page_title: Near-Earth object
section_title: Missions to NECs
hierarchical_section_title: Near-Earth object / Exploratory missions / Missions to NECs
caption_attribution_description: English: Mosaic of four images taken by Rosetta's navigation camera (NAVCAM) on 19 September 2014 at 28.6&#160;km (17.8&#160;mi) from the centre of comet 67P/Churyumov–Gerasimenko. The images used for this mosaic were taken in sequence as a 2×2 raster over an approximately 20 minute period, meaning that there is some motion of the spacecraft and rotation of the comet between the images. The four individual full-frame images are also available as related images below. Note this mosaic has been rotated by 180 degrees and cropped. The mosaic has been put together using Microsoft ICE. This left a few small regions requiring slight exposure adjustments using Adobe LightRoom. The full image has then been lightly contrast enhanced to bring out the activity without increasing the background noise too much. Español: Mosaico de cuatro imágenes tomadas por la cámara de navegación de Rosetta (NavCam) el 19 de septiembre de 2014 a una distancia de 28,6 km del centro del cometa 67P/Churyumov-Gerasimenko. Français&#160;: Mosaïque de quatre photographies de la comète 67P/Tchourioumov-Guérassimenko prises par la sonde Rosetta en septembre 2014. Русский: Снимок кометы Чурюмова — Герасименко, сделанный 19 сентября 2014 года камерой КА «Розетта». Türkçe: 67P/Churyumov-Gerasimenko adlı kuyrukluyıldızın Rosetta isimli uzay aracı tarafından 19 Eylül 2014 tarihinde, kuyrukluyıldızın merkezinden 28,6 km uzaklıktan çekilen fotoğrafı. Українська: Знімок комети Чурюмова — Герасименко, зроблений 19 вересня 2014 року камерою КА «Розетта».
context_page_description: A near-Earth object is any small Solar System body whose orbit brings it to proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun is less than 1.3 astronomical units. If a NEO's orbit crosses the Earth's, and the object is larger than 140 meters across, it is considered a potentially hazardous object. Most known PHOs and NEOs are asteroids, but a small fraction are comets.
  There are over 20,000 known near-Earth asteroids, over a hundred short-period near-Earth comets, and a number of solar-orbiting meteoroids large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of greater awareness of this potential danger. Asteroids as small as 20 m can damage the local environment and populations. Larger asteroids penetrate the atmosphere to the surface of the Earth, producing craters if they impact a continent or tsunamis if they impact sea.
context_section_description: The first near-Earth comet visited by a space probe was 21P/Giacobini–Zinner in 1985, when the NASA/ESA probe International Cometary Explorer (ICE) passed through its coma. In March 1986, ICE, along with Soviet probes Vega 1 and Vega 2, ISAS probes Sakigake and Suisei and ESA probe Giotto flew by the nucleus of Halley's Comet. In 1992, Giotto also visited another NEC, 26P/Grigg–Skjellerup.
  In November 2010, the NASA probe Deep Impact flew by the near-Earth comet 103P/Hartley. Earlier, in July 2005, this probe flew by the non-near-Earth comet Tempel 1, hitting it with a large copper mass.
  In August 2014, ESA probe Rosetta began orbiting near-Earth comet 67P/Churyumov–Gerasimenko, while its lander Philae landed on its surface in November 2014. After the end of its mission, Rosetta was crashed into the comet's surface in 2016.
caption: 67P/Churyumov–Gerasimenko as seen by ESA's Rosetta probe
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