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Definition of planet
The definition of "planet" has for some time been the subject of intense debate. Although the word dates back thousands of years, no officially decreed scientific definition of "planet" existed before the early 21st century. Until the beginning of the 1990s, there was little need for one, as astronomers had only a single sample of planets in solar system to study, and one small enough for its many irregularities to be dealt with individually.
However, after 1992 and the discovery of the myriad tiny worlds beyond the orbit of Neptune, the size of the sample rose from nine to at least several dozen. Following the discovery of the first extrasolar planet beyond our solar system in 1992, the number of samples has now reached hundreds. These revelations not only increased the number of potential planets, but, in their variety and peculiarity (some nearly large enough to be stars, others smaller than our Moon) challenged long perceived notions of what a planet could be.
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Space & Time News
October 13, 2026
Oct. 12, 2026 Europe's Sentinel-3C satellite has returned breathtaking images of Earth just two weeks after launch, revealing the snowy Alps, frozen Arctic islands, and brilliant turquoise Caribbean waters. Its ...
Oct. 10, 2026 Scientists in Vienna have achieved a major breakthrough in timekeeping by creating the world’s first self-stabilizing nuclear clock, a technology that could eventually surpass even the most precise atomic clocks. Instead of relying on electrons in ...
Oct. 8, 2026 NASA is preparing for humanity’s first Moon base with three investigations that will hunt for underground shelters, uncover hidden ice, and track dangerous conditions on the lunar surface. The findings could reveal how astronauts can survive and ...
Oct. 7, 2026 Earth’s center of mass is constantly on the move, shifting by a few millimeters as enormous amounts of water, ice, and even air migrate around the planet with the seasons. NASA scientists have developed a more precise way to track these tiny ...
Oct. 5, 2026 NASA has selected the GIMLI project to investigate whether the Marius Hill Pit opens into a vast underground cave or lava tube. Using radar, seismic sensors, gravity measurements, and cameras, researchers will search beneath the lunar surface and ...
Oct. 4, 2026 A meteor crater buried beneath Oklahoma has turned out to be nearly 100 million years younger than scientists thought. Zircon crystals show the Ames impact occurred about 370 million years ago, meaning it was not part of the mysterious Ordovician ...
Oct. 3, 2026 Ultra-detailed simulations are showing how the first stars lit up the dark Universe and seeded space with elements such as carbon, oxygen, and iron. The MEGATRON project could bridge JWST observations of the earliest galaxies with chemical clues ...
Oct. 2, 2026 NASA’s Roman Space Telescope has demonstrated remarkable pointing stability and given its powerful planet-imaging coronagraph its first look at the cosmos. The telescope can already stay locked on a target with precision comparable to aiming a ...
Sep. 28, 2026 CosmoCube will use the far side of the Moon as a shield from Earth’s radio noise to search for a faint signal from the universe before the first stars existed. The suitcase-sized satellite could reveal how the cosmic dark ages ended and how dark ...
Sep. 28, 2026 Spaceflight may dramatically change the gut within weeks, causing bacteria to break down more protein as food moves more slowly through the intestines. The shift could help explain astronaut constipation and may have wider effects on health, making ...
Sep. 25, 2026 Scientists think beneficial fungi could help transform nutrient-poor lunar and Martian regolith into a material capable of supporting crops. By helping plants access nutrients and withstand harsh conditions, these microbes could someday make ...
Sep. 22, 2026 An amateur astronomer searching satellite maps for a Quebec camping spot accidentally discovered a massive ancient impact crater. Scientists later found shatter cones that confirmed the ...
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Oct. 13, 2026 NASA’s James Webb Space Telescope has revealed an ancient galaxy cluster with an unexpectedly dense concentration of dark matter, challenging ...
Oct. 11, 2026 An astronaut aboard the International Space Station photographed a remarkable formation in Madagascar that looks surprisingly similar to the Moon’s bright highlands. Made of anorthosite, a rock ...
Oct. 10, 2026 Astronomers have discovered a bizarre star system about 300 light-years from Earth where a small star is slowly devouring a nearby brown dwarf, an object too massive to be a planet but too small to ...
Oct. 9, 2026 A strange chemical signature in old Hubble observations may point to a planet that formed after its star had already died. Astronomers found unusually high levels of niobium around the white dwarf HS ...
Oct. 9, 2026 A Canadian radio telescope has detected the faint glow of hydrogen from billions of years ago using only its own observations, proving a long-awaited way to map the distant universe can actually ...
Oct. 8, 2026 NASA’s SpaceX Crew-12 astronauts have returned to Earth after 237 days in space, traveling more than 100 million miles and completing over 3,792 orbits while conducting research to prepare for ...
Oct. 8, 2026 October’s skies are packed with celestial surprises, from Jupiter disappearing behind the Moon to two meteor showers lighting up the darkness. NASA highlights four must-see events, including ...
Oct. 8, 2026 Einstein Probe revealed nearly 10 minutes of soft X-ray activity following a short gamma-ray burst, exposing a phase of neutron star mergers that previous missions may have missed. The prolonged ...
Oct. 7, 2026 NASA’s James Webb Space Telescope is giving astronomers a glimpse of the kinds of violent collisions that may have shaped our own solar system, including the giant impact thought to have created ...
Oct. 7, 2026 The James Webb Space Telescope has found strong evidence that the rocky lava world HD 3167 b has an atmosphere, despite circling its star every 24 hours under extreme heat. The surprising discovery ...