NASA’s Kepler spacecraft has shaken its one-thousandth planet from the sky. Eight new worlds beyond our solar system boost the number of Kepler’s confirmed planets to 1,004 (if you’re keeping count). (National Geographic News)
Teachers, scroll down for a short list of key resources in our Teachers’ Toolkit.
- Kepler, NASA’s amazing mission to search for planets outside our solar system, just found more “Earthlike” planets—bringing the number to about 8 out of 1,004. Astrophysicists think Earthlike planets are rocky and lie in the “habitable zone” of their own planetary systems. (Most of the rest are so-called “hot Jupiters.” Read more about those weird planets here.) What is a “habitable zone”?
- A habitable zone is a region around a star where conditions can support liquid water on the planet’s surface.
- Why is liquid water necessary for a planet to be considered “habitable”? This fantastic essay from the brainiacs at NOVA Online gives some great reasons.
- Why liquid?
- The biochemical reactions that sustain life need a fluid in order to operate. In a liquid, molecules can dissolve and chemical reactions occur. [Liquid also] effectively conveys vital substances . . . from one place to another, whether it’s around a cell, an organism, an ecosystem, or a planet.
- Why water?
- Water is [one of] our only naturally occurring inorganic liquids, the only one not arising from organic growth.
- Water dissolves just about anything.
- Water is the only chemical compound that occurs naturally on Earth’s surface in all three physical states: solid, liquid, and gas. Good thing, otherwise the hydrological cycle that most living things rely on to ferry water from the oceans to the land and back again would not exist.
- Water also has an extremely large liquid range. Pure water freezes at 0°C (32°F) and boils at 100°C (212°F). Add salt and you can lower the freezing temperature. Add pressure and you can raise the boiling temperature. . . [This means that temperatures] can undergo extreme variations—between night and day, say, or between seasons—without water freezing or boiling away.
- Unlike most other liquids when they freeze, water expands and becomes less dense. [Frozen water floats, not sinks.] If it sank, ice, being unable to melt because of the insulating layer of water above it, would slowly fill up lakes and oceans in cold climates, making sea life in those parts of the world a challenging prospect.
- Water plays another key role in the biochemistry of life: bending enzymes. Enzymes are proteins that catalyze chemical reactions, making them occur much faster than they otherwise would. To do their handiwork, enzymes must take on a specific three-dimensional shape. Never mind how, but it is water molecules that facilitate this.
- Take it from rock star astrophysicist Neil deGrasse Tyson: “Given that life on Earth is so dependent on water, and given that water is so prevalent in the universe, we don’t feel that we’re going out on a limb to say that life would require liquid water.”
- Why liquid?
- What are some conditions that may put a planet in the “habitable zone”? Why do astrophysicists nickname these elusive conditions the “Goldilocks zone”?
- Temperature, largely determined by distance from the planet’s parent star, is a key factor in assessing if a planet is in a habitable zone:
- A planet’s atmospheric pressure determines if liquid water can exist there.
- Not too solid—molecules can’t get where they need to go.
- Not too vaporous—molecules can’t stay put at all.
- Atmospheric or geologic conditions may also contribute to the creation of a habitable zone. Two of these conditions are tidal heating—one of my favorite geologic processes!—and radioactive decay. Nat Geo Emerging Explorer Kevin Hand, for instance, thinks that geologic activity may help create a habitable zone on Jupiter’s icy moon Europa. Watch to our favorite astrobiologist in this terrific NG Live! video.
- A “Goldilocks” habitable zone is where conditions are just right for supporting liquid water on the planet’s surface.
- Hydrogen and oxygen (the components of water) are two of the most abundant elements in the universe, and astrophysicists think there may be 40 billion Earthlike planets in the Milky Way, our home galaxy. Why have they only identified eight?
- It’s a great big galaxy, and we are only starting to explore it!
Nat Geo: What is a planet?
NOVA: Life’s Little Essential
(extra credit! NASA: Exoplanet Archive)