ANYONE HOME ISYour guide to exoplanet habitability ? (for life as we know it) STARS

ACTIVITY AGE SIZE AND TYPE Some stars may be good for life, others may just be too extreme. These stellar factors Stars release UV determine where a habitable planet might be found and if life could even survive there light, X-rays, and at all. energetic particles, all of which can be More Active and Longer-lasting Calmer and Shorter-lived harmful to life and strip away a planet’s atmosphere. Old stars expand quickly and can eat planets near to it.

Some stars are more active than others. Planets around small stars must be very Planets around large stars have to be far Young stars are often close to their volatile hosts. Any life could from their star and may not have enough very active. be fried by stellar activity. time to develop life before the star dies. PLANETS

ORBITS Planets in eccentric orbits — PLANET SIZE How and where a planet orbits its star is or those experiencing dramatic The size of a planet plays a large role in how much atmosphere it can hold. very important for its habitability. changes in tilt — could have igh Pressu extreme seasons. H re Stellar winds blow away important elements

Planets which orbit too closely to each L e ig c other can affect the h fa t r Habitable planets are likely found in the Ca Su stability of each n’t Reach the Goldilocks zone, meaning they’re just the other’s orbits and Planets that are too large have Small planets aren’t able to keep right distance from their star for liquid climates. water to exist on the surface. surfaces hidden under thousands stellar winds from blowing away an of miles of atmosphere. atmosphere. MAGNETIC FIELDS COMPOSITION On Earth, magnetic fields are produced by a spinning A planet must include the elements needed for life. molten iron core. Water, especially liquid water, is considered the But too much of them key component for life. could disrupt the planet’s chemistry, climate or plate tectonics.

The field protects the planet’s atmosphere from harmful activity from its star, which could impact Radioactive elements help drive life-supporting processes the habitability for some forms of life. like plate tectonics and magnetic field formation.

ATMOSPHERE

TEMPERATE CLIMATE This means an atmosphere that supplies the To keep oceans of liquid water, a planet right amount of global warming. requires a temperate climate.

O2 H2O O O3 2 O3 O2 O3 CH4 H O O Water, carbon dioxide, methane, 2 3 clouds and particles all can impact surface temperature. Detecting gases that are made by life is one way we could confirm a planet’s habitability

WATER

ICE CAPS ICY OCEAN WORLDS TIDES As on Earth, ice caps help regulate Like Jupiter’s moon Europa, exoplanets may have Tides on Earth are powered by the Moon and the Sun. They the climate of a planet by reflecting vast oceans hidden beneath thick layers of ice. help stabilize the orbit and tilt of the planet, as well as slow energy from its star. the spin rate.

The larger the ice caps, the colder Tidal forces the atmosphere, meaning more ice can form.

Planet’s spin If the caps become too large, they can lead to an extreme ice age! In It’s possible that life thrives in these oceans if tidal response the planet will accumulate heating and radioactivity keep them warm. The ice greenhouse gases, heat up and would protect life from dangerous activity from the melt the ice. star. If the tidal force is too strong the planet could experience tidal locking, which would dramatically alter the planet’s climate. OCEANS HYDROTHERMAL VENTS H O 2 Water is essential for life as we These vents are like deep sea H O 2 know it, because it acts as a mini-volcanoes that create solvent for organic chemistry, nutrient-rich hot water. H O 2 the foundation of life on Earth.

They are possible Deep oceans can protect early life from places for early an active star. They also help stabilize the life to form. climate and transport energy across its Tides help warm oceans, circulate nutrients all over the surface. planet, move currents, and influence plate tectonics. SURFACE

CARBON CYCLE FEEDBACK PLATE TECTONICS VOLCANISM

This process, which involves volcanoes, As the plates move into the planet’s Volcanoes bring important elements like CO2, nitrogen and water from oceans, atmosphere, geology and other interior, they carry important elements deep within a planet to the surface in a process called mantle outgassing. factors, controls how much carbon dioxide that have settled on the seafloor. Not only are these elements important for life, but as a greenhouse gas

(CO2) is in the atmosphere. CO2 also helps the atmosphere retain heat.

50 60 40 70 0 3 8 0

0 2 Like a thermostat, 9 0

0

the carbon cycle 1 1

0

0 maintains the

0 perfect temperature for life Without volcanic The right level of With too much ash At 1-10 million by balancing CO volcanic activity in an atmosphere, times Earth’s 2 activity putting CO2 levels. in a planet’s supports life by sunlight could be current volcanic atmosphere, it will delivering blocked from the activity, lakes of likely be too cold important elements surface, affecting lava may form on As a greenhouse gas, it directly affects for life. to the surface. life. the surface. These elements are then brought back to how much of the star’s heat the the surface by volcanic activity and the atmosphere retains. creation of new plates.

INTERIOR

CORE Some planets with iron cores, like Earth, SOURCES A liquid iron core is important start with a completely liquid core which Based on “Impact of Space Weath- for protecting life on a planet’s crystallizes over time. er on Climate and Habitability of surface. The movement of Terrestrial Type of Exoplanets,” molten iron generates a Airapetian et al. (2019). magnetic field, which shields Specific contributions from Ravi the atmosphere from stellar Kumar Kopparapu, Wade Henning activity. and Joshua Schlieder. Billions of Years For planets with small cores, the core may completely solidify, turning off the magnetic field.