Saturn’s moon may have rings – the first ever discovered

An artist's impression of Rhea's rings | Image: NASA

Everyone knows that Saturn has rings, but what about its moons? Surely they don’t have rings as well? Well actually, Rhea, a moon of Saturn that is usually overlooked, may be the first moon ever discovered to have rings, thanks to new research from the NASA/ESA Cassini-Huygens mission.

Rhea’s rings aren’t particularly impressive compared to Saturn’s – after all, it’s hard to imagine anything having a more impressive ring system that the huge gas giant Saturn. In fact, they haven’t even been photographed yet, but there is strong evidence to show that they exist.

Saturn | Image: Wikipedia How did the scientists work out that Rhea had rings without even seeing them? It’s all down to electrons, tiny charged particles that surround Saturn in its magnetic field. Because Rhea lies within the magnetic field of Saturn, it was expected to be seen ‘clearing up’ some of the electrons, because Rhea would absorb electrons from the magnetic field.

Saturn's rimgs, as imaged by Cassini | Image: NASA / ESA Rhea certainly did clear up the electrons – but it did it far better than expected, absorbing electrons about 7 times further away than it should have done. Why? The only feasible answer seems to be that Rhea has a ring system, and that the ring particles are absorbing the extra electrons.

Rhea is just one of a group of Saturn’s 52+ moons that are intriguing scientists: Rhea’s cousin Titan has methane lakes and rain; Iapetus is half-black and half-white; Enceladus has an atmosphere. The Cassini-Huygens mission is making it obvious that Saturn’s moons are just as interesting as the ringed planet itself.

Advertisements

Venus: The planet where it rains acid

Venus in visible light | Image: Wikipedia

Everyone seems to complain whenever it rains here on Earth, but on Venus you might actually have good reason to moan. Instead of water Venus’s clouds are made of corrosive sulfuric acid, and if you got covered in that, chances are you wouldn’t be around very long to tell the tale.

In reality it never rains sulfuric acid (at least not down to ground level) on Venus, because it evaporates before it has time to hit the ground – in fact, surface temperatures on Venus are hot enough to melt lead.

New research from ESA’s Venus Express probe is starting to reveal some of the secrets of Venus’s atmosphere, and some of them are very surprising indeed.

Unlike on Earth, where clouds tend to move only a few hundred miles at most, sulfuric acid clouds on Venus have ben seen moving from the poles to the equator, then back to the poles again, in just a few days.

Venus Express, which is due to end its mission in May 2009 | Image: ESABut wait a minute… where does all this sulfuric acid come from? After all, Venus is sometimes known as ‘Earth’s evil twin’ because of its runaway global warming, caused by excess carbon dioxide levels.

In fact, 97% of Venus’s atmosphere is made of CO2, although there are small amounts of gases such as sulfur dioxide and water vapor.

Recently discovered by the Venus Express probe is that the sulfuric acid is created when the sulfur dioxide and water vapor rise to the top of the atmosphere and are exposed to ultraviolet rays from the Sun, causing them to react and form sulfuric acid.

Why do they rise up? That’s one of the many things that remains to be found out, hopefully during this last year of the phenomenal Venus Express mission.

Click here for an interactive guide to Venus

Mars in 3D for the first time

The new 3D view from Mars Express | Image: National Geographic / ESA We’ve seen Mars from an aerial view, we’ve seen it from the ground, but what about in 3D? Well now we can do that too, thanks to Europe’s Mars Express probe.

The 3D shot (right) of Olympus Mons, the biggest volcano or mountain anywhere in the Solar System, shows the topography of Mars in unprecedented detail. There are amazing possibilities for this kind of information when it is combined with aerial views, such as the one to the below.

But why do we want to know loads about the altitudes of different bits of Mars? Well, it could actually play a pivotal role in the search for life, because by analyzing the altitudes of hills and surface features, scientists are able to tell where water has once flowed. It is thought that life could only ever have existed where water was present.

An aerial view of Olympus Mons | Image: WikipediaAnother big question: how on Earth do you get 3D shots like this? The obvious first thought would be radar or lasers, which NASA has previously used on its Mars Global Surveyor mission. However, these only provide the height at the exact point under the probe.

To get detailed measurements over a wide area, Mars Express used a technique that involved taking three photos: one slightly before it was overhead Olympus Mons, one above it, and one slightly after it had flown over it. By combining these three different angles, scientists were able to construct a 3D image.

We’ve only just started our exploration of Mars; there are loads more probes set to explore the Red Planet before 2030, NASA’s target date for the First Man on Mars. It’s a pretty exciting time to be in for space exploration! The Mars Express probe | Image: ESA