An asteroid is a minor planet—an object that is neither a true planet nor an identified comet— that orbits within the inner Solar System. They are rocky, metallic, or icy bodies with no atmosphere, classified as C-type (carbonaceous), M-type (metallic), or S-type (silicaceous). The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across and larger than meteoroids, to Ceres, a dwarf planet almost 1000 km in diameter. A body is classified as a comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum between these types of bodies.
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.
Comet Shoemaker–Levy 9 was a comet that broke apart in July 1992 and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide. The collision provided new information about Jupiter and highlighted its possible role in reducing space debris in the inner Solar System.
Comet Hale–Bopp is a long-period comet that was one of the most widely observed of the 20th century and one of the brightest seen for many decades.
Leo is one of the constellations of the zodiac, between Cancer the crab to the west and Virgo the maiden to the east. It is located in the Northern celestial hemisphere. Its name is Latin for lion, and to the ancient Greeks represented the Nemean Lion killed by the mythical Greek hero Heracles as one of his twelve labors. Its old astronomical symbol is (♌︎). One of the 48 constellations described by the 2nd-century astronomer Ptolemy, Leo remains one of the 88 modern constellations today, and one of the most easily recognizable due to its many bright stars and a distinctive shape that is reminiscent of the crouching lion it depicts.
A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance. This definition applies to the object's orbit around the Sun, rather than its current position, thus an object with such an orbit is considered an NEO even at times when it is far from making a close approach of Earth. If an NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but about 0.35% are comets.
Armageddon is a 1998 American science fiction disaster film produced and directed by Michael Bay, produced by Jerry Bruckheimer and released by Touchstone Pictures. The film follows a group of blue-collar deep-core drillers sent by NASA to destroy a gigantic asteroid, which is the size of Texas, on a collision course with Earth. It stars an ensemble cast including Bruce Willis with Billy Bob Thornton, Liv Tyler, Ben Affleck, Will Patton, Peter Stormare, Keith David, Owen Wilson, William Fichtner and Steve Buscemi.
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Very intense or unusual meteor showers are known as meteor outbursts and meteor storms, which produce at least 1,000 meteors an hour, most notably from the Leonids. The Meteor Data Centre lists over 900 suspected meteor showers of which about 100 are well established. Several organizations point to viewing opportunities on the Internet. NASA maintains a daily map of active meteor showers.
Leo Minor is a small and faint constellation in the northern celestial hemisphere. Its name is Latin for "the smaller lion", in contrast to Leo, the larger lion. It lies between the larger and more recognizable Ursa Major to the north and Leo to the south. Leo Minor was not regarded as a separate constellation by classical astronomers; it was designated by Johannes Hevelius in 1687.
Téa Leoni is an American actress. In her early career, she starred in the television sitcoms Flying Blind (1992–93) and The Naked Truth (1995–1998). Her breakthrough role was in the 1995 action comedy film Bad Boys. Leoni had lead roles in films such as Deep Impact (1998), The Family Man (2000), Jurassic Park III (2001), Spanglish (2004), and Fun with Dick and Jane (2005). From 2014 to 2019, she starred as Elizabeth McCord, Secretary of State, in the CBS political drama series Madam Secretary.
A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a synonym for a fireball, sometimes specific to those with an apparent magnitude of −4 or brighter.
Deep Impact was a NASA space probe launched from Cape Canaveral Air Force Station on January 12, 2005. It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the Impactor successfully collided with the comet's nucleus. The impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than had been expected. The impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater.
Brian Geoffrey Marsden was a British astronomer and the longtime director of the Minor Planet Center (MPC) at the Center for Astrophysics | Harvard & Smithsonian.
The Nibiru cataclysm is a supposed disastrous encounter between Earth and a large planetary object that certain groups believed would take place in the early 21st century. Believers in this doomsday event usually refer to this object as Nibiru or Planet X. The idea was first put forward in 1995 by Nancy Lieder, founder of the website ZetaTalk. Lieder claims she is a contactee with the ability to receive messages from extraterrestrials from the Zeta Reticuli star system through an implant in her brain. She states that she was chosen to warn mankind that the object would sweep through the inner Solar System in May 2003 causing Earth to undergo a physical pole shift that would destroy most of humanity.
The Hammer of God is a science fiction novel by Arthur C. Clarke originally published in 1993. Set in the year 2109, it deals with the discovery of an asteroid to be on course to collide with Earth and depicts the mission for deflecting the asteroid by using fusion thermal rockets.
EPOXI was a compilation of NASA Discovery program missions led by the University of Maryland and principal investigator Michael A'Hearn, with co-operation from the Jet Propulsion Laboratory and Ball Aerospace. EPOXI uses the Deep Impact spacecraft in a campaign consisting of two missions: the Deep Impact Extended Investigation (DIXI) and Extrasolar Planet Observation and Characterization (EPOCh). DIXI aimed to send the Deep Impact spacecraft on a flyby of another comet, after its primary mission was completed in July 2005, while EPOCh saw the spacecraft's photographic instruments as a space observatory, studying extrasolar planets.
Comet Hartley 2, designated as 103P/Hartley by the Minor Planet Center, is a small periodic comet with an orbital period of 6.48 years. It was discovered by Malcolm Hartley in 1986 at the Schmidt Telescope Unit, Siding Spring Observatory, Australia. Its diameter is estimated to be 1.2 to 1.6 kilometres.
Harold James Reitsema is an American astronomer who was part of the teams that discovered Larissa, the fifth of Neptune's known moons, and Telesto, Saturn's thirteenth moon. Reitsema and his colleagues discovered the moons through ground-based telescopic observations. Using a coronagraphic imaging system with one of the first charge-coupled devices available for astronomical use, they first observed Telesto on April 8, 1980, just two months after being one of the first groups to observe Janus, also a moon of Saturn. Reitsema, as part of a different team of astronomers, observed Larissa on May 24, 1981, by watching the occultation of a star by the Neptune system.
A Fire in the Sky is a made-for-television disaster movie that debuted on NBC on November 26, 1978. The movie is based on a story by Paul Gallico where the earth is threatened by a large comet, which impacts near Phoenix and causes massive destruction there. It is a Bill Driskill Production in association with Columbia Pictures Television.
In modern times, numerous impact events on Jupiter have been observed, the most significant of which was the collision of Comet Shoemaker–Levy 9 in 1994. Jupiter is the most massive planet in the Solar System and thus has a vast sphere of gravitational influence, the region of space where an asteroid capture can take place under favorable conditions.
