Space
Astronomy and space exploration
Articles in this category are re-verified roughly every 60 days.
Space
Aditya-L1
Aditya-L1 is India's first space-based solar observatory, operated by the Indian Space Research Organisation (ISRO). Launched in September 2023, it entered a halo orbit around the Sun–Earth L1 point in January 2024, about 1.5 million kilometres from Earth. Its seven instruments observe the Sun remotely and measure particles and magnetic fields in the surrounding space, supporting research into solar physics and the origins of space-weather phenomena.
Updated 30 Oct 2026
Space
Apollo Program
The Apollo program was NASA’s human spaceflight effort to send astronauts to the Moon and return them safely to Earth. Announced as a national goal in 1961, it combined crewed flight tests, lunar-orbit missions and six crewed Moon landings between 1969 and 1972. Its rockets and spacecraft also enabled scientific exploration; Apollo astronauts returned hundreds of kilograms of lunar material that researchers continue to study.
Updated 21 Oct 2026
Space
Aryabhata (satellite)
Aryabhata was India's first satellite, designed and fabricated by the Indian Space Research Organisation (ISRO). Launched on 19 April 1975 by a Soviet Kosmos-3M rocket from Kapustin Yar, it carried experiments in X-ray astronomy, aeronomy and solar physics. A power failure curtailed its scientific experiments after only a few days, but the project gave India important experience in designing, building and operating spacecraft. Aryabhata remained in orbit for nearly 17 years before re-entering Earth's atmosphere in February 1992.
Updated 1 Nov 2026
Space
Asteroid Bennu
Bennu is a near-Earth asteroid whose carbon-rich, primitive material preserves evidence about early Solar System chemistry. NASA's OSIRIS-REx mission returned samples in 2023, enabling laboratory studies that identified minerals formed from ancient brines and a diverse set of organic compounds. These results illuminate conditions that may have supplied some ingredients for life, but they are not evidence that life existed on Bennu or its parent body.
Updated 24 Oct 2026
Space
BepiColombo
BepiColombo is a joint European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) mission to investigate Mercury and its space environment. Launched in October 2018, it consists of ESA's Mercury Planetary Orbiter (MPO) and JAXA's Mercury Magnetospheric Orbiter (Mio), which travelled together with a transfer module. Following separation of the transfer module in September 2026, the spacecraft are approaching Mercury; orbit insertion is planned for November 2026, with routine science observations scheduled to begin in 2027.
Updated 30 Oct 2026
Space
Black holes
A black hole is a region of space containing so much concentrated mass that, inside its event horizon, no signal or matter can escape to the outside. Astronomers study black holes through their effects on nearby gas, stars, light and spacetime. They range from objects formed by the collapse of massive stars to supermassive black holes found at the centers of many large galaxies.
Updated 13 Oct 2026
Space
Blue straggler stars
Blue straggler stars are unusually hot and luminous stars that appear beyond the main-sequence turn-off in the colour–magnitude diagrams of stellar populations. Their properties suggest that they gained mass or were rejuvenated after the rest of their coeval population began evolving away from the main sequence; mass transfer in binaries and stellar mergers are leading formation pathways.
Updated 26 Oct 2026
Space
Bow shock
A bow shock is a curved shock wave that forms upstream of an obstacle when a flowing medium approaches it faster than disturbances can travel upstream. In space plasmas, such shocks arise where stellar winds encounter planetary magnetospheres or where fast-moving stars interact with surrounding gas. Earth's bow shock lies sunward of the magnetosphere and provides a natural site for studying how collisionless plasmas slow down, heat and accelerate particles.
Updated 29 Oct 2026
Space
Callisto
Callisto is Jupiter's second-largest moon and one of the most heavily cratered worlds in the Solar System. Observations by NASA's Galileo spacecraft suggest that a salty ocean may lie beneath its ancient icy crust, although the interpretation of magnetic measurements remains under study. Its surface preserves a record of impacts, while future exploration by ESA's JUICE mission will add observations of this Galilean moon.
Updated 6 Nov 2026
Space
Carrington Event
The Carrington Event was an exceptionally severe geomagnetic storm in late August and early September 1859. It followed solar activity observed by astronomers Richard Carrington and Richard Hodgson and produced widespread auroras and major disturbances to telegraph systems. Historical records of the event remain important for understanding how solar activity can affect technology on Earth.
Updated 26 Oct 2026
Space
Ceres
Ceres is a dwarf planet in the main asteroid belt between Mars and Jupiter and the belt's largest body. First identified in 1801, it was classified as a dwarf planet in 2006. NASA's Dawn mission, which orbited Ceres from 2015 to 2018, found a water-rich, differentiated world with salts, ice and evidence of comparatively recent geological activity, especially around Occator Crater.
Updated 26 Oct 2026
Space
Chandrasekhar limit
The Chandrasekhar limit is the approximate upper mass at which a white dwarf can remain stable against its own gravity. For the usual idealized model, it is about 1.4 times the Sun’s mass. The limit follows from the way quantum-supported electron pressure changes as a stellar remnant becomes more massive and compact. It helps explain why some white dwarfs can undergo thermonuclear explosions, while sufficiently massive stellar remnants may collapse into denser objects.
Updated 22 Oct 2026
Space
Chandrayaan-1
Chandrayaan-1 was India's first lunar exploration mission, launched by the Indian Space Research Organisation (ISRO) on 22 October 2008. Its orbiter carried scientific instruments from India and international partners to map the Moon's surface and composition. The mission ended in August 2009 after completing its principal objectives. Among its most important findings, NASA's Moon Mineralogy Mapper aboard the spacecraft detected spectral evidence of water- and hydroxyl-bearing material on the Moon, advancing lunar science and establishing a landmark in India's planetary exploration programme.
Updated 1 Nov 2026
Space
Chandrayaan-2
Chandrayaan-2 was India's second lunar exploration mission, launched by the Indian Space Research Organisation (ISRO) on 22 July 2019. The mission combined an orbiter, the Vikram lander and the Pragyan rover to study the Moon's surface, composition and tenuous exosphere, with emphasis on the lunar polar regions. Vikram lost communication during its attempted landing, but the orbiter entered its planned lunar orbit and continued its scientific mission, returning observations used in lunar research.
Updated 31 Oct 2026
Space
Chandrayaan-3
Chandrayaan-3 was an Indian lunar mission that demonstrated a controlled soft landing and rover operations on the Moon. Launched by the Indian Space Research Organisation (ISRO) in July 2023, it delivered the Vikram lander and Pragyan rover to the Moon's southern high-latitude region on 23 August. Their instruments studied local conditions and surface composition during a planned lunar-day mission.
Updated 30 Oct 2026
Space
Circumstellar habitable zone
A circumstellar habitable zone is the range of orbital distances around a star where a rocky planet could, under suitable atmospheric conditions, maintain liquid water on its surface. It is a useful guide for selecting exoplanets for study, but location within the zone alone does not establish that a world is habitable or inhabited.
Updated 28 Oct 2026
Space
Coronal mass ejection
A coronal mass ejection (CME) is a large eruption of magnetized plasma from the Sun's corona into interplanetary space. CMEs expand as they travel, and an Earth-directed event can interact with Earth's magnetosphere. Its effects depend on its speed, direction, and magnetic-field orientation; a CME is distinct from a solar flare, though the events can occur together.
Updated 29 Oct 2026
Space
Cosmic distance ladder
The cosmic distance ladder is a sequence of astronomical techniques used to measure distances beyond the range of any single method. Nearby stellar parallaxes provide geometric calibration; variable stars such as Cepheids and standardized Type Ia supernovae extend measurements to other galaxies. Each method is calibrated using nearer distances, so uncertainties in earlier steps affect later estimates of cosmic scale and expansion.
Updated 23 Oct 2026
Space
Cosmic Microwave Background
The cosmic microwave background (CMB) is relic radiation from the early universe, released when the cosmos became transparent about 380,000 years after the Big Bang. Its nearly uniform microwave glow and tiny temperature variations provide evidence about the universe’s early conditions and later evolution.
Updated 7 Nov 2026
Space
Cryovolcanism
Cryovolcanism is the eruption or extrusion of liquids and vapours made of substances that are normally solid at the very low surface temperatures of icy worlds. Instead of molten silicate rock, cryovolcanic activity can involve water, water-rich mixtures, or other volatile materials. Plumes at Saturn’s moon Enceladus are directly observed, while proposed cryovolcanic landforms on distant worlds such as Pluto are interpreted from spacecraft images and remain dependent on geological analysis.
Updated 24 Oct 2026
Space
Dark matter
Dark matter is the name given to matter inferred from gravitational effects that cannot be accounted for by visible matter alone. Evidence comes from observations at different cosmic scales, including galaxy dynamics, gravitational lensing and the cosmic microwave background. Its fundamental nature remains unknown: proposed particle candidates have not been confirmed.
Updated 28 Oct 2026
Space
Dione (moon)
Dione is an icy moon of Saturn discovered by Giovanni Cassini in 1684. Cassini spacecraft observations revealed a heavily cratered surface, bright fractured cliffs and evidence of past geological activity. Gravity-data analyses have also suggested a deep subsurface ocean, although the interpretation and present state of that ocean remain subjects of scientific study.
Updated 27 Oct 2026
Space
Earthshine
Earthshine is sunlight reflected from Earth onto the Moon’s night-facing side and then reflected back toward observers on Earth. It is most noticeable as a faint glow on the dark portion of a thin crescent Moon. Because Earth’s reflectance varies with clouds, snow, ice and surface conditions, carefully calibrated earthshine observations can also help estimate large-scale changes in Earth’s albedo.
Updated 23 Oct 2026
Space
Eclipse seasons
An eclipse season is a roughly five-week interval when the Sun is near one of the nodes of the Moon’s tilted orbit, making solar or lunar eclipses possible. Eclipse seasons occur about 173 days apart, so two usually begin in a calendar year. Their timing explains why eclipses cluster instead of occurring at every new and full moon.
Updated 25 Oct 2026
Space
Enceladus
Enceladus is a small icy moon of Saturn whose south-polar jets eject water vapour and ice particles from a subsurface saltwater ocean. Observations by the Cassini mission revealed an active world with internal heat and chemistry of interest to research on potentially habitable environments; no life has been detected there.
Updated 22 Oct 2026
Space
Euclid (space telescope)
Euclid is a European Space Agency space telescope designed to investigate dark matter and dark energy by mapping the large-scale structure of the universe. Launched in 2023, it observes galaxies in optical and near-infrared light and uses their shapes, positions and spectra to trace cosmic structure and expansion across time. Its wide survey is intended to cover roughly one-third of the sky, providing a large data set for cosmology and other astronomical research.
Updated 25 Oct 2026
Space
Europa (moon)
Europa is one of Jupiter’s four largest moons, known for its bright, fractured icy surface and strong evidence of a salty ocean beneath its crust. The ocean’s possible water, chemistry and energy sources make Europa a leading target in the search for environments that could support life, although no mission has established that life exists there.
Updated 19 Oct 2026
Space
Europa Clipper
Europa Clipper is a NASA spacecraft launched in October 2024 to investigate whether Jupiter's moon Europa has environments that could support life. After reaching Jupiter in 2030, it is planned to make 49 close flybys of Europa, combining measurements from nine science instruments and a gravity experiment to study the moon's ice shell, subsurface ocean, surface, and thin atmosphere. It is designed to assess habitability, not to detect life itself.
Updated 6 Nov 2026
Space
Exoplanet
An exoplanet, or extrasolar planet, is a planet beyond the Solar System, usually orbiting another star. Because these worlds are faint and distant, astronomers commonly detect them indirectly: by measuring a star’s motion under a planet’s gravity or the small dip in starlight when a planet crosses in front of it. These observations can reveal properties such as orbital period, approximate size and, in some cases, atmospheric characteristics, but their interpretation depends on the available measurements.
Updated 22 Oct 2026
Space
Exoplanets
Exoplanets, or extrasolar planets, are planetary bodies beyond the Solar System that orbit other stars. Astronomers detect most of them indirectly, by measuring how they affect starlight or their host stars, and use complementary observations to estimate their sizes, masses, orbits, and atmospheres. Their wide range of properties has revealed planetary systems unlike our own, while also highlighting the limits that observation and detection methods place on what is known.
Updated 14 Oct 2026
Space
Fermi bubbles
The Fermi bubbles are two enormous lobes of gamma-ray emission extending above and below the Milky Way’s centre. Revealed in observations from the Fermi Gamma-ray Space Telescope, they are among the Galaxy’s largest high-energy structures. Their sharply bounded shape and energetic radiation point to a major episode of activity in the Galactic centre, but the precise origin and history remain unsettled.
Updated 27 Oct 2026
Space
Fermi paradox
The Fermi paradox is the question of why, despite the enormous size and age of the universe, humanity has not detected clear evidence of extraterrestrial technological civilizations. It juxtaposes estimates or intuitions that life and intelligence might arise elsewhere with the absence of confirmed signs. The tension depends on uncertain assumptions about how often life emerges, how long technological societies last, whether they expand or communicate, and what humans can detect; it is an open problem, not evidence that extraterrestrial life is impossible.
Updated 20 Oct 2026
Space
Ganymede
Ganymede is Jupiter’s largest moon and the largest moon in the Solar System. It is the only known moon with an internally generated magnetic field, which creates a small magnetosphere within Jupiter’s much larger one. Spacecraft and telescope observations also provide evidence for a deep subsurface saltwater ocean, though details of its structure remain under study.
Updated 25 Oct 2026
Space
Great Red Spot
The Great Red Spot is a vast, long-lived anticyclonic storm in Jupiter’s atmosphere, visible as a reddish oval in the planet’s southern hemisphere. Earth-based observers have followed it for nearly two centuries, although the storm’s size changes over time and its exact origin and future remain uncertain. Measurements by NASA’s Juno spacecraft show that the vortex extends hundreds of kilometres below the visible cloud tops, revealing a deep atmospheric structure rather than a surface marking.
Updated 22 Oct 2026
Space
Halley's Comet
Halley's Comet, formally designated 1P/Halley, is a short-period comet that returns to the inner Solar System roughly every 75–76 years. Its repeated appearances helped establish that comets can orbit the Sun; the last return was in 1986, and the next is expected in 2061.
Updated 19 Oct 2026
Space
Heliopause
The heliopause is the outer boundary of the heliosphere, where the Sun’s solar-wind bubble meets the surrounding interstellar environment. It is a changing transition region rather than a solid surface. NASA’s Voyager 1 and Voyager 2 spacecraft crossed it in 2012 and 2018, respectively, measuring changes in particles, plasma and magnetic fields.
Updated 25 Oct 2026
Space
Hertzsprung–Russell diagram
The Hertzsprung–Russell diagram, usually called the H–R diagram, plots stars by luminosity or absolute magnitude against surface temperature, colour or spectral class. Stars cluster in recognizable regions rather than appearing randomly: the broad main sequence, giant and supergiant regions, and the white-dwarf region. By comparing a star’s position with stellar models and other observations, astronomers study stellar properties and stages of evolution.
Updated 23 Oct 2026
Space
Hohmann Transfer Orbit
A Hohmann transfer is a two-impulse orbital maneuver that uses an elliptical transfer path to move a spacecraft between circular, coplanar orbits around the same central body. In the idealized case, the spacecraft accelerates to enter the transfer ellipse, coasts for half an orbit, then performs a second burn to join the target orbit. The method is especially useful for explaining fuel-efficient transfers, though real missions account for planetary positions and other constraints.
Updated 26 Oct 2026
Space
Hubble Space Telescope
The Hubble Space Telescope is a joint NASA–European Space Agency observatory in low Earth orbit. Launched in 1990, it observes ultraviolet, visible and near-infrared light from above Earth's atmosphere, producing high-resolution images and spectra. Designed for astronaut servicing, it underwent five shuttle servicing missions, including the 1993 correction of an optical flaw and a major 2009 upgrade. Its observations and public archive support research across astronomy.
Updated 17 Oct 2026
Space
Huygens probe
The Huygens probe was a European Space Agency lander carried to Saturn by NASA's Cassini spacecraft. On 14 January 2005 it descended by parachute through the dense atmosphere of Titan, returning the first direct measurements and images from the surface of the distant moon. Its brief surface operation and in-situ sampling transformed Titan from a hazy point of light into a world with weather, complex atmospheric chemistry and terrain shaped by flowing liquids.
Updated 28 Oct 2026
Space
International Space Station
The International Space Station (ISS) is a permanently crewed laboratory in low Earth orbit, developed and operated through cooperation among the United States, Russia, Japan, Canada and European partners. Its modular structure was assembled in orbit beginning in 1998, and people have lived aboard it continuously since 2000. The station supports research in life and physical sciences, technology testing and human spaceflight, while relying on shared international systems for assembly, supply and maintenance.
Updated 14 Oct 2026
Space
James Webb Space Telescope
The James Webb Space Telescope (JWST) is a space observatory developed through an international partnership of NASA, the European Space Agency and the Canadian Space Agency. Launched on 25 December 2021, it observes the universe primarily in infrared wavelengths, enabling studies of early galaxies, stars and planetary systems. Its segmented 6.6-metre primary mirror, large sunshield and four scientific instruments operate near the Sun–Earth L2 region, about 1.5 million kilometres from Earth. Webb began science operations in July 2022.
Updated 1 Nov 2026
Space
Jupiter
Jupiter is the fifth planet from the Sun and the Solar System’s largest, a hydrogen- and helium-rich giant without a solid surface. Its fast-moving cloud bands, long-lived storms and powerful magnetic environment make it an unusually active planetary system. The planet is orbited by many moons, including Io, Europa, Ganymede and Callisto, whose distinct geology has become a major subject of exploration. Spacecraft observations have revealed that Jupiter is both a planet in its own right and a complex system of worlds and rings.
Updated 12 Oct 2026
Space
Jupiter Icy Moons Explorer
The Jupiter Icy Moons Explorer (Juice) is an European Space Agency mission to study Jupiter and its large icy moons Ganymede, Europa and Callisto. Launched in April 2023, the spacecraft is scheduled to arrive in the Jupiter system in July 2031. After multiple moon flybys, it is planned to enter orbit around Ganymede, making it the first spacecraft to orbit a moon in the outer Solar System.
Updated 8 Nov 2026
Space
Kardashev Scale
The Kardashev scale is a theoretical framework for classifying hypothetical technological civilizations by the amount of energy they can harness, from planetary to stellar and galactic scales. Proposed by Nikolai Kardashev in 1964 for thinking about detectable extraterrestrial civilizations, it remains a conceptual tool rather than an observed ranking of alien societies.
Updated 10 Nov 2026
Space
Kármán Line
The Kármán line is a conventional altitude used to distinguish Earth's atmosphere from outer space. The Fédération Aéronautique Internationale uses 100 kilometres above mean sea level as a boundary for astronautical records, but the atmosphere thins gradually and has no sharp physical edge. Other conventions place the boundary near 80 kilometres, and scientists have debated which altitude best represents the transition from aerodynamic flight to spaceflight.
Updated 22 Oct 2026
Space
Kepler Space Telescope
NASA’s Kepler space telescope was a planet-hunting observatory that measured tiny changes in stellar brightness to find exoplanets transiting their stars. Its original survey and extended K2 mission expanded knowledge of planetary systems and established that planets are common throughout the Milky Way.
Updated 10 Nov 2026
Space
Kepler's laws of planetary motion
Kepler's laws of planetary motion are three mathematical rules describing how planets orbit the Sun. Johannes Kepler formulated them from astronomical observations, including Tycho Brahe's detailed measurements of Mars. They describe elliptical paths, changes in orbital speed, and the relationship between a planet's orbital period and the size of its orbit; Isaac Newton later explained these patterns through gravitational theory.
Updated 22 Oct 2026
Space
Kessler syndrome
Kessler syndrome describes a possible self-reinforcing increase in orbital debris: collisions generate fragments, which raise the likelihood of further collisions. Proposed by Donald J. Kessler and Burton G. Cour-Palais in 1978, the idea is a model of long-term debris growth, not a claim that every orbit is already caught in an unstoppable cascade. Its likelihood and consequences depend on the population, altitude and behaviour of objects in particular orbital regions.
Updated 23 Oct 2026
Space
Kuiper Belt
The Kuiper Belt is a broad, disk-shaped region of icy small bodies beyond Neptune. Often described as extending from about 30 to 50 astronomical units from the Sun, it contains Pluto and many other objects left from the solar system's formation; its outer boundary is not sharply defined. Observations of Kuiper Belt objects help scientists investigate the history of the outer solar system, and NASA's New Horizons mission has explored Pluto and Arrokoth up close.
Updated 22 Oct 2026
Space
Lagrange point
A Lagrange point is a position in a rotating two-body system where the gravity of two large bodies and the motion of a much smaller object combine so that the small object can remain in a fixed configuration relative to the larger pair. The restricted three-body problem has five such points, labeled L1–L5. The collinear points L1, L2 and L3 are dynamically unstable, while L4 and L5 can be stable under the appropriate mass-ratio condition. Space missions use these regions for solar monitoring, astronomy and other observations.
Updated 24 Oct 2026
Space
Lagrange points
Lagrange points are five positions defined by the gravity of two large bodies and the orbital motion of a much smaller object in their shared rotating system. Space missions use the regions around some of these points as observing locations: the Sun–Earth L1 is useful for monitoring the Sun, while the Sun–Earth L2 provides a view of deep space. Spacecraft generally orbit near a point and make adjustments rather than remaining motionless on it.
Updated 19 Oct 2026
Space
Laser Interferometer Space Antenna (LISA)
The Laser Interferometer Space Antenna (LISA) is a planned ESA-led space observatory, developed with NASA collaboration, designed to detect gravitational waves. Three spacecraft will fly in a triangular formation and use laser interferometry to measure changes in their separations caused by passing waves. Its launch is planned for 2035.
Updated 8 Nov 2026
Space
Lunar eclipse
A lunar eclipse occurs when the Moon passes into Earth's shadow, which happens when the Sun, Earth and Moon align near a full Moon. Depending on how deeply the Moon enters the shadow, the event is classified as total, partial or penumbral. During totality, sunlight filtered through Earth's atmosphere can give the Moon a reddish appearance.
Updated 21 Oct 2026
Space
Lunar Gateway
Lunar Gateway is a planned crewed space station in orbit around the Moon, developed through NASA's Artemis programme with contributions from international partners. Its modular elements are intended to provide living and working space, communications, logistics and propulsion support for missions in deep space. The station's near-rectilinear halo orbit is designed to balance access to the lunar surface with fuel-efficient operations and sustained communication with Earth.
Updated 25 Oct 2026
Space
Lunar laser ranging
Lunar laser ranging is a geodetic technique that measures the Earth–Moon distance by timing laser pulses sent from Earth to retroreflectors on the Moon and back. Since the first Apollo-era measurements, long-running observations have refined models of lunar motion and Earth–Moon dynamics, tracked the Moon’s gradual recession, and enabled tests of gravitational physics.
Updated 26 Oct 2026
Space
Lunar libration
Lunar libration is the apparent, periodic change in the Moon’s orientation as seen from Earth. Although the Moon is tidally locked and generally keeps the same hemisphere facing Earth, its slightly elliptical, tilted orbit and the observer’s changing position reveal small additional portions of the lunar surface over time. The combined effect lets observers see about 59 percent of the Moon’s surface, rather than exactly one half.
Updated 23 Oct 2026
Space
Lunar standstill
A lunar standstill is a period when the Moon’s monthly north–south range in the sky reaches either a maximum (major standstill) or a minimum (minor standstill). The cycle repeats about every 18.6 years as the orientation of the Moon’s inclined orbital plane changes. During a major standstill, the Moon can rise and set at unusually far-north and far-south points on the horizon; the extreme pattern is observable for roughly two years.
Updated 7 Nov 2026
Space
Lunar swirls
Lunar swirls are distinctive bright, sinuous markings on the Moon, often interwoven with darker patches and found in both maria and highland terrain. Orbital observations show that mapped swirls coincide with localized crustal magnetic anomalies, and several lines of research support a role for these magnetic fields in limiting solar-wind weathering. Their detailed formation remains unresolved: differences in soil composition, grain properties and topography suggest that more than one process may contribute.
Updated 24 Oct 2026
Space
Magnetar
A magnetar is a neutron star whose exceptionally strong magnetic field is thought to power intense bursts of X-rays and gamma rays. These compact stellar remnants are observed as transient high-energy sources, including soft gamma repeaters and anomalous X-ray pulsars. Sudden changes in their crust or magnetic field can release large amounts of energy, and observations of one Milky Way magnetar emitting a fast radio burst have linked at least some such radio flashes to this class of object.
Updated 25 Oct 2026
Space
Mars
Mars is the fourth planet from the Sun, a rocky world with a thin, carbon-dioxide-rich atmosphere and a surface colored red by oxidized iron minerals. Its day is close in length to Earth's, but its year is longer, and it has two small moons, Phobos and Deimos. Geological features and minerals record a past in which liquid water was more widespread. A 2025 peer-reviewed study reported potential biosignatures in a Perseverance sample, but these are not proof of life and require further study.
Updated 14 Oct 2026
Space
Milky Way
The Milky Way is the barred spiral galaxy that contains the Solar System and billions of other stars, along with gas, dust, and dark matter. Its flattened stellar disc and spiral arms surround a dense, elongated central bulge. From Earth, the disc appears as a pale band across the night sky; modern surveys map the galaxy from our position inside it.
Updated 18 Oct 2026
Space
Mimas
Mimas is a small icy moon of Saturn, discovered by William Herschel in 1789. Its heavily cratered surface is dominated by the 130-kilometre-wide Herschel impact crater. Cassini observations also prompted a 2024 study to infer a possible young global subsurface ocean from Mimas’s orbital motion, a result that remains an active subject of scientific investigation.
Updated 24 Oct 2026
Space
Moon
Earth's Moon is its only natural satellite and the nearest large celestial body to our planet. Its orbit and synchronous rotation shape the phases we see, while its gravity contributes to ocean tides. A surface marked by impact craters, ancient lava plains and bright highlands preserves evidence of the early Solar System; samples and observations from space missions continue to inform research into its origin and evolution.
Updated 13 Oct 2026
Space
NavIC
NavIC (Navigation with Indian Constellation), formerly known as the Indian Regional Navigation Satellite System (IRNSS), is India's regional satellite navigation system. Developed by the Indian Space Research Organisation, it provides positioning, navigation and timing services over India and a surrounding region. It offers a civilian Standard Positioning Service and a Restricted Service, and its newer satellite generation adds signals in the L1 band alongside L5 and S-band navigation signals.
Updated 6 Nov 2026
Space
Near-rectilinear halo orbit
A near-rectilinear halo orbit (NRHO) is a highly elongated, three-dimensional orbit near a celestial body, including a family of trajectories around the Moon. Its geometry can offer spacecraft recurring close approaches while spending much of each revolution far from the body. NASA selected an NRHO for the planned lunar Gateway because it balances access to the lunar surface, communications with Earth and propellant-efficient station keeping. Gateway's program status has since changed; the orbit remains an important example of trajectory design for lunar exploration.
Updated 28 Oct 2026
Space
Oort Cloud
The Oort Cloud is a hypothesized, roughly spherical reservoir of icy bodies on extremely distant orbits around the Sun. Astronomers infer it chiefly from the origins and directions of long-period comets. Unlike the nearer, disk-shaped Kuiper Belt, the cloud has not been observed directly, and its size, population and detailed structure remain uncertain.
Updated 17 Oct 2026
Space
Orbital debris
Orbital debris is human-made material in orbit around Earth that no longer serves a useful function. It ranges from retired spacecraft and spent rocket stages to fragments and tiny particles. Travelling at orbital speeds, debris can damage working spacecraft, while collisions and break-ups can create additional fragments. International guidance therefore emphasizes preventing debris generation and limiting its persistence after missions end.
Updated 25 Oct 2026
Space
Orbital resonance
Orbital resonance occurs when orbiting bodies repeatedly influence one another gravitationally because their orbital periods, or related orbital frequencies, are close to a simple ratio of whole numbers. Resonances can shape the long-term arrangement and evolution of planetary systems: they may help maintain stable orbital patterns or contribute to complex and chaotic motion. Jupiter’s moons Io, Europa and Ganymede provide a well-studied example, with orbital periods in an approximate 1:2:4 relationship.
Updated 22 Oct 2026
Space
OSIRIS-REx
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) was a NASA sample-return mission to near-Earth asteroid Bennu. It collected surface material in 2020 and returned the sample capsule to Earth in September 2023. The mission's measurements and returned material provide researchers with direct evidence about Bennu and primitive solar-system matter.
Updated 8 Nov 2026
Space
Pale Blue Dot (photograph)
The Pale Blue Dot is a Voyager 1 image of Earth made on 14 February 1990, when the spacecraft was leaving the planetary region of the Solar System. Earth appears as a tiny point within scattered sunlight in a frame from a wider set of images known as the Solar System Family Portrait. The photograph became widely known through astronomer Carl Sagan's advocacy and later writing, and is often used to reflect on Earth's scale and place in space.
Updated 27 Oct 2026
Space
Parker Solar Probe
Parker Solar Probe is a NASA spacecraft designed to investigate the Sun's outer atmosphere and the solar wind. Launched in 2018, it follows a close, elliptical orbit around the Sun and uses a heat shield to protect its instruments. In 2021 it became the first spacecraft confirmed to pass through the solar corona, sampling particles and magnetic fields in a region previously studied mainly from afar.
Updated 23 Oct 2026
Space
Parker spiral
The Parker spiral is the large-scale spiral pattern of the Sun’s magnetic field carried through interplanetary space by the solar wind. It forms because the solar wind streams outward while the Sun rotates, winding magnetic field lines into a curved geometry. The pattern shapes how charged particles travel through the heliosphere and is a key part of models of the interplanetary magnetic field.
Updated 27 Oct 2026
Space
Pioneer 10
Pioneer 10 was a NASA spacecraft that made the first close-up exploration of Jupiter and opened the way for later missions to the outer planets. Launched in 1972, it crossed the asteroid belt, flew past Jupiter in December 1973, and continued returning data from the outer Solar System for decades. The spacecraft also carried a small plaque depicting human figures and Earth's location for any distant finder.
Updated 30 Oct 2026
Space
Pioneer anomaly
The Pioneer anomaly was a small, unexpected Doppler-tracking signal associated with Pioneer 10 and Pioneer 11 as they travelled through the outer Solar System. Early analyses interpreted it as an apparent acceleration toward the Sun, raising questions about spacecraft forces and gravity. Later thermal modelling using spacecraft design records and flight telemetry showed that anisotropic heat emission could account for the signal; after accounting for thermal recoil, the 2012 analysis found no statistically significant residual anomalous acceleration.
Updated 26 Oct 2026
Space
Pioneer plaque
The Pioneer plaques are gold-covered aluminium panels carried by the Pioneer 10 and Pioneer 11 spacecraft, launched in 1972 and 1973. Designed by Carl Sagan and Frank Drake, with artwork by Linda Salzman Sagan, they use diagrams to identify the spacecraft's origin and provide a symbolic description of Earth and humanity. The plaques were intended as messages for any extraterrestrial beings that might encounter the probes, though such an encounter is considered highly unlikely.
Updated 22 Oct 2026
Space
Pluto
Pluto is a dwarf planet in the Kuiper Belt beyond Neptune. Discovered in 1930 and reclassified under the International Astronomical Union’s planet definition in 2006, it is a complex icy world with a thin atmosphere and five known moons. NASA’s New Horizons spacecraft made the first close flyby of Pluto in 2015.
Updated 20 Oct 2026
Space
Pulsar
A pulsar is a rapidly rotating neutron star observed through regular pulses of electromagnetic radiation. Strong magnetic fields channel radiation into beams; as the star spins, a beam may sweep across Earth, producing a pulse each time it comes into view. Pulsars are studied as unusual stellar remnants and, in binary systems, as highly precise clocks for measuring stellar motion and testing gravity.
Updated 20 Oct 2026
Space
Radio astronomy
Radio astronomy studies celestial objects and processes through radio-frequency radiation. Antennas and sensitive receivers capture signals from planets, interstellar gas, stars, and galaxies; processing turns those measurements into spectra and images. Arrays that combine separated antennas can produce fine detail, while human-made radio interference remains a significant challenge because cosmic signals are extremely faint.
Updated 18 Oct 2026
Space
Roche limit
The Roche limit is the distance from a primary body within which the tidal difference in its gravitational pull can overcome the self-gravity holding a nearby satellite together. Its value depends on the bodies’ densities and on assumptions about the satellite’s shape, strength and internal structure. It helps explain why many planetary rings lie close to their planets, but it is not a universal sharp boundary at which every object must break apart.
Updated 23 Oct 2026
Space
Roche-lobe overflow
Roche-lobe overflow is mass transfer in a close binary system that begins when one star expands to fill the gravitational region associated with it. Gas can then pass through the inner Lagrange point toward its companion, changing the stars' evolution and sometimes powering accretion-related events such as novae and X-ray emission.
Updated 26 Oct 2026
Space
Rogue planet
A rogue planet, also called a free-floating planet, is a planetary-mass object that travels through space without being gravitationally bound to a star. Some may have been ejected from planetary systems, while others may have formed in relative isolation through the collapse of gas and dust; definitions near the boundary with brown dwarfs remain debated.
Updated 28 Oct 2026
Space
Saros (astronomy)
The Saros is an eclipse cycle of about 6,585.3 days—roughly 18 years, 11 days and 8 hours—after which the Sun, Earth and Moon return to similar relative positions. Eclipses separated by one Saros have similar geometry, but are generally visible from different parts of Earth because the cycle is not a whole number of days. Successive eclipses of a Saros series form a long-lived sequence that gradually shifts across the globe.
Updated 6 Nov 2026
Space
Saturn
Saturn is the sixth planet from the Sun and the second largest in the Solar System. This hydrogen-and-helium gas giant is known for its extensive rings, made mostly of icy and rocky particles, and its varied moons. NASA's Cassini mission transformed understanding of Saturn and its system before ending in a deliberate plunge into the planet in 2017.
Updated 6 Nov 2026
Space
Solar eclipse
A solar eclipse occurs when the Moon passes between the Sun and Earth and its shadow falls on part of Earth, obscuring some or all of the Sun's bright disk for observers in the shadow. The geometry produces partial, annular, total and, in some cases, hybrid eclipses. Eclipses occur only when a new Moon passes close to the points where its tilted orbit crosses Earth's orbital plane, so they do not happen at every new moon. Safe observation requires proper solar filters except during the brief total phase of a total eclipse, and only within the path of totality.
Updated 16 Oct 2026
Space
Solar flare
A solar flare is a sudden release of energy in the Sun's atmosphere, observed as an intense burst of electromagnetic radiation. Flares often occur in magnetically active regions near sunspots, when stressed magnetic fields reorganize, and can affect Earth's sunlit ionosphere and radio communications. A flare is a burst of radiation, not the same thing as a coronal mass ejection, although the two phenomena may occur together.
Updated 28 Oct 2026
Space
Solar sail
A solar sail is a spacecraft propulsion system that uses the momentum carried by sunlight to produce thrust. A large, lightweight reflective surface converts the tiny pressure of photons into continuous acceleration without consuming onboard propellant. The resulting force is small, so solar sailing is most useful when a mission can exploit it over long periods and carefully control the sail's orientation.
Updated 25 Oct 2026
Space
Solar wind
The solar wind is the continuous outflow of plasma from the Sun's outer atmosphere, the corona. Composed chiefly of protons and electrons and carrying the Sun's magnetic field, it varies in speed and density; fast streams are commonly associated with coronal holes. The wind fills the heliosphere and interacts with planets and their magnetic environments. At Earth, these interactions help produce auroras and can contribute to geomagnetic storms that affect technology.
Updated 18 Oct 2026
Space
Space elevator
A space elevator is a proposed transportation system that would move payloads between Earth’s surface and space along a long, tensioned tether. In the commonly discussed Earth design, the tether extends from a low-latitude anchor through geostationary orbit to an outer counterweight, with electrically powered climbers carrying cargo. The concept remains unbuilt; creating a continuous tether with sufficient strength, low mass and practical manufacturing quality is a central challenge.
Updated 27 Oct 2026
Space
Space exploration
Space exploration is the investigation of outer space and celestial bodies using remote observations, robotic spacecraft and human missions. Since the first artificial satellites, exploration has advanced from Cold War-era competition to planetary probes, crewed lunar flights and international orbital research, expanding scientific knowledge while demanding substantial technical, financial and human resources.
Updated 12 Oct 2026
Space
Stellar parallax
Stellar parallax is the apparent yearly shift in a nearby star's position against much more distant stars, caused by Earth's changing viewpoint as it orbits the Sun. Measuring this tiny angle allows astronomers to infer stellar distances geometrically. When the parallax p is expressed in arcseconds, the distance d in parsecs is d = 1/p.
Updated 27 Oct 2026
Space
Tholin
Tholins are complex, dark organic materials produced in laboratory simulations of the chemistry of planetary atmospheres and icy surfaces. The term was introduced by Carl Sagan and Bishun Khare for laboratory products that helped model the reddish haze observed at Titan. Tholins are not a single pure chemical compound: their composition and properties depend on the starting materials and the energy used to process them, so researchers treat them as analogues for studying organic chemistry on worlds such as Titan and other outer Solar System bodies.
Updated 27 Oct 2026
Space
Tidal disruption event
A tidal disruption event (TDE) occurs when a star passes close enough to a black hole that the difference in gravitational pull across the star overcomes its self-gravity and tears it apart. Some stellar debris escapes, while some returns toward the black hole and can form hot, luminous gas that produces a transient flare. Surveys detect these rare events as changing sources of light, allowing astronomers to study otherwise inconspicuous black holes and the environments around them.
Updated 24 Oct 2026
Space
Tidal locking
Tidal locking is a long-term rotational state in which an orbiting body's spin becomes synchronized with its motion around a companion. In the familiar 1:1 case, the same hemisphere continually faces the companion, as the Moon does toward Earth. Gravitational tides deform the bodies, and the dissipation of energy in those deformations changes their spins and orbits over time.
Updated 21 Oct 2026
Space
Titan
Titan is Saturn's largest moon and the only moon known to have a dense atmosphere. Its nitrogen-rich air, methane-based weather, surface rivers and lakes of liquid hydrocarbons, and possible subsurface water ocean make it a distinctive world for planetary science. NASA's Cassini orbiter and ESA's Huygens probe transformed knowledge of Titan, while NASA's Dragonfly rotorcraft is planned to investigate its surface chemistry and habitability in the future.
Updated 6 Nov 2026
Space
Transient lunar phenomenon
A transient lunar phenomenon (TLP), also called a lunar transient phenomenon (LTP), is a brief, reported change in the Moon’s appearance, such as a localized brightening, color change or obscuration. Reports are historically catalogued, but their causes and interpretation remain debated.
Updated 8 Nov 2026
Space
Triton (moon)
Triton is Neptune’s largest moon and an unusual satellite whose orbit runs opposite Neptune’s rotation. The retrograde orbit, along with its size and other characteristics, suggests it was captured by Neptune rather than forming in place. Observations by Voyager 2 during its 1989 flyby revealed a cold, icy world with a thin nitrogen-rich atmosphere, geologically young terrain and active geyser-like plumes.
Updated 30 Oct 2026
Space
Uranus (planet)
Uranus is the seventh planet from the Sun and one of the Solar System’s two ice giants. Its atmosphere gives it a blue-green appearance, and its axis is tilted so far that it rotates nearly on its side. The planet has a faint ring system and dozens of known moons; Voyager 2 remains the only spacecraft to have made a close flyby.
Updated 31 Oct 2026
Space
Valles Marineris
Valles Marineris is an immense canyon system near the Martian equator, east of the Tharsis region. Extending roughly 4,000 kilometres, it is among the largest canyon systems known in the Solar System. Evidence indicates that crustal rifting associated with the Tharsis region initiated the system, while later processes including erosion and mass movement helped shape it.
Updated 7 Nov 2026
Space
Van Allen radiation belts
The Van Allen radiation belts are regions of energetic charged particles trapped by Earth's magnetic field. Their particle populations and intensity vary over time, making them important to understand for spacecraft design, space-weather research and crewed missions beyond low Earth orbit.
Updated 7 Nov 2026
Space
Venus
Venus is the second planet from the Sun, a rocky world similar in size to Earth but with a very different environment. Its dense, carbon-dioxide-rich atmosphere and sulfuric-acid clouds obscure the surface and produce an intense greenhouse effect, making Venus the Solar System’s hottest planet. The planet rotates slowly in a retrograde direction, and radar observations from spacecraft have revealed volcanic plains, mountains and other surface features.
Updated 19 Oct 2026
Space
Voyager 1
Voyager 1 is a NASA robotic spacecraft launched in 1977 to study Jupiter and Saturn. Its flybys returned detailed observations of the giant planets and their moons, including evidence of active volcanism on Jupiter's moon Io. In August 2012 it crossed the heliopause into interstellar space, becoming the first spacecraft to do so. The long-running mission continues to use its remaining instruments to study the distant space environment while engineers manage its declining power supply.
Updated 19 Oct 2026
Space
Voyager 2
Launched by NASA in 1977, Voyager 2 is a robotic spacecraft that surveyed Jupiter, Saturn, Uranus and Neptune before continuing outward. Its close encounters revealed new details about the giant planets and their moons; in 2018 it crossed the heliopause into interstellar space, extending its work from planetary exploration to measurements beyond the Sun's wind-dominated bubble.
Updated 28 Oct 2026
Space
Voyager Golden Record
The Voyager Golden Record is a gold-plated copper phonograph disc carried by both Voyager spacecraft, launched in 1977. Created as a message for any extraterrestrial intelligence that might encounter a probe, it combines encoded images, spoken greetings, natural and human-made sounds, and music. Its contents present a deliberately selected portrait of Earth and its inhabitants rather than a comprehensive record of humanity.
Updated 23 Oct 2026
Space
White dwarf stars
White dwarfs are compact stellar remnants left after many stars, including the Sun, shed their outer layers. Roughly Earth-sized but containing a substantial fraction of a solar mass, they are supported by electron degeneracy pressure rather than ongoing core fusion. They cool over time and provide important evidence about stellar evolution, binary systems and thermonuclear supernovae.
Updated 6 Nov 2026