APOD: Saturns Moon Helene in Color (2012 May 02)

[APOD Robot]

Saturns Moon Helene in Color

Explanation: Although its colors may be subtle, Saturn's moon Helene is an enigma in any light. The moon was imaged in unprecedented detail last June as the robotic Cassini spacecraft orbiting Saturn swooped to within a single Earth diameter of the diminutive moon. Although conventional craters and hills appear, the above image also shows terrain that appears unusually smooth and streaked. Planetary astronomers are inspecting these detailed images of Helene to glean clues about the origin and evolution of the 30-km across floating iceberg. Helene is also unusual because it circles Saturn just ahead of the large moon Dione, making it one of only four known Saturnian moons to occupy a gravitational well known as a stable Lagrange point.

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[ta152h0]

WHOA !! something just happened on M83, like a black hole sent out a giant greeting card. Sorry for the off-topic.Back to the nice picture of a Saturnian moon.

[neufer]

Planetary astronomers are inspecting these detailed images of Helene to glean clues about the origin and evolution of the 30-km across floating iceberg. Helene is also unusual because it circles Saturn just ahead of the large moon Dione, making it one of only four known Saturnian moons to occupy a gravitational well known as a stable Lagrange point.

Helene: 43.4 × 38.2 × 26 km [11 to 25 trillion tonnes]

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<<Iceberg B-15 is the world's largest recorded iceberg. It measured around 295 km long and 37 km wide, with a surface area of 11,000 km² — larger than the island of Jamaica. The mass was estimated around three [trillion?] tonnes. After almost a decade, parts of B-15 still have not melted. Calved from the Ross Ice Shelf near Roosevelt Island in March 2000, B-15 broke up into several pieces in 2000, 2002 and 2003, the largest of which, B-15A, covered 6,400 km² of the sea surface. In November 2003, after the separation from B-15J iceberg, B-15A drifted away from Ross Island on the open waters of the Ross Sea. On 21 November 2006 several large pieces were seen just 60 km off the coast of Timaru, New Zealand. The largest measured about 1.8 km, rising 37 m from the surface of the ocean.>>

[Moonlady]

I can only see shades of gray...

Saturn was the first planet I telescoped, good memory

[JohnD]

Theories for those streaks?
Helene is described as a 'iceberg' and as having approx. one seventh of Earth surface gravity.
The streaks look like flow patterns, running off highlands to a central glacier or ice field.
Where they are interrupted by a crater, they 'flow' into the crater, filling that with ice. Eg Seven o'clock.
What ice is Helene made of and will it flow in those circumstances?

John

[Flase]

This is the sort of thing I like to imagine for Sci Fi.

What would it be like to build a moon base and explore the surface? You could use skis.

Would the people on the base be dominated by an oppressive regime exploiting them as cheap mining labour or will we have an enlightened and intelligent society?

[K1NS]

Helene is described as a 'iceberg' and as having approx. one seventh of Earth surface gravity.

That thing is only 35 km across. The gravity must be considerably weaker than that.

The thing that strikes me about Helene is the paucity of craters. I can see less than a dozen. Is Helene a new object, broken from something else? Or else how is its surface being smoothed over?

[orin stepanek]

Fantastic picture; kind of looks like a mummified skull!

[neufer]

The thing that strikes me about Helene is the paucity of craters. I can see less than a dozen. Is Helene a new object, broken from something else? Or else how is its surface being smoothed over?

Helene orbits at the leading Lagrangian point, L4, of the much larger Dione. Dione is rubber & Helene is glue such that much of the crater eject from Dione ends up sticking onto the leading hemisphere of Helene (which is what is shown here in today's APOD). The flow features are essentially sands in an hour glass.

[Chris Peterson]

Helene is described as a 'iceberg' and as having approx. one seventh of Earth surface gravity.

Helene's surface gravity is about 1/5000 that of Earth's (0.002 m/s² vs. 9.8 m/s²).

[bystander]

WHOA !! something just happened on M83, like a black hole sent out a giant greeting card.

http://asterisk.apod.com/viewtopic.php?t=28399

[neufer]

Helene is described as a 'iceberg' and as having approx. one seventh of Earth surface gravity.

Helene's surface gravity is about 1/5000 that of Earth's (0.002 m/s² vs. 9.8 m/s²).

Helene's surface gravity is about 1/1850 that of Earth's (0.0053 m/s² vs. 9.8 m/s²).

(Helene is ~ 370 times smaller and ~ 5 times less dense than Earth.)

Note, however, that Helene's escape velocity of 30 mph ( = 25,000 mph/[370 * sqrt(5)] ) is indeed approximately one seventh the maximal 210 mph terminal velocity of a human sky diver in the bullet shaped position. This may be related Emily Lakdawalla's "Ski Helene?" article.

[Chris Peterson]

Helene's surface gravity is about 1/5000 that of Earth's (0.002 m/s² vs. 9.8 m/s²).

Helene's surface gravity is about 1/1850 that of Earth's (0.0053 m/s² vs. 9.8 m/s²).
(Helene is ~ 370 times smaller and ~ 5 times less dense than Earth.)

I guess it depends where you get your numbers. I used the NASA Fact Sheet for planetary moons in the Solar System, which gives a surface gravity of 0.002 m/s² for Helene (and also gives a mean density 11 times less than Earth). With these smaller moons, I guess many of the values aren't well determined.

[neufer]

Helene's surface gravity is about 1/5000 that of Earth's (0.002 m/s² vs. 9.8 m/s²).

Helene's surface gravity is about 1/1850 that of Earth's (0.0053 m/s² vs. 9.8 m/s²).
(Helene is ~ 370 times smaller and ~ 5 times less dense than Earth.)

I guess it depends where you get your numbers. I used the NASA Fact Sheet for planetary moons in the Solar System, which gives a surface gravity of 0.002 m/s² for Helene (and also gives a mean density 11 times less than Earth). With these smaller moons, I guess many of the values aren't well determined.

This may indeed be more correct if Helene is mostly a loose pile of ice like Halley's Comet.

Halley's Comet mean density = 0.6 (estimates range from 0.2 to 1.5 g/cm³ )

[twixter]

That's it. The rebels are there.

[ashogun]

I did some simple color enhancement on the Helene image.
Looks like varying surface properties show up.
It's here: http://uuca.x10.mx/helene2_cassini_enh.jpg
cheers, Gary

[Ann]

I did some simple color enhancement on the Helene image.
Looks like varying surface properties show up.
It's here: http://uuca.x10.mx/helene2_cassini_enh.jpg
cheers, Gary

Thanks, ashogun!

Still, we are lucky to live on a world where we don't have to enhance things to see blue sky and green vegetation!

Ann

[FloridaMike]

That's it. The rebels are there.

*LIKE*

[Chris Peterson]

Still, we are lucky to live on a world where we don't have to enhance things to see blue sky and green vegetation!

So, are we unlucky to live on a world where we do have to enhance things to see the ultraviolet flowers and the infrared leaves? <g>

[JohnD]

At least my quick and wrong post about Helene's gravity got you talking about science, instead of art and beauty.
Which it is. Beautiful.
My apologies - I did a quick google and took the first g-figure I found.

So at such a low surface gravity, and like Phobos' grooves, it seems unlikely that any surface bound process can have caused these flow-like markings. Unlike Phobos, they curve across the surface as if they moved at right angles to contours, like a downward flow would do. Could that be some extra-Hellenic cloud, ice crystals thrown off Dione by the large impact that span it again after it was tidally locked to Saturn, so that now, after becoming locked again, its most heavily cratered hemisphere faces forward?

John

[ta152h0]

Beach bunnies. Now there are celestial object that don't need enhancing. Just a plain box camera will do. My first one did, a KODAK instamatic ( c. 1963 )

[Boomer12k]

I think the artist forgot his palate....

:---[===] *

[quigley]

Could Helene have a rocky core?

[Chris Peterson]

Could Helene have a rocky core?

I think it's unlikely. But it isn't apparent that an accurate mass (and therefore density) has actually been determined for Helene. Determining the mass of bodies like this isn't trivial; usually it requires a near flyby such that gravitational perturbation can be measured. I haven't done a detailed literature search, but nothing popped up in a casual search suggesting any rigorous mass analysis has been performed.

[pferkul]

Here's what it looks like if you supersaturate the existing colors:
(I also rotated it 90 degrees.)

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