[WASP-17]]. Its discovery was announced on 11 August 2009.<ref name="Anderson2010"/> It is the first planet discovered to have a [[retrograde orbit]], meaning it orbits in a direction counter to the rotation of its host star.<ref name="Anderson2010"/> This discovery challenged traditional planetary formation theory.<ref>[http://www.physorg.com/news/2011-06-planet-wrong.html "A planet going the wrong way"], Phys Org. June 7, 2011. Accessed June 10, 2011</ref> In terms of diameter, WASP-17b is one of the [[List of largest exoplanets|largest exoplanets]] discovered and at half [[Jupiter]]'s [[Jupiter mass|mass]], this made it the most [[puffy planet]] known in 2010.<ref>{{cite web |url=http://news.nationalgeographic.com/news/2009/08/090817-new-planet-orbits-backward.html |archive-url=https://web.archive.org/web/20090820034615/http://news.nationalgeographic.com/news/2009/08/090817-new-planet-orbits-backward.html |url-status=dead |archive-date=August 20, 2009 |title="Backward" Planet Has Density of Foam Coffee Cups |first=Rachel |last=Kaufman |date=17 August 2009 |work=[[National Geographic (magazine)|National Geographic]] |publisher=[[National Geographic Society]] |access-date=6 February 2011}}</ref> On 3 December 2013, scientists working with the [[Hubble Space Telescope]] reported detecting [[water]] in the [[exoplanet]]'s [[atmosphere]].<ref name="NASA-20131203">{{cite web |title=Hubble Traces Subtle Signals of Water on Hazy Worlds |url=http://www.nasa.gov/content/goddard/hubble-traces-subtle-signals-of-water-on-hazy-worlds/|website=[[NASA]] |date=3 December 2013|access-date=4 December 2013}}</ref><ref name="ApJ-20131203">{{cite journal |last1=Mandell |first1=Avi M. |last2=Haynes |first2=Korey |last3=Sinukoff |first3=Evan |last4=Madhusudhan |first4=Nikku |last5=Burrows |first5=Adam |last6=Deming |first6=Drake |title=Exoplanet Transit Spectroscopy Using WFC3: WASP-12 b, WASP-17 b, and WASP-19 b |date=3 December 2013 |journal=[[Astrophysical Journal]] |volume=779 |issue=2 |page=128 |doi=10.1088/0004-637X/779/2/128 |arxiv = 1310.2949 |bibcode = 2013ApJ...779..128M |s2cid=52997396 }}</ref>

WASP-17b's name was selected in the [[NameExoWorlds]] campaign by [[Costa Rica]], during the 100th anniversary of the [[International Astronomical Union]]. Ditsö̀ is the name that the god [[Sibú|Sibö̀]] gave to the first [[Bribri people]] in [[Talamancan mythology]].<ref>{{Cite web|url=http://www.nameexoworlds.iau.org/final-results|title=Approved names|website=NameExoworlds|language=en|access-date=2020-01-02}}</ref><ref>{{Cite web|url=https://www.iau.org/news/pressreleases/detail/iau1912/|title=100 000s of People from 112 Countries Select Names for Exoplanet Systems In Celebration of IAU's 100th Anniversary |website=International Astronomical Union |access-date=2020-01-02}}</ref>

==Discovery==
A team of researchers led by David Anderson of [[Keele University]] in [[Staffordshire]], [[England]], [[Methods of detecting exoplanets#Transit photometry|discovered]] the [[gas giant]], which is about {{Convert|1000|ly|pc|abbr=off|lk=on}} from Earth, by observing it [[Astronomical transit|transiting]] its host star [[WASP-17]]. Such [[Photometry (astronomy)|photometric]] observations also reveal the planet's size. The discovery was made with a telescope array at the [[South African Astronomical Observatory]]. Due to the involvement of the [[Wide Angle Search for Planets]] (SuperWASP) consortium of universities, the exoplanet, as the 17th found to date by this group, was given its present name.<ref name=BBC>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8197683.stm|title=New planet displays exotic orbit|work=[[BBC News]]|first=Paul |last=Rincon|date=August 13, 2009|access-date=2009-08-13}}</ref>

Astronomers at the [[Observatory of Geneva]] were then able to use characteristic [[redshift]]s and [[blueshift]]s in the host star's [[spectrum]] as its [[radial velocity]] [[Doppler spectroscopy|varied over the course of the planet's orbit]] to measure the planet's mass and obtain an indication of its [[orbital eccentricity]].<ref name="Anderson2010"/> Careful examination of the [[Doppler effect|Doppler shifts]] during transits also allowed them to determine the direction of the planet's orbital motion relative to its parent star's rotation via the [[Rossiter–McLaughlin effect]].<ref name="Anderson2010"/>

==Orbit==
WASP-17b is thought to have a [[retrograde orbit]] (with a sky-projected [[Orbital inclination#Natural and artificial satellites|inclination]] of the orbit normal against the stellar spin axis of about 149°,<ref>Amaury H.M.J. Triaud et al. ''Spin-orbit angle measurements for six southern transiting planets''. Accepted for publication in [[Astronomy and Astrophysics|A&A]] 2010. [https://arxiv.org/abs/1008.2353 arXiv preprint]</ref> not to be confused with the [[Orbital inclination#Exoplanets and multiple star systems|line-of-sight inclination]] of the orbit, given in the table, which is near 90° for all transiting planets), which would make it the first planet discovered to have such an orbital motion. It was found by measuring the [[Rossiter–McLaughlin effect]] of the planet on the star's Doppler signal as it transited, in which whichever of the star's hemispheres is turning toward or away from Earth will show a slight blueshift or redshift which is dampened by the transiting planet. Scientists are not yet sure why the planet orbits opposite to the star's rotation. Theories include a [[gravitational slingshot]] resulting from a near-collision with another planet, or the intervention of a smaller planet-like body working to gradually change WASP-17b's orbit by tilting it via the [[Kozai mechanism]].<ref name=NewScientist>{{cite magazine|url=https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html?full=true|title=Planet found orbiting its star backwards|magazine=[[New Scientist]]|first=Lisa|last=Grossman|date=August 13, 2009|access-date=2009-08-13}}</ref>
Spin-orbit angle measurement was updated in 2012 to −148.7{{±|7.7|6.7}}°.<ref>{{citation|arxiv=1206.6105|title=Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments|year=2012|doi=10.1088/0004-637X/757/1/18|last1=Albrecht|first1=Simon|last2=Winn|first2=Joshua N.|last3=Johnson|first3=John A.|last4=Howard|first4=Andrew W.|last5=Marcy|first5=Geoffrey W.|last6=Butler|first6=R. Paul|last7=Arriagada|first7=Pamela|last8=Crane|first8=Jeffrey D.|last9=Shectman|first9=Stephen A.|last10=Thompson|first10=Ian B.|last11=Hirano|first11=Teruyuki|last12=Bakos|first12=Gaspar|last13=Hartman|first13=Joel D.|journal=The Astrophysical Journal|volume=757|issue=1|page=18|bibcode=2012ApJ...757...18A|s2cid=17174530 }}</ref>

==Physical properties==
[[File:Exoplanet Comparison WASP-17 b.png|thumb|left|Size comparison of [[Jupiter]] with Ditsö̀]]
WASP-17b has a [[radius]] between 1.5 and 2 times that of [[Jupiter]] and about half the [[Jupiter mass|mass]].<ref name="Anderson2010"/> Thus its mean [[density]] is between 0.08 and 0.19 g/cm<sup>3</sup>,<ref name="Anderson2010"/> compared with Jupiter's 1.326 g/cm<sup>3</sup><ref name="Jupiter Fact Sheet">{{Cite web |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html |title=Jupiter Fact Sheet |access-date=2009-08-13}}</ref> and [[Earth]]'s 5.515 g/cm<sup>3</sup> (the density of water is 1&nbsp;g/cm<sup>3</sup>). The unusually low density is thought to be a consequence of a combination of the planet's orbital eccentricity and its proximity to its parent star (less than one seventh of the distance between [[Mercury (planet)|Mercury]] and the [[Sun]]), leading to [[Tidal acceleration#Tidal heating|tidal flexing and heating]] of its interior.<ref name="Anderson2010"/> The same mechanism is behind the intense volcanic activity of Jupiter's moon [[Io (moon)|Io]]. [[WASP-39b]] has a similarly low estimated density.

Exoplanetary [[sodium]] in the [[atmosphere]] of the [[WASP-17]] has been detected in 2018,<ref name="AandA2018"/> but was not confirmed by 2021. Instead, the spectral signatures of [[water]], [[aluminium oxide]] ([[Aluminium(II) oxide|AlO]]) and [[titanium hydride]] ([[Titanium hydride|TiH]]) were detected.<ref>{{citation|arxiv=2108.13721|year=2022|title=The Transmission Spectrum of WASP-17 b from the Optical to the Near-infrared Wavelengths: Combining STIS, WFC3, and IRAC Data Sets|doi=10.3847/1538-3881/ac6c01 |last1=Saba |first1=Arianna |last2=Tsiaras |first2=Angelos |last3=Morvan |first3=Mario |last4=Thompson |first4=Alexandra |last5=Changeat |first5=Quentin |last6=Edwards |first6=Billy |last7=Jolly |first7=Andrew |last8=Waldmann |first8=Ingo |last9=Tinetti |first9=Giovanna |journal=The Astronomical Journal |volume=164 |issue=1 |page=2 |bibcode=2022AJ....164....2S |s2cid=237363318 |doi-access=free }}</ref> The [[water]] signature was confirmed in 2022, together with [[carbon dioxide]] absorption.<ref>{{citation|arxiv=2203.02434|year=2022|title=A comprehensive analysis of WASP-17b's transmission spectrum from space-based observations|doi=10.1093/mnras/stac661 |last1=Alderson |first1=L. |last2=Wakeford |first2=H. R. |last3=MacDonald |first3=R. J. |last4=Lewis |first4=N. K. |last5=May |first5=E. M. |last6=Grant |first6=D. |last7=Sing |first7=D. K. |last8=Stevenson |first8=K. B. |last9=Fowler |first9=J. |last10=Goyal |first10=J. |last11=Batalha |first11=N. E. |last12=Kataria |first12=T. |journal=Monthly Notices of the Royal Astronomical Society |volume=512 |issue=3 |pages=4185–4209 |doi-access=free }}</ref> In 2023, evidence of [[cloud]]s made of [[quartz]] was detected on the [[planet]] by the [[James Webb Space Telescope]].<ref name="Grant2023" /><ref name="JWST-20231016" />

[[File:Clear to cloudy hot Jupiters.jpg|thumb|center|400px|{{center|Comparison of "[[hot Jupiter]]" exoplanets (artist concept)}}<br />From top left to lower right: [[WASP-12b]], [[WASP-6b]], [[WASP-31b]], [[WASP-39b]], [[HD 189733 b]], [[HAT-P-12b]], WASP-17b, [[WASP-19b]], [[HAT-P-1b]] and [[HD 209458 b]]]]

[[File:Composition of cloud particles - hot gas giant exoplanet WASP-17b (WASP17b).jpg|thumb|center|400px|This is a transmission spectrum of the hot gas giant exoplanet WASP-17 b captured by Webb's Mid-Infrared Instrument (MIRI) on 12–13 March 2023. It reveals the first evidence for quartz (crystalline silica, SiO<sub>2</sub>) in the clouds of an exoplanet.<ref>{{cite news |url=https://esawebb.org/images/WASP17b/|title=Composition of cloud particles - hot gas giant exoplanet WASP-17b.  |date=October 20, 2023}}</ref>]]

==See also==
*[[HAT-P-7b]], another exoplanet announced to have a retrograde orbit the day after the WASP-17b announcement
*[[TrES-4b]], another large exoplanet with a low density
*[[List of exoplanet extremes]]

==References==
{{reflist|refs=

<ref name="Anderson2010">{{cite journal | title=WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit | last1=Anderson | first1=D. R. | last2=Hellier | first2=C. | last3=Gillon | first3=M. | last4=Triaud | first4=A. H. M. J. | last5=Smalley | first5=B. | last6=Hebb | first6=L. | last7=Collier Cameron | first7=A. | last8=Maxted | first8=P. F. L. | last9=Queloz | first9=D. | last10=West | first10=R. G. | last11=Bentley | first11=S. J. | last12=Enoch | first12=B. | last13=Horne | first13=K. | last14=Lister | first14=T. A. | last15=Mayor | first15=M. | last16=Parley | first16=N. R. | last17=Pepe | first17=F. | last18=Pollacco | first18=D. | last19=Ségransan | first19=D. | last20=Udry | first20=S. | last21=Wilson | first21=D. M. | display-authors=1 | journal=The Astrophysical Journal | volume=709 | issue=1 | pages=159–167 | year=2010 | arxiv=0908.1553 | bibcode=2010ApJ...709..159A | doi=10.1088/0004-637X/709/1/159 | s2cid=53628741 }}</ref>

<ref name="Bonomo2017">{{cite journal |last1=Bonomo |first1=A. S. |last2=Desidera |first2=S. |display-authors=etal |date=June 2017 |title=The GAPS Programme with HARPS-N at TNG. XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets |journal=[[Astronomy & Astrophysics]] |volume=602 |issue= |pages=A107 |doi=10.1051/0004-6361/201629882 |arxiv=1704.00373 |bibcode=2017A&A...602A.107B|s2cid=118923163 }}</ref>

<ref name="AandA2018">{{cite journal |last1=Khalafinejad |first1=Sara |last2=Salz |first2=Michael |display-authors=etal |date=October 2018 |title=The atmosphere of WASP-17b: Optical high-resolution transmission spectroscopy |journal=[[Astronomy & Astrophysics]] |volume=618 |pages=A98 |doi=10.1051/0004-6361/201732029 |doi-access=free |arxiv=1807.10621 |bibcode=2018A&A...618A..98K |s2cid=119007114}}</ref>

<ref name="Grant2023">{{cite journal |last1=Grant |first1=David |last2=Lewis |first2=Nikole K. |display-authors=etal |date=October 2023 |title=WST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b |journal=[[The Astrophysical Journal Letters]] |volume= 956|issue= 2|pages= L29|doi= 10.3847/2041-8213/acfc3b|arxiv=2310.08637 |bibcode=2023ApJ...956L..32G |doi-access=free }}</ref>

<ref name="JWST-20231016">{{cite web |url=https://webbtelescope.org/contents/news-releases/2023/news-2023-140 |title=NASA's Webb Detects Tiny Quartz Crystals in Clouds of Hot Gas Giant |date=16 October 2023 |website=webbtelescope.org |publisher=[[STScI]] |access-date=16 October 2023}}</ref>

}}

==External links==
{{commons category-inline|WASP-17 b|WASP-17b}}
*Alexander, Amir. Scientists Detect "Wrong-Way" Planet. [http://www.planetary.org/news/2009/0812_Scientists_Detect_WrongWay_Planet.html] {{Webarchive|url=https://web.archive.org/web/20090816085545/http://www.planetary.org/news/2009/0812_Scientists_Detect_WrongWay_Planet.html |date=2009-08-16 }} [[The Planetary Society]], August 12, 2009. Accessed August 14, 2009.

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[[Category:Exoplanets discovered in 2009]]
[[Category:Exoplanets discovered by WASP]]
[[Category:Giant planets]]
[[Category:Hot Jupiters]]
[[Category:Transiting exoplanets]]
[[Category:Scorpius]]
[[Category:Exoplanets with proper names]]