Comet 41P In The Dragon’s Gaze / Saturn’s Flying Saucer Moon

Comet 41P/T-G-K swings past the head of Draco this week, passing just ½° from Rastaban, one of the dragon’s eyes (Eltanin is the other) on Thursday night, April 20. The map shows the comet’s position nightly at 10 p.m. local time April 14-22 facing north. 41P will be about three fists up in the northeastern sky at the time. Created with Stellarium

Now that the waning gibbous moon rises after 11 o’clock, we’ve got an expanding dark sky window to catch up with 41P/Tuttle-Giacobini-Kresak. When we last left the comet, it was sailing across the Big Dipper and visible as a 6th magnitude smudge-ball in binoculars. It passed closest to Earth on April 1 at 13 million miles.

On April 9, 41P/T-G-K (right of center) snugged up close to the spiral galaxy, NGC 6015, located 44 million light years from Earth. Credit: Gianluca Masi

What’s it doing now? Well, it’s still a smoky-looking glow or haze moving along at a good clip, but now it’s skirting the head of Draco the Dragon. The little boxy trapezoid-shaped figure is easy to find if you start with the Little Dipper and look four fists to the lower right of the North Star (Polaris). The brightest star in the trapezoid is Eltanin; at magnitude +2, it’s brightness is matches that of the stars that outline the Big Dipper, now located high overhead.

This is a “negative” version of the first map. Some observers prefer this map style for comet seeking. Click for the large file and make a print out to use outside. Created with Stellarium

Still at magnitude +6.5, 50mm or larger binoculars will show the comet as a hazy spot about half the size of the full moon. 41P/T-G-K is slowly fading as its distance from Earth increases. Through a telescope, you’ll see a ball of haze, the comet’s coma, with a brighter center and a hint of tail to the northeast.

We have two comets — C/2017 E4 Lovejoy and C/2015 ER61 PanSTARRS — that are also binocular objects, but we’ll have to wait for the bright moon to vacate the premises for a good view. That will happen in about 9 days.

Ingredients for Life at Saturn’s Moon Enceladus

There’s been a lot of Saturn news this week in particular about the discovery of hydrogen molecules in the vapor plumes that blast from cracks in the surface of the planet’s icy moon, Enceladus (en-CELL-uh-duss). We know there’s an ocean of warm water beneath the moon’s icy crust. On Oct. 28, 2015, NASA’s Cassini probe sampled the plume’s composition during flybys and determined that nearly 98% of the gas in the plume is water, about 1% is hydrogen and the rest is a mixture of other molecules including carbon dioxide, methane and ammonia.

This graphic illustrates how scientists on NASA’s Cassini mission think water interacts with rock at the bottom of the ocean of Saturn’s icy moon Enceladus, producing hydrogen gas (H2). The top image is a cross-cut through the moon showing its frozen surface, warm subsurface ocean and hydrothermal vents. Credit: NASA/JPL-Caltech/Southwest Research Institute

It may sound weird to our ears, but hydrogen is candy to certain forms of bacteria. They combine it with carbon dioxide to create the energy needed to survive and reproduce. Black smokers that bubble from hydrothermal vents in the inky depths of Earth’s oceans provide the hydrogen and minerals to support thriving colonies of the organisms. In turn, larger creatures feed on the bacteria to create a food chain.

While no microbes have been discovered at Enceladus, we now know that this remote locale possesses all the right ingredients for life to thrive. Life as we know it requires three primary ingredients: liquid water, a source of energy for metabolism and the right chemical ingredients — primarily carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Although Cassini didn’t find phosphorus and sulfur, there’s common in meteorites and likely within the rocky core at the heart of Enceladus.

The Cassini spacecraft took this photo of the strange-shaped moon Atlas during a close flyby on April 12. Credit: NASA/JPL-Caltech

Cassini also returned some fantastic new photos of another of Saturn’s moons, the tiny, UFO-shaped Atlas,  just 19 miles (30 km) across. Atlas orbits just outside of Saturn’s A ring, the outermost of the three brightest rings visible in small telescopes. The picture was taken on April 12 when the spacecraft flew just 7,000 miles (11,000 km) from the moon and are the closest ever taken of Atlas.

Atlas orbits between Saturn’s A and F-rings. Because the rings and ring material is only about 30 feet (10 meters) thick, most of the ice Atlas sweeps up accumulated along its equator, the reason for its pancake shape. Credit: NASA/JPL-Caltech

Much like Pan, which also orbits within the plane of Saturn’s rings, Atlas has a broad, flat ridge around its equator. The most likely explanation for this striking feature is that ring material gets swept up by the moon as it orbits the planet, but because the rings are so thin, most of the material accumulates along the equator.

If you’d like to see Saturn, it comes up after midnight. The waning gibbous moon will be to the planet’s upper right on Sunday morning the 16th and to its left on the 17th.

2 Responses

    1. astrobob

      Hi Carol,

      Just a hunch, but two things: Atlas is very small and may only be able to attract and hold the smallest of the ring particles it sweeps through. Small enough that Cassini’s camera can’t resolve textures much like it can’t show individual ring particles. Or … the particular region Atlas sweeps only holds fine material smaller than the resolution of Cassini’s camera. Or both possibilities. Atlas orbits in a region between two brighter rings that appears ringless but it definitely has particles – they’re far more sparse than say the A or B-rings and may be smaller and therefore reflect less light.

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