AST 111 Exoplanets II

What can we measure? Orbital period – Look at doppler shift or just watch it Orbital distance – Kepler’s 3 rd Law with orbital period Orbital shape – Look at symmetry of doppler shift or just watch it Mass – Need star’s orbital speed (about CM) Size – Must come from transit Density Composition – Must come from transit

The Count 725 confirmed exoplanets ( ) – 4 of these may be habitable

Several “Super-Earths” have been discovered. These are a few times larger than Earth.

Pending Confirmation 2321 candidate exoplanets – 207 Earth-sized – 1181 Neptune-sized – 203 Jupiter-sized – 55 Larger than Jupiter 48 are thought to be in the habitable zone Two Earth-like planets found orbiting a Sun-like star!

Estimates 5.4% of all stars have Earth-like planets 17% of all stars have multiple planets

Notable Finds Earth-sized planet around Proxima Centauri – Inside orbit of Mercury; not habitable Cannonball Planet – 20x closer to parent star than Mercury is to Sun. Orbits in 0.84 days! – 1.4x larger than Earth and 4.6x more massive – Density similar to iron 4-Planet system with 8 : 6 : 4 : 3 resonance One planet orbiting two stars

Extrasolar Planets vs. Solar System Other solar systems seem to have both terrestrial and Jovian planets Many observed exoplanets are “Hot Jupiters” – Close to parent stars – H-compounds would boil away – “Clouds of rock dust”

Extrasolar Planets vs. Solar System Hot Jupiters would actually glow! The heat “inflates” the atmosphere – Lower density Hot surface and rapid rotation lead to winds that create bands

Extrasolar Hot Jupiters vs. Our Jupiter

Formation of Other Solar Systems Planetary migration: – “Hot Jupiters” formed in the outer solar system… – Migrated inward? Waves can propagate through gaseous disk – Causes matter to bunch – Can pull on planets Our Solar System: – Solar wind cleared out the gas before waves could happen

Formation of Other Solar Systems Nebular theory holding up well – Just by virtue of finding exoplanets Planets should form more easily where there’s rock and ice – More planets found around stars that contain these ingredients Some stars have “unusual assortment” in outer layers – THEY ATE THE PLANETS!

Formation of Other Solar Systems Challenges to nebular theory: – Jovian planets should only form past a frost line and have somewhat circular orbits – We see massive extrasolar planets on elliptical orbits close to stars

Formation of Other Solar Systems Elliptical orbits may be due to: – Close encounter between two large Jovian-like planets One goes inward, the other goes outward – Orbital resonances

Extrasolar Systems vs. Solar System The planets in our Solar System more or less “ignore each other” – No orbital resonances Other planetary systems’ planets interact strongly – Crowding and orbital resonances

Exoplanet Hunters Dedicated observatories being set up that will observe tens of thousands of star systems Theoretically capable of spotting Earth-sized planets

Kepler – Orbits the Sun – Looks at constellation Cygnus – Will watch 145,000 stars Can see transits of Earth- sized planets Can see Mercury-sized planets for dimmer stars

Telescopes in Formation Interferometry uses multiple smaller telescopes to act like one big one Astrometry would work: – Resolution of 1 micro-arcsecond Could find Earth-sized planets around nearest dozen stars Could find Jupiter-sized planets up to 3000 LY away!