Cómo funcionan los planetas nómadas

Piensa en cada película espacial que hayas visto y nombra la peor forma imaginable de que un personaje haya sido asesinado (y trata de olvidarte del bebé alienígena que sale del pecho de ese tipo ). ¿Entiendo? ESTÁ BIEN. La segunda peor manera de morir en el espacio seguramente debe ser alejarse flotando de la nave nodriza, simplemente estando solo, sin control sobre la dirección o el destino (aunque sería una muerte muy rápida).

Ahora imagine que puede haber millones de planetas desconectados de la nave nodriza en la vida real. Se llaman planetas nómadas (también conocidos como planetas flotantes , interestelares o huérfanos ), y los astrónomos y fanáticos de la ciencia ficción han estado reflexionando sobre su existencia desde hace un tiempo.

Estos planetas, que existen en el inframundo entre los sistemas solares, pueden surgir después de ser expulsados ​​de sus órbitas, o pueden formarse después del colapso de una nube interestelar. En cualquier caso, terminan vagando por la Vía Láctea . ¿Podría la Tierra obtener la patada también? ¿Podría un planeta rebelde chocar contra nuestro sistema solar? El descubrimiento de los planetas nómadas nos ha obligado a reexaminar algunos conceptos muy básicos, que van desde cómo se forman los planetas hasta cómo mantienen su lugar en órbita.

Al mismo tiempo, estos vagabundos nos han hecho darnos cuenta de que no estamos tan solos como creíamos a nivel planetario. De hecho, podríamos tener mucha más compañía de la que proporcionan los exoplanetas. Sí, los planetas nómadas pueden contarse en cuatrillones, según una estimación del Dr. Louis Strigari, astrofísico del Instituto Kavli de Astrofísica y Cosmología de Partículas.

Dado que este es un concepto tan nuevo, la comunidad científica todavía está trabajando arduamente para confirmar la existencia de planetas que no están vinculados a una estrella. En este artículo, exploraremos cómo se hacen los planetas nómadas, cómo pueden volverse rebeldes, hacia dónde se dirigen y, finalmente, si podrían sustentar la vida.

Todavía hay mucho que no sabemos sobre los planetas nómadas, pero eso es parte de lo que los hace tan emocionantes.

1. Primero, las cosas aterradoras sobre los planetas nómadas
2. ¿De dónde vienen los planetas nómadas?
3. ¿Cómo podrían ser las condiciones en un planeta nómada?
4. ¿Podría existir vida en los planetas nómadas?

Gran parte del mundo se enteró por primera vez de los planetas nómadas a mediados de 2011, cortesía de un estudio escrito por Takahiro Sumi, astrofísico de la Universidad de Osaka en Japón. El equipo de Sumi se basó en la microlente gravitacional , que es la misma técnica utilizada para descubrir exoplanetas en toda la galaxia. La técnica se basa en la luz de una fuente de fondo, como una estrella , que se distorsiona cuando un objeto pasa entre la estrella de fondo y la Tierra; de hecho, esa luz se magnifica temporalmente. Sumi y sus colegas detectaron 10 planetas con una masa aproximadamente del tamaño de Júpiter que no parecían seguir una órbita reconocible [fuente: Sumi ]. La noticia iluminó las paredes de Facebook y Twitter de los adictos al espacio más rápido que un anuncio de la película "Próxima generación".

Como dijimos, la teoría es que estos meandros crónicos pueden desarrollarse a partir de las mismas nubes de gas y polvo de las que nacen las estrellas o los sistemas solares pueden expulsarlas de la órbita. En una nota relacionada, los sistemas solares podrían atraer y atrapar planetas nómadas cercanos en órbitas amplias. Es muy posible que, en algún momento, nuestro sistema solar tuviera más planetas de los que conocemos actualmente. Quizás arrojar algunos planetas extraños es lo que hizo posible que la Tierra encontrara su posición de Ricitos de Oro en relación con nuestro sol.

En cuanto al temor de que la Tierra pueda chocar con un planeta rebelde, sí, existe una pequeña posibilidad de que suceda, pero nuestra galaxia está repleta de amenazas más pequeñas, más comunes e igualmente letales (traducción: asteroides ) de las que preocuparse. Nuestras posibilidades de ser eliminados por un cometa o un asteroide de unas pocas millas de ancho son mucho mayores, aunque aún son relativamente escasas en el gran esquema de las cosas [fuente: Mosher ].

El estudio original de Sumi estimó que podría haber dos o tres planetas nómadas por cada estrella de nuestra galaxia. Otro estudio, menos de un año después, realizado por el Instituto Kavli de Stanford, aumentó la estimación y dijo que podría haber hasta 100.000 planetas nómadas por cada estrella de la Vía Láctea.

La palabra clave en esa última oración es "could". La estimación de Kavli se determinó teniendo en cuenta cosas como las siguientes [fuente: Freeberg ]:

Si es correcta, esa teoría cuestiona cómo se forman los planetas y qué papel tienen los planetas nómadas en nuestra galaxia. Por ahora, trabajemos en lo que sabemos y exploremos las posibilidades de lo que podría ser.

Let's get some background on what could prove to be very common planets. So far, much of what scientists have assumed about nomad planets is derived from what we've already learned from studying our own solar system and younger solar systems in our galaxy.

As far as we know, they can range in a variety of sizes and makeups. Remember, the first nomad planets to appear in Sumi's findings were Jupiter-class planets. So it's not unreasonable to assume that smaller planets with less mass could go rogue, too. In fact, the smaller ones may be better candidates for being pushed out of a young planetary system; the larger ones may be "born" rogue; that is, arise from star-forming clusters.

The idea behind ejection is that nomad planets are subject to gravitational pulls from a variety of sources, ranging from other stars to nearby planets. To give an example of how this might work, scientists have observed Jupiter-sized planets in other solar systems that maintain orbits very close to their sun (think Mercury or Venus close). Now imagine if our own Jupiter started slowly shortening its orbit and moving closer to the sun. Its mass is more than 300 times greater than Earth's, giving it a substantial gravitational field.

As a planet the size of Jupiter moves inward, it would disrupt the path of many planets, moons and dwarf planets in its vicinity by drawing smaller planets toward it. The on-and-off tug of a passing large planet could pull smaller planets out of their orbital paths. As their orbits changed, they could get slung from the solar system and into the void. It's a lot like how we use the gravitational pulls of planets and moons to slingshot satellites farther out into space, only this time we're talking about a planet, rather than a spacecraft, being given a gravity assist. That's just one example of how a planet can get thrown off course.

Another proposal holds that a planet could be ejected from its solar system if its star turns into a supernova . Of course, some planets would be destroyed in the violent explosion, but those orbiting farther out would get pushed outward into space, untethered to a home star.

Once outside of a solar system, a nomad planet can fall under a variety of gravitational influences. Computer models have shown that if a planet is tossed out early in a star cluster's life, that planet is more likely to be drawn into a wide, loose orbit around another neighboring star. The bigger the star, the more likely it is to recapture a nomad planet. Computer models also show that it's highly possible for nomad planets to be captured by the gravitational pull of black holes [source: Perets].

Other possibilities include planets traveling within the larger orbit of the Milky Way galaxy. This means that they are still on the galactic dance floor and moving with the crowd, but they just aren't traveling within a group. And finally, it's completely possible that two nomad planets could meet and form their own binary system -- just a couple of lonely planets romantically twirling around each other in the emptiness of space. Suddenly nomad planets sound a lot less menacing, right?

We won't know for sure until we get to study a nomad planet, but there are some basic assumptions to be made based on what we already know from observing planets, dwarf planets and moons within our own solar system and beyond. So let's explore some of the possible attributes of nomad planets.

Could they have day and night? No. As we already know, our daylight is generated by our position in relation to the sun. Without that nearby sun, there is no daylight as we know it. That being said, you can presumably cross photosynthesis off the list, too.

Could they have an atmosphere? Yes, it's entirely possible for a nomad planet to have an atmosphere. In order to maintain an atmosphere, planets must have sufficient gravity to hold onto the gasses and temperatures low enough that gasses aren't broken down and allowed to escape into space. As you look toward the outer reaches of our solar system, even tiny Pluto maintains a hold on its atmosphere. So yes, a nomad planet could maintain an atmosphere, but that's not to say it would be breathable by Earth's standards.

What climate could they have? Let's just say you'll probably want to bring a heavy jacket if you're visiting the surface of most nomad planets. Most of Earth's surface temperatures are dictated by sunlight. Without that sun, things will get pretty chilly pretty quick. But that's not to say every nomad planet will be an infertile chunk of icy death. Most of the Earth's subterranean temperatures come from the forces of radioactivity, friction and pressure working at the planet's center. While their surfaces might be cold, some nomad planets could generate warmer, life-sustaining temperatures toward their centers, given enough mass. If they have a thick enough atmosphere, they even stand a chance of having some warmth at their surfaces [source: Freeberg].

Could they have water? It's a possibility that water -- or more likely ice -- could exist on some nomad planets. Using unmanned robots and satellites, scientists have detected ice on Mars and evidence of ancient liquid water there, too. Farther out in the solar system, Europa (one of Jupiter's moons) is believed to have a surface consisting of ice, covering an ocean of water. If we're finding water on other planets and moons in our own solar system, the likelihood of it existing on some nomad is high as well. Multiply that by up to 100,000 nomad planets per star in our galaxy, and the possibilities grow rapidly.

Life ... now that's the game-changing question. Is the interstellar space in our galaxy actually full of life? Possibly. From what we know of other planets, we have to assume that nomad planets will share some similarities. And from what we've discovered so far, we know that most planets couldn't support life as we know it. But the law of averages on a galactic scale says that life can exist. We're living proof of that.

Even Louis Strigari, the leader of the team behind the 100,000 nomad-planet-per-star-estimate, said this to Stanford News: "If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist." In this case, some rare planets could harbor life forms that have adapted to live in the most extreme conditions in our galaxy.

Likewise, some nomad planets might be carrying the remnants -- or building blocks, depending on which way you choose to view it -- of life in their previous solar systems. Given enough random encounters with asteroids and other debris, they could be spreading that material across the galaxy.

Finally, it's entirely plausible that humans could inhabit a nomad planet one day in the future. Proxima Centauri, the closest star to our sun , is a considerable 4.22 light-years away from Earth. Nomad planets could become the space bases of human space travel. Once we break out of our solar system, we could use hospitable nomad planets to island-hop our way across to another star system. Then again, with so many planets out there, we might not even need to go all the way to another star to explore new ones. That big, empty blackness between the sun and the stars is suddenly full of potential -- and questions to be answered.

Author's Note: How Nomad Planets Work

"Wait. What?!" That's response I received from every single person when I said that I was working on an article about nomad planets. This is a subject that elicits equal amounts fear and fascination. And the more I've learned about this very new subject, the more captivated I've become. The possibility of visiting planets just outside of our own solar system is nothing short of captivating.

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