by Spencer Wallace | Jun 27, 2019 | Daily Paper Summaries | 0 comments, Title: The hot Jupiter period-mass distribution as a signature of in situ formation, Authors: Elizabeth Bailey, Konstantin Batygin. The vast majority of hot Jupiters lie above and to the right of this line. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe. To summarize, there are three main theories as to how hot Jupiters get so close to their parent stars. These worlds most certainly formed further out and lost orbital angular momentum to a companion planet and do not fit into the framework described here. But Madhusudhan says the new findings suggest that these theories may have to be revised. All rights reserved. If this core grows larger than about 10x the mass of the Earth, its gravitational pull becomes strong enough for the planet to accumulate a gaseous envelope. Next, the authors use this battle between the disruptive magnetic field of the star and the inwardly streaming protoplanetary disk material to explain the observed lack of close-in, less massive hot Jupiters. How do we think hot Jupiters formed? Had these bodies formed elsewhere in the disk and moved around, the distribution would not follow this cutoff so closely. How do we think hot Jupiters formed? The first exoplanets were ‘hot Jupiters’, massive gas giants larger than Jupiter that orbited their star in days or even hours. [NASA/JPL/Caltech/R. How 'hot Jupiters' got so close to their stars: Extrasolar planet research sheds light on our solar system Date: May 12, 2011 Source: Northwestern University Why didn’t one form in our solar system? How 'hot Jupiters' got so close to their stars: ... "This becomes interesting because that means whatever orbit they were formed on isn't necessarily the orbit they will stay on forever. Had these bodies formed elsewhere in the disk and moved around, the distribution would not follow this cutoff so closely. Finally, it is worth noting that there exists a small but significant population of hot Jupiters that have highly eccentric orbits. Of the 400-odd systems with multiple planets, almost none of them have a hot Jupiter. Why didn’t one form in our solar system? Because this also implies that the magnetic truncation radius is smaller, one should expect larger hot Jupiters to lie slightly closer to the star. This is a strong indication that the gaseous envelopes of these worlds, which make up most of their mass, were constructed at or near their present locations. Even very highly irradiated Jupiter-sized planets only ever lose about 1% of their mass. Eventually, the gaseous envelope becomes too hot for material to continue to condense and the growth is throttled. In one, the gas giants form in place. The prevalent view is formation via orbital migration. Last unit, we learned about the formation of our own solar system, in which small, rocky planets formed close to the Sun, and large, gas giants formed far from the Sun (past the frost line). This results in a dearth of close-in planets around 1/10 the mass of Jupiter. [Bailey & Batygin 2018]. As the disk loses angular momentum due to its inherent viscosity, material continually falls inward onto the star. Above about 1 Jupiter mass, there are a handful of planets that do not seem to follow the cutoff denoted by the solid line. Hot Jupiters, sometimes also called "roaster planets", are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital period (<10 days). The authors explain this discrepancy as a result of tidal evolution. Figure 2: Orbital distance vs mass for all known exoplanets. Figure 2: Orbital distance vs mass for all known exoplanets. The hot Jupiters are the cluster of points towards the top left of the diagram. Twenty years after they were first discovered, ‘hot Jupiters’, gas giant planets that orbit very close to their star, are still enigmatic objects. To make a hot Jupiter, first you must form a gas giant. The authors argue that the sharp cutoff is evidence that worlds are being constructed in place right up to the magnetic truncation boundary. Based on current data, planetary systems appear to be: present around at least 99% of all stars. Interior to the truncation radius, the protoplanetary disk becomes too disrupted for planet formation to occur. The fact that the majority of known hot Jupiters lie above the cutoff described by the model in this paper suggests that most hot Jupiters do not undergo orbital migration. There appears to be a very sharp cutoff, below which hot Jupiters that are too small and close to their host stars simply don’t exist. 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