Portia is an inner satellite

Inner satellite

In astronomy, an inner moon is a natural satellite following a prograde, low inclination orbit inwards of the large satellites of the parent planet. They are generally thought to have been formed in situ at the same time as the coalescence of the original planet...

 of Uranus

Uranus

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

. It was discovered from the images taken by Voyager 2

Voyager 2

The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

on 3 January 1986, and was given the temporary designation S/1986 U 1. The moon is named after Portia

Portia (Merchant of Venice)

Portia is the heroine of William Shakespeare's The Merchant of Venice. A rich, beautiful, and intelligent heiress, she is bound by the lottery set forth in her father's will, which gives potential suitors the chance to choose between three caskets composed of gold, silver and lead...

, the heroine of William Shakespeare

William Shakespeare

William Shakespeare was an English poet and playwright, widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's national poet and the "Bard of Avon"...

's play The Merchant of Venice

The Merchant of Venice

The Merchant of Venice is a tragic comedy by William Shakespeare, believed to have been written between 1596 and 1598. Though classified as a comedy in the First Folio and sharing certain aspects with Shakespeare's other romantic comedies, the play is perhaps most remembered for its dramatic...

. It is also designated Uranus XII.

Portia is the second-largest inner satellite of Uranus after Puck

Puck (moon)

Puck is an inner moon of Uranus. It was discovered in December 1985 by the Voyager 2 spacecraft. The name Puck comes from Celtic mythology and English folklore. The orbit of Puck lies between the rings of Uranus and the first of Uranus' large moons, Miranda. Puck is approximately spherical in...

. The Portian orbit, which lies inside Uranus' synchronous orbital radius

Synchronous orbit

A synchronous orbit is an orbit in which an orbiting body has a period equal to the average rotational period of the body being orbited , and in the same direction of rotation as that body.-Properties:...

, is slowly decaying due to tidal deceleration. The moon will one day either break up into a planetary ring

Planetary ring

A planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in a flat disc-shaped region.The most notable planetary rings known in Earth's solar system are those around Saturn, but the other three gas giants of the solar system possess ring systems of their...

 or hit Uranus.

It heads a group of satellites called the Portia Group, which includes Bianca

Bianca (moon)

Bianca is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on January 23, 1986, and was given the temporary designation S/1986 U 9. It was named after the sister of Katherine in Shakespeare's play The Taming of the Shrew...

, Cressida

Cressida (moon)

Cressida is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 9 January 1986, and was given the temporary designation S/1986 U 3. It was named after the Trojan daughter of Calchas, a tragic heroine who appears in William Shakespeare's play Troilus and...

, Desdemona

Desdemona (moon)

Desdemona is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 13 January 1986, and was given the temporary designation S/1986 U 6. Desdemona is named after the wife of Othello in William Shakespeare's play Othello...

, Juliet

Juliet (moon)

Juliet is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 3 January 1986, and was given the temporary designation S/1986 U 2. It is named after the heroine of William Shakespeare's play Romeo and Juliet...

, Rosalind

Rosalind (moon)

Rosalind is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 13 January 1986, and was given the temporary designation S/1986 U 4. It was named after the daughter of the banished Duke in William Shakespeare's play As You Like It...

, Cupid

Cupid (moon)

Cupid is an inner satellite of Uranus. It was discovered by Mark Showalter and Jack J. Lissauer in 2003 using the Hubble Space Telescope. It was named after a character in William Shakespeare's play Timon of Athens....

, Belinda

Belinda (moon)

- External links :* by *...

 and Perdita

Perdita (moon)

Perdita is an inner satellite of Uranus. Perdita's discovery was complicated. The first photographs of Perdita were taken by the Voyager 2 spacecraft in 1986, but it was not recognized from the photographs for more than a decade. In 1999, the moon was noticed by Erich Karkoschka and reported...

. These satellites have similar orbits and photometric properties.

Little is known about Portia beyond its size of about 140 km, orbit, and geometric albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 of about 0.08.

In the Voyager 2 images, Portia appears as an elongated object whose major axis points towards Uranus. The ratio of axes of the Portia's prolate spheroid

Prolate spheroid

A prolate spheroid is a spheroid in which the polar axis is greater than the equatorial diameter. Prolate spheroids stand in contrast to oblate spheroids...

 is 0.8 ± 0.1. Its surface is grey in color. Observations with Hubble Space Telescope

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 and large terrestrial telescopes found water ice absorption features in the spectrum of Portia.

External links

• Portia Profile by NASA's Solar System Exploration
• Uranus' Known Satellites (by Scott S. Sheppard
  Scott S. Sheppard
  Scott S. Sheppard is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Science. Starting as a graduate student at the Institute for Astronomy at the University of Hawaii, he was credited with the discovery of many small moons of Jupiter, Saturn, Uranus, and...
  
  )