Help understanding this unsettling image of Titan, Epimetheus, and Saturn's rings?

Question

The NY Times article Saturn’s Rings Are Sculpted by a Crew of Mini-Moons is really interesting and links to the recent paywalled paper in Science Close Cassini flybys of Saturn’s ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus

But I absolutely can't understand one of the photos in the NY Times article, shown below. Titan seems to be...

1. behind Saturn's rings, and yet it is
2. huge relative the spacing of the rings, and yet it
3. appears to be out of focus while the rings and Epimetheus are in focus.

Can someone help me understand how all of these can be true at the same time?

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In the foreground, the moon Epimetheus appearing to hover above Saturn's rings. Epimetheus is dwarfed by Titan in the background.CreditNASA/JPL/Space Science Institute

Answer 1

This NASA page says this photo was taken on April 28 2006.

Using Celestia, I managed to find the picture from Cassini that best lines up with the photo. It doesn't match up precisely, but that's to be expected as the calculated orbital elements of all these moons (and cassini) in the software won't necessarily match up to reality precisely.

Below is the zoomed out version of this shot. You can see Titan in the centre and Epimetheus as a dot on top. And here is the top down shot from Cassini to the moons. Circled are Epimetheus and Titan.

So to answer your question: Titan is really big compared to epimetheus (about 50x), Titan has an atmosphere and so appears fuzzy (It is actually in focus, everything in space is very far away and so is effectively at infinity for focusing purposes), and the rings are highly oblique, so you only see a small slice of them.

Answer 2

The JPL Solar System Simulator doesn't show Epimetheus but does show Titan behind the Encke gap at 2006-04-28 08:12 UTC.

The simulated surface texture is probably composed of VIMS images in infrared wavelengths where Titan's atmosphere is relatively transparent. On the real Titan, haze scatters visible light so strongly that the surface is indistinct and the edge looks fuzzy.

If we zoom out, we see that we are looking near the outer edge of the rings at a very shallow angle. This is why they cover less than half of Titan's 10-arcminute apparent diameter.

Since Epimetheus appears above the rings while we are looking from below, it must be in front of them.

Simulated images courtesy NASA/JPL-Caltech

Answer 3

note: This is a supplemental answer adding some details to @ Ingolifs' excellent answer.

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At roughly 2006-Apr-28 08:30 UTC Cassini was both 1,800,000 km from Titan and 667,000 km from Epimetheus at the same time.

I used JPL's Horizons and saved the positions in the Saturn body centered coordinates every 5 minutes then ran the python script below to plot. I am not sure how to get the plane of the rings this way easily.

class Body(object):
    def __init__(self, name):
        self.name = name

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

fnames = ['Titan photo Cassini horizons_results.txt',
          'Titan photo Titan horizons_results.txt',
          'Titan photo Epimetheus horizons_results.txt' ]

names  = ['Cassini', 'Titan', 'Epimetheus']

bodies = []

for name, fname in zip(names, fnames):

    with open(fname, 'r') as infile:

        lines = infile.read().splitlines()

    iSOE = [i for i, line in enumerate(lines) if "$$SOE" in line][0]
    iEOE = [i for i, line in enumerate(lines) if "$$EOE" in line][0]

    print iSOE, iEOE, lines[iSOE], lines[iEOE]

    lines = zip(*[line.split(',') for line in lines[iSOE+1:iEOE]])

    JD  = np.array([float(x) for x in lines[0]])
    pos = np.array([[float(x) for x in lines[i]] for i in 2, 3, 4])
    vel = np.array([[float(x) for x in lines[i]] for i in 5, 6, 7])

    body = Body(name)
    bodies.append(body)
    body.JD  = JD
    body.pos = pos
    body.vel = vel

Cassini, Titan, Epimetheus = bodies

r_Titan      = np.sqrt(((Cassini.pos - Titan.pos     )**2).sum(axis=0))
r_Epimetheus = np.sqrt(((Cassini.pos - Epimetheus.pos)**2).sum(axis=0))

hours = 24 * (JD - JD[0])

r_Titan_target      = 1.8E+06 
r_Epimetheus_target = 6.67E+05

hours_Titan      = hours[np.argmax(r_Titan < r_Titan_target)]
hours_Epimetheus = hours[np.argmax(r_Epimetheus[30:] > r_Epimetheus_target)+30]

print hours_Titan, hours_Epimetheus
if True:    
    fig = plt.figure()

    plt.subplot(2, 1, 1)
    plt.plot(hours, r_Titan)
    plt.plot(hours, 1.8E+06 * np.ones_like(r_Titan), '-k')
    plt.ylabel('Cassini-Titan distance (km)', fontsize=16)

    plt.subplot(2, 1, 2)
    plt.plot(hours, r_Epimetheus)
    plt.plot(hours, 6.67E+05 * np.ones_like(r_Epimetheus), '-k')
    plt.ylabel('Cassini-Epimetheus distance (km)', fontsize=16)
    plt.xlabel('2006-Apr-28 hours', fontsize=16)

    plt.show()