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back to article Curiosity looks up, spies Martian double-mooning

As Curiosity trundles across the Martian surface, the bulk of NASA's interest has been focused downwards at the ground, but the rover has also been looking up and has captured some remarkable video of the two moons of Mars overlapping each other overhead. The images captured by the telephoto lens in Curiosity's Mast Camera …

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Alien

That's really cool! Although the big one is suspiciously potato like in appearance.

I wonder how two moons affect the tides on Mars?

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Alien

>I wonder how two moons affect the tides on Mars?

Eh?

There hasn't been a tide around here for beeeellllions of years mate.

Knotted handkerchief removed for portrait --->

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The tidal effects still exist, even though there are no seas to rise and fall. Our moon is ~6 million times the mass of Phobos, while Phobos is ~40x closer to its planet (less than 10,000 km), which means the tides (inversely proportional to distance cubed) are about 100 times less.

Even though Phobos is a bit of a flyspeck, because it's so close to Mars it actually appears about one quarter of the size of Earth's Moon from the surface there.

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Fun Fact: Earth's Moon, Luna, is moving away from Earth at the rate of about 1.5" per year.

This means that early in Earth's history Luna orbited more closely and faster, and the Earth's days were shorter, than today. This has been corroborated by studies of growth-rings in (hundreds of millions of years old) fossil corals.

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Actually, that should be:

the tides ... are about 100 25 times less

and

appears about one quarter one half of the size of Earth's Moon

Phobos is so close that Mars's radius significantly affects the answer. Also the tides are much stronger on the side of the planet facing the moon (unlike on Earth where the tides 12 hours apart are of similar strength).

Deimos is both smaller and much further away, so the tidal effects it generates are swamped by the eccentricity of Phobos's orbit.

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> >I wonder how two moons affect the tides on Mars?

> There hasn't been a tide around here for beeeellllions of years mate.

Exactly!

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There have been tides for all those years, just not the liquid water ones that you're thinking of. The Earth's Moon actually stretches the solid Earth, the oceans and the atmosphere. The rock tides are so small you can't see them without instruments, the air tides are also are invisible to the unaided human observer, so we tend to focus on the water tides as 'the tides'. But the other ones are still there.

Similarly for Phobos and Mars. There is no liquid water to make water tides, but there are both rock tides and air tides. And as already shown above, they're actually comparable in size to the ones we have here.

Or in other words, the forces are there and they will do things; the mere absence of liquid water won't make them go away.

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PPS

And the tide from Phobos is about one fifth that from the Sun. which therefore dominates tidal effects on Mars.

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" Fun Fact: Earth's Moon, Luna, is moving away from Earth at the rate of about 1.5" per year."

Which means 65 million years ago, it was only 25ft away. Which explains the extinction of the dinosaurs (or the tall ones, anyway).

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Lovely Movie

I wish there was a real-time version though. Fifty-five seconds isn't too long to wait, and I would have liked to have had the realistic experience.

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Re: Lovely Movie

i don't think they have a full 60 fps video, what you see is what they have. the 55 second version just has longer pauses between frames

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Go

Re: Lovely Movie

From the text in the video, they only had 41 frames, so running it for 55 seconds means more than a second per frame. Not quite so movie like, more a picture slideshow...

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Pint

Nice to know this video is real and not something from Hollywood. My only regret is not being born a century or two later. I love space so much.

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Def
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Happy

Maybe you should just plan on living longer.

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Personally I plan to live forever, or die trying!

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Coat

How do we know this wasn't filmed in the Nevada desert?

It's easy to live for ever. You only need to do two simple things:

1) Never, ever, say anything that isn't true.

2) Say this today: "I will repeat this sentence tomorrow"

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Anonymous Coward

immortality by induction. nice

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So, what do we call this...

Not a lunar eclipse, that involves shadows. I suppose it isn't really an eclipse at all: a conjunction maybe?

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Re: So, what do we call this...

An occultation?

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Re: So, what do we call this...

syzygy ? (although obviously you're sat on one of the three)

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An amazing thing to see, I never tire of Space Exploration.

Did anyone else get the immediate feeling of watching the old Asteroids arcade game?

I had and urge to shoot Phobos but no little spaceship with a blaster on screen

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I was reminded of a description from much earlier.

Now we can actually see The hurtling moons of Barsoom

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Reminded

I was reminded of Millennium 2.2 and Deuteros from the Amiga. Ian Bird, what happened to him?

It's weird just how fast something that big moves, it has an orbit just under 8 hours. Even at proper speed that's darn quick across the sky, horizon to horizon.

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Alien

I never tire of Space Exploration either. I have only recently returned to Earth after seven millennia of travel. I have seen much and learned even more. I know how you all shall perish.

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Anonymous Coward

Occulted?

I am sure they meant occluded...

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Re: Occulted?

Occult originally just means 'hidden' (e.g. occult knowledge), but in astronomy it means a body being hidden by another one passing between it and an observer. Occlude means to obstruct completely - e.g. the sky is currently occluded by cloud.

Sorry, if my irony detector is malfunctioning :)

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Happy

Disgusting! Will nobody think of the children.

Oh, wait - That's rather cool actually.

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To quote Arthur C. Clarke

"What the hell is phobusordeemus?"

Well, one of his characters anyway. Fountains of Paradise, I think.

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Xzibit was quoted as saying....

"Yo Dawg, I herd you like moons, so I put an extra moon in your lunar eclipse so you can hide one moon while you look at another moon."

...and if you look really closely, you can see two imps and a Hell Knight drinking the blood of some UAC employees while some lone grunt with a chainsaw in his hands looks on looking rather angry.

Steven "Yeah, I know it's probably not a proper lunar eclipse but I don't know how to descrive it to fit that meme so why don't you come up with something better. Although I hope you like the Doom reference" Raith

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Thumb Up

Great stuff by Curiosity

Haven't been able to spot Phobos or Deimos myself (despite observing Mars many times). I need a bigger telescope!

(that's called aperture fever)

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