Full Worm Moon wriggles up, shows its head tonight

The nearly full moon rises within the framework of Duluth, Minnesota's iconic Aerial Lift Bridge yesterday evening March 4. Credit: Bob King

The nearly full moon rises within the framework of Duluth, Minnesota’s iconic Aerial Lift Bridge yesterday evening March 4. March’s Full Worm Moon is named for the time when the ground softens and earthworms show their heads again. Credit: Bob King

With 14 below on the thermometer this morning I don’t think Full Worm Moon quite fits as a description for tonight’s full moon. How about the Sap Moon, named for the time when sap begins to run again in maple trees? No, a little too early for that. These traditional Native American moon names obviously applied to other more clement regions of the country where March really does mean the start of spring.

More like the Full Stubborn Moon in my town. Yet the signs of spring are unmistakable. Longer days, shorter nights, a steeper slant to the sunlight. Spring stars are pushing up in the east as well – scintillatious Arcturus is up by 9:30 in the northeast, followed by Virgo’s Spica an hour or so later.

Last month's just-past-full moon rises below Jupiter over the ice-covered shore of Lake Superior in Duluth. Watch for the Full Worm Moon tonight. Click image to find the moonrise time for your location. Credit: Bob King

Last month’s just-past-full moon rises below Jupiter over the ice-covered shore of Lake Superior in Duluth. Watch for the Full Worm Moon tonight. Click image to find the moonrise time for your location. Credit: Bob King

We enjoy watching these seasonal changes. They help us get out of bed and renew that enjoyable sense of anticipation at what’s around the next corner. Constant motion. We’ve been told everything’s in continual movement. If you could shrink down to size of a bacterium you’d never be able to sit still. At that level, you’d feel the pinging of millions of molecules called Brownian motion. Getting up and walking to another room you’d be pelted by a hail of molecular snowballs.

Lucky then that humans are big enough to escape such atomic beatings. But the incredible variety of motions still can throw us off. The stars rise and set, reflecting the rotation of our planet, constellations shift westward with the seasons as Earth orbits the Sun, the moon and planets march east, contrary to the motion of the stars.

The Earth's rotation dominates the moon's apparent motion across the sky, causing it rise in the east and set in the west. Meanwhile, the moon itself is moving much more slowly toward the east or back down toward the horizon. Credit: Bob King

The Earth’s rotation dominates the moon’s apparent motion across the sky, causing it rise in the east and set in the west. The moon is simultaneously moving much more slowly toward the east or back down toward the horizon. Credit: Bob King

When you watch the moon rise tonight, be aware that as the Earth’s rotation brings it into view, the moon’s orbital movement wants to drag it back down to the horizon. Reminds me of trying to get a teenager out of bed. The Earth wins of course because the moon is far enough away that its apparent motion to the east amounts to only 1/2° or one moon diameter per hour. Meanwhile, Earth’s west-to-east rotation uproots our satellite and whips it to the west 30 times faster. Sorry moon, you lose.

It’s all illusion of course. The moon’s doing most of the moving. Its nightly rising in the east and setting in the west are nothing more than a reflection of our planet’s spin. Fake motion. By the way, those little 1/2 degrees add up – every 24 hours the moon moves more than a fist to the east.

Phobos, the larger of Mars' two moons, orbits just 3,700 miles above the planet's surface, so close it takes just 7 hours 39 minutes to complete its orbit. Phobos is only about 12 miles across. Credit: NASA/JPL-Caltech

Phobos, the larger of Mars’ two moons, orbits just 3,700 miles above the planet’s surface, so close it takes just 7 hours 39 minutes to complete its orbit. Phobos is only about 12 miles across. Credit: NASA/JPL-Caltech

While the moon may appear to lose to Earth, this isn’t true with Mars’ moon Phobos, which lies so close to the planet that it takes just 7 1/2 hours to orbit it. Moving eastward at 45° per hour (90 times faster than the moon), Phobos rises in the west and sets in the east after only 4 hours. Four hours later’ it’s back again at the western horizon ready for another trip across the night sky. Mars’ rotation rate of 24 hours 37 minutes just can’t keep up with this insanely fast moon.

While I’d be the first to purchase a cheap ticket to Mars just to see crazy Phobos, I rather like the unhurried and deliberate moon that rises over Earth. Time to watch moonlight transform the landscape and help us slow down a little after a busy day.

Moon gives us a wink / Mars near and afar

Tonight (Oct. 25) the thin lunar crescent appears again at dusk low in the southwestern sky near the planet Saturn. This map shows the sky about 20 minutes past sunset. Source: Stellarium

After a splendid eclipse performance, the Moon returns at dusk this evening low in the southwestern sky after sunset. Reborn as a waxing crescent, it will slip away from the Sun in the coming days and gently light the night.

For those who like something much more challenging than spying the Moon, try finding Saturn about 3 degrees to its west. Binoculars required!

India’s Mars Orbiter tweeted this full-color photo of the planet earlier this month. It features the hemisphere of Mars rich in ancient volcanoes, the brown, circular structures that look like anthills.  The largest, Olympus Mons, is visible at far left center. The planet’s north polar region is covered in clouds. Credit: ISRO

Farther east, Mars, though low, is still an easy catch with the naked eye. Most of us gave up looking at it in a telescope several months ago, since the planet has shrunk to 5.6″ in diameter, not quite twice as big as Uranus’ apparent size. Mars is far from Earth and presently in in its “orange blip” phase. Even at 300x magnification, such a tiny disk shows little detail.

Little Phobos, only 10 by 14 by 11 miles (17 by 22 by 18 km), looks tiny indeed against the backdrop of the mother planet. Credit: ISRO

No matter. So many space probes now orbit the planet, close-up views are available at the click of a mouse. The Mars Orbiter Mission (MOM) has sent back some excellent color images of the planet recently including one showing Mars’ small moon Phobos in orbit.

Photos taken by the Mars Curiosity rover on June 28, 2013 show the moon Phobos rising in the Martian sky. White dots are hot pixels and flashes are cosmic rays. 

Another view of Phobos taken by ESA’s Mars Express. This small, dark moon orbits 5,826 miles (9,380 km) above the planet. Credit: NASA

Curiosity snaps sharpest-ever photos of “ring of fire” eclipse on Mars

Phobos, the larger of the two Martian moons at 17 miles across (27 km), creates an annular or ring eclipse as seen through the telephoto eye of the Mars Curiosity rover on Aug. 17. Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.

Now that’s what I call crisp! NASA just released a series of high resolution pictures of Phobos transiting the sun on August 17. Taken with the 100mm telephoto lens mounted on Curiosity’s mast, they’re the sharpest ever of an eclipse from another world.

Curiosity paused during its drive toward Mt. Sharp and aimed its mast camera straight at the sun to make the sequence of views three seconds apart. Because the sun was nearly directly overhead at the time, Phobos was at its closest and biggest, covering the maximum amount of the sun’s disk as possible.

Sequence showing the sun before, during and immediately after an annular or “ring of fire” eclipse. This eclipse occurred on May 10, 1994 over central Illinois. Credit: Bob King

When one object passes in front of another but only blocks a small portion of it, astronomers call it a transit, but Phobos is big enough and its passage so central, this event is better described as an annular or ring eclipse. We have ring eclipses on Earth too, but because the moon is nearly spherical and much larger than Phobos, it leaves a much narrower “ring of fire”.

Two additional photos from the Phobos eclipse sequence showing the moon entering (left) and exiting the sun. Credit: NASA

Astronomers will measure the moon’s position as it moved across the sun to more precisely calculate Phobos’ orbit. As described in a recent blog, Phobos is gradually moving closer to Mars and will one day be broken to pieces. If you care to browse additional and original pix of the eclipse, check out this Curiosity raw image page and scroll down to the Mast Cam section.

Curiosity sees unearthly moondance in Martian skies

Mars’ moon Deimos is occulted by Phobos on Aug. 1 as seen by Curiosity

What fun to live on a planet with TWO moons. Imagine stepping out into the Martian night to watch the moons Phobos and Deimos chase each other across the sky. NASA’s Curiosity rover did just that on Aug. 1 when mission control pointed its mast camera at the pair of tiny moons and snapped 41 photos as the larger and closer Phobos passed directly in front of little Deimos. In real time the “eclipse” took 55 seconds; the movie compresses that to 11. Even on Mars it was a marvelous night for a moondance.

With only one moon here on Earth, we miss out on the pleasures of dual moon gazing. The only thing that might come close is watching a cargo ship like the recent HTV-4 catch up and dock with the International Space Station.

Phobos orbits closer to Mars than Deimos and therefore completes a revolution around the planet more quickly, regularly overtaking its brother. The photos are the very first ever taken from Mars of an eclipse of one moon by the other.

Comparison showing how big the moons of Mars appear to be, as seen from its surface, in relation to the size that our moon appears to be seen from the Earth’s surface. Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.

A 100mm telephoto lens was used to make the images which clearly show some of the larger craters on Phobos.

Both moons are tiny compared to our own. Deimos’ diameter is 7.5 miles (12 km) and Phobos 14 miles (22 km). It takes me longer to drive to work than cross the length of Deimos.

Even though Phobos is only about twice the size of Deimos, it appears much larger from the surface because it orbits much closer to the Red Planet – 3,700 miles (6,000 km) vs.12,400 miles (20,000 km).

Orbiting above the Martian equator and so close to the surface, Phobos can’t be seen from Mars’ polar regions. Its great speed also means it overtakes the planet’s rotation rate, rising in the west and setting in the east during the Martian night. Here on Earth, the moon moves in the same west to east direction but much more slowly, so that the faster-rotating Earth shuttles it from east to west during the night.

Phobos and Deimos up close as photographed by spacecraft. NASA scientists are studying the recent Curiosity images to determine precise orbits for the two moons as well as to gain a better understanding of the interior of Mars. Credit: NASA

Phobos’ tight orbit will ultimately lead to its demise. Its gravity induces tidal bulges in the crust of Mars which lag behind the fast-orbiting moon, causing it to gradually slow down and drop closer to the planet’s surface. In 50-100 million years Phobos will spiral in close enough for Mars’ gravity to break it to pieces. Deimos alone will remain to dimly light the Martian night.

Mars rovers capture loony moons and blue sunsets

Phobos and Deimos, photographed here by the Mars Reconnaissance Orbiter, are tiny, irregularly-shaped moons that are probably strays from the main asteroid belt. Credit: NASA

Mars has two tiny moons. Phobos, the larger of them, is a spud-shaped object about 14 miles (22 km) across. Deimos (DEE-mohs or DYE-mohs) is a bumpy ball with an average diameter of 8 miles (13 km). Compared to our moon’s 2,159 mile (3,474 km) diameter, these guys are truly small potatoes.

Phobos passing overhead after sunset as seen by NASA’s Curiosity Rover last month. Time-lapse images were taken over 27 minutes.

Both the Curiosity rover and the Spirit and Opportunity rovers have taken time out from staring at the ground to occasionally look up at the moons of Mars at dusk or dawn. This week NASA released a short video of Phobos crossing through the sky after sunset. I like the fresh perspective. Seeing how the Martian sky differs from Earth’s makes that planet feel all the more an alien.

The Spirit Rover captured this transit of Phobos across the sun in 2005. Credit:NASA

If you could stand next to Curiosity and look up, you’d see that Phobos looks considerably smaller than Earth’s moon – only a third as big. Like our moon, it occasionally crosses in front of the sun, an event known as a transit.

While it’s too small to completely eclipse the sun it makes a striking silhouette in the video.

Deimos looks even smaller both because of its smaller size and it’s more than twice as far from the planet as Phobos. To the naked eye, Deimos would look like a brilliant star to everyone but  keen-eyed skywatchers who might glimpse its teensy shape with a little concentration.

95 images of the Sun taken by Curiosity early in the mission were aligned to make this animation of Deimos transiting the Sun. Look closely and you’ll see it spinning.
NASA / JPL / MSSS / Emily Lakdawalla

Because they resemble asteroids in size and composition, many astronomers think Deimos and Phobos were captured by Mars in the distant past. Nowadays they circle the planet in 30.3 hours (Deimos) and 7.6 hours (Phobos). While they’re every bit a moon like our own familiar orb, their behavior in the sky is something altogether different.

Phobos orbits at an average distance of 5,830 miles from Mars. Its extreme closeness to the planet means it moves rapidly across the sky as seen from the ground. Phobos rises in the west and sets in the east, crossing the sky in just 5 1/2 hours. Wait another 5 1/2 and you can watch it rise again in the west. On a long winter night, an astronaut on Mars would see Phobos rise twice and set once!

Deimos, which orbits further from the planet, rises in the east like a normal moon or star, but because its orbital period is so close to that of Mars (24 hours and 37 minutes) it moves very slowly upward from the horizon and doesn’t set in the west until almost 3 days later. One moon’s on steroids; the other putters about as if it had all the time in the world.

Colorized sunset shot by Curiosity’s black-and-white navcam from inside Gale Crater on June 22, 2013. Credit: NASA/JPL-Caltech

Curiosity also snapped a few photos of sunset on Mars on June 22. Martian sunsets and sunrises aren’t quite the visual feast they are on Earth. There’s so much dust suspended in the planet’s atmosphere, the sky glows a monotone reddish brown with a large pale blue aureole surrounding the sun.

True color photo of sunset over Gusev Crater on Mars taken by the Spirit Rover in 2005. Credit: NASA/JPL-Caltech

“The blue color comes from the way Mars’ dust scatters light,” says Mark Lemmon, associate professor of atmospheric sciences and a camera operator on the twin rovers Spirit and Opportunity.

“The blue light is scattered less, and so it stays near the sun in the sky, while red and green are all over the sky. On Earth, blue light is scattered all over by gas molecules, but there are not enough of these on Mars, which has less than 1 percent of Earth’s atmosphere, to accomplish this.”

My favorite Martian

The first Martian (top) sighted on Mars smiles back from the rover’s calibration panel. The panel also features a 1909 Lincoln penny. Look closely at the penny and you’ll see a grain of Mars sand under Lincoln’s ear. It’s only 0.2 mm (.008 inches) across. Geologists classify sand grains this size as “fine sand”. Credit: NASA/JPL-Caltech/MSSS

Curiosity has traveled all of 466 feet along the dust, gravelly floor of Gale Crater since landing on August 6. It’s on its way to Glenelg to scoop up and analyze a soil sample. Earlier this week, mission controllers opened the recloseable dust cover on the Mars Hand Lens Imager (MAHLI) mounted on the rover’s robotic arm and snapped closeups of Curiosity’s underbelly, wheels and calibration target. The camera can focus on objects less than an inch away and acts as a magnifying glass similar to what a geologist would use in the field.

Wide view of Curiosity’s calibration target taken by the MAHLI imager. You can already see the orange coating of  Mars dust. Credit: NASA/JPL-Caltech/MSSS

My favorite photo of the bunch is the calibration target showing color reference swatches, a metric bar graphic, a penny and below it, a stair-step pattern for depth calibration. The 1909 VDB penny harks back to the geologists’ tradition of placing a coin,  rock pick or another object of known size in pictures of individual rocks or rock formations. It gives the viewer an idea of a feature’s size at a glance. Ken Edgett, MAHLI principal investigator, purchased the penny for the mission.

Moving in closer, we see there’s something else in the MAHLI image – a drawing of a Martian waving from a rock!

“Joe the Martian” is a character created by Edgett for the children’s science periodical “The Red Planet Connection” when Edgett directed the Mars outreach program at Arizona State University in the 1990s.

MAHLI photo of the underside of Curiosity with a view out to the horizon. Since the camera can focus anywhere from 0.8 inches all the way to infinity  it can capture both extreme closeups and landscapes. Credit: NASA/JPL-Caltech/MSSS

Joe goes back even further to when Edgett was 9 years old. He drew the character as part of a school project at the time of the 1975 Viking missions to Mars, the first to safely land probes on the planet. It was Viking that inspired him to become a Mars researcher. Joe’s appearance on Mars is most fitting.

Back in the 1960s I enjoyed watching episodes of My Favorite Martian, a TV sitcom about a Martian spaceship that crash lands near Los Angeles. Tim O’Hara, an LA Times reporter, discovers the wreck and the pilot, a Martian anthropologist dressed in a shiny aluminum jump suit. O’Hara nicknames him “Uncle Martin”. Antics ensue. Joe now joins Uncle Martin as my two favorite Martians.

12-mile-diameter Phobos nudges into the sun on September 13. Curiosity aimed its mastcam camera skyward and used a solar filter to take the photo. Credit: NASA

Digging through Curiosity’s stockpile of raw images today, I found this one taken by the mastcam of the moon Phobos partially eclipsing the sun on September 13. Nice bite!

Eclipse is slightly inaccurate. Because Phobos is so small, it’s technically called a transit. The little moon is only 3600 miles from Mars – much closer than the moon is from the Earth – so eclipses (transits) are fairly common.

According to Phil Plait of Bad Astronomy, Phobos crosses the sun about once a year from Curiosity’s site. Scientists  study transits of Phobos and Mars’ other moon Deimos to gauge the thickness of clouds and dust in the atmosphere. More images of the event should show up in the next few days. When they do, I’ll post a higher res version.

Transits of Phobos have been photographed before by the Mars Opportunity Rover. Click the video to see one recorded on November 9, 2010. 

What does Earth look like from Mars?

Curiosity is inside Gale Crater far to the east of the planet’s most prominent telescopic feature Syrtis Major. Credit: NASA/ESA/ Hubble

Now that Curiosity’s safe and secure on the Red Planet and snapping photos of everything in sight, I hope it focuses its cameras on Earth sometime soon.

The rover sits inside the 96-mile-wide Gale Crater in Mars’ eastern hemisphere just 5.4 degrees south of the equator. I was curious what the sky looks from Curiosity’s location and fired up Stellarium to see.

It didn’t take long to find Earth, low in the northeastern sky in morning twilight not far from the planet Venus.

Seen from Gale Crater on Mars, Earth is a brilliant blue “star” in the constellation Pisces on August 10. Not far below shine the planet Venus. The view shows the sky facing east about 45 minutes before Martian sunrise. Maps created with Stellarium

Since Earth is an “inner planet” from Mars’ perspective, the same way Venus and Mercury are inner planets for us, it never strays too far from the sun and goes through phases just like the moon and other inner planets. Curiosity will see Earth best during morning and evening twilight. At Mars current distance from Earth of 154 million miles, our planet shines at magnitude -1.4 or nearly same as Sirius, the brightest star in the sky.

To the eye, Earth would shine a pale ocean water blue. Venus would still be the brightest planet (magnitude -3.0) but distinctly dimmer than when viewed from Earth, because it’s farther from Mars than it is from our planet.

Earth and moon seen through binoculars from Curiosity’s landing site this morning.

According to my calculation, the moon would be slightly less than one arc minute from Earth and probably not visible as a separate point of light with the naked eye. However, you could easily see it directly below Earth through a pair of binoculars. The two would appear as a beautiful double planet!

The moon is much darker than Earth and would only shine at magnitude 2.5, about the same brightness as one of the Big Dipper stars. Through a small telescope magnifying around 60x Earth would appear as a tiny gibbous moon or a little more than 3/4 full.

More sky wonders await Curiosity’s cameras. Mars’ two moons cycle through the sky just like our moon.

Mars’ moon Phobos joins Earth and Venus shortly before sunrise on the morning of August 12.

Phobos, the larger, is 14 miles wide and orbits only 3,700 miles from Mars’ surface. It’s so close that it moves around Mars faster than the planet rotates. Instead of rising in the east and setting in the west, Phobos rises in the west and sets in the east. Nuts, right? It moves so fast it crosses the entire sky in just four hours and 15 minutes. If you could be there in person, you’d see it move in real time like a very slow satellite.

While Phobos is one of the darkest, least reflective bodies in the solar system, its proximity to the planet means it’s brighter than you’d expect, easily outshining Earth and Venus at magnitude -5 at midmonth. Wait a minute – that’s brighter than Venus is from Earth!

A gorgeous sight for Curiosity’s eyes – Venus, Earth, Phobos and Deimos in morning twilight on August 31. Foreground image shows the Opportunity rover’s solar panels. Sorry, I don’t have Curiosity in my software yet!

The smaller moon Deimos is about 7 miles wide and orbits far enough from the planet to rise in the east and set in the west like our moon does. Things really get fun later this month on the morning of 31st. That’s when Earth, Venus, Phobos and Deimos are all together in the eastern sky before sunrise. Wouldn’t it be cool if NASA pointed one of the high-resolution cameras for an awesome family portrait?

Mars’ north polar axis points toward Deneb and the Northern Cross which are part of the larger Summer Triangle. This view shows the sky from mid-northern latitudes on Mars. From roughly 10 degrees north of the Martian equator to the north pole, Deneb never sets.

One last tidbit. Mars’ axis is tipped 25.2 degrees, nearly the same as Earth’s 23.5 degrees. That’s why both planet’s have seasons. Despite similar inclinations, Mars’ axis points to a different direction in the Martian sky. Earth’s north polar axis points to the venerable North Star in the Little Dipper. Mars’ “north star” is close to Deneb, the bright star that marks the head of the Northern Cross or constellation Cygnus. Mars’ southern polestar is near the naked eye star Kappa Velorum.

It’s fun and fascinating to imagine how the planets and stars look on other worlds, especially the one we’re exploring with robotic eyes at this very moment. Seeing Earth from far away allows us to put our planet in perspective – we’re  a point of light dancing among the stars just like all the other planets.

Earth – that tiny point of light near the top – photographed by the Spirit Rover on Mars. Credit: NASA

Creepy crawlies aboard mission to Mars’ moon Phobos

Phobos, the destination of the Russian Phobos-Grunt mission, is seen here in orbit about Mars through the eyes of the Mars Express orbiter. The moon is only 14 miles across and orbits the planet in just over 11 hours or twice during each Martian day of 24 hours 37 minutes. Click to enlarge. Credit: G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA

The Russians will soon return to Mars with the launch of the Phobos-Grunt probe on or around November 8. Russia hasn’t had a successful interplanetary mission in decades. The last attempt was the Mars 96 probe launched in 1996 which quickly ended when a rocket engine failed while still in Earth orbit. We hope all goes well on this multifaceted and imaginative mission.

The Phobos-Grunt probe being prepared for vacuum chamber testing. Credit: NITs RKP

Phobos-Grunt (‘grunt’ is Russian for ‘soil’ or ‘dirt’) is an unmanned mission of the Russian Federal Space Agency that will land on the Martian moon Phobos and return a soil sample to Earth. This is the first-ever attempt to sample a planetary moon. Assuming a successful liftoff, the probe will reach Mars next October and dispatch the Yinghuo-1 Chinese satellite to orbit and study the planet’s surface. Over the next several months, Phobos-Grunt will study Mars, the Martian moons and search for a safe landing spot as it slowly pulls up alongside Phobos. Touchdown is scheduled for sometime in February 2013.

15 instruments will study the little moon and a robotic arm and drill will gather up soil samples.  Liftoff  from the moon happens in early 2014. The return capsule, expected to arrive back on Earth later that August, will contain 200 grams (just under 1/2 lb.) of soil and include a life science experiment of The Planetary Society, called Living Interplanetary Flight Experiment, or LIFE.

Tardigrades are found everywhere on Earth and have survival skills that would put humans to shame. A sample of them is headed for a round-trip journey to Mars moon Phobos.

The special ‘bio-module’ will hold representatives from all three major domains of earthly life to find out how well they survived for several years in the extremes of outer space. Among the 10 creatures included will be four types of bacteria, three bacteria-like organisms called archaea that thrive in extreme conditions and three species from the domain of eukaryotes or organisms with more complicated cell structures. You and I belong to this last group. Standing in for us will be a fungus (yeast), seeds from the mouse-ear cress plant and my personal favorite – tardigrades or ‘water bears’. These microscopic animals with 8 legs only grow to about a millimeter and are found all over the planet. They’re able to survive in temperatures ranging from near absolute zero (459 below) to 300 above, can handle far more radiation than most animals and live up to 10 years without water. That’s one tough bug!

Phobos is pocked with craters including one very large one named Stickney (far right edge) that nearly shattered the moon. Credit: NASA

Phobos is a fascinating moon. It’s only 14 miles across and orbits 5,827 miles above the surface of Mars. That’s close enough for its orbital motion to outpace the slower rotation of Mars (24 hours 37 minutes) making the moon rise in the west and set in the east in just 4 hours and 15 minutes as seen from the Martian surface.

Based on its density and how the moon absorbs and reflects sunlight, astronomers have determined it’s composed of a mix of rock and ice with the ice locked somewhere below the surface. Its composition matches a group of dark carbon and water-rich meteorites called carbonaceous (car-bon-NAY-shuss) chondrites (KON-drites). Since similar carbonaceous asteroids are known to inhabit the asteroid belt, it’s believed Phobos as well as the smaller Martian moon Deimos were stray asteroids captured by Mars long ago.

A humble moon sneaks by the biggest planet

Video made using images taken by NASA’s Solar Dynamics Observatory of the June 7 prominence eruption

A little more than a week ago I posted a must see video of a huge prominence eruption on the sun. Now you can watch it again in not one but four different wavelengths of ultraviolet light. The eruption appears to take only seconds, but we see it compressed in time. The event lasted some three hours – what a spectacle!

In this frame, Phobos and Jupiter are exactly aligned or in conjunction from the viewpoint of the Mars Express craft on June 1, 2011. Click the photo for a 3D version - don't forget your red-blue glasses! Credit: ESA/DLR/FU Berlin (G. Neukum)

Still earlier this month on June 1, the European Space Agency’s Mars Express craft, in orbit about the Red Planet since Christmas 2003, sent back a close-up photo of a conjunction of Mars’ moon Phobos with the planet Jupiter. Just released Friday, it’s certainly the first conjunction of its kind seen by earthlings. Diminutive Phobos is only 16 miles across, but at the moment the photo was taken, the craft was just 7,077 miles from the moon and 329 million miles from Jupiter. Being close counts when it comes to apparent size, which is why Phobos appears so much larger than the giant planet. Yet in spite of the millions of miles that separate them, you can still clearly see Jupiter’s equatorial belts of clouds. Amazing!

A movie of Phobos passing under Jupiter compiled from 104 still images.

Of course, the space agency had a more serious purpose that simply watching a conjunction, although we thank them for that. By knowing exactly where the spacecraft and Jupiter were located when Phobos swung by, the moon’s orbit could be further refined.

A slice of the carbonaceous chondrite NWA 3118 found in Morocco in 2003. The little round circles are chondrules, which grew from the original dust cloud in the early solar system. Credit: Mario Müller

Phobos is a heavily cratered, porous and very dark moon. Every planet and moon in the solar system absorbs certain colors of sunlight and reflects others. Based on the light Phobos reflects back to us, astronomers  have determined its composition is similar to a group of meteorites called the carbonaceous chondrites. As the name suggests, these meteorites are rich in carbon as well as water and clays. Some also contain amino acids, chemical compounds our DNA directs into the fashioning of proteins that build and sustain our bodies.

Artist's view of the early Earth still under bombardment by comets and meteorites. The moon was closer to our planet four billion years ago and rotated faster than it does today. Credit: Dr. David Aguilar

It’s a mighty leap from raw amino acids in meteorites to proteins, but amino acids brought to Earth by meteorites when our planet formed 4.6 billion years ago may have played a part in the origin of life. Add in comets, which scientists think contributed significant amounts of water to the cooling Earth, and you’ve got at least two key ingredients essential to life. How wonderful to think that these minor solar system bodies crashing onto our planet during its infancy may have been the stimulus for the life that’s unfolded since.

Eclipses here are a dime a dozen

The thick lunar crescent (here overexposed) lights the evening sky earlier this week. Jupiter is visible to the left of the moon. Credit: Bob King

The moon’s been out in the evening the past week. I got this shot of it two nights ago before the clouds thickened. Once or twice a year, the moon lines up squarely between the sun and Earth and covers the sun completely in a total solar eclipse. When the alignment is close but not dead-on, the moon covers only� part of the sun in a partial solar eclipse. 2011 is a little unusual in having no total solar eclipses. Instead, we’ll be graced with four partials, the next one happening over northern Canada, Alaska, Siberia and Greenland on June 1.

Deimos crosses in front of the sun during an "eclipse" as photographed by the Opportunity rover. Astronomers more properly call this event a transit because the eclipsing body is only a fraction of the sun's size. Credit: NASA/JPL

Earth isn’t the only planet where sky watchers can enjoy solar eclipses. Mars has two little moons named Phobos and Deimos (DEE-mohs) after the Greek gods Fear and Panic. Perfect companions for a planet named for the Roman god of war. Deimos measures 9 x 7 miles across and at a distance of 14,577 miles appears only 1/12 the size of the moon.

The sun from Mars appears only two-thirds as big as seen from Earth because the planet’s average distance from the solar hearth is 136 million miles compared to Earth’s 93 million. Just the same, little Deimos is too small to cover it during an eclipse. If you were standing on Mars, you probably wouldn’t even notice when it passed over the sun’s face. A safe solar filter held up to your eye would show the moon as a crisp, black dot cruising from one side of the sun to the other. Be sure you’re there on time to watch. A Deimos eclipse lasts just under a minute!

Cheerios, anyone? During an eclipse or transit of the sun by Phobos, you can clearly see the moon's irregular shape. Credit: NASA/JPL

Phobos is 17 x 11 miles across, not much bigger than Deimos, but its solar eclipses are more impressive because the moon travels in a much lower orbit, only 3,728 miles from Mars. So it appears larger and travels much faster across the Martian sky. Indeed, no moon is closer to its planet than Phobos. In the span of one Martian day, which is just 37 minutes longer than an Earth day, Phobos zips around the planet two and a half times compared to nearly a month for our moon to do the same. This provides numerous opportunities to catch an eclipse, so long as your near the equator. Phobos is so close to Mars, it’s never makes it above the horizon in the Martian polar regions. From Mars’ equator, Phobos eclipse the sun once a day; Deimos about once a month.

Phobos partially eclipses the sun in this approximately true-speed movie simulation using
images from the Mars Spirit Rover.

Because Phobos covers about 50% of the sun during an eclipse, you’d be able to detect subtle changes in the play of light on the landscape around you. Once again, you’d have to pay attention. Phobos eclipses are even shorter than its brother moon’s, lasting 20-30 seconds. My guess is that an eclipse would feel like a shadow seen from the corner of your eye. Sort of a “did-something- just-happen?” moment.

You might be wondering if Phobos and Deimos are eclipsed like our own moon when the pass behind the planet into its shadow. The answer is yes. And though Mars has a thin atmosphere of mostly carbon dioxide, it’s thick enough to bend or refract a bit of sunlight into the shadow to weakly illuminate the moons during a total Phobosian or Deimosian eclipse. Click HERE to watch a movie of Phobos in eclipse.

1999 total solar eclipse from Earth. Credit: Luc Viatour

It’s interesting to realize that eclipses happen lots of places in the solar system, with Mars as one example. None however offer the grandeur of a total solar eclipse on Earth, where the moon fits so tightly over the sun’s face, everyone from cruise ship eclipse chasers to the Neanderthals have been stopped dead in their tracks in admiration or fear.