Hot Jupiter radius inflation
Some giant planets close to their stars are larger than ordinary cooling models predict. What keeps them inflated?
Explore all problems.
Multiple populations in globular clusters
Stars within one globular cluster can have different light-element abundances. Their common origin is still debated.
Pulsar radio emission
A pulsar’s rotating beam is familiar. The plasma process that makes its exceptionally bright radio waves is less certain.
Stellar angular momentum transport
A star’s core and outer layers exchange rotational motion. Which internal processes set that exchange as stars evolve?
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?
Mitochondrial gene retention
Mitochondria keep some genes while many others reside in the nucleus. Why do different lineages retain different sets?
Meiotic homologue recognition
During egg formation in fruit flies, matching chromosomes must find one another. How do repeated DNA sequences help them recognize a match?
Insect photoperiodic timing
Insects use day length to prepare for seasonal dormancy. How do daily clock signals become a seasonal decision?
Co-translational membrane-protein folding
How do α-helical membrane proteins fold while they are made, as sequence, synthesis and the surrounding membrane determine their route?
Non-photochemical quenching
Plants safely release excess absorbed light as heat. How does their light-harvesting machinery switch this protection on and off?
Polyploid establishment
A plant with extra chromosome sets may have few compatible mates. Which conditions let a new polyploid population persist?
Segregation Distorter mechanism
A selfish chromosome in fruit flies disables competing sperm. How does its genetic machinery cause that selective failure?
Gravity sensing in plants
Roots and shoots can tell which way gravity points. How do settling structures inside cells become a directional growth signal?
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?
Pulsar glitches
Some pulsars suddenly spin faster. What triggers the rapid transfer of rotational motion that produces a large glitch?
Turbulence intermittency
Turbulent motion concentrates into rare, intense bursts. Can the fluid equations predict how those bursts scale?
EMC effect
Quark distributions change when protons and neutrons are bound in nuclei. What physical mechanism causes those changes?
Proton spin
A proton’s total spin is known. How is it shared among quark spin, gluon spin and their orbital motion?
Hadronic vacuum polarization
Different methods still disagree on parts of the hadronic contribution to the muon’s magnetic moment. Which data or corrections explain the differences?
Luminous fast blue optical transients
Cow-like transients brighten and fade rapidly while emitting powerful X-rays and radio waves. Which stellar events produce them?
Sr₂RuO₄ pairing symmetry
Sr₂RuO₄ is a superconductor, but experiments still do not select one consistent symmetry for its paired-electron state.
Herbertsmithite ground state
Herbertsmithite is a leading candidate for a quantum spin liquid. Which low-temperature state is intrinsic to its kagome layers?
Mercury’s formation
Mercury has an unusually large metal core. Which formation history produced it while leaving the planet’s other observed properties?