APOD: Juno Approaching Jupiter (2016 Jul 01)

[APOD Robot]

Juno Approaching Jupiter

Explanation: Approaching over the north pole after nearly a five-year journey, Juno enjoys a perspective on Jupiter not often seen, even by spacecraft from Earth that usually swing by closer to Jupiter's equator. Looking down toward the ruling gas giant from a distance of 10.9 million kilometers, the spacecraft's JunoCam captured this image with Jupiter's nightside and orbiting entourage of four large Galilean moons on June 21. JunoCam is intended to provide close-up views of the gas giant's cloudy zoned and belted atmosphere and on July 4 (July 5 UT) Juno is set to burn its main engine to slow down and be captured into its own orbit. If all goes well, it will be the first spacecraft to orbit the poles of Jupiter, skimming to within 5,000 kilometers of the Jovian cloud tops during the 20 month mission.

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[Guest]

What are the light areas directly around Jupiter? I assume some kind of camera artifact. Can anyone explain?

[Bill Melater]

On a similar note, from this vantage point, Jupiter is obviously half-lit by the sun; why don't its moons appear half-lit as well?

[JohnD]

What are the light areas directly around Jupiter? I assume some kind of camera artifact. Can anyone explain?

The two light dots, equidistant from the equator and less than a quarter of a diameter from the Poles?
Aurorae?
Lightning?
But the first is seen over the Poles, http://science.nasa.gov/science-news/sc ... igauroras/
and the second mainly in equatorial regions. http://www.nasa.gov/centers/goddard/mul ... tning.html

Guessing, the moons are too small to be resolved, just as we see planets naked eye as points, and stars however large the telescope.

I don't know!
John

[geckzilla]

The dots are nothing more than JPEG compression artifacts.

[heehaw]

I'm so overjoyed to, unexpectedly, finally, see Io, Europa, Ganymede, and Callisto out-of-plane .... I think I'll get half-lit myself!

[hamilton1]

When I hold my iphone at the eyepiece I get better photos than this!

[neufer]

When I hold my iphone at the eyepiece I get better photos than this!

<<JunoCam is the visible-light camera/telescope of the Juno Jupiter orbiter. JunoCam has a field of view that is too wide to resolve any detail in the Jovian moons beyond 232 kilometers per pixel. Jupiter itself will only appear to be 75 pixels across from JunoCam when Juno reaches the furthest point of its orbit around the planet. At its closest approaches JunoCam could achieve 15 km/pixel resolution from 4300 km, while Hubble has taken images of up to 119 km/pixel from 600 million km.>>

[stolenmoment]

Is there a good diagram of the approach geometry? The text implies that Juno is approaching over the North Pole, yet the bands indicate that we're not that far off the equatorial plane (in degrees anyway; I haven't done the trig with that angle and ~11million km...).

[JohnD]

Here's where it will end up, they hope: https://www.google.co.uk/#q=Juno+course ... +insertion

Lots more here; look for "Period Reduction Maneuver" about two thirds the way down the page, click on the pic and then scroll the gallery.
http://spaceflight101.com/juno/juno-mis ... ry-design/

John

[stolenmoment]

Here's where it will end up, they hope: https://www.google.co.uk/#q=Juno+course ... +insertion

Lots more here; look for "Period Reduction Maneuver" about two thirds the way down the page, click on the pic and then scroll the gallery.
http://spaceflight101.com/juno/juno-mis ... ry-design/

John

Thanks! Just what i was looking for!

[somebodyshort]

Ted Walton · Victoria, British Columbia

I still find the in-joke here quite clever. For those not up on their Greco-Roman mythology, Jupiter is the Roman name for the Greek god Zeus. Most people know a few things about him. He was king of the gods, he was the guy with the thunderbolts, and he was also an incorrigible womanizer. He was constantly sneaking out of Olympus to bed a mortal female that caught his eye. Jupiter's moons are named after these women. So they sent a satellite named after Juno, the Roman name for Hera, his wife.

They sent his "wife" to check up on on the big cheater! LOL

[Chris Peterson]

On a similar note, from this vantage point, Jupiter is obviously half-lit by the sun; why don't its moons appear half-lit as well?

The moons are unresolved. You can tell that because if their diameters were actually seen in this image, they would be on the order of 10% the size of Jupiter itself- larger than the Earth! Optically, the moons are just point sources, with their light spread out by diffraction and upscaling of the raw image. That means that no structure is resolved- including how they are illuminated.

[minkfarms]

Great trailer. Some posters seem to forget how important PR is to NASA projects. While the Juno project is important (and exciting) to scientists, if the public can't feel it some politicians are going to start cutting funding. I wouldn't be too critical of NASA's Hollywood promos. I am reassured, when chewing fat with Virgil over our shared fence, he mentions how great his GMA beans are in the same breath of the Juno mission.

[heehaw]

"Jupiter's moons are named after these women" Ganymede was male.

[neufer]

"Jupiter's moons are named after these women"

Ganymede was male.

http://asterisk.apod.com/viewtopic.php? ... 05#p160705

[MarkBour]

Speaking of how various solar system bodies appear from each other ...

I like to imagine a civilization on either Ganymede or Titan arising on the "outer" side of these tidally-locked moons, and its inhabitants like unto us in our early exploratory periods of around the 1400s and 1500s. One day an intrepid resident of one of those two moons takes a journey, far from her home. As she progresses around the moon, she would come to see a most amazing sight arising on the horizon (but only with her movement).

What would this first encounter with Jupiter or Saturn in the sky look like? How large and how bright?

Someone should check my calculations. I have:
Luna R = 1737 km, Earth R = 6371 km, Jupiter R = 69,911 km, Saturn R = 58,232 km (without rings)
Earth-Lunar distance = 384,400 km, Ganymede-Jupiter distance = 1,070,400 km, Titan-Saturn distance = 1,221,870 km.

From these, I'd estimate that Saturn, hanging in the sky of Titan, is around 10.5 times the visual angle of the Moon from Earth. Jupiter, hanging in the sky of Ganymede is roughly 14.5 times the visual angle of our Moon from Earth! (Of course on our own Moon, such a traveler, when encountering Earth's beautiful blue orb, would see something roughly 3.6 times the visual angle of the Moon from our skies. But from our knowledge of life on Earth, I never thought much about inhabitants of the Moon.) Still, I like to imagine how amazingly beautiful and awe-inspiring such a first encounter would be. And how ridiculous it would sound when this traveler told her countrymen back home what she had found. Especially the rings on Saturn ... they would claim her journey caused hallucinations and lunacy.

[geckzilla]

The view from Titan under all that haze might not be very impressive. It's debatable whether even the Sun is visible through its haze. Think of an overcast day on Earth.

[neufer]

[b][color=#0000FF]Near-infrared radiation from the Sun reflecting off Titan's hydrocarbon seas[/color][/b]

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I'd estimate that Saturn, hanging in the sky of Titan, is around 10.5 times the visual angle of the Moon from Earth. Still, I like to imagine how amazingly beautiful and awe-inspiring such a first encounter would be. And how ridiculous it would sound when this traveler told her countrymen back home what she had found. Especially the rings on Saturn ... they would claim her journey caused hallucinations and lunacy.

The ring shadow might be more impressive than the rings themselves.

The view from Titan under all that haze might not be very impressive.

• Of course, Titanians would probably have evolved near-infrared eyes.

(And, probably, those who lived on the Saturn side were astonished to see the Milky Way when they first ventured around to the backside.)

It's debatable whether even the Sun is visible through its haze. Think of an overcast day on Earth.

<<Titan receives about 1% as much sunlight as Earth. Before sunlight reaches the surface, about 90% has been absorbed by the thick atmosphere, leaving only 0.1% of the amount of light Earth receives.>>

[geckzilla]

Of course, Titanians would probably have evolved near-infrared eyes.

Heh, yeah, that would probably be rather advantageous. If they visited us, they might wonder why we put opaque windows on our houses and wear transparent clothing sometimes...

[neufer]

Of course, Titanians would probably have evolved near-infrared eyes.

Heh, yeah, that would probably be rather advantageous. If they visited us, they might wonder why we put opaque windows on our houses and wear transparent clothing sometimes...

That would probably be FAR-infrared eyes.

(Or do you, in fact, wear transparent clothing sometimes?)

[geckzilla]

It was just a guess. I know that consumer DSLRs have infrared filters in them to prevent recording of transparent-looking clothing. I figure it's not that far into infrared if a regular old DSLR detector can pick it up no problem.

[neufer]

Click to play embedded YouTube video.

[MarkBour]

The view from Titan under all that haze might not be very impressive. It's debatable whether even the Sun is visible through its haze. Think of an overcast day on Earth.

Thanks for pointing that out, geck. Unless neufer's intriguing and reasonable evolutionary idea can rescue my scenario, then I guess I'll have to switch to, say Dione, instead of Titan.

Of course imagining a civilization on a moon of a gas giant, is clearly far-fetched. I think at best we're hoping to find microbes somewhere else in the Solar system. For this, I feel like the consensus is that the moons of the gas giants are being viewed as more likely locations than the planets themselves. But (probably continuing my naivete) I wonder if the great red spot gets its color from some sort of microbes. Anyone who knows better want to give me a lecture on the likelihood of that?

[neufer]

The view from Titan under all that haze might not be very impressive. It's debatable whether even the Sun is visible through its haze. Think of an overcast day on Earth.

Thanks for pointing that out, geck. Unless neufer's intriguing and reasonable evolutionary idea can rescue my scenario, then I guess I'll have to switch to, say Dione, instead of Titan.

• However, for a good view of Saturn's rings one really needs to be
  on a high inclination satellite like Siarnaq or Albiorix.

[size=115][b]Irregular prograde groups of Saturn satellites: [color=#0000FF]Inuit (blue)[/color] & [color=#FF0000]Gallic (red)[/color]. The eccentricity of the orbits is represented by the yellow segments extending from the pericentre to the apocentre.[/b][/size]

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<<Siarnaq (SEE-ar-nahk) is a prograde irregular satellite of Saturn. It was named after the giant Siarnaq of Inuit mythology, it is the largest member of the Inuit group of irregular satellites.

Siarnaq is thought to be about 40 kilometers in diameter. It orbits Saturn at an average distance of 17.5 million km in 895 days. The rotation period was measured by the Cassini spacecraft to approximately 10 hours and 9 minutes; this is the shortest rotation period of all prograde irregular moons of Saturn.

It is light red in color, and the Siarnaupian (Siarnaqan) spectrum in the infrared is very similar to the Inuit-group satellites Paaliaq and Kiviuq, supporting the thesis of a possible common origin in the break-up of a larger body.

Siarnaq has been found to be in a secular resonance with Saturn, involving the precession of its periapsis and that of the planet. The studies of these resonances are key to understand the capture mechanism for the irregular satellites and, assuming a common origin of a given dynamical group in the break-up of a single body, to explain today’s dispersion of the orbital elements.>>
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<<Albiorix (AL-bee-ORR-iks) is a prograde irregular satellite of Saturn. Albiorix is the largest member of the Gallic group of irregular satellites. It was named in August 2003 for Albiorix, "a Gallic giant who was considered to be the king of the world." The name is known from an inscription found near the French town of Sablet which identifies him with the Roman god Mars (an interpretatio romana).

Albiorix orbits Saturn at a distance of about 16 million km in 783 days. and its diameter is estimated at 32 kilometers, assuming an albedo of 0.04. The rotation period was measured by the ISS camera of the Cassini spacecraft to 13 hours and 19 minutes.

Given the similarity of the orbital elements and the homogeneity of the physical characteristics with other members of the Gallic group, it was suggested that these satellites could have a common origin in the break-up of a larger moon. Varying colours revealed recently suggest a possibility of a large crater, leading to an alternative hypothesis that Erriapus and Tarvos could be fragments of Albiorix following a near-break-up collision with another body.>>