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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 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.
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a 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 a small fraction are comets.
Triton is the largest natural satellite of the planet Neptune, and was the first Neptunian moon to be discovered, on October 11, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. Because of its retrograde orbit and composition similar to Pluto, Triton is thought to have been a dwarf planet, captured from the Kuiper belt.
Rosetta was a space probe built by the European Space Agency launched on 2 March 2004. Along with Philae, its lander module, Rosetta performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P). During its journey to the comet, the spacecraft performed flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after SOHO / Cluster and XMM-Newton.
Stardust was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysis. It was the first sample return mission of its kind. En route to Comet Wild 2, it also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth.
The Infrared Astronomical Satellite (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten months. The telescope was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC). Over 250,000 infrared sources were observed at 12, 25, 60, and 100 micrometer wavelengths.
The Discovery Program is a series of Solar System exploration missions funded by the U.S. National Aeronautics and Space Administration (NASA) through its Planetary Missions Program Office. The cost of each mission is capped at a lower level than missions from NASA's New Frontiers or Flagship Programs. As a result, Discovery missions tend to be more focused on a specific scientific goal rather than serving a general purpose.
Ernst Wilhelm Leberecht Tempel, normally known as Wilhelm Tempel, was a German astronomer who worked in Marseille until the outbreak of the Franco-Prussian War in 1870, then later moved to Italy.
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.
55P/Tempel–Tuttle is a retrograde periodic comet with an orbital period of 33 years. It fits the classical definition of a Halley-type comet with a period of between 20 and 200 years. It was independently discovered by Wilhelm Tempel on December 19, 1865, and by Horace Parnell Tuttle on January 6, 1866.
Tempel 1 is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.6 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 14, 2011 and came back to perihelion in August 2016. On 26 May 2024 it will make a modest approach of 0.55 AU to Jupiter which will lift the perihelion distance and 9P will next come to perihelion on 12 February 2028 when it will be 1.77 AU from the Sun.
Marc William Buie is an American astronomer and prolific discoverer of minor planets who works at the Southwest Research Institute in Boulder, Colorado in the Space Science Department. Formerly he worked at the Lowell Observatory in Flagstaff, Arizona, and was the Sentinel Space Telescope Mission Scientist for the B612 Foundation, which is dedicated to protecting Earth from asteroid impact events.
Wide-field Infrared Survey Explorer is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2011, before being re-activated in 2013 and renamed the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE). WISE discovered thousands of minor planets and numerous star clusters. Its observations also supported the discovery of the first Y-type brown dwarf and Earth trojan asteroid.
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.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
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.
Double Asteroid Redirection Test (DART) was a NASA space mission aimed at testing a method of planetary defense against near-Earth objects (NEOs). It was designed to assess how much a spacecraft impact deflects an asteroid through its transfer of momentum when hitting the asteroid head-on. The selected target asteroid, Dimorphos, is a minor-planet moon of the asteroid Didymos; neither asteroid poses an impact threat to Earth. Launched on 24 November 2021, the DART spacecraft successfully collided with Dimorphos on 26 September 2022 at 23:14 UTC about 11 million kilometers from Earth. The collision shortened Dimorphos' orbit by 32 minutes, greatly in excess of the pre-defined success threshold of 73 seconds. DART's success in deflecting Dimorphos was due to the momentum transfer associated with the recoil of the ejected debris, which was substantially larger than that caused by the impact itself.
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.
References
- ↑ "JPL Science Division". Archived from the original on 29 September 2006. Retrieved 27 March 2012.
- ↑ Goguen, James; Buratti, B.J.; Li, J.-Y.; Mosher, J.A.; Hicks, M.D.; Schmidt, B.E.; Goguen, J.D. (2010). "Direct Detection of Seasonal Changes on Triton with Hubble Space Telescope". The Astrophysical Journal. 723 (1): L49–L52. Bibcode:2010ApJ...723L..49B. doi: 10.1088/2041-8205/723/1/L49 .
- ↑ Moore, Patrick (27 July 2005). "Fallout from Deep Impact". BBC One. Retrieved 27 March 2012.
- ↑ "Palomar Telescope Observes Collision of Deep Impact Probe With Comet Tempel 1".
- ↑ [https://www.astro.umd.edu/~farnham/tt/tthist.html}
- ↑ "WISE Captures Key Images of Comet Mission's Destination". 5 October 2010. Archived from the original on 11 March 2012. Retrieved 27 March 2012.
- ↑ "Comet Hartley 2 Leaves a Bumpy Trail". Science Daily. 18 July 2011. Retrieved 27 March 2012.
- http://scitechdaily.com/astronomers-reveal-the-true-identity-of-mysterious-centaurs/
- http://www.space.com/18364-comet-breakup-inner-solar-system.html
- https://web.archive.org/web/20150524233040/http://scaapt.org/meetings/2013mtg1spr/report.pdf
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