Category: lua

Moon and Venus

Moon and Venus

Credit: U. Reichert

Aldebaran few moments after the end of the o…

Aldebaran few moments after the end of the occultation by a crescent Moon (7.7% illuminated)

by Fausto Lubatti

Total Lunar Eclipse, 2011-06-15 by Michael…

Total Lunar Eclipse, 2011-06-15

by

Michael Karrer

Russia’s Mir space station and the moo…

Russia’s Mir space station and the moon share a 70mm frame exposed by one of the STS-91 crew members aboard the Earth-orbiting Space Shuttle Discovery as it passed over a line of heavy thunderstorms on Earth. Credit: NASA

Conjunction at Sunset (Moon and Venus)Image …

Conjunction at Sunset (Moon and Venus)

Image Credit: Stefano De Rosa

In early 2001 during a launch of Atlantis, t…

In early 2001 during a launch of Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence.

Image Credit: Pat McCracken, NASA

Titan: Ligeia Mare and environs Numerous lake…

Titan: Ligeia Mare and environs

Numerous lakes of hydrocarbons and seas are visible: at the top is the prominent body of liquid known as Ligeia Mare; the main centers are in the northernmost part of Kraken Mare and on the island of Mayda Insula; and in the bottom center is a portion of Punga Mare. In the lower right corner, Jingpo Lacus reveals a series of sinuous canals in its lake bed, while Bolsena Lacus appears in the lower left corner.

Credit: NASA/JPL-Caltech/Space Science Institute/Ian Regan

Saturn and Titan Credit: NASA/JPL-Caltech/Spa…

Saturn and Titan

Credit: NASA/JPL-Caltech/Space Science Institute

In December of 1972, Apollo 17 astronauts Eu…

In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon in the Taurus-Littrow valley, while colleague Ronald Evans orbited overhead. This sharp image was taken by Cernan as he and Schmitt roamed the valley floor. The image shows Schmitt on the left with the lunar rover at the edge of Shorty Crater, near the spot where geologist Schmitt discovered orange lunar soil. 

Image Credit: Apollo 17 Crew, NASA

Can a Natural Satellite Have Its Own Natural S…

Can a Natural Satellite Have Its Own Natural Satellite?

In all known planetary systems, natural satellites occur in a restricted dynamical phase space: planets orbit stars and moons orbit planets. It is natural to ask, can submoons  orbit moons? If so, why don’t any of the known moons of the Solar System have their own submoons? One possibility is that the formation mechanism of planetmoon systems precludes their formation. Another possibility, is that these bodies are dynamically unstable and are rapidly scoured from their system after formation. Here, we investigate the latter hypothesis. 

What are the requirements for stability of a submoon?  To ensure dynamical stability, the host moon must have a  Hill sphere that is larger than its physical radius as well  as its Roche limit. The submoon must also survive any  long-term dynamical effects such as tidal evolution.

Only large moons on wide-separation  orbits can host long-lived submoons. This is mainly because  massive, distant moons have larger Hill radii that  provide more stable real estate for submoons

The researchers calculated that in the Solar System, 4 natural satellites could have their own natural satellite.

Our Moon, Callisto of Jupiter, and Titan and Iapetus of Saturn.

These satellites are relatively large, are relatively distant from their planets, ie there is a small area around them that could have a natural satellite and that satellite would not be stolen by the planet.

Recalling that this is a theoretical exercise, to date no natural satellite around another natural satellite has been detected. source, article.