Phobos & Deimos — The Moons of Mars Explained

Where did Mars’ moons Phobos and Deimos come from? How did they end up in orbit around Mars? This cool video from the folks at Kurzgesagt answers the most-oft asked questions about these mini moons.

You should also check out their other wonderful videos, like the one about our own Moon, below, which explains how big our Moon really is. The answer might surprise you.

Who is Kurzgesagt? They are video designers who create fun and intellectually stimulating content about space, science and many other topics. “Kurz gesagt” is a German expression for “to make a long story short” and the Kurzgesagt team says it precisely conveys their goal to present complex topics in a short and understandable way to the world. “Also, we want to make stuff that simply looks awesome.”

Mission accomplished! Look for more videos from Kurzgesagt on Universe Today in the future.

Check out their website here and all their videos on their You Tube page.

Asteroids VS. Your Hometown: Fun but Frightening Graphics Compare Asteroid Sizes to Places on Earth

So, how big is that space rock?

Sometimes when I see data on sizes and distances in relation to stuff out in space, it’s hard to get a frame of reference, since those two categories tend to lean towards the super-big. But now, I’ve got a little help. Space enthusiast and software engineer Ciro Villa has brought some of these references closer to home with these fun graphics that provide accurate size ratios and proportions of objects in space compared to places on Earth.

Villa calls these graphics “hovering celestial objects” and while all of these scenarios are impossible in real life, he’s placed large asteroids and moons next to Earthly locations to provide a good frame of reference for dimensions. Please note that most of these objects have absolutely no chance of colliding with Earth as they are not anywhere near our neighborhood and are not expected to visit it either.

“My representations are is purely for illustrative purposes,” Villa said. “I have maintained the size ratios and proportions as accurately as possible just to demonstrate the dimensions. This is mostly a ‘fun’ exercise.”

For example, I regularly drive through the St. Louis, Missouri metro area, so I have a sense of how big it is. Above, Villa places Asteroid 243 Ida — which has an average diameter of 31.4 km (19.5 miles) — to hover right above St. Louis. 31 km is about the distance from East St. Louis, Illinois to Creve Coeur, Missouri, which are the generally accepted eastern and western borders of the St. Louis metro area. I could probably drive across Ida in about 30 minutes — if it’s not rush hour, that is!

To create these graphics, Villa uses Google Maps, NASA data and Gimp image editing software. Again, these graphics are for fun, but I really find them useful!

And Villa provided a caveat: “Please note that I am not a professional graphic artist, so I’m sure people are going to find plenty of imperfections in these depictions,” he said. “The important point I am trying to convey is mainly the size dimensions comparing with a known area of Earth.”

Here are more:

Asteroids Orcus and Vanth hovering over Eastern Texas and Western Arkansas. Credit and copyright: Ciro Villa.
Asteroids Orcus and Vanth hovering over Eastern Texas and Western Arkansas. Credit and copyright: Ciro Villa.

Here are a bigger pair of objects in comparison to an area of Eastern Texas and Western Arkansas. 90482 Orcus is a trans-Neptunian Kuiper belt object that is about 800 kilometers in diameter. Orcus has a fairly large moon orbiting it named Vanth, which is about 300 km in diameter.

Asteroid 433 Eros over Kennedy Space Center, Florida. Credit and copyright: Ciro Villa.
Asteroid 433 Eros over Kennedy Space Center, Florida. Credit and copyright: Ciro Villa.

This asteroid might pay Earth a close visit, but not for a couple of million years. Eros is the second largest NEO (Near Earth Object), with a diameter of approximately 34 kilometers, and here Villa imagines Eros centered over the VAB (Vehicle Assembly Building) at Cape Canaveral, covering the Cape area from approximately the southern end of the Canaveral National Seashore to the Pine Island Conservation area, with the VAB in about the middle, as the crow (or sandhill crane) flies.

While Eros is technically an NEO, it made one of its closest passes of Earth in 2012 of 16.6 million miles (26.7 million km) and won’t pass that close again until 2056. A look ahead with orbital mechanics suggests that Eros may move to an Earth-crossing orbit in about two million years, given the right perturbations by gravitational interactions.

216 Kleopatra is an asteroid belt object shaped like a dog bone (or a deformed dumbell).  Its length is approximately 217 kilometers; just about the size of New Jersey. Credit and copyright: Ciro Villa.
216 Kleopatra is an asteroid belt object shaped like a dog bone (or a deformed dumbell). Its length is approximately 217 kilometers; just about the size of New Jersey. Credit and copyright: Ciro Villa.

And to show the scale of several moons in our Solar System, Villa made these comparisons:

An imaginary graphic depicting how Deimos would look if it hovered over Paris, France. Credit and copyright: Ciro Villa.
An imaginary graphic depicting how Deimos would look if it hovered over Paris, France. Credit and copyright: Ciro Villa.

“Deimos is about 15 kilometers across, so I have measured a portion of the city of Paris, France of about 5 Kilometers and properly scaled Deimos,” Villa said. “For added dramatics, I have purposely shown enough of Deimos hovering to show about 5 kilometers of Paris, to show some of the landmarks (notice the Eiffel tower). Had I decided to show all of Deimos, the scale would have been too large to recognize any of the landmarks of Paris.”

How Saturn's moon Enceladus would look if it hovered over southern England. Credit and copyright: Ciro Villa.
How Saturn’s moon Enceladus would look if it hovered over southern England. Credit and copyright: Ciro Villa.

Continuing these imaginary montages, here is one of our favorite moons, Enceladus, with an approximate diameter of about 500 kilometers, seen drifting over Southern England. That’s about the same distance from Plymouth to Leigh-on-the-Sea in the UK.

A graphic of imagining the moon Phoebe (Saturn IX) hovering Central Florida. Credit and copyright: Ciro Villa.
A graphic imagining asteroid Phoebe (Saturn IX) hovering Central Florida. Credit and copyright: Ciro Villa.

This last one is a bit personal for Villa, since he lives in Florida. Here, Saturn’s moon Phoebe hangs over Central Florida. “Phoebe shares an approximate diameter of 200 kilometers with the central portion of the state,” Villa said, “and I wanted to ‘play’ with my imagination a bit!”

Thanks to Ciro Villa for sharing his “hovering celestial objects” with Universe Today. Check out his informative and entertaining G+ feed here.

Watch Two Dark Moons Sneak Into Cassini’s Shots

On March 11, NASA’s Cassini spacecraft was acquiring some images of Saturn’s back-lit limb when two of its moons decided to make an entrance. Like stage hands in a darkened theatre the moons quickly passed  across the scene, moving between Saturn and the spacecraft and, because of exposure time and spacecraft motion, getting a bit blurred in the process.

In the image above the silhouette of one moon can be seen at bottom right — Mimas, perhaps — while another’s crescent can be made out at upper left… possibly Enceladus. Very cool!

Watch an animation of the moons below:

Two of Saturn's moons drift into the scene on March 11, 2014 (NASA/JPL-Caltech/SSI. Animation by Jason Major.)
Two of Saturn’s moons drift into the scene on March 11, 2014 (NASA/JPL-Caltech/SSI. Animation by Jason Major.)

While I admit I’m not 100% sure which moons these are, based on their apparent shapes, positions, and relative sizes I’d make my guess that these are 318-mile (511-km) -wide Enceladus and the 246-mile (395-km) -wide Mimas.

Possible location of icy spray, if this is Enceladus
Possible location of icy spray, if Enceladus is in fact this moon’s real name

Cassini was 843,762 miles (1,357,903 km) from Saturn when the images were acquired. And, if the larger moon at left is Enceladus, I’m thinking south in these images is up based on the barely-perceptible presence of a lighter area along its top edge that could be icy spray from its southern geysers. (See enlarged detail at right.)

Saturn, of course, is on the right. A small segment of the bright arc of its backlit limb is what’s running diagonally down across the image.

These images have not yet been calibrated or cataloged by NASA or the Cassini team.

See the latest raw images from Cassini on JPL’s mission page here.

*I say “dark moons” but actually Enceladus and Mimas are pretty bright, both being composed of a lot of ice. Enceladus is actually the most reflective world in the Solar System!

A Distant View of Janus, One of Saturn’s ‘Dancing Moons’

One of 62 moons discovered thus far orbiting giant Saturn, Janus is a 111-mile (179-km) -wide pockmarked potato composed of rock and ice rubble. The image above shows Janus as seen with Cassini’s narrow-angle camera on September 10, 2013, from a distance of 621,000 miles (1 million km), floating against the blackness of space.

Despite its apparent isolation in the image above, though, Janus isn’t alone. It shares its orbit around Saturn with its slightly smaller sister moon Epimetheus, and they regularly catch up to each other — and even switch places.

Janus and Epimetheus: Saturn's "dancing moons" (NASA/JPL/SSI)
Janus and Epimetheus: Saturn’s “dancing moons” (NASA/JPL/SSI)

Janus and Epimetheus travel in nearly the same track, about 94,100 miles (151,500 km) out from Saturn. They occasionally pass each other, their gravity causing them to switch speeds and positions as they do; Janus goes faster and higher one time, slower and lower the next – but the two never come within more than about 6,200 miles of each other.

The two moons switch positions roughly every four years.

This scenario is referred to in astrophysics as a 1:1 resonance. Astronomers were initially confused when the moons were discovered in 1966 as it wasn’t known at the time that there were actually two separate moons in a single orbit. (This wasn’t confirmed until Voyager 1’s visit to Saturn in 1980.) It’s been suggested that Janus and Epimetheus will eventually come to orbit a single Lagrangian point around Saturn instead of trading places… in about another 20 million years.

The view above looks toward the Saturn-facing side of Janus. Covered in both dark and light colored material, Janus’ surface is thought to be coated with a layer of fine dust that slides down its steeper slopes, revealing the brighter ice beneath.

Cassini image of Janus from April 2010 (NASA/JPL-Caltech/SSI)
Cassini image of Janus from April 2010 (NASA/JPL-Caltech/SSI)

Want to see more images of Janus? Click here.

Source: Cassini Solstice Mission release


An Occult Occurrence: Saturn’s Moon Iapetus Blocks a Background Star

It’s a cosmic cover-up! No, don’t put your tinfoil* hats on, this isn’t a conspiracy — it’s just Saturn’s moon Iapetus drifting in front of the bright star Gamma Orionis (aka Bellatrix) captured on Cassini’s narrow-angle camera on August 10, 2013.

Such an event is called an occultation, a term used in astronomy whenever light from one object is blocked by another — specifically when something visually larger moves in front of something apparently smaller. (The word occult means to hide or conceal… nothing mystical implied!)

The animation above was assembled from 19 raw images publicly available on the JPL Cassini mission site, stacked in Photoshop and exported as a gif. They’ve been rotated 90º from the originals but otherwise they’re right from Cassini’s camera.

Iapetus, seen above as just a thin crescent, is best known for its two-toned appearance. One half of the 914-mile-wide moon is bright and icy, the other coated with a layer of dark reddish material, giving it a real “yin-yang” appearance. (Ok, I guess that’s a little mystical. But purely coincidental.)

The Tao of Iapetus (NASA/JPL-Caltech/SSI)
The Tao of Iapetus (NASA/JPL-Caltech/SSI)

It’s thought that the dark material originates from a more distant moon, Phoebe, which is being pelted by micrometeorites and shedding its surface out into orbit around Saturn, which eventually gets scooped up by the backwards-orbiting Iapetus.

The difference in albedo affects how Iapetus absorbs solar radiation too, causing the water ice beneath the darker material to evaporate over the course of its 79-Earth-day rotation and migrate around its surface, creating a sort of positive feedback loop.

While neat to look at, occultations are important to science because they provide a way to briefly peer into a world’s atmosphere (or in a small moon’s case, exosphere). Watching how light behaves as it passes behind the limb of a planet or moon lets researchers learn details of the air around it — however tenuous — pretty much for free… no probes or flybys needed!

The occulted star above is Bellatrix, the 1.6-magnitude star that marks Orion’s left shoulder.

Iapetus orbits Saturn at the considerable distance of 2,212,889 miles (3,561,300 km). Learn more about Iapetus here, and as always you can find more fantastic Cassini images from Carolyn Porco’s team at the Space Science Institute in Boulder, Colorado at the CICLOPS site here.


*Do they still make foil out of tin any more? 

Waltz Around Saturn With This Beautiful Animation

In honor of this today’s Wave at Saturn and The Day the Earth Smiled events, celebrating images to be taken of Earth from Saturn, here’s a wonderful movie showing highlights from Cassini’s exploration of the giant planet, its magnificent rings, and fascinating family of moons.

Assembled by Fabio Di Donato in memory of astrophysicist, author and activist Margherita Hack, who passed away June 29 at the age of 91, this video is an impressive tour of the Saturnian system — and a truly stunning tribute as well.

“She made me love the stars,” Fabio wrote.

This video shows a selection from more than 200,000 pictures taken by the Cassini spacecraft around Saturn’s rings in a period between 2005 and 2013. RAW images were processed to PNG thanks to the Vicar-to-PNG procedure provided by Jessica McKellar.

The music is Jazz Suite No.2: VI Waltz 2 by Shostakovich, performed by the Armonie Symphony Orchestra.

As always, you can see the latest images and news from the Cassini mission here, and find out how your photo is going to be taken from 900 million miles away (and also 60 million miles away from Mercury!) here.

Video: Fabio Di Donato. Original images: NASA/JPL-Caltech/SSI.

P.S.: Want to get a personalized certificate saying you “Waved at Saturn?” Click here.

Pluto May Soon Have a Moon Named Vulcan (Thanks to William Shatner)

The votes have been tallied and the results are in from the SETI Institute’s Pluto Rocks Poll: “Vulcan” and “Cerberus” have come out on top for names for Pluto’s most recently-discovered moons, P4 and P5.

After 450,324 votes cast over the past two weeks, Vulcan is the clear winner with a landslide 174,062 votes… due in no small part to a little Twitter intervention by Mr. William Shatner, I’m sure.

In other words… yes, the Trekkies have won.

Screen Shot 2013-02-25 at 2.32.53 PMDuring a Google+ Hangout today, SETI Institute senior scientist Mark Showalter — who discovered the moons and opened up the poll — talked with SETI astronomer Franck Marchis and MSNBC’s Alan Boyle about the voting results. Showalter admitted that he wasn’t quite sure how well the whole internet poll thing would work out, but he’s pleased with the results.

“I had no idea what to expect,” said Showalter. “As we all know the internet can be an unruly place… but by and large this process has gone very smoothly. I feel the results are fair.”

As far as having a name from the Star Trek universe be used for an actual astronomical object?

“Vulcan works,” Showalter said. “He’s got a family tie to the whole story. Pluto and Zeus were brothers, and Vulcan is a son of Pluto.”

And what can you say when even Mr. Spock agrees?

Leonard Nimoy's tweet

The other winning name, Cerberus, is currently used for an asteroid. So because the IAU typically tries to avoid confusion with two objects sharing the same exact name, Showalter said he will use the Greek version of the spelling: Kerberos.

Cerberus (or Kerberos) is the name of the giant three-headed dog that guards the gates to the underworld in Greek mythology.

Now that the international public has spoken, the next step will be to submit these names to the International Astronomical Union for official approval, a process that could take 1–2 months.

(Although who knows… maybe Bill can help move that process along as well?)

Read more about the names on the Pluto Rocks ballot here, and watch the full recorded Google+ Hangout below:

Help Name Pluto’s Newest Moons!

Today marks seven months since the announcement of Pluto’s fifth moon and over a year and a half since the discovery of the one before that. But both moons still have letter-and-number designations, P5 and P4, respectively… not very imaginative, to say the least, and not really fitting into the pantheon of mythologically-named worlds in our Solar System.

Today, you can help change that.

According to the New Horizons research team, after the discovery of P4 in June 2011 it was decided to wait to see if any more moons were discovered in order to choose names that fit together as a pair, while a*lso following accepted IAU naming practices. Now, seven months after the announcement of P5, we think a decision is in order… and so does the P4/P5 Discovery Team at the SETI Institute.

"Hey, I can be democratic about this!"
“Hey, I can be democratic about all this!”

Today, SETI Senior Research Scientist Mark Showalter revealed a new poll site, Pluto Rocks, where visitors can place their votes on a selection of names for P4 and P5 — or even write in a suggestion of their own. In line with IAU convention these names are associated with the Greek and Roman mythology surrounding Pluto/Hades and his underworld-dwelling minions.

“In 1930, a little girl named Venetia Burney suggested that Clyde Tombaugh name his newly discovered planet ‘Pluto.’ Tombaugh liked the idea and the name stuck. I like to think that we are doing honor to Tombaugh’s legacy by now opening up the naming of Pluto’s two tiniest known moons to everyone.”

– Mark Showalter, SETI Institute

As of the time of this writing, the ongoing results look like this:

Results of Pluto Rocks voting as of Feb. 11, 2013 at 10 am EST (15:00 UT)
Results of Pluto Rocks voting as of Feb. 11, 2013 at 10 am EST (15:00 UT)

Do you like where the voting is headed? Are you hellishly opposed? Go place your vote now and make your opinion count in the naming of these two distant worlds!

(After all, New Horizons will be visiting Pluto in just under two and a half years, and she really should know how to greet the family.)

Voting ends at noon EST on Monday, February 25th, 2013.

The SETI team welcomes you to submit your vote every day, but only once per day so that voting is fair.

UPDATE: On Feb. 25, the final day of voting, the tally is looking like this:

PlutoRocks results as of Feb. 25, 2013 - Vulcan is in the lead, thanks to publicity from Mr. William Shatner
PlutoRocks results as of Feb. 25, 2013 – Vulcan is in the lead, thanks to publicity from Mr. William Shatner

Thanks in no small part to a bit of publicity on Twitter by Captain Kirk himself, Mr. William Shatner (and support by Leonard Nimoy) “Vulcan” has made the list and warped straight to the lead. Will SETI and the IAU honor such Trek fan support with an official designation? We shall soon find out…

The Rings on the Planet Go ‘Round and ‘Round…

Raw wide-angle Cassini image of Saturn’s rings (NASA/JPL/SSI)

Recently I posted an image of two of Saturn’s shepherd moons, Pandora and Prometheus, captured by Cassini in a face-off across the spindly F ring. Now here’s a much wider-angle view of the gas giant’s rings, seen by Cassini  two days later on December 20, and the same two moons can still be seen staring each other down… two tiny points of light visible across the wavering line of the F ring at lower center.

This is just one raw image in a series of 56 that Cassini captured on the 20th, and I’ve combined them together to make a GIF animation — click below to watch:

Animation of Saturn’s rings made from raw images acquired by Cassini on Dec. 20, 2012 (NASA/JPL/SSI. Animation by J. Major)

In the animation you can see Pandora and Prometheus promenade around Saturn (detail at right) as well as a “spoke” of light material moving within the inner dark edge of the A ring. Also many clumps are visible in the thin F ring — caused by embedded moonlets and the gravitational influence of the shepherd moons.

Saturn’s enormous shadow engulfs the entire ring system at the top of the scene.

Cassini was moving relative to Saturn while these images were captured so some background stars make brief appearances, as well as a couple of pixel flares and a cosmic ray hit. These are common in Cassini images.

See more news and images from the Cassini mission here.


Shepherd Moon Face-Off!

Raw Cassini image acquired on Dec. 18, 2012 (NASA/JPL/SSI)

Two of Saturn’s shepherd moons face off across the icy strand of the F ring in this image, acquired by the Cassini spacecraft on December 18, 2012.

In the left corner is Pandora, external shepherd of the ropy ring, and in the right is Prometheus, whose gravity is responsible for the subtle tug on the wispy ring material. (Please don’t blame the moon for any recent unsatisfying sci-fi films of the same name. There’s no relation, we promise.)

Similar in size (Pandora is 110 x 88 x 62 km, Prometheus 148 x 100 x 68 km) both moons are porous, icy, potato-shaped bodies covered in craters — although Prometheus’ surface is somewhat smoother in appearance than Pandora’s, perhaps due to the gradual buildup of infalling material from the F ring.

Check out some much closer images of these two moons below, acquired during earlier flybys:

Here’s Pandora, as seen by Cassini on September 5, 2005:

False-color image of Pandora (NASA/JPL/SSI)

…and here’s Prometheus, seen during a close pass in 2010 and color-calibrated by Gordan Ugarkovic:

 Prometheus casting a shadow through F ring haze (NASA/JPL/SSI/Gordan Ugarvovic)

The external edge of the A ring with the thin Keeler gap and the wider Encke gap can be seen at the right of the top image. Both of these gaps also harbor their own shepherd moons — Daphnis and Pan, respectively.

These moons keep their gaps clear, as well as maintain the crisp edge shapes of the nearby rings — hence the term “shepherd.”

Image credit: NASA/JPL/Space Science Institute