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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
August 8, 2026
Aug. 7, 2026 A ten-month Antarctic experiment found that astronauts may struggle not only with loneliness but also with spending too much time around the same people. Frequent contact was linked to greater ...
Aug. 7, 2026 Metal-rich asteroids could one day become hardware stores for Mars, supplying the materials needed to build and repair a growing colony. A new analysis shows that carefully selected asteroids may be reachable with current spacecraft technology. Some ...
July 31, 2026 Scientists have built the first all-optical photonic time crystal, allowing them to reshape the behavior of terahertz light at extraordinary speeds. The breakthrough could open the door to ultrafast computing, smarter communication systems, advanced ...
July 30, 2026 Astronomers may have been listening for alien civilizations in only a small slice of the radio spectrum while overlooking a largely unexplored range of higher frequencies. Using archived data from the ALMA telescope in Chile, researchers conducted ...
July 28, 2026 NASA’s Psyche spacecraft aced its Mars flyby, using the planet’s gravity to speed toward its 2029 encounter with a metal-rich asteroid. The spacecraft tested its cameras, magnetometer, and ...
July 23, 2026 NASA is preparing for future astronaut landings on the Moon with an unusually ambitious orbital rehearsal. During Artemis III in 2027, Orion astronauts will rendezvous and dock separately with ...
July 21, 2026 China’s Chang’e-6 samples have uncovered a surprising difference between the Moon’s two hemispheres. Solar wind particles penetrated deeper into the far-side soil because Earth’s ...
July 19, 2026 The asteroid that wiped out the dinosaurs was likely an exceptionally rare CO chondrite from a distant region of the solar system. Its unusual chemistry suggests that planet-cooling dust and debris, ...
July 18, 2026 A catastrophic asteroid breakup may have triggered a huge wave of impacts across the inner solar system about 800 million years ago. The debris was launched from near a gravitational gateway controlled by Jupiter, sending fragments toward Earth, the ...
July 17, 2026 Scientists say new technologies have reopened the debate over whether Mars could someday be terraformed, turning a once impossible idea into a serious research topic. Before anyone tries to reshape the Red Planet, though, researchers say we must ...
July 15, 2026 NASA's PACE satellite captured the Black Sea glowing turquoise during its annual phytoplankton bloom. The vivid color comes from massive numbers of coccolithophores, microscopic organisms whose reflective shells brighten the water enough to be seen ...
July 15, 2026 NASA has chosen 41 commercial technology projects that could solve critical challenges for future missions to the Moon and Mars. From powering lunar outposts to protecting spacecraft from Moon dust, the innovations are designed to push both space ...
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Aug. 8, 2026 A rare meteorite that crashed through a New Jersey roof contains evidence of ancient salty fluids, organic compounds, and amino acids from a ...
Aug. 8, 2026 Scientists have discovered incredibly tiny plasma whirlpools swirling across the Sun’s surface, some just 20 kilometers wide. These previously invisible vortices may twist magnetic fields and help ...
Aug. 6, 2026 A supermassive black hole has been found lurking about 30,000 light-years from the center of its galaxy—the first dormant black hole detected so far from a galactic core. It revealed itself only ...
Aug. 5, 2026 August brings four major celestial events, including a solar eclipse and the peak of the Perseid meteor shower. Dark New Moon skies could make the Perseids especially impressive, while Venus will ...
Aug. 4, 2026 Photons traveling through a cloud of atoms can emerge so early that they appear to have spent a negative amount of time inside. Researchers tested ...
Aug. 3, 2026 Hidden moon ice may reveal itself through the way it bends and reflects vibrations from moonquakes. The technique could help astronauts locate vital water supplies and uncover clues about the origins ...
Aug. 3, 2026 The solar wind may be stripping away Mars’ atmosphere by creating giant rolling waves along its outer edge. Data from MAVEN and Tianwen-1 show that these waves form plasma clouds that carry ...
Aug. 2, 2026 Dark matter particles may exert a hidden force on one another, but its effects are stranger than expected. An extra attraction helps the particles cluster, yet it also makes dark matter effectively ...
Aug. 1, 2026 Scientists have identified LHAASO J1912+1014u as a cosmic accelerator that can push protons beyond one quadrillion electron volts. The finding may ...
Aug. 1, 2026 NASA’s Curiosity rover has entered a Martian valley covered by an astonishing “sea” of tiny polygon-shaped fractures. The honeycomb patterns, each only a few inches wide, stretch across the ...