Research › Daylight
This page features research centered around observations or models of comets and asteroids too close to the Sun to be fully studied at night, requiring specialized space- and/or ground-based instruments adapted to safely look near the Sun.
Sodium Vapor from Asteroid (3200) Phaethon
Asteroid (3200) Phaethon is best known for the dense stream of dust it presumably laid along its orbit, producing Geminids meteors each December, yet has always looked like an inert rock through nighttime telescopes. Phaethon, however, also approaches the Sun to 0.14 au—less than half the distance Mercury does—where it does briefly turn active with a visible tail under the intense solar heating. Zhang et al. (2023; PSJ, 4, 70) used coronagraphic and heliospheric imagery by the SOHO and STEREO spacecraft, respectively, to show that this visible activity captures Phaethon's ongoing loss of sodium vapor, which fluoresces brightly in sunlight, and could serve as a tracer of more substantial mass loss in the past.