How to Build a Planet

Even in time to receive more and more information about planetary bodies in the galaxy's departments, Govert Schilling, an astronomy writer, offers us a "recipe" of the living planet.
The planets in our solar system seem to be a good group. They move in the same plane and orbit the Sun in the same direction. In the mid-18th century, German philosopher Immanuel Kant first drew a logical conclusion: the planets must have formed into a disk of spinning matter that surrounds the newborn Sun.
Astronomers today know that such "protoplanetary discs" are common. In addition, hundreds of exoplanets - those we could see and analyze elsewhere than in the solar system - have helped to better understand how they are formed. But what have I learned so far about the genesis of a planet? And how easy would it be to build a living world outside the Earth?

Condensate a cloud
Before the planets, you have to form a sun. And that's easy, because gravity does practically all the work. Take a large portion of cosmic molecular gas and season with sterile dust. No matter the composition of the dust. Let nature have a headache. The cloud is compressed by its own gravity, generating small clumps of matter, such as dusty gems that gather under the furniture. Keeping the kinetic momentum (or the angular impulse - the skaters that turn faster when they retract their arms in a pirouette) and centrifugal forces (like pizza dough that stretches evenly and thin when it's spinning) turns all mini-clouds into flat, rotating discs, around the birth star. And, ready, we have the protoplanetary disc!

Protect delicate disks

Young protoplaner discs are very vulnerable. If you want them to form planets, you must avoid their possible disintegration. According to recent observations made with infrared telescopes, this can easily happen in crowded stellar nurseries, such as the Molecular Orion Cloud. The massive newborn stars emit massive amounts of ultraviolet light and generate fierce solar winds. The winds in question can cut large holes in that cloud, eroding everything in their way, including the protoplanetary discs around the smaller stars. In fact, these discs are not a great thing, containing on average only a percentage of their astronomical mass. So you have to keep them from cosmic action. A quiet environment would be ideal.

Watch out for binary stars!

Binary stars are being killed by planets. Yes, NASA's Kepler Telescope has recently discovered "Tatooine Planets," with two stars in the sky, as the world Luke Skywalker grew up in the Star Wars War cinema. But computerized simulations show us that although binary systems are very, very common in the Milky Way, such "circumnavigation" planets are rather rare. "Star pairs can truncate protoplanetary discs through gravitational perturbations," says Dimitar Sasselov, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
In other words, star pairs pose many problems. Single stars are better parents.

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Supplement with solids
To initiate planetary formation, your disk must also contain solid particles that can clump - either microscopic fragments of silicon dust and a bit of iron or minicristale frozen by molecules such as water, methane or ammonia. The more the content of the disc is richer in heavier elements than hydrogen and helium, the larger the planets can grow. Near the star, the particles accumulate in dust, pebbles, boulders, asteroids and solid planets. At longer distances, the frozen particles gather in comets and eventually into planetary nuclei that attract most of the gas from the initial disk, becoming giants like Jupiter. Mix and wait.

Grab the dust
The millimeter particles are slowed by the gas in the disk and tend to move inwardly. If you want them to gather in bigger pieces, you need "traps" to catch them. Observations made with the ALMA telescope have revealed the existence of such traps in a 15-million-year-old star disc, probably due to gas density differentials.

Caring for moves
            Even giant planets can migrate to the inside of the system as a result of interacting with the remains of the disk. Such cases end up with "Hot Jupiter", driving around the mother's stomach to just a few million miles. Could a smaller and stronger planet survive the passing of such a colossus? Probably not, admits the same Sasselov. "But migration can take millions of years. Solid planets can aggregate from the remaining disk after passing gaseous giants, "he adds.
Moreover, says the astrophysicist, hot giants are very, very rare. On the other hand there is also group planetary migration, which leads to the formation of small, compact multiplanar systems such as those that orbiting Kelpler-II and Gliese 667C.

Check the dough
If you've managed to "cook" a planet of Earth size, check if it's what you wanted. It may well be that instead of a dense planet with a nickel and iron core, a mini-Neptune fluid has been obtained - and yet one with the hydrogen fused by moving closer to the mother-star. For terrestrial worlds, astronomers do not yet know the proportion of dense planets / low density planets. To get an estimate as accurate as we should be able to measure the masses of the planets, something extremely difficult and relatively small astronomical distances. "But the number of small planets, especially those around red dwarfs, is much higher than we anticipated," Sasselov says. "Even though much of them would prove to be low-density worlds, the number of planets similar to Earth must be huge."

Keep warm
With luck, your world is staring in the "Goldilocks" area of ​​the star, that is, in that area where the surface planetary temperature is only good to allow the existence of liquid water. The red dwarf stars - very rich in planets - this comfort zone is closer to the center of the system than to hot stars such as our Sun. And if you managed to grow here a planet, then the gases released by the rocks will form an atmosphere, and the water will flow to the surface. What remains to be done is to relax and wait for the sky to make it, probably on board asteroids and comets, complex organic molecules that eventually lead to the appearance of life. And if your planet orbits your mother-star beyond the living area, do not panic. In just a few billions of years, the star will grow in diameter and unfold it.

Surviving planetary hunting
The relatively short history of planetary hunters has provided us with a lot of news and has often made us draw erroneous conclusions about the way new worlds are born. Here are only three discoveries that radically changed what we thought we knew about the genesis of planetary bodies.

Hot giants
            The first discovered extrasolar planets have proven to be very different from those known in the Solar System. They were at least as massive as Jupiter and orbit their mother-stars just a few million miles away. Was that a galactic norm? No, definitely. In fact, hot giants are rare, but because they produce the most significant and visible movements in the star-orbit of the stars, they stand out as painful bubbles. It is believed that there are many more "solid" planets than gaseous giants.

Heavy metals
            A decade ago, it seemed that the stars that had a high proportion of "metals" in their outer layers (the astronomical term for heavier elements than hydrogen and helium) were most likely to "produce" planets. The reasoning was that a metal-rich star also has a planetary metal-rich disk, essential to the formation of the planets. But it turned out that this is the case only in systems containing hot giants. Astronomers now know that the planets can form in discussions where the concentrations of "metals" vary greatly.

Solar systems
Until now, no exoplanetary system has been discovered that sounds like our own Solar System. But that does not mean that we are unique in the Universe. The problem is that systems with large, gaseous planets on the outside and small "solid" planets in the interior are exceptionally hard to find with the tools and technology today. They can exist with the billions, waiting for the creation of new space telescopes or human exploration technologies.

There are planets of all shapes and sizes - and these variables have major implications on their chances of hosting life.

The Fire Globe - Kepler-10B
Announced in January 2011, the extra-solar planet Kepler-10B is the first planetary body discovered by NASA's Kepler Telescope. It is only 40% larger than Terra, and astronomers have estimated it has a high density mineral composition - rocks and metals. But it is only 2.5 million kilometers from the mother-star, which means that its surface is a hell surface, covered by molten lava oceans and temperatures of 1,550 degrees Celsius.

Water World - GJ 1214B
GJ 1214B is an exoplanet almost three times as Earth in diameter but with a low net density. Its total average density was estimated at 2g / cm of cube, which may mean a world of water, a relatively small solid nucleus, and a global cloak of water plus a dense and hot atmosphere. Even though the surface temperature of the planetary ocean is somewhat elevated - about 200 degrees Celsius, this "mini-Neptune" could accommodate simple water life forms.

A hot Jupiter - HD 189733B
The HD 189733B Exoplanet is a "hot Jupiter" and orbits a shiny star in just 2.2 days. It is also one of the promising extrasolar planets studied so far: its atmosphere has been detected by water vapor, oxygen, methane and carbon monoxide. Recent Hubble observations have revealed that the planet has a blue-azure color due to the silicate particles in the atmosphere. The proximity to the harsh rays of the mother-star determines the relatively rapid evaporation of this planet, which in each second loses approximately 10,000 tons of space in space.

The wounded wound - PSR B1257 + 12A
PSR B1257 + 12A is a bizarre animal. It is one of three planets orbiting a pulsar - the small and very compact corpse of a former giant star, dead as a supernova. This planet has a mass only twice that of our Moon and almost certainly its composition is mineral and dense. The pulsar planets could have formed after the supernova explosion. They are constantly invalidated in the X-rays of the pulsar's high energy, conditions in which no living cell could live, so it is unlikely that they will host life in some form known to us. >>

Article taken from Science World, November-December 2013, Number 15

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