Exoplanet Quiz: Questions About Exoplanets and Beyond

Exoplanets are planets outside the Solar System, with over 5,366 confirmed exoplanets in 3,962 planetary systems as of May 2023, with the potential for billions more. The most common methods of detecting exoplanets include transit photometry and Doppler spectroscopy, but these methods have an observational bias that favors the detection of planets near the star. Almost all of the exoplanets detected so far are within the Milky Way, but there is evidence that extragalactic planets may exist. The discovery of exoplanets has intensified interest in the search for extraterrestrial life, especially in planets that orbit in a star's habitable zone. Rogue planets, which do not orbit any star, are also considered a separate category of planets. The International Astronomical Union (IAU) has a working definition of an exoplanet, but other definitions exist. Claims of exoplanet detection have been made since the nineteenth century, but the first definitive detection of an exoplanet orbiting a main-sequence star was made in 1995. The discovery of exoplanets has been recognized by a share of the 2019 Nobel Prize in Physics.Exoplanets: Detection Methods, Formation, Host Stars, and Characteristics

High-resolution spectroscopy led to the detection of many new exoplanets by measuring their gravitational influence on the motion of their host stars.
Most early known exoplanets were "hot Jupiters," massive planets orbiting very close to their parent stars, contrary to theories of planetary formation.
NASA announced the discovery of 715 newly verified exoplanets around 305 stars in 2014, most between the size of Neptune and the size of Earth.
Kepler-452b, a near-Earth-sized planet orbiting the habitable zone of a G2-type star, was discovered in 2015.
Wolf 503b, twice the size of Earth and orbiting an "Orange Dwarf," was discovered in 2018 and is the only exoplanet of that size found near the so-called Fulton gap.
TOI 700 d, the first Earth-sized planet in the habitable zone detected by TESS, was discovered in 2020.
NASA's Kepler and TESS missions had identified 4374 planetary candidates yet to be confirmed, some nearly Earth-sized and located in the habitable zone.
Direct imaging of exoplanets is challenging due to the extreme brightness of parent stars, requiring extreme optothermal stability to block out the star's glare.
Indirect methods, such as measuring the planet's effect on the parent star or observing transits, are commonly used to detect exoplanets.
Planets may form within a few to tens of millions of years of their star forming and may have large radii due to the accretion of hydrogen/helium envelopes.
Most known exoplanets orbit stars similar to the Sun, but red dwarfs are less likely to have detectable planets.
Exoplanets have varying characteristics, including color, brightness, magnetic field, plate tectonics, volcanism, rings, moons, and atmospheres.
Atmospheres have been detected around several exoplanets, and a comet-like tail was observed on KIC 12557548 b, a small rocky planet orbiting very close to its star.Exoplanets: Surface, Habitable Zones, and Potentially Habitable Planets
Some exoplanets have a trail of cloud and dust like a comet due to the evaporation of their atmosphere.
The insolation pattern of tidally locked planets will result in a hot spot that resembles a pupil or an eyeball, and planets with an eccentric orbit could be locked in other resonances.
Spectroscopy can distinguish between surface and atmospheric features, and the temperature of an exoplanet can be estimated by measuring the intensity of light it receives from its star.
The habitable zone around a star is where liquid water can exist on a planet's surface, and the location of the zone depends on the size and age of the star, as well as the atmospheric conditions of the planet.
Tidally locked planets can be habitable due to the effect of clouds, which can greatly increase the planetary albedo and reduce surface temperatures.
Planets can periodically become frozen, and planets with a large axial tilt are less likely to enter snowball states.
Eccentric planets in the radiative habitable zone can be too hot for liquid water, but tidal heating can create a subsurface ocean.
Kepler-62f, Kepler-186f, and Kepler-442b are the best candidates for being potentially habitable exoplanets.
The Kepler-223 system contains four planets in an 8:6:4:3 orbital resonance, and some hot Jupiters orbit their stars in the opposite direction to their stars' rotation.
The search for exoplanets involves various projects, such as the Kepler mission, the Transiting Exoplanet Survey Satellite (TESS), and the James Webb Space Telescope (JWST).
Proxima Centauri b is the nearest terrestrial exoplanet candidate, with an estimated equilibrium temperature of -39 °C.
In the earlier era of the universe, the temperature of the cosmic microwave background would have allowed rocky planets to have liquid water on their surface regardless of their distance from a star.