Hot Jupiters are wacky Wonder Worlds that cling closely to their parent-stars in incredibly speedy, roasting orbits. These bewitching behemoths are gas giant exoplanets with orbital periods that are less than 10 days long, and their extremely hot orbits around their roiling, broiling, fiery stars usually carry them less than 0.1 Astronomical Units (AU) from their stellar hosts–which amounts to only one-tenth of the distance between Earth and Sun. One AU is the distance between our planet and our Star, which is 93,000,000 miles. Ever since astronomers first calculated the immense size of these weird exoplanets almost a generation ago, they have confronted a tantalizing mystery–how did these searing-hot, distant, and puffy alien “oddballs” manage to grow so large? In November 2017, thanks to a recent discovery of tattle-tale twin planets, a team of astronomers are getting closer and closer to solving this puffy planet puzzle.
The astronomers, who detected this dynamic duo of twin planets, are led by graduate student Samuel Grunblatt of the University of Hawaii’s Institute for Astronomy (IfA). Thanks to this team of University of Hawaii astronomers, we are now getting closer to an answer of how these puffy, hot, giant planets form.
Gas giant planets are mostly made up of hydrogen and helium–the two lightest atomic elements in the Universe–and they are at least four times the diameter of Earth. There are no hot Jupiters in our own Solar System, and these alien and exotic planets hug their parent stars in scorching orbits–hence, their designation as “hot Jupiters”. These gas giant planets sport masses that are similar to the two gas giant planets inhabiting our own Solar System–Jupiter and Saturn. However, these enormous hot Jupiter worlds tend to be much larger than the two gaseous behemoths that orbit our Star in the chilly outer region of our Solar System, far from the golden light and heat of our Sun. Some of the hot Jupiter exoplanets are puffed up to enormous sizes that make them even larger than the smallest stars.
The first batch of exoplanet discoveries, that came at the end of the 20th century, were dominated by hot Jupiters. This is because they are the easiest exoplanets to discover by astronomers using the original radial velocity (Doppler) method and the transit method. The Doppler method favors the discovery of hot giant worlds hugging their parent-stars fast and close, because these behemoth worlds provide the greatest tug on their stellar parents. The Doppler method searches for a tiny repetitive wobble that indicates the presence of a giant world close to its star. The transit method, on the other hand, searches for an almost imperceptible blotting of a fiery star’s brilliant light when a planet travels in front of its glaring face. The larger the planet, the more stellar light is blocked.
Even though hot Jupiters dominated exoplanet discoveries at first, the occurrence rate differs by a factor of 2-3 between Doppler planet surveys and transit planet surveys.
Other nagging mysteries remain. For example, hot Jupiters are much too massive to be born close to their parent-stars in tight, roasting orbits. This is because of a lack of planet building materials close to their stellar hosts. One possible solution to this puzzle is that hot Jupiters are born further out, where there is sufficient material to build such gigantic planets, but then travel inward to their current broiling positions.
Several scenarios have been proposed to explain what triggers this inward migration. Some scientists think that an imbalance occurring in the protoplanetary accretion disk itself is the true culprit. Other scientists, however, suggest that the orbits of hot Jupiters are excited to an extremely high eccentricity. The high eccentricity causes the migrating hot Jupiter to wander towards the central star–approaching its fiery stellar parent so close that the orbital energy of the hot Jupiter is tidally dissipated. The tidal energy dissipation shrinks and circularizes the orbits of hot Jupiters. However, what triggers the high eccentricity is another mystery, and a source of considerable debate. Some astronomers propose that planet-planet scattering is the true underlying cause, while others think that the perturbation of a companion star is the true trigger. 720p mkv movies download