Planetesimal formation
Planetary systems start with small solid grains. How do these become gravitationally bound bodies before collisions or inward drift remove them?
Planets and rings
Planet formation, atmospheres, thermal histories, distant orbits and Saturn’s moons and rings.
Also in Inside planets and stars
Subjects: Planetary science
Problems in this collection
15 problemsMoon formation
A giant impact is the leading explanation for the Moon’s origin. Its exact sequence must account for the Moon’s composition, orbit and relationship to Earth.
Jupiter’s interior
Juno’s measurements suggest that Jupiter’s core blends gradually into its hydrogen-rich surroundings. How large is this region, what is it made of, and how did it form?
Uranus’s internal heat
Uranus does release heat from its interior, despite older claims that it does not. How does its interior lose heat and produce the seasonal energy budget we observe?
Hot Jupiter radius inflation
Some giant planets close to their stars are larger than ordinary cooling models predict. What keeps them inflated?
Age of Saturn’s rings
Saturn’s icy rings look relatively clean. Does that reveal when they formed, or how they lose and retain pollution?
Venus’s climate history
Venus and Earth began as similar rocky planets. Did Venus ever have oceans, or did its water remain steam and escape before oceans could form?
Early Mars climate
Ancient Martian rocks and landforms record liquid water under a fainter Sun. What climate sustained it, and how persistent were those wet conditions?
Venus’s ultraviolet absorber
An unidentified absorber darkens Venus’s clouds in near-ultraviolet light. Which chemicals produce it and keep it present?
Ganymede’s dynamo
Ganymede generates its own magnetic field. What keeps the conducting material inside it moving?
Mercury’s formation
Mercury has an unusually large metal core. Which formation history produced it while leaving the planet’s other observed properties?
Martian methane
A rover reports methane near the surface; an orbiter finds none. Even the reliability of the rover detections is disputed.
Planet Nine
Some distant orbits suggest an unseen planet beyond Neptune. Searches have narrowed the possibilities without finding it.
Exoplanet radius valley
Close-in small planets cluster into two size groups. Which formation and atmospheric processes produce the gap between them?
Saturn’s tidal dissipation
Saturn transfers spin to its moons, moving them outward. The strength and frequency pattern of this transfer point to unusually effective internal energy loss. Which interior processes set those rates and their evolution?