How can Jupiter-like planets exist closer to their sun than Mercury does to ours? How can the gas remain?

Question

I thought the gasses could not survive such proximity.

Answer 1

The Jupiter-like planets that have been discovered around other stars are Jupiter-like in the sense of having a large mass (Jupiter is mush larger than the other planets in our system), not in the sense of being gas giants.

In fact, you are right. Most of the gasses would have boiled away on these planets and they are probably rocky. If they are *very* large, the gasses may still be around because the gravity would be enough to keep them, but for most the temperature means the gas molecules will have more than the escape velocity.

Answer 2

If a gas giant like Jupiter is close to its star, then the gasses in the outer part of that planet are likely being evaporated. This takes some time, however, perhaps a billion years, more or less. That indicates that these systems are not too old, and that they will evolve significantly over the next few billion years.

It seems likely that in those systems, the gas giant migrated inwards from an orbit like that of Jupiter (10 to 20 astronomical units) to the orbit we see today (less than 0.1 astronomical units). The reason for the migration is interaction between the planet and the material in the protoplanetary disk. This effect may come to an end or slow down once the gas giant gets close to the star, because there is little gas remaining in the disk, so that the planet gets close to the star but doesn't actually fall into it.

This is all a topic of current research, and the answers are not at all certain. One interesting question: back when the solar system was forming, 5 billion years ago, why didn't Jupiter migrate inwards, destroying the Earth?

Answer 3

Most astronomers were surprised at discovering that some of the large exoplanets they have found were "Hot Jupiters" unexpectedly orbiting at less than 1 AU from their stars,

It is thought that perhaps they are not gas giants as we know them, therefore, The prevalent theory is that they are formed at greater distances from their suns than this but migrate inwards over time.

However that theory is having to be rethought as a result of he discovery of a system with 3 stars, and a planet known as HD 188753 Ab. In July, 2005, astronomers announced the discovery of a planet in a relatively tight triple star system, a finding that challenges current theories of planetary formation.

The planet, a gas giant slightly larger than Jupiter, orbits the main star of the HD 188753 system, in the constellation Cygnus, and is hence known as HD 188753 Ab. The stellar trio (yellow, orange, and red) is about 149 light years away.

The planet orbits the main star (HD 188753 A) about once every 3.3 days, at a distance of about a twentieth the distance between Earth and the Sun. The other two stars whirl tightly around each other in 156 days, and circle the main star every 25.7 years at a distance from the main star that would put them between Saturn and Uranus in our own Solar system.

The latter stars call into question the leading hot Jupiter formation theory, which holds that these planets form at "normal" distances and then migrate inward through some debatable mechanism. Such migration could not have occurred here, since the outer star pair would have disrupted outer planet formation.

So there is much we don't know yet and much we are still trying to make sense of. But your question is a good one.

Answer 4

Not sure exactly why you think "gasses" or a gaseuos planet would not survive close to the sun?

The sun is made of gas... and it's in close proximity to it's self. Binary stars are in "close" proximity and they survive. Gas is a state of matter; add enough energy to any element and it will become a gas, conversely removing energy from gasses will produce liquids and solids.

If you're thinking that the gasses would burn up:
Not all gases "burn" and in order to burn they need the presence of oxygen to do so.

Answer 5

Earthlike planets covered with deep oceans that could harbor life may be found in as many as a third of solar systems discovered outside of our own.

These solar systems feature gas giants known as "Hot Jupiters," which orbit extremely close to their parent stars -- even closer than Mercury to our sun.

The close-orbiting gassy planets may help encourage the formations of smaller, rocky, Earthlike planets.

The team from Colorado, Penn State University and NASA's Goddard Space Flight Center Maryland ran computer simulations of various types of solar systems forming.

The gas giants may help rocky planets form close to the suns, and may help pull in icy bodies that deliver water to the young planets.

As many as 40 % of the 200 or so known planets around other stars are Hot Jupiters.

Answer 6

Depends on the size of the sun it's orbiting. T

he planets that are being discovered 'seem' to have these extremely close periods... I tend to agree that it's odd that something so BIG could orbit so quick.

Answer 7

I suspect the gravity of a planet the size of jupiter would retain most of its gas. Mercury doesn't have enough gravity to retain its atmosphere.

Answer 8

Both have a common sun. Gravity is the answer