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WASP-17b
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<h2 id="discovery">Discovery</h2> <p>A team of researchers led by David Anderson of <a href="/facts/Keele_University/3JumIoNJ">Keele University</a> in <a href="/facts/Staffordshire/w4KJHAXz">Staffordshire</a>, <a href="/facts/England/U9mE5bGL">England</a>, <a href="/facts/Methods_of_detecting_exoplanets/vFIblQe9">discovered</a> the <a href="/facts/Gas_giant/pmF6KztG">gas giant</a>, which is about 1,000 <a href="/facts/Light-year/IGc5NdQb">light-years</a> (310 <a href="/facts/Parsec/SwSsk57J">parsecs</a>) from Earth, by observing it <a href="/facts/Astronomical_transit/4s6Mll1a">transiting</a> its host star <a href="/facts/WASP-17/dydfsAWU">WASP-17</a>. Such <a href="/facts/Photometry_(astronomy)/fnV9JdSa">photometric</a> observations also reveal the planet's size. The discovery was made with a telescope array at the <a href="/facts/South_African_Astronomical_Observatory/F1cjYtGC">South African Astronomical Observatory</a>. Due to the involvement of the <a href="/facts/Wide_Angle_Search_for_Planets/fp58Y205">Wide Angle Search for Planets</a> (SuperWASP) consortium of universities, the exoplanet, as the 17th found to date by this group, was given its present name.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p><p>Astronomers at the <a href="/facts/Observatory_of_Geneva/Lzpkhjq0">Observatory of Geneva</a> were then able to use characteristic <a href="/facts/Redshift/Qfl4VjDF">redshifts</a> and <a href="/facts/Blueshift/v8XBtGKH">blueshifts</a> in the host star's <a href="/facts/Spectrum/wPUjkpqI">spectrum</a> as its <a href="/facts/Radial_velocity/B3NmbVLP">radial velocity</a> <a href="/facts/Doppler_spectroscopy/0uTvj3pq">varied over the course of the planet's orbit</a> to measure the planet's mass and obtain an indication of its <a href="/facts/Orbital_eccentricity/WGlB4NBn">orbital eccentricity</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Careful examination of the <a href="/facts/Doppler_effect/bzrK1BKf">Doppler shifts</a> during transits also allowed them to determine the direction of the planet's orbital motion relative to its parent star's rotation via the <a href="/facts/Rossiter%E2%80%93McLaughlin_effect/QEMgxao5">Rossiter–McLaughlin effect</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h2 id="orbit">Orbit</h2> <p>WASP-17b is thought to have a <a href="/facts/Retrograde_orbit/1HCbwQqy">retrograde orbit</a> (with a sky-projected <a href="/facts/Orbital_inclination/TQCFWyfd">inclination</a> of the orbit normal against the stellar spin axis of about 149°,<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> not to be confused with the <a href="/facts/Orbital_inclination/TQCFWyfd">line-of-sight inclination</a> 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 <a href="/facts/Rossiter%E2%80%93McLaughlin_effect/QEMgxao5">Rossiter–McLaughlin effect</a> 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 <a href="/facts/Gravitational_slingshot/4sqIByot">gravitational slingshot</a> 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 <a href="/facts/Kozai_mechanism/KujDlqLG">Kozai mechanism</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> Spin-orbit angle measurement was updated in 2012 to −148.7+7.7−6.7°.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="physical-properties">Physical properties</h2> <p>WASP-17b has a <a href="/facts/Radius/9Gr9deYD">radius</a> between 1.5 and 2 times that of <a href="/facts/Jupiter/95m7XjMT">Jupiter</a> and about half the <a href="/facts/Jupiter_mass/EtLUmeEN">mass</a>.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> Thus its mean <a href="/facts/Density/92p6hh9I">density</a> is between 0.08 and 0.19 g/cm3,<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> compared with Jupiter's 1.326 g/cm3<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> and <a href="/facts/Earth/HLLmDfj0">Earth</a>'s 5.515 g/cm3 (the density of water is 1 g/cm3). 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 <a href="/facts/Mercury_(planet)/lVa1GIyX">Mercury</a> and the <a href="/facts/Sun/CadPCVHh">Sun</a>), leading to <a href="/facts/Tidal_acceleration/PwDTMyjb">tidal flexing and heating</a> of its interior.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> The same mechanism is behind the intense volcanic activity of Jupiter's moon <a href="/facts/Io_(moon)/p3Uc8FmK">Io</a>. <a href="/facts/WASP-39b/qm4Wkud0">WASP-39b</a> has a similarly low estimated density. </p><p>Exoplanetary <a href="/facts/Sodium/eYuSPu2V">sodium</a> in the <a href="/facts/Atmosphere/oUpLaGRF">atmosphere</a> of the <a href="/facts/WASP-17/dydfsAWU">WASP-17</a> has been detected in 2018,<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> but was not confirmed by 2021. Instead, the spectral signatures of <a href="/facts/Water/0lkXnJPK">water</a>, <a href="/facts/Aluminium_oxide/wXM9P6pI">aluminium oxide</a> (<a href="/facts/Aluminium(II)_oxide/JK0YNwcG">AlO</a>) and <a href="/facts/Titanium_hydride/q00w7qep">titanium hydride</a> (<a href="/facts/Titanium_hydride/q00w7qep">TiH</a>) were detected.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> The <a href="/facts/Water/0lkXnJPK">water</a> signature was confirmed in 2022, together with <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> absorption.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> In 2023, evidence of <a href="/facts/Cloud/KDgo0Wqu">clouds</a> made of <a href="/facts/Quartz/4n86tE2G">quartz</a> was detected on the <a href="/facts/Planet/rbPjE6Bx">planet</a> by the <a href="/facts/James_Webb_Space_Telescope/w4GAWnWX">James Webb Space Telescope</a>.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a><a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/HAT-P-7b/zNPHDB1X">HAT-P-7b</a>, another exoplanet announced to have a retrograde orbit the day after the WASP-17b announcement</li> <li><a href="/facts/TrES-4b/YQvRgQs8">TrES-4b</a>, another large exoplanet with a low density</li> <li><a href="/facts/List_of_exoplanet_extremes/wLlzMLT2">List of exoplanet extremes</a></li></ul> <h2 id="external-links">External links</h2> <p> Media related to WASP-17b at Wikimedia Commons </p> <ul><li>Alexander, Amir. Scientists Detect "Wrong-Way" Planet. <a href="http://www.planetary.org/news/2009/0812_Scientists_Detect_WrongWay_Planet.html">[1]</a> <a href="https://web.archive.org/web/20090816085545/http://www.planetary.org/news/2009/0812_Scientists_Detect_WrongWay_Planet.html">Archived</a> 2009-08-16 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> <a href="/facts/The_Planetary_Society/rAuRH7IK">The Planetary Society</a>, August 12, 2009. Accessed August 14, 2009.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"A planet going the wrong way", Phys Org. June 7, 2011. Accessed June 10, 2011 <a href="http://www.physorg.com/news/2011-06-planet-wrong.html" target="_blank">http://www.physorg.com/news/2011-06-planet-wrong.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Kaufman, Rachel (17 August 2009). ""Backward" Planet Has Density of Foam Coffee Cups". National Geographic. National Geographic Society. Archived from the original on August 20, 2009. Retrieved 6 February 2011. <a href="https://web.archive.org/web/20090820034615/http://news.nationalgeographic.com/news/2009/08/090817-new-planet-orbits-backward.html" target="_blank">https://web.archive.org/web/20090820034615/http://news.nationalgeographic.com/news/2009/08/090817-new-planet-orbits-backward.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Hubble Traces Subtle Signals of Water on Hazy Worlds". NASA. 3 December 2013. Retrieved 4 December 2013. <a href="https://www.nasa.gov/content/goddard/hubble-traces-subtle-signals-of-water-on-hazy-worlds/" target="_blank">https://www.nasa.gov/content/goddard/hubble-traces-subtle-signals-of-water-on-hazy-worlds/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Mandell, Avi M.; Haynes, Korey; Sinukoff, Evan; Madhusudhan, Nikku; Burrows, Adam; Deming, Drake (3 December 2013). "Exoplanet Transit Spectroscopy Using WFC3: WASP-12 b, WASP-17 b, and WASP-19 b". Astrophysical Journal. 779 (2): 128. arXiv:1310.2949. Bibcode:2013ApJ...779..128M. doi:10.1088/0004-637X/779/2/128. S2CID 52997396. <a href="/wiki/Astrophysical_Journal" target="_blank">/wiki/Astrophysical_Journal</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Approved names". NameExoworlds. Retrieved 2020-01-02. <a href="http://www.nameexoworlds.iau.org/final-results" target="_blank">http://www.nameexoworlds.iau.org/final-results</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"100 000s of People from 112 Countries Select Names for Exoplanet Systems In Celebration of IAU's 100th Anniversary". International Astronomical Union. Retrieved 2020-01-02. <a href="https://www.iau.org/news/pressreleases/detail/iau1912/" target="_blank">https://www.iau.org/news/pressreleases/detail/iau1912/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Rincon, Paul (August 13, 2009). "New planet displays exotic orbit". BBC News. Retrieved 2009-08-13. <a href="http://news.bbc.co.uk/2/hi/science/nature/8197683.stm" target="_blank">http://news.bbc.co.uk/2/hi/science/nature/8197683.stm</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Amaury H.M.J. Triaud et al. Spin-orbit angle measurements for six southern transiting planets. Accepted for publication in A&A 2010. arXiv preprint <a href="/wiki/Astronomy_and_Astrophysics" target="_blank">/wiki/Astronomy_and_Astrophysics</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Grossman, Lisa (August 13, 2009). "Planet found orbiting its star backwards". New Scientist. Retrieved 2009-08-13. <a href="https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html?full=true" target="_blank">https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html?full=true</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Albrecht, Simon; Winn, Joshua N.; Johnson, John A.; Howard, Andrew W.; Marcy, Geoffrey W.; Butler, R. Paul; Arriagada, Pamela; Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B.; Hirano, Teruyuki; Bakos, Gaspar; Hartman, Joel D. (2012), "Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments", The Astrophysical Journal, 757 (1): 18, arXiv:1206.6105, Bibcode:2012ApJ...757...18A, doi:10.1088/0004-637X/757/1/18, S2CID 17174530 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"Jupiter Fact Sheet". Retrieved 2009-08-13. <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html" target="_blank">https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Anderson, D. R.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Khalafinejad, Sara; Salz, Michael; et al. (October 2018). "The atmosphere of WASP-17b: Optical high-resolution transmission spectroscopy". Astronomy & Astrophysics. 618: A98. arXiv:1807.10621. Bibcode:2018A&A...618A..98K. doi:10.1051/0004-6361/201732029. S2CID 119007114. <a href="https://doi.org/10.1051%2F0004-6361%2F201732029" target="_blank">https://doi.org/10.1051%2F0004-6361%2F201732029</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Saba, Arianna; Tsiaras, Angelos; Morvan, Mario; Thompson, Alexandra; Changeat, Quentin; Edwards, Billy; Jolly, Andrew; Waldmann, Ingo; Tinetti, Giovanna (2022), "The Transmission Spectrum of WASP-17 b from the Optical to the Near-infrared Wavelengths: Combining STIS, WFC3, and IRAC Data Sets", The Astronomical Journal, 164 (1): 2, arXiv:2108.13721, Bibcode:2022AJ....164....2S, doi:10.3847/1538-3881/ac6c01, S2CID 237363318 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Alderson, L.; Wakeford, H. R.; MacDonald, R. J.; Lewis, N. K.; May, E. M.; Grant, D.; Sing, D. K.; Stevenson, K. B.; Fowler, J.; Goyal, J.; Batalha, N. E.; Kataria, T. 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Retrieved 16 October 2023. <a href="https://webbtelescope.org/contents/news-releases/2023/news-2023-140" target="_blank">https://webbtelescope.org/contents/news-releases/2023/news-2023-140</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> </ol>