The Largest Planet In The Universe.

Exoplanet TrES-4b comparison with Jupitar and earth.

What is the largest planet ever discovered in the universe yet? The answer is TrES-4b. Yes, TrES-4b is an extrasolar planet discovered in 2006 and announced in 2007 by the Trans-Atlantic Exoplanet Survey using the transit method. It is 1,430 light-years (440 pc) away in the constellation Hercules.

TrES-4b is one of the largest exoplanets ever found, after WASP-12b, WASP-17b, CT Chamaeleontis b (though the latter may be a brown dwarf), and GQ Lupi b. It was discovered in 2006, and announced in 2007, by the Trans-Atlantic Exoplanet Survey, using the transit method. It is approximately 1,400 light-years (430 pc) away orbiting the star GSC 02620-00648, in the constellation Hercules.  

The largest planet ever discovered is also one of the strangest and theoretically should not even exit, scientists say.

Dubbed TrES-4, the planet is about 1.7 times the size of Jupiter and belongs to a small subclass of "puffy" planets that have extremely low densities.

"Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood," said study leader Georgi Mandushev of the Lowell Observatory in Arizona. "And because of the planet's relatively weak pull on its upper atmosphere, some of the atmospheres probably escapes in a comet-like tail."

The planet's large mass-to-density ratio makes it an anomaly among known exoplanets, and its existence cannot be explained by current models. 

 

Orbit

A 2008 study concluded that the GSC 06200-00648 system (among others) is a binary star system allowing even more accurate determination of stellar and planetary parameters. TrES-4 orbits its primary star every 3.543 days and eclipses it when viewed from Earth. The study in 2012, utilizing a Rossiter–McLaughlin effect, has determined the planetary orbit is probably aligned with the equatorial plane of the star, misalignment equal to 6.3±4.7°.

 

Physical characteristics

The planet is slightly less massive than Jupiter (0.919 ± 0.073 MJ) but its diameter is 79.9% larger; it was considered the largest planet ever found at the time, giving it an average density of only about 1/3 gram per cubic centimeter, approximately the same as Saturn's moon Methone. This made TrES-4 both the largest known planet and the planet with the lowest known density at the time of its discovery.

 

TrES-4's orbital radius is 0.05091 AU, giving it a predicted surface temperature of about 1782 K. This by itself is not enough to explain the planet's low density, however. It is not currently known why TrES-4 is so large. The probable causes are the proximity to a parent star that is 3–4 times more luminous than the Sun as well as the internal heat within the planet.

 

 

 

A planet anomaly

"TrES-4 is way bigger than it's supposed to be," Mandushev told SPACE.com. "For its mass, it should be much smaller. It basically should be about the size of Jupiter and instead it's almost twice as big." 

"TrES-4 appears to be something of a theoretical problem," said study team member Edward Dunham, also of the Lowell Observatory. "Problems are good, though, since we learn new things by solving them." 

The planet is located about 1,400 light-years away from Earth and zips around its parent star in only three and a half days. An international team of astronomers discovered it using a network of automated telescopes called the Trans-Atlantic Exoplanet Survey. TrES-4 was detected as it passed in front of, or "transited," its parent star, called GSC 02620-00648. The transit technique is the only planet-finding method that allows scientists to calculate the size of a planet. TrES-4 "is the largest planet found so far for which we actually know the size," Mandushev said in a telephone interview. "There could be larger planets, but we have no way of measuring their sizes because they don't transit." 

 

Speeded up star

The parent star of TrES-4 is also unusual in that it is about the same age as our sun but much farther along in its evolutionary history. "Because it is more massive, it has evolved much faster," Mandushev explained. "It has become what astronomers call a subgiant or a star that has exhausted all of its hydrogen fuel in the core and is on its way to becoming a red giant." 

Our sun is not expected to become a red giant for another 5 to 7 billion years. When it does, the sun will expand to engulf the inner planets and possibly Earth. Because TrES-4 orbits so close to its star, it is certain to be consumed once the star becomes a red giant in about a billion years, Mandushev said. GSC 02620-00648 is much more luminous than our sun and emits three to four times more energy per second. As a general rule, gas planets that orbit larger, more luminous stars tend to be puffier, but this does not explain TrES-4's anomalously large size. 

"We actually looked at the energy which the planet gets from the star, and there's no way this can be the only explanation for how big the planet is," Mandushev said.