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They are small, scorching hot, and reside in a pretty odd solar system.

Earlier today, NASA announced the discovery of two Earth-sized planets – a first for the Kepler mission. The planets are part of the Kepler 20 system, which also includes three larger planets.

This artist's conception illustrates Kepler-20e. Image credit: NASA/Ames/JPL-Caltech

The newly discovered planets – dubbed Kepler-20e and Kepler-20f – orbit extremely close to its star, making it almost impossible for life as we know to survive. A planet must be within the “habitable zone” for it to have a chance at harboring life, scientists say. If a planet is too close to its star, water evaporates. If its too far, water freezes. That’s why the “habitable zone” is often called the “Goldilocks zone.” Life only forms when things are just right.

This artist's conception illustrates Kepler-20f. Image credit: NASA/Ames/JPL-Caltech

But, that information is based on what we know about our solar system and our way of life. For all we know, planets could harbor some sort of life – microbial or intelligent – and not be located in the “habitable zone.” Perhaps, life doesn’t necessarily need water. Who really knows?

You see, scientists are learning more and more about peculiar planets and systems that don’t necessarily make sense. This discovery, for example, shows a very different kind of solar system when compared to ours.

According to NASA:

The system has an unexpected arrangement. In our solar system, small, rocky worlds orbit close to the sun and large, gaseous worlds orbit farther out. In comparison, the planets of Kepler-20 are organized in alternating size: large, small, large, small and large.

“The Kepler data are showing us some planetary systems have arrangements of planets very different from that seen in our solar system,” said Jack Lissauer, planetary scientist and Kepler science team member at NASA’s Ames Research Center in Moffett Field, Calif. “The analysis of Kepler data continue to reveal new insights about the diversity of planets and planetary systems within our galaxy.”

Scientists think that these planets were once further away from the sun, but “migrated” inward. Hmm, they got an answer for everything, right? Is it really impossible for large, gaseous planets to form close to its sun? That would change everything we know about planet formation. More on that later.

Let’s get back to the point: This discovery is huge, according to scientists. It shows that Kepler can detect smaller, Earth-sized planets.

This chart compares artist's concept images of the first Earth-size planets found around a sun-like star to planets in our own solar system, Earth and Venus. Image credit: NASA/Ames/JPL-Caltech

So far, Kepler has confirmed 33 planets and has found more than 2,300 planetary candidates.

Earlier this month, NASA announced the discovery of Kepler 22-b, a planet believed to be habitable. Read more about that discovery, and its controversy, here.

In other exoplanet news, scientists discovered a massive gas giant orbiting a “rapidly pulsating” star called NY Vir. There is, perhaps, another planet on the system, according to the abstract.

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