Comet Grigg–Skjellerup (formally designated 26P/Grigg–Skjellerup) is a periodic comet. It was visited by the Giotto probe in July 1992.[5] The spacecraft came as close as 200 km, but could not take pictures because some instruments were damaged from its encounter with Halley's Comet.[5]

Discovered in 1902 by John Grigg of New Zealand, and rediscovered in its next appearance in 1922 by John Francis Skjellerup, an Australian then living and working for about two decades in South Africa where he was a founder member of the Astronomical Society of Southern Africa.

In 1987, it was belatedly discovered by Ľubor Kresák that the comet had been observed in 1808 as well, by Jean-Louis Pons.

The comet has often suffered the gravitational influence of Jupiter, which has altered its orbit considerably. For instance, its perihelion distance has changed from 0.77 AU in 1725 to 0.89 AU in 1922 to 0.99 AU in 1977 and to 1.12 AU in 1999.

Having its recent perihelion so close to Earth's orbit made it an easy target to reach for the Giotto mission (spacecraft) in 1992, whose primary mission was to Comet Halley. Giotto had a closest approach to Grigg–Skjellerup of 200 km, much closer than its approach to Comet Halley, but was unable to obtain images as its camera was destroyed during the Halley rendezvous in 1986.

In 1972 the comet was discovered to produce a meteor shower, the Pi Puppids, and its current orbit makes them peak around April 23, for observers in the southern hemisphere, best seen when the comet is near perihelion.

The 2002 return (expected perihelion around October 8, 2002) was very unfavorable and no observations were reported.

The comet nucleus is estimated to be 2.6 kilometers in diameter.[4]

The comet is a type locality for the mineral brownleeite.[6][7]

Grigg-Skjellerup Eso9209a
Discovered byJohn Grigg and John Francis Skjellerup
Discovery date1902 and 1922
1808 C1; 1808 III;
1902 O1; 1902 II;
1902c; 1922 K1;
1922 I; 1922b;
1927 F1; 1927 V;
1927e; 1932 II;
1932d; 1937 III;
1937e; 1942 V;
1942d; 1947 II;
1947a; 1952 IV;
1952b; 1957 I;
1956i; 1961 IX;
1961g; 1967 I;
1966f; 1972 II;
1972b; 1977 VI;
1977b; 1982 IV;
1982a; 1987 X;
1986m; 1992 XVIII
Orbital characteristics A
EpochApril 10, 2007 (JD 2454200.5)
Aphelion4.9332 AU
Perihelion1.1168 AU
Semi-major axis3.0437 AU
Orbital period5.31 a
Earth MOID0.079 AU (11,800,000 km)[4]
Last perihelion2018-Oct-01[1]
July 6, 2013[2][3]
March 23, 2008
Next perihelion2023-Dec-25 (JPL Horizons last obs 2018-02-14)

Popular culture

  • In Neal Stephenson's science fiction novel, Seveneves, 26P/Grigg–Skjellerup serves as a potential source of water and rocket propellant for the "Cloud Ark" survivors, and is frequently referred to by the nickname "Greg's Skeleton".


  1. ^ "26P/Grigg-Skjellerup Orbit". Minor Planet Center. Retrieved 2014-06-16.
  2. ^ Syuichi Nakano (2010-04-08). "26P/Grigg-Skjellerup (NK 1908)". OAA Computing and Minor Planet Sections. Retrieved 2012-02-18.
  3. ^ 26P past, present and future orbital elements
  4. ^ a b "JPL Small-Body Database Browser: 26P/Grigg–Skjellerup" (2008-08-07 last obs). Jet Propulsion Laboratory. Retrieved 2010-02-25.
  5. ^ a b ESA - Giotto, ESA's first deep-space mission: 25 years ago (2011)
  6. ^ Comet 26P/Grigg-Skjellerup, Outer Space at www.mindat.org. Retrieved 3 Apr 2017.
  7. ^ NASA Finds New Type of Comet Dust Mineral at www.nasa.gov. Retrieved 3 Apr 2017.

External links

Numbered comets
26P/Grigg–Skjellerup Next
1985 in spaceflight

The following is an outline of 1985 in spaceflight.


25D/Neujmin, otherwise known as Comet Neujmin 2, is a periodic comet in the solar system discovered by Grigory N. Neujmin (Simeis) on February 24, 1916. It was last observed on February 10, 1927.It was confirmed by George Van Biesbroeck (Yerkes Observatory, Wisconsin, United States) and Frank Watson Dyson (Greenwich Observatory, England) on March 1.A prediction by Andrew Crommelin (Royal Observatory, Greenwich, England) for 1921 was considered unfavourable and no observations were made. The comet was recovered in 1926. Searches in 1932 and 1937 were unsuccessful.Consequently, this comet has remained a lost comet since 1927. As of 2019 and using the JPL Horizons nominal orbit, the comet is still expected to come to perihelion around 1.3 AU from the Sun.


276P/Vorobjov (previously P/2012 T7 (VOROBJOV)) is a Jupiter-family comet discovered on 15 October 2012 by Tomáš Vorobjov on three 120-s images taken remotely using the 0.81-m f/7 Ritchey-Chretien Schulman Telescope located at the Mt. Lemmon SkyCenter via the Sierra Stars Observatory Network in the course of a minor-planet search survey undertaken as part of the International Astronomical Search Collaboration (IASC) school campaigns. After posting on the Minor Planet Center's NEOCP webpage, other observers have commented on the object's cometary appearance. The discovery was announced by the Minor Planet Center on 18 October, three days after the discovery.


Comet Crommelin, also known as Comet Pons-Coggia-Winnecke-Forbes, is a periodic comet with an orbital period of almost 28 years. It fits the classical definition of a Halley-type comet with (20 years < period < 200 years). It is named after the British astronomer Andrew C. D. Crommelin who calculated its orbit in 1930. It is one of only four comets not named after their discoverer(s), the other three being Comets Halley, Encke, and Lexell.

The first observation was by Jean-Louis Pons (Marseille, France) on February 23, 1818, he followed the comet until February 27 but was prevented further by bad weather. Johann Franz Encke attempted to calculate the orbit but was left with very large errors.

In 1872, John R. Hind produced a rough orbital calculation and observed it was close to that of Comet Biela, based on these observations, Edmund Weiss later speculated it may have been part of Biela's comet.

The next observation was on November 10, 1873, by Jérôme E. Coggia (Marseille, France), and again on November 11 by Friedrich A. T. Winnecke (Strasbourg, France), but it was lost by November 16. Weiss and Hind took up the calculations and tried to match it again with the 1818 appearance.

A third discovery was by Alexander F. I. Forbes (Cape Town, South Africa) on November 19, 1928, and confirmed by Harry E. Wood (Union Observatory, South Africa) on November 21. It was Crommelin who eventually established the orbit and finally linked the 1818 (Pons) and 1873 (Coggia-Winnecke) comets to it (also see Lost comet).

On its latest return, 27P/Crommelin was recovered on May 12, 2011, at apparent magnitude 18.7 and peaked at magnitude 10.7 at perihelion on August 3.

Astronomical Society of Southern Africa

The Astronomical Society of Southern Africa (ASSA), formed in 1922, is a widespread body consisting of both amateur and professional astronomers. The Council of ASSA meets by Skype. There are eight autonomous centres throughout Southern Africa.

Bow shocks in astrophysics

Bow shocks form the boundary between a magnetosphere and an ambient (or at least surrounding) magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma. For example, when the solar wind, flowing with a relative speed of order 400 km/s, encounters the magnetic field of Earth, a bow shape boundary forms. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium.


Brownleeite is a silicide mineral with chemical formula MnSi. It was discovered by researchers of the Johnson Space Center in Houston while analyzing the Pi Puppid particle shower of the comet 26P/Grigg-Skjellerup. The only other known natural manganese silicide is mavlyanovite, Mn5Si3.

C/2012 E2 (SWAN)

Comet C/2012 E2 (SWAN) was a Kreutz group sungrazing comet discovered by Vladimir Bezugly in publicly available images taken by the SWAN instrument (Solar Wind ANisotropies) on board the SOHO spacecraft. It is recognized for being the first Kreutz sungrazer observed in SWAN imagery.

C/2015 F3

Comet C/2015 F3 (SWAN) was discovered in March 2015 by Rob Matson, Vladimir Bezugly and Michael Matiazzo in near real time images taken by the SWAN instrument aboard the SOHO spacecraft. At discovery the comet was already shining at around 10th magnitude as it was already near perihelion

. Orbital studies revealed C/2015 F3 to be a related fragment to long periodic comets C/1988 A1 (Liller) and C/1996 Q1 (Tabur), which were already thought to have broken off each other at a previous perihelion passage. As of May 2015, Comet SWAN was fading rapidly, as both C/1988 A1 and C/1996 Q1 ultimately did. .

C/2015 F5 (SWAN-XingMing)

Comet C/2015 F5 (SWAN-XingMing) was discovered on March 29, 2015 in near real time SWAN images of the SOHO spacecraft, by Szymon Liwo and Worachate Boonplod. It was also independently discovered on April 4, 2015 by Guoyou Sun and Gao Xing at the XingMing observatory near Ürümqi, China. At discovery, the comet had just passed perihelion and was only 0,35 AU from the Sun, shining at about +10 mag. As of May 2015 the comet had faded below mag +13. The comet is periodic with an orbital period of about 61 years .

Giotto (spacecraft)

Giotto was a European robotic spacecraft mission from the European Space Agency. The spacecraft flew by and studied Halley's Comet and in doing so became the first spacecraft to make close up observations of a comet. On 13 March 1986, the spacecraft succeeded in approaching Halley's nucleus at a distance of 596 kilometers. It was named after the Early Italian Renaissance painter Giotto di Bondone, who draw free hand perfect circles according to Giorgio Vasari biography. He had observed Halley's Comet in 1301 and was inspired to depict it as the star of Bethlehem in his painting Adoration of the Magi.

John Francis Skjellerup

John Francis Skjellerup (16 May 1875 – 6 January 1952) was an Australian who spent about a decade working as a telegraphist in South Africa, and was an astronomer.

Some sources give his name as James Francis Skjellerup; in any case, apparently he preferred to be known as Frank. His father Peder Jensen Skjellerup was Danish and died when he was young; his mother was Margaret Williamson, born in England. He was born in Cobden, Victoria, Australia.

Trained as a telegraphist, he went to South Africa when that country needed telegraphists after the Second Boer War. Apparently he was an excellent golfer as well as an astronomer. He married his wife Mary Peterson (South African) and returned with her to Australia in 1923; she died in 1950 and there were no children.

He took up astronomy in South Africa and discovered or co-discovered various comets in both South Africa and Australia, including the periodic comet 26P/Grigg-Skjellerup in South Africa and the very bright Skjellerup-Maristany (C/1927 X1) (visible mostly from the southern hemisphere) in Australia.

In addition to comets, he was also a variable star observer.

John Grigg (astronomer)

John Grigg (4 June 1838 – 20 June 1920) was a New Zealand astronomer.

He was born in London and married Emma Mitchell in 1858. In 1863 they emigrated to New Zealand and settled in Auckland, however Emma died in 1867. Grigg then moved to the town of Thames. During this time he was seller of musical instruments, piano tuner, music teacher and conductor.He married his second wife Sarah Allaway in 1871 but she died in 1874. He later married his third wife, Jane Henderson, in 1887. In all, he had six sons and three daughters by his three wives.

The 1874 transit of Venus awakened his interest in astronomy, which he pursued full-time starting in 1894. He began systematic searches for comets in that year.

He is best known for his co-discovery of the periodic comet 26P/Grigg-Skjellerup in 1902, which was his first discovery of a new comet.

List of Solar System probes

This is a list of space probes that have left Earth orbit (or were launched with that intention but failed), organized by their planned destination. It includes planetary probes, solar probes, and probes to asteroids and comets, but excludes lunar missions, which are listed separately at List of lunar probes and List of Apollo missions. Flybys (such as gravity assists) that were incidental to the main purpose of the mission are also included. Flybys of Earth are listed separately at List of Earth flybys. Confirmed future probes are included, but missions that are still at the concept stage, or which never progressed beyond the concept stage, are not.

List of meteor showers

Named meteor showers recur at approximately the same dates each year. They appear to "radiate" from a certain point in the sky (the radiant) and vary in the speed, frequency and brightness of the meteors. As of November 2018, there are 112 established meteor showers.

List of missions to comets

As of 2013, the United States, Soviet Union, Japan and the European Space Agency have conducted missions to comets.

Meteor shower

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.

Pi Puppids

The Pi Puppids are a meteor shower associated with the comet 26P/Grigg-Skjellerup.

The meteor stream was viewable around April 23 but only in years around the parent comet's perihelion date, the last being in 2003. However, as the planet Jupiter has now perturbed the comet's perihelion to beyond Earth's orbit it is uncertain how strong the shower will be in the future.

The Pi Puppids get their name because their radiant appears to lie in the constellation Puppis, at around Right ascension 112 degrees and Declination −45 degrees. This made them only visible to southern observers.

They were discovered in 1972 and have been observed about every 5 years - at each perihelion passage of the comet - but often at very low rates per hour.

Planetary flyby

A planetary flyby is the act of sending a space probe past a planet or a dwarf planet close enough to record scientific data. This is a subset of the overall concept of a flyby in spaceflight.

Flybys commonly use gravity assists to "slingshot" a space probe on its journey to its primary objective, but may themselves be used as primary means.

The first flyby of another planet with a functioning spacecraft took place on December 14, 1962, when Mariner 2 zoomed by the planet Venus.New Horizons performed flyby maneuvers of Jupiter, Pluto and its moons in the 21st century. This type of maneuver allowed it to reach Pluto at high velocity without the complications of slowing down, after which it proceeded into the Kuiper belt on a solar system escape trajectory.

For comparison, New Horizons reached Jupiter in just over year (launched in January 2006) it flewby in February 2007. In contrast, Galileo spacecraft took about six years (launched 1989, arrive at Jupiter 1995) and when it got there it had expend fuel to slow down to enter orbit, and was overall much heavier. The atmospheric entry probe did not slow down but required an advanced entry shield and the atmosphere of Jupiter to slow down. (See also Aerobraking)

There also an even closer version of flyby, a sort of fly in where the spacecraft actually enters and passes through a bodies atmosphere, called a Aerogravity assist. This could be compared to the natural phenomenon of Earth-grazing fireball

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