Extrasolar planet List of extrasolar planets
Size comparison of WASP-18b with Jupiter.
Parent star

<tr> <td colspan="2">Star</td> <td>WASP-18</td></tr><tr> <td colspan="2">Constellation</td> <td>Phoenix[1]</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>01h 37m 24.95s[1]</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>−45° 40′ 40.8″[1]</td></tr><tr> <td>Apparent magnitude</td> <td style="text-align: center">(mV)</td> <td>9.29[1]</td></tr><tr><td colspan="2">Distance</td><td>330 ± 30 ly
(100 ± 10[2] pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>F9[2]</td></tr><tr> <td>Mass</td> <td style="text-align: center">(m)</td> <td>1.25[3] M</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>0.02026 ± 0.00068[2] AU</td></tr><tr> <td>Periastron</td> <td style="text-align: center">(q)</td> <td>0.02007 AU</td></tr><tr> <td>Apastron</td> <td style="text-align: center">(Q)</td> <td>0.02045 AU</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0.0092 ± 0.0028[2]</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>0.94145299[1] d</td></tr><tr><td> </td> <td style="text-align: center"> </td> <td>(22.59487 h)</td></tr><tr> <td>Inclination</td> <td style="text-align: center">(i)</td> <td>86 ± 2.5[2]°</td></tr><tr> <td>Argument of
</td> <td style="text-align: center">(ω)</td> <td>96 ± 10[2]°</td></tr><tr> <td>Time of transit</td> <td style="text-align: center">(Tt)</td> <td>2454221.48163 ± 0.00038[2] JD</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>10.3 ± 0.69[2] MJ</td></tr><tr><td>Radius</td><td style="text-align: center">(r)</td><td>1.106+0.072
[2] Template:Jupiter radius</td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>August 27, 2009[4]</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Hellier et al. (SuperWASP)[4]</td></tr><tr> <td colspan="2">Discovery method</td> <td>Transit[4] (including secondary eclipses)</td></tr><tr> <td colspan="2">Other detection methods</td> <td>Radial velocity</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published[4]</td></tr>

Other designations
HD 10069 b, HIP 7562 b

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>

WASP-18b is an extrasolar planet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses,[4] just below the boundary line between planets and brown dwarfs, about 13 Jupiter masses. Due to tidal deceleration, it is expected to spiral towards and eventually merge with its host star, WASP-18, in less than a million years.[4] The planet is approximately 3.1 million kilometres (1.9 million miles) from its star, which is about 325 light years from Earth. It was discovered by Coel Hellier, a professor of astrophysics at Keele University in England.[5]

File:Planet WASP-18 b.png

Scientists at Keele and at the University of Maryland are working to understand whether the discovery of this planet so shortly before its expected demise (with less than 0.1% of its lifetime remaining) was fortuitous, or whether tidal dissipation by WASP-18 is actually much less efficient than astrophysicists typically assume.[4][6] Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying.[7]

The closest example of a similar situation in the Solar System is Mars's moon Phobos. Phobos orbits Mars at a distance of only about 9,000 km (5,600 mi), 40 times closer than the Moon is to the Earth,[8] and is expected to be destroyed in about eleven million years.[9]

See also Edit

References Edit

  1. 1.0 1.1 1.2 1.3 1.4 WASP-18b. Exoplanet Transit Database. Retrieved 2009-08-29.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Notes for planet WASP-18b. The Extrasolar Planets Encyclopaedia. Retrieved 2009-09-15.
  3. PlanetQuest: WASP-18 b
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 (2009). An orbital period of 0.94days for the hot-Jupiter planet WASP-18b. Nature 460 (7259): 1098–1100.
  5. Suicidal planet seems on death spiral into star,, August 26, 2009
  6. Hamilton, D. P. (2009-08-27). Extrasolar planets: Secrets that only tides will tell. Nature 460 (7259): 1086–1087.
  7. Thompson, Andrea (2009-08-26). Newfound Planet Might Be Near Death. Space.Com. Imaginova. Retrieved 2009-08-28.
  8. Astrophysicists puzzle over planet that's too close to its sun, Los Angeles Times, August 27, 2009
  9. Template:Cite arXiv

External linksEdit

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Coordinates: Sky map 01h 37m 25s, −45° 40′ 41″

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