- How do astronomers use Lyman series lines today to study hydrogen gas across the universe?
Asteroids, Comets, and Small Bodies
Minor planets, comets, and other small solar system objects.
- Why did the Tunguska explosion flatten a huge area of Siberian forest without leaving an impact crater?
- How large was the object believed to have caused the Tunguska event, and how much energy did it release?
- Why did it take nineteen years for a scientific expedition to reach and investigate the Tunguska site?
- Why did astronomers say the comet's tail posed no real danger despite containing a poisonous compound?
- How did Barnard's Star later become a subject of Project Daedalus, a study of interstellar probe design?
- Why do astronomers think comets from the Oort Cloud are making their first pass through the inner solar system?
- What evidence led Alvarez and his son to propose that an asteroid impact ended the age of dinosaurs?
- Why was it uncertain whether a spacecraft could survive passing through the asteroid belt before Pioneer 10?
- What is the purpose of the plaque carried aboard Pioneer 11 as it heads beyond the heliosphere?
- How far has Voyager 1 traveled, and how long does its signal now take to reach Earth?
- What did Luis and Walter Alvarez find in the clay layer at the Cretaceous-Paleogene boundary near Gubbio, Italy?
- Why is the presence of iridium in a rock layer considered evidence of an extraterrestrial impact?
- Why were paleontologists initially skeptical of the Alvarez hypothesis for the mass extinction that killed the dinosaurs?
- What discovery in 1991 provided physical confirmation of the Alvarez hypothesis?
- How fast is Pioneer 10 traveling through interstellar space today?
- Why had no one ever seen the nucleus of Halley's Comet before the 1986 spacecraft encounters?
- What did ESA's Giotto probe reveal about the size, shape, and color of Halley's nucleus during its close pass?
- How did the 1986 flybys confirm Fred Whipple's 'dirty snowball' hypothesis about comet composition?
- Where is Voyager 2 now, and what is it still transmitting from interstellar space?
- What evidence did the Alvarez hypothesis rely on before a crater was identified?
- Where had the evidence for the Chicxulub crater been sitting undetected for decades?
- How big is the Chicxulub crater and what confirmed it as an impact structure?
- How close did the Galileo spacecraft come to asteroid Gaspra, and why was the flyby significant?
- What surface features did Galileo's cameras reveal that contradicted expectations about asteroids?
- What unexpected signal hinted at a magnetic field around such a small body?
- Why did Comet Shoemaker-Levy 9 break into at least twenty-one fragments before it struck Jupiter?
- How large were the scars left in Jupiter's atmosphere by the impacts, and how were they visible from Earth?
- What longstanding question in planetary science did the 1994 impacts help settle?
- How did Alan Hale and Thomas Bopp independently discover the same comet on the same night?
- What made Comet Hale-Bopp visible to the naked eye for a record eighteen months?
- Why was NEAR Shoemaker's landing on Eros unusual given that the spacecraft had no landing gear?
- How long did NEAR Shoemaker continue transmitting data after touching down on Eros?
- What did the close-up images from Eros reveal about the asteroid's surface?
- How did the Stardust spacecraft use aerogel to capture particles from comet Wild 2?
- What surprising minerals did scientists find in the returned comet dust, and what did they imply?
- Why does finding inner-solar-system minerals in an outer-solar-system comet challenge older formation models?
- What technical failures did the Hayabusa spacecraft survive during its mission to Itokawa?
- How did scientists find asteroid dust in the sample capsule despite the collection mechanism failing?
- What did the recovered dust grains reveal about S-type asteroids?
- How did NASA use plasma wave data to confirm Voyager 1 had crossed the heliopause?
- How long does it take a signal from Voyager 1 to reach Earth, and what does that reveal about its distance?
- How large was the Chelyabinsk asteroid and how much energy did it release when it exploded in the atmosphere?
- Why were most of the 1,500 injuries caused by shattered glass rather than the fireball itself?
- Why is it especially notable that Chelyabinsk went undetected on the same day astronomers were tracking asteroid 2012 DA14?
- Why did Philae bounce twice instead of anchoring on its first touchdown on Comet 67P?
- How did landing in the shadow of a cliff limit the power available to Philae's solar panels?
- What organic molecules did Philae detect during its sixty hours of operation, and why did they matter to origin-of-life questions?
- What made Rosetta the first spacecraft to achieve orbit around a comet?
- Why did the Philae lander's mission have limited scientific life after it bounced on landing?
- What did Rosetta discover about water ice, organic molecules, and magnetic fields on comet 67P?
- How did mission controllers end the Rosetta mission, and why choose a controlled impact?
- What about ʻOumuamua's trajectory proved it originated outside our solar system?
- What physical features made ʻOumuamua's shape and tumbling motion so unusual?
- Why did ʻOumuamua's unexplained acceleration lead to competing theories, including Avi Loeb's alien-technology hypothesis?
- Why is it notable that Voyager 1 was still functioning and repairable while in interstellar space, decades after launch?
- How did 3I/ATLAS's speed reveal that it was not gravitationally bound to the Sun?
- How does 3I/ATLAS compare to the two previous interstellar objects, 'Oumuamua and 2I/Borisov?
- Why does the rising detection rate of interstellar objects suggest the interstellar medium contains more of them than previously assumed?
- What kinds of solar system objects were included in the 11,000 newly catalogued bodies?
- How had some of these objects' orbits been inferred before Vera Rubin's direct observations confirmed them?