# Tag Info

30

A recent study indicates that Cold Jupiters similar to Saturn and Jupiter greatly outnumber Hot Jupiters. The authors studied 18 years worth of data to find long-period exoplanets, that is planets far from their host star. Cold Jupiters, being farther from their host star, have longer periods than Hot Jupiters. Therefore, they need to be observed over a ...

12

This is a fairly loaded question in that it depends heavily on what a "hot Jupiter" actually is defined to be. What is "hot"? What is a "Jupiter"? In reality, there's a continuum of planetary masses and distances from their parent star, and in the literature you'll commonly see references to "hot Neptunes", "hot Saturns," etc. The predominant theory as to ...

7

In 2011, about 20% of the exoplanets found were hot Jupiters. That is a lot, but it is strongly biased simply because there are the easiest planets to detect. You can detect exoplanets by transit (that means that the planet passes in front of its host star which decreases the luminosity of the observed star during the transit), hot Jupiters being closer to ...

7

Stars turn into Red Giants not because they're running out of fuel, but because they're accumulating material they can't use for fusion (yet) in the core. The star isn't so much dying of starvation as it is wallowing in its own muck. Red giants form when the fusion is no longer taking place in the centre of the star, but instead in a shell around the centre....

6

An explanation could be provided by irradiation and evaporation of planetary envelopes. The introduction in the article by Bourrier et al. 2018, which is the source of the NASA press release, explains that as exoplanets migrate inwards, they are increasingly challenged to hang on to their envelopes due to irradiation and heating (insolation) by their star. ...

4

The short answer is pela's comment: more mass equals shorter life. For a bit of a longer explanation... The only way the life of the star could be prolonged is if the new material can be transported to the core. This requires convection. Most stars are not fully convective, having distinct layers of either convective or radiative zones. The net effect of ...

4

I found one "hot Jupiter" in the Kepler data (Kepler 45b). The star is a M dwarf with an effective temperature of 3820K. The planet has an estimated mass of 160.5 M(Earth) and radius of 10.76 R(Earth). This gives a density of about 0.8 g/cm2 which is consistent. The planet is located at approximately 0.03 AU from the star with an orbital eccentricity of 0.11....

4

Metallic hydrogen is an odd substance. When you push hydrogen atoms very close together, their electrons can come free, and move around, instead of being tightly bound to the atomic nuclei. As this form of hydrogen would conduct electricity, it behaves like a metal. At least this is the theory. Nobody has been able to produce enough pressure to actually make ...

4

In the case of WASP-12b, at least, the close proximity to the star has actually deformed the planet so much that it is overflowing its Roche-lobe, the area around a planet or star that . We can show this mathematically by finding the approximate Roche-lobe of the planet using: $\frac{r_1}{A}=.46224\sqrt[3]{\frac{M_1}{M_1+M_2}}$ for $\frac{M_1}{M_2}<.8$ (...

4

The answer to the question depends on the exact definition of planet that is used. A possible example is the L dwarf 2M 0746+20 (2MASS J07464256+2000321) and its planet 2M 0746+20 b. The radius of the planet is 12% greater than the radius of the star. \begin{array}{lll} \hline \text{} & \text{Mass} & \text{Radius}\\ \hline \text{Planet} & 12....

3

It's not proof that they've ejected other inner planets, because there are plenty of other explanations for why we haven't observed companions. Steffen et al. (2012) analyzed Kepler data - likely some of the same examples you've looked at - and came up with several explanations besides the no-companions-because-of-planet-planet scattering hypothesis: Inner ...

3

Neither of these, interestingly enough, is the first time iron has been detected in an exoplanetary atmosphere. Other groups (Hoeijmakers et al. 2018, cited by both papers) have detected absorption lines of iron and other metals in the day-night transition zone of exoplanets, during transit. Ehrenreich et al. 2020, the new ESO paper, did something similar. ...

3

Beyond red dwarfs, another possibility is that of a planet orbiting a type B subdwarf star. Some features of such stars: Composed almost entirely of helium Thought to be formed through the merger of two white dwarfs or at a specific point in the evolution of some red giants Temperatures range from 20,000 K to 40,000 K Brightness is between 10 - 100 times ...

2

I think we can broadly distinguish two classes of effects here: Flares directly affecting the planet The by-products of the flare affecting the planet I can loosely tell you what I know (although my knowledge here is far from being complete) Direct effects include: Magnetic field geometries: Far-away from their host star (>0.05AU) planets usually have ...

2

I completely agree with the answer from MBR. The number is actually $1.20\pm 0.38$ per cent, is published by Wright et al. (2012) and is the fraction of F, G, K stars that have a hot Jupiter defined as being larger than 0.1 Jupiter masses and having an orbital period less than 10 days. Table 2 of that paper summarises results from other workers, who obtain ...

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Sun is more than one thousand times the mass of Jupiter, so it seems unlikely that even a very close approach by a "hot Jupiter" to its host star would cause a flare, and especially not a superflare.

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Just going off the Wikipedia article you posted, it says the hot jupiter superflare theory was abandoned. The flares were initially explained by postulating giant planets in very close orbits, such that the magnetic fields of the star and planet were linked. The orbit of the planet would warp the field lines until the instability released magnetic ...

1

Giant planets like Jupiter form through accretion in the outer part of the disk, beyond the frost line where the material is cool enough for volatile icy compounds to remain solid. These planets cannot form closer to their host star, since there is there is not enough matter in the protoplanetary disk at smaller radii. Due to interactions with other ...

1

The primary effects wouldn't be the things you ask about. First, an object the size of Jupiter would change the day and night sky drastically. The sky now is basically, Sun, Moon and a bunch of yellow dots (and one reddish dot) mostly fixed, 4 move around visibly to the naked eye (Venus, Mars, Jupiter, Saturn). Venus stands out a little as larger ...

1

Just for fun I did a limited analysis of Jupiter size planets found using radial velocity or astrometry (mostly the former) techniques with the following criteria: 1) Data from the on-line sources http://exoplanet.eu/catalog/bd%2B15_2375_b/ and http://www.exoplanets.org/ giving planets discovered through Apr. 2016. 2) Msini: 0.5-10 M(J) 3) Distance to star ...

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