Category: satellite

In 40 million years, Mars may have a ring (a…

In 40 million years, Mars may have a ring (and one fewer moon)

Nothing lasts forever – especially Phobos, one of the two small moons orbiting Mars. The moonlet is spiraling closer and closer to the Red Planet on its way toward an inevitable collision with its host. But a new study suggests that pieces of Phobos will get a second life as a ring around the rocky planet.

A moon – or moonlet – in orbit around a planet has three possible destinies. If it is just the right distance from its host, it will stay in orbit indefinitely. If it’s beyond that point of equilibrium, it will slowly drift away. (This is the situation with the moon; as it gradually pulls away from Earth, its orbit is growing by about 1.5 inches per year.) And if a moon starts out on the too-close side, its orbit will keep shrinking until there is no distance left between it and its host planet.

The Martian ring will last for at least 1 million years – and perhaps for as long as 100 million years, according to the study.

The rest of Phobos will probably remain intact, until it hits the Martian surface. But it won’t be a direct impact; instead, the moonlet’s remains will strike at an oblique angle, skipping along the surface like a smooth stone on a calm lake.

This has probably happened before – scientists believe a group of elliptical craters on the Martian surface were caused by a small moon that skidded to its demise. (If this were to happen on Earth, our planet’s greater mass would produce a crash as big as the one that wiped out the dinosaurs, the researchers noted as an aside.)


images: NASA/JPL,

Tushar Mittal using Celestia 2001-2010, Celestia Development Team.

The two largest satellites of Jupiter: Ganymed…

The two largest satellites of Jupiter: Ganymede and Callisto

Credit: NASA/JPL/

Iapetus is the third-largest natural satelli…

Iapetus is the third-largest natural satellite of Saturn, eleventh-largest in the Solar System, and the largest body in the Solar System known not to be in hydrostatic equilibrium. Iapetus is best known for its dramatic “two-tone” coloration. Discoveries by the Cassini mission in 2007 revealed several other unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon.

Iapetus was discovered by Giovanni Domenico Cassini, an Italian astronomer, in October 1671. He had discovered it on the western side of Saturn and tried viewing it on the eastern side some months later, but was unsuccessful. This was also the case the following year, when he was again able to observe it on the western side, but not the eastern side. Cassini finally observed Iapetus on the eastern side in 1705 with the help of an improved telescope, finding it two magnitudes dimmer on that side.

Cassini correctly surmised that Iapetus has a bright hemisphere and a dark hemisphere, and that it is tidally locked, always keeping the same face towards Saturn. This means that the bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and that the dark hemisphere is visible when Iapetus is on the eastern side. The dark hemisphere was later named Cassini Regio in his honor.

The original dark material is believed to have come from outside Iapetus, but now it consists principally of lag from the sublimation of ice from the warmer areas of Iapetus’s surface. It contains organic compounds similar to the substances found in primitive meteorites or on the surfaces of comets; Earth-based observations have shown it to be carbonaceous, and it probably includes cyano-compounds such as frozen hydrogen cyanide polymers.

Easter füll moon on Good Friday by Ritzelmu…

Easter füll moon on Good Friday by


Craters on Moon:1° From crater Theophilus (100…

Craters on Moon:

1° From crater Theophilus (100km diameter) below to crater Langrenus above.

2° From bottom to top, dark titanium rich lava in the Sea of Fertility then the diamond shaped patch is the Marsh of Sleep. Small bright crater Proclus is thought to be a recent impact crater and has thrown out bright ejecta that is much lighter than the surrounding ancient weathered rock. Above is the rather hexagonal Mare Crisium.

3° From the Sinus Iridium top left through the Mare Imbrium with the Alpine Valley in the centre. (This original image is horizontal)

4° At the middle and bottom of this image, sunlight is shining on a mountain peak in the Alexander crater which lies beyond the day/night terminator.

Image credit: John Purvis

SpaceX successfully launched TESS yesterday! W…

SpaceX successfully launched TESS yesterday! We’re going to discover so many new exoplanets.

Apollo 13’s view from Aquarius as it rounds …

Apollo 13’s view from Aquarius as it rounds the Moon, with the Command Module at right.

Credit: NASA/Johnson Space Center. 

Saturn’s moon Dione drifts before the planet…

Saturn’s moon Dione drifts before the planet’s rings, seen here almost edge on. For all their immense width, the rings are relatively paper-thin, about 30 feet (10 meters) in most places. For its part, Dione is about 698 miles (1,123 kilometers) across.

Credit: NASA/JPL-Caltech/Space Science Institute

Pan (moon of Saturn) – March 07 2017

Pan (moon of Saturn) – March 07 2017

NASA/JPL-Caltech/SSI/Kevin M. Gill

Reprocessed Galileo image of Europa’s …

Reprocessed Galileo image of Europa’s frozen surface by Ted Stryk (NASA/JPL/Ted Stryk)