Comet Elst–Pizarro is a body that displays characteristics of both

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s and

comet 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 (cometary), coma surrounding ...

s, and is the prototype of

active asteroid Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show a coma, tail, or other visual evidence of mass-loss (like a comet), but their orbits remain within Jupite ...

s. Its orbit keeps it within the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

, yet it displayed a dust tail like a comet while near

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

in 1996, 2001, and 2007. * As a comet it is formally designated 133P/Elst–Pizarro. * As an asteroid it is designated 7968 Elst–Pizarro. Elst–Pizarro was reported in 1979 as minor planet , with its image on a photographic plate being completely stellar in appearance. Its orbit remains entirely within the orbits of

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

and

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, with

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

0.165, typical of a

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

in the

. However, the images taken by Eric W. Elst and Guido Pizarro in 1996, when it was near

, clearly show a cometary tail. Since this is not normal behaviour for asteroids, it is suspected that Elst–Pizarro has a different, probably icy, composition. The cometary nature of Elst–Pizarro was first discovered when a linear dust feature was observed with the ESO 1-metre Schmidt telescope at

La Silla Observatory La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory (ESO). Several other telescopes are also located at the site and are partly maintained by ESO. The observato ...

on 7 August 1996. Subsequently, around the next perihelion in November 2001, the cometary activity appeared again, and persisted for 5 months. It again came to

on 8 February 2013. The outgassing was found to happen only on small part of the surface measuring less than in effective diameter, likely being the relatively recent (younger than 100 million years) impact crater. At present, seven other objects that are cross-listed as both comets and asteroids:

2060 Chiron 2060 Chiron is a ringed small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs— ...

(95P/Chiron), 4015 Wilson–Harrington (107P/Wilson–Harrington), 60558 Echeclus (174P/Echeclus), 118401 LINEAR (176P/LINEAR), (282P/2003 BM₈₀), (288P/2006 VW₁₃₉), (362P/2008 GO₉₈), and (433P/2005 QN₁₇₃). As a dual status object,

astrometric Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. History ...

observations of 7968 Elst–Pizarro should be reported under the minor planet designation.

Exploration

''Castalia'' is a proposed mission concept for a robotic spacecraft to explore Pizarro and make the first ''in situ'' measurements of water in the asteroid belt, and thus, help solve the mystery of the origin of Earth's water. The lead is Colin Snodgrass, from

The Open University The Open University (OU) is a Public university, public research university and the largest university in the United Kingdom by List of universities in the United Kingdom by enrolment, number of students. The majority of the OU's undergraduate ...

in the UK. ''Castalia'' was proposed in 2015 and 2016 to the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

within the Cosmic Vision programme missions M4 and M5, but it was not selected. The team continues to mature the mission concept and science objectives. Because of the construction time required and orbital dynamics, a launch date of October 2028 was proposed. ''Castalia'' mission scientists are now considering instrument contributions for the Chinese ZhengHe comet exploration mission, which will conduct detailed remote sensing and in-situ measurements at Elst–Pizarro in 2032 following a proposed launch in 2025.

References

External links

* * {{DEFAULTSORT:Elst-Pizarro 007968 007968 0133 007968 007968 Discoveries by Eric Walter Elst Discoveries by Guido Pizarro (astronomer) Named minor planets 19790724 19960714