All posts by Tom

You’ve Probably Never Seen a Moon Like Pan

Just when you thought a moon was a more-or-less spherical body, we have the Saturn moon Pan.  What in the world universe would create this?

From NASA:
These two images from NASA’s Cassini spacecraft show how the spacecraft’s perspective changed as it passed within 15,300 miles (24,600 kilometers) of Saturn’s moon Pan on March 7, 2017. This was Cassini’s closest-ever encounter with Pan, improving the level of detail seen on the little moon by a factor of eight over previous observations.

The views show the northern and southern hemispheres of Pan, at left and right, respectively. Both views look toward Pan’s trailing side, which is the side opposite the moon’s direction of motion as it orbits Saturn.

Cassini imaging scientists think that Pan formed within Saturn’s rings, with ring material accreting onto it and forming the rounded shape of its central mass, when the outer part of the ring system was quite young and the ring system was vertically thicker. Thus, Pan probably has a core of icy material that is denser than the softer mantle around it.

The distinctive, thin ridge around Pan’s equator is thought to have come after the moon formed and had cleared the gap in the rings in which it resides today. At that point the ring was as thin as it is today, yet there was still ring material accreting onto Pan. However, at the tail end of the process, that material was raining down on the moon solely in (or close to) its equatorial region. Thus, the infalling material formed a tall, narrow ridge of material. On a larger, more massive body, this ridge would not be so tall (relative to the body) because gravity would cause it to flatten out. But Pan’s gravity is so feeble that the ring material simply settles onto Pan and builds up. Other dynamical forces keep the ridge from growing indefinitely.

These views are also presented in stereo (3-D) in PIA21435. The images are presented here at their original size.

The views were acquired by the Cassini narrow-angle camera at distances of 15,275 miles or 24,583 kilometers (left view) and 23,199 miles or 37,335 kilometers (right view). Image scale is 482 feet or 147 meters per pixel (left view) and about 735 feet or 224 meters per pixel (right view).

See PIA09868 and PIA11529 for more distant context views of Pan.

Image: NASA/JPL-Caltech/Space Science Institute

Star Orbiting a Black Hole

Not just orbiting, but very closely orbiting, only about 2.5 Earth-Moon distances or about 961,000 km / 598,000 miles according to astronomical research coming out of Michigan State University.


The MSU press release:

Astronomers have found evidence for a star that whips around a black hole about twice an hour. This may be the tightest orbital dance ever witnessed for a black hole and a companion star.

Michigan State University scientists were part of the team that made this discovery, which used NASA’s Chandra X-ray Observatory as well as NASA’s NuSTAR and the Australia Telescope Compact Array.

The close-in stellar couple – known as a binary – is located in the globular cluster 47 Tucanae, a dense cluster of stars in our galaxy about 14,800 light years away from Earth.

While astronomers have observed this binary for many years, it wasn’t until 2015 that radio observations revealed the pair likely contains a black hole pulling material from a companion star called a white dwarf, a low-mass star that has exhausted most or all of its nuclear fuel.

New Chandra data of this system, known as X9, show that it changes in X-ray brightness in the same manner every 28 minutes, which is likely the length of time it takes the companion star to make one complete orbit around the black hole. Chandra data also shows evidence for large amounts of oxygen in the system a characteristic of white dwarfs. A strong case can, therefore, be made that that the companion star is a white dwarf, which would then be orbiting the black hole at only about 2.5 times the separation between the Earth and the moon.

Continue reading

Goodbye Mimas

Yesterday we saw Mimas and the colossal crater Herschel.  Today the other side.  this will also be our last close-in view of the moon.

There was also a version of this image release adjusted so the entire hemisphere is lit.

From NASA:

In its season of “lasts,” NASA’s Cassini spacecraft made its final close approach to Saturn’s moon Mimas on January 30, 2017. At closest approach, Cassini passed 25,620 miles (41,230 kilometers) from Mimas. All future observations of Mimas will be from more than twice this distance.

This mosaic is one of the highest resolution views ever captured of the icy moon.

Close approaches to Mimas have been somewhat rare during Cassini’s mission, with only seven flybys at distances of less than 31,000 miles (50,000 kilometers).

Mimas’ surface is pockmarked with countless craters, the largest of which gives the icy moon its distinctive appearance. (See PIA12568 for more info on Mimas’ distinctive crater, Herschel.)

Two versions of the mosaic are provided. In one, the left side, which is lit by reflected light from Saturn, has been enhanced in brightness in order to show the full surface. The second version features more natural illumination levels (Figure 1).

Imaging scientists combined ten narrow-angle camera images to create this mosaic view. The scene is an orthographic projection centered on terrain at 17.5 degrees south latitude, 325.4 degrees west longitude on Mimas. An orthographic view is most like the view seen by a distant observer looking through a telescope.

This mosaic was acquired at a distance of approximately 28,000 miles (45,000 kilometers) from Mimas. Image scale is approximately 820 feet (250 meters) per pixel. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 30, 2017.

Images: NASA/JPL-Caltech/Space Science Institute


Happy PI Day!

Almost missed it being  in the middle of a snow storm, right now  and all.  The snow is  coming down about 5 or so cm per hour (2 inches).  Been snowing at that rate for some time and it will continue until we finish up with a forecasted 60 cm / 24 inches.  I’m figuring we will make that number easy enough.

The snow is pretty dry so far, about a 15:1 ratio, snow to water.  That’s good for moving the stuff, light weight and not sticky.  What the wind will do is a whole other story and that chapter is supposed to be written later on.  No, I’m not doing either of my two driveways completely.  I am just doing the interfaces with the highway so the plow doesn’t put a huge snowbank in the way.  Been there and done that. . . didn’t like it at all.

So back to PI Day.  I memorized PI to 3.141592653589793238462643383279502 once and still can get almost that many digits now.  Funny what you can remember.

So want to see PI to a million digits?  I know you do (LOL), check out this site:




Herschel Crater

What a great look at the crater Herschel on the Saturn moon Mimas.

Herschel crater is 130 km / 80.8 miles across about a third the diameter of the moon itself. The walls of the crater are around 5 km / 3.1 miles high and a central peak is about 6 km / 3.7 miles tall, the impact was colossal.

Here’s NASA’s description:
Mimas’ gigantic crater Herschel lies near the moon’s limb in this Cassini view.

A big enough impact could potentially break up a moon. Luckily for Mimas, whatever created Herschel was not quite big enough to cause that level of disruption.

When large impacts happen, they deliver tremendous amounts of energy — sometimes enough to cause global destruction. Even impacts that are not catastrophic can leave enormous, near-permanent scars on bodies like Mimas (246 miles or 396 kilometers across).

This view looks toward the anti-Saturn hemisphere of Mimas. North on Mimas is up and rotated 32 degrees to the left. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 19, 2016.

The view was acquired at a distance of approximately 53,000 miles (85,000 kilometers) from Mimas. Image scale is 1,677 feet (511 meters) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

The Europa Clipper

NASA – NASA’s upcoming mission to investigate the habitability of Jupiter’s icy moon Europa now has a formal name: Europa Clipper.

The moniker harkens back to the clipper ships that sailed across the oceans of Earth in the 19th century. Clipper ships were streamlined, three-masted sailing vessels renowned for their grace and swiftness. These ships rapidly shuttled tea and other goods back and forth across the Atlantic Ocean and around globe.

In the grand tradition of these classic ships, the Europa Clipper spacecraft would sail past Europa at a rapid cadence, as frequently as every two weeks, providing many opportunities to investigate the moon up close. The prime mission plan includes 40 to 45 flybys, during which the spacecraft would image the moon’s icy surface at high resolution and investigate its composition and the structure of its interior and icy shell.

Europa has long been a high priority for exploration because it holds a salty liquid water ocean beneath its icy crust. The ultimate aim of Europa Clipper is to determine if Europa is habitable, possessing all three of the ingredients necessary for life: liquid water, chemical ingredients, and energy sources sufficient to enable biology.

“During each orbit, the spacecraft spends only a short time within the challenging radiation environment near Europa. It speeds past, gathers a huge amount of science data, then sails on out of there,” said Robert Pappalardo, Europa Clipper project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Previously, when the mission was still in the conceptual phase, it was sometimes informally called Europa Clipper, but NASA has now adopted that name as the former title for the mission.

The mission is being planned for launch in the 2020s, arriving in the Jupiter system after a journey of several years.

JPL manages the mission for the agency’s Science Mission Directorate in Washington.

Finding the Rings of Uranus

The discovery of rings of Uranus is generally accepted to be on 10 March 1977 by by James L. Elliot, Edward W. Dunham, and Jessica Mink. That’s 40 years ago today and I mention “generally accepted” because the great William Herschel claims to have seen rings around the planet and who knows maybe he did because in his notes in 1789 he noted a ring was suspected (see “Uranus rings were seen in 1700s“).

I’m sticking with 1977 and that by the way,  is a great story because at the time the trio were actually in the Kuiper Airborne Observatory planning on seeing the planet occult a star (SAO 158687). Read the story.

Much more about Uranian system can be found at our site with some great mystery questions at the end. No missions are scheduled, pity, much to be be learned.

The picture at the top (and you should click it to make it a bit larger) gives an annotated view from Hubblesite from 2005. In 2007 the Hubble took images of the rings edge on and the last time we “saw” the rings edge on, we did not even know they existed. Look how wide they are:

Images: Hubblesite