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On the anatomy of extrasolar planets

The 18 planets that were discovered (up to the date of this article) around other Saturn stars cause a rethinking regarding the process of the formation of the planets

Avi Blizovsky

Discoveries of planets around other stars turned astronomers into pleasure seekers. It's not that they eat every day with festive cutlery, drink champagne or dress elegantly for candlelit meals all long nights under the dome of the observatory; They're still eating the same miserable sandwiches and gobbling up the snack bags, thank you very much. But today their taste moves more in the direction of the cosmic musings of the founder of heretical philosophy.
Epicurus, a Greek philosopher who lived in the fourth century BC, did not exactly predict the existence of planets around stars other than the sun, but he believed in the infinity of worlds, that is, in the existence of systems organized according to order and method that lie beyond the visible universe, as it was then perceived. This approach clashed with the earth-centered cosmos approach of his contemporary Aristotle, whose cosmology dominated Western thinking for over 2000 years.
Only in the last three decades have astronomers verified the existence of the heretical speculations regarding the multiplicity of worlds, a concept that in recent centuries has taken on the meaning of the existence of planets beyond the boundary of the solar system, some of which may even be inhabited. But while astronomers take their hats off to Epicurus, they would like him to give them advice on understanding the distant planets they spot in their telescopes.
Discovering something is not the same as understanding what has been discovered. The more astronomers study the body of evidence that is accumulating on the subject of the existence of planets outside the solar system, the less they resemble the only planetary system they knew and based their theories on: the solar family of planets.
At last count it appears that astronomers from the United States and Europe have spotted 18 sun-like stars whose oscillations seem to be affected by the gravitational pull of the invisible planets orbiting around them, and they certainly expect to find more. But they suspect they've seen enough to start re-engineering the way nature creates and destroys planets, planning their minuet dances.
Nine of these planets are closer to their parent stars than Mercury (Hema's planet) is to the Sun, closer than standard theory predicts as the reasonable distance between planets and their Sun, one of them is so close that it completes a perfect revolution _ a full year _ Every 3.1 Earth days. The other nine move in a strange elliptical, or oval, orbit, with some of them dipping very close to their sun and then receding to a great distance. The orbits in our solar system are almost circular. Some of the planets outside the solar system have a mass almost three times greater than that of Jupiter, the largest planet in the solar system, and one is estimated to have a mass 11 times greater than itself _ which causes the question of what is the maximum possible mass of the planets to be raised.
Dr. Jeffrey W. Marcy, the astronomer at the University of San Francisco who had a hand in most of the discoveries, was as surprised as anyone. "From these revelations emerges a trend that we honestly thought would not survive," he said.
But she survived, and the questions keep piling up. Many stars have planets, as the discoveries suggest, but is there a typical pattern? Is it possible that the solar system is the exception? If so, does this decrease the chances of intelligent life elsewhere in the universe?
Dr. Alan F. Boss, a planetary systems theorist at the Carnegie Institution in Washington, thinks that eventually astronomers "will find systems similar to our solar system." He admits that they may also "find more surprises that will make us rethink what we are doing."
The astronomers admit that so far their sample of exoplanets may not be representative, but only a reflection of their detection ability. They have no proof of the existence of another Sun-like star with more than one planet orbiting it, or another much smaller than Jupiter. But it is easier to understand the effects of the gravitational force of the planets of the type of Jupiter, in particular those very close to the stars around which they move. It takes years of repeated observations to gather reliable evidence of the planets moving in the longer orbits and greater distances from the star. And it is still not possible to discern any orbit, near or far, of a planet similar in size to Earth or even Saturn.
The latest discovery, announced last month, was about the smallest planet discovered outside the solar system, with a mass less than half that of Jupiter and only 1.4 times that of Saturn. The planet, moving in a tight orbit of 3.5 days around the star, HD 75289, was discovered by a team of Swiss astronomers headed by Dr. Michael Muir of the Geneva Observatory, who reported in October 1995 on the proven discovery of the first planet discovered orbiting another sun-like star.
In the next decade, NASA hopes to fly several space telescopes to conduct a more comprehensive scan of the holiday planets around stars relatively close to the solar system. On the drawing board is an advanced satellite called the Planet Finder that will one day be able to send back the first images of Earth-like planets outside the solar system.
"Right now this is a very exciting field," said Dr. Steven Lobo, an astrophysicist at the Space Telescope Science Institute in Baltimore. The discoveries in Prosh have opened a new window for understanding the nature of the planets in the universe.
The first discoveries of planets outside the solar system should have prepared astronomers to expect the unexpected. In 1992, radio astronomers reported the first strong evidence for the existence of these objects, but these two planets did not orbit a normal star. They accompanied a pulsar (a star that emits electromagnetic radiation at regular intervals), the dense remains of an exploded star, a region where life is unlikely to exist.
Dr. Muir and Dr. Didier Clouse from Switzerland, located a planet near 51 Pegasi, a star very similar to the Sun, something that was first confirmed by Dr. Marcy and his colleague, Dr. R. Paul Butler. The first confirmation of the existence of a planet moving around another star surprised astronomers. Both teams were surprised to find that the planet, which has a small mass of half that of the planet Jupiter, moves in a circular orbit less than one-sixth the equivalent distance between Jupiter and the Sun.
Since then, theorists have wrestled with the question of how some of the larger planets -- dubbed "hot Jupiters" due to their proximity to the intense heat of their stars -- managed to be where they are. Why were they not at the same distance as that existing between the planet Jupiter and the Sun? Since the known laws of physics exclude the possibility of the formation of large planets in such close proximity to the star, the theorists think that they were formed in the more pleasant and distant atmosphere and migrated inward. The unlucky planets apparently smashed into their stars. The others somehow settled into convenient orbits less than a quarter of an astronomical unit, the standard measure of distance in outer space where one distance unit is equal to the distance from the Sun to Earth, or 150 million km.
The migration theory that received the most attention was presented by Dr. Douglas Lin from the University of California at Santa Cruz, Dr. Peter Bodenheimer from the University of Santa Barbara campus and Dr. Derek Richardson from the University of Washington. Dr. William Ward of the Southeast Research Institute in Boulder, Colorado, conducted research based on this idea, and developed theories that explain the mutual influence that exists between the rings and the satellites surrounding the planet Saturn.
According to the prevailing theory, a system of planets forms from a disk of gas, dust and rocks surrounding a newborn star. The heat of the star will drive the gas away from the interior of the disk and prevent the formation of gaseous planets. These planets will develop in the outer part of the gas-rich disk.
During the formation of the planets the disk is full of gas and dust. The young star pulls inward into the disc material and this may pull many of the large planets out of their original orbits. Astrophysicists assume that there are phenomena that prevent at least some of the planets from crashing into their stars. One is that when the star was young it rotated at a greater speed, which created tidal forces that halt the star's migration towards a guaranteed holocaust. Another idea, suggested by observing young stars, is based on the possibility that the gravitational or magnetic forces of newly formed stars remove all the remaining material from the disk in their immediate vicinity, leaving a hole in the center like the one in yours. Here the transiting planets settle in their final orbits.
Dr. Lin, who wondered why something like this did not happen to the planet Jupiter, decided that the early "Jupiters" in the solar system probably wandered until they smashed into the sun. Jupiter, and the planets that exist in our solar system represent the last generation, formed when the planetary disk dispersed and left behind more stable conditions. Or the preplanetary disk may not have had enough gas and dust to disturb the orbits of the new planets.
A more recent modification of the migration theory was presented by a team of theorists from the University of Toronto headed by Dr. Norman Murray. During their early evolution, they argue, the planets may have moved through a disk of small rocky objects that collided with or were ejected from the planets.
One of the first bodies noticed by the team was Marcy Butler, reported in January 1996, causing further confusion. The mass of the planet discovered as a holiday around _ 70 Virginis was more than seven times that of the planet Jupiter and it was also not as close to its star as the others, but its orbit was also very elliptical. Discoveries of other planets have revealed similar characteristics. The planet orbiting 16 Cygni B had the most elliptical orbit. If it were in the solar system it would approach until the distance equal to that between Venus and the sun and then it would move away to the asteroid belt between Mars and Jupiter.
Some of the strongest gravitational forces say astrophysicists must have disturbed the orbits of the planets. A planet coming too close to the same system may throw the planets out of their circular orbits.
Another possibility is that the parent star of that planet is itself part of a system of double stars (a pair of stars moving in a gravitational embrace) where the companion star may change the orbits of the planets.
Dr. Frederick A. Rasio from MIT in Massachusetts, together with Dr. Eric Ford, came up with an idea of ​​gravitational dispersion that naturally and simply explains the existence of planets with elliptical orbits. According to their approach, the idea involves two or more giant planets that are very close to each other so that they form a kind of gravitational slingshot. The forces may knock one of those planets out of the common orbit into the inner solar system while the other may fly to the edges of the solar system and possibly even escape into interstellar space.
Such a script may also explain why astronomers have so far not found more than one planet orbiting a single star. Any other large star that might have been there was blown into a deeper, farther orbit and was undetectable in the short time that astronomers searched for evidence of planets moving around other glasses.
Furthermore, just one planet moving in an elliptical orbit would herald a holocaust for the smaller planets repeatedly bumping into its path, knocking them out of their orbits or destroying them with its massive gravitational forces.
"If our planet Jupiter were moving in an elliptical orbit, Earth and Mars would probably be pushed out of the solar system," said Dr. Marcy. "Hence, our existence depends on both the planet Jupiter and the Earth remaining in stable and circular orbits."
The implications are profound for the search for life on extraterrestrial planets. "The giant thugs cleaned out the terrestrial planets from those solar systems and left them with no possible equivalent to Earth," said Dr Marcy.
However, Dr. Marcy takes a more optimistic approach. Of all the sun-like stars examined so far for the purpose of searching for planets. Only five percent were found to have Jupiter-like stars moving in elliptical orbits. This leaves 95% of the systems free from the forces of destruction and may serve as safe havens for life-bearing planets.
All theories explaining those planets that have just been discovered around other stars, said Dr. Rasio, remain at an initial stage only. The theorists suffer from a paucity of observations and it is still necessary to locate more than one planet moving around sun-like planets. The two or three objects moving around the pulsar that were discovered together gave the smallest glimpse. Previous reports of possible discoveries of two planets around Lalande 21185 have not yet been confirmed.
"If you only see one companion around a star, you can't say it's a solar system," said Dr. Rasio. "This will be the big breakthrough coming, finding a large number of planets and then placing certain limits on the properties and behavior of other solar systems. This is our holy grail."
Planet hunters such as Dr. Marcy continue to search. They talk about a number of interesting hints, but nothing that would be cause for celebration for the new Epicians.

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