Extrasolar planet List of extrasolar planets
Size comparison of HAT-P-4b with Jupiter.
Parent star

<tr> <td colspan="2">Star</td> <td>HAT-P-4</td></tr><tr> <td colspan="2">Constellation</td> <td>Boötes</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>15h 19m 58s</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>+36° 13′ 47″</td></tr><tr><td colspan="2">Distance</td><td>1010 ± 100 ly
(310 ± 30 pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>F</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>0.0446 ± 0.0012 AU</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>3.056536 ± 0.000057 d</td></tr><tr> <td>Orbital speed</td> <td style="text-align: center">(υ)</td> <td>158.55 km/s</td></tr><tr> <td>Inclination</td> <td style="text-align: center">(i)</td> <td>89.9 +0.1
°</td></tr><tr> <td>Argument of
</td> <td style="text-align: center">(ω)</td> <td>12.33°</td></tr><tr> <td>Time of periastron</td> <td style="text-align: center">(T0)</td> <td>2,454,245.8154 JD</td></tr><tr> <td>Semi-amplitude</td> <td style="text-align: center">(K)</td> <td>76.93 m/s</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>0.68 ± 0.04 MJ
(216 ± 13 M)</td></tr><tr><td>Radius</td><td style="text-align: center">(r)</td><td>1.27 ± 0.05 Template:Jupiter radius
(14.2 Template:Earth radius)</td></tr><tr><td>Density</td><td style="text-align: center">(ρ)</td><td>410 ± 60 kg m-3</td></tr><tr><td>Surface gravity</td><td style="text-align: center">(g)</td><td>10.5 m/s² (1.07 g)</td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>Oct 2, 2007</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Kovacs et al.</td></tr><tr> <td colspan="2">Discovery method</td> <td>transit</td></tr><tr> <td colspan="2">Discovery site</td> <td>Mass., Template:Country data USA</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr> <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>

HAT-P-4b is an extrasolar planet orbiting the star HAT-P-4 over 1000 light years away in Boötes constellation. It was discovered by transit on October 2, 2007, which looks for slight dimming of stars caused by planets that passed in front of them. It is the fourth planet discovered by the HATNet Project.[1]

It is a hot Jupiter with 68% the mass and 127% the radius of Jupiter, and 41% the density of water (31% of Jupiter). Since the inclination is known by transit observation, the true mass is known.


  1. (2007). HAT-P-4b: A Metal-rich Low-Density Transiting Hot Jupiter. The Astrophysical Journal Letters 670 (1): L41–L44.

External linksEdit


Coordinates: Sky map 15h 19m 58s, +36° 13′ 47″

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