Need an easy way to remember the order of the planets in our Solar System? The technique used most often to remember such a list is a mnemonic device. This uses the first letter of each planet as the first letter of each word in a sentence. Supposedly, experts say, the sillier the sentence, the easier it is to remember.
So by using the first letters of the planets, (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), create a silly but memorable sentence.
Here are a few examples:
My Very Excellent Mother Just Served Us Noodles (or Nachos)
Mercury’s Volcanoes Erupt Mulberry Jam Sandwiches Until Noon
Very Elderly Men Just Snooze Under Newspapers
My Very Efficient Memory Just Summed Up Nine
My Very Easy Method Just Speeds Up Names
My Very Expensive Malamute Jumped Ship Up North
The Sun and planets to scale. Credit: Illustration by Judy Schmidt, texture maps by Björn Jónsson
If you want to remember the planets in order of size, (Jupiter, Saturn, Uranus, Neptune, Earth, Venus Mars, Mercury) you can create a different sentence:
Just Sit Up Now Each Monday Morning
Jack Sailed Under Neath Every Metal Mooring
Rhymes are also a popular technique, albeit they require memorizing more words. But if you’re a poet (and don’t know it) try this:
Amazing Mercury is closest to the Sun,
Hot, hot Venus is the second one,
Earth comes third: it’s not too hot,
Freezing Mars awaits an astronaut,
Jupiter is bigger than all the rest,
Sixth comes Saturn, its rings look best,
Uranus sideways falls and along with Neptune, they are big gas balls.
Or songs can work too. Here are a couple of videos that use songs to remember the planets:
If sentences, rhymes or songs don’t work for you, perhaps you are more of a visual learner, as some people remember visual cues better than words. Try drawing a picture of the planets in order. You don’t have to be an accomplished artist to do this; you can simply draw different circles for each planet and label each one. Sometimes color-coding can help aid your memory. For example, use red for Mars and blue for Neptune. Whatever you decide, try to pick colors that are radically different to avoid confusing them.
Or try using Solar System flash cards or just pictures of the planets printed on a page (here are some great pictures of the planets). This works well because not only are you recalling the names of the planets but also what they look like. Memory experts say the more senses you involve in learning or storing something, the better you will be at recalling it.
Planets made from paper lanterns. Credit: TheSweetestOccasion.com
Maybe you are a hands-on learner. If so, try building a three-dimensional model of the Solar System. Kids, ask your parents or guardians to help you with this, or parents/guardians, this is a fun project to do with your children. You can buy inexpensive Styrofoam balls at your local craft store to create your model, or use paper lanterns and decorate them. Here are several ideas from Pinterest on building a 3-D Solar System Model.
If you are looking for a group project to help a class of children learn the planets, have a contest to see who comes up with the silliest sentence to remember the planets. Additionally, you can have eight children act as the planets while the rest of the class tries to line them up in order. You can find more ideas on NASA’s resources for Educators. You can use these tricks as a starting point and find more ways of remembering the planets that work for you.
Global Color Mosaic of Triton, taken by Voyager 2 in 1989. Credit: NASA/JPL/USGS
The planets of the outer Solar System are known for being strange, as are their many moons. This is especially true of Triton, Neptune’s largest moon. In addition to being the seventh-largest moon in the Solar System, it is also the only major moon that has a retrograde orbit – i.e. it revolves in the direction opposite to the planet’s rotation. This suggests that Triton did not form in orbit around Neptune, but is a cosmic visitor that passed by one day and decided to stay.
And like most moons in the outer Solar System, Triton is believed to be composed of an icy surface and a rocky core. But unlike most Solar moons, Triton is one of the few that is known to be geologically active. This results in cryovolcanism, where geysers periodically break through the crust and turn the surface Triton into what is sure to be a psychedelic experience!
Discovery and Naming:
Triton was discovered by British astronomer William Lassell on October 10th, 1846, just 17 days after the discovery of Neptune by German astronomer Johann Gottfried Galle. After learning about the discovery, John Herschel – the son of famed English astronomer William Herschel, who discovered many of Saturn’s and Uranus’ moons – wrote to Lassell and recommended he observe Neptune to see if it had any moons as well.
New Horizons image of Neptune and its largest moon, Triton, taken by the LORRI instrument on June 23, 2010. Credit: NASA
Lassell did so and discovered Neptune’s largest moon eight days later. Thirty-four years later, French astronomer Camille Flammarion named the moon Triton – after the Greek sea god and son of Poseidon (the equivalent of the Roman god Neptune) – in his 1880 bookAstronomie Populaire. It would be several decades before the name caught on however. Until the discovery of the second moon Nereid in 1949, Triton was commonly known simply as “the satellite of Neptune”.
Size, Mass and Orbit:
At 2.14 × 1022 kg, and with a diameter of approx. 2,700 kilometers (1,680 miles) km, Triton is the largest moon in the Neptunian system – comprising more than 99.5% of all the mass known to orbit the planet. In addition to being the seventh-largest moon in the Solar System, it is also more massive than all known moons in the Solar System smaller than itself combined.
With no axial tilt and an eccentricity of virtually zero, the moon orbits Neptune at a distance of 354,760 km (220,438 miles). At this distance, Triton is the farthest satellite of Neptune, and orbits the planet every 5.87685 Earth days. Unlike other moons of its size, Triton has a retrograde orbit around its host planet.
Most of the outer irregular moons of Jupiter and Saturn have retrograde orbits, as do some of Uranus’s outer moons. However, these moons are all much more distant from their primaries, and are rather small in comparison. Triton also has a synchronous orbit with Neptune, which means it keeps one face aimed towards the planet at all times.
As Neptune orbits the Sun, Triton’s polar regions take turns facing the Sun, resulting in seasonal changes as one pole, then the other, moves into the sunlight. Such changes were observed in April of 2010 by astronomers using the European Southern Observatory’s Very Large Telescope.
Another all-important aspect of Triton’s orbit is that it is decaying. Scientists estimate that in approximately 3.6 billion years, it will pass below Neptune’s Roche limit and will be torn apart.
Composition:
Triton has a radius, density (2.061 g/cm3), temperature and chemical composition similar to thatof Pluto. Because of this, and the fact that it circles Neptune in a retrograde orbit, astronomers believe that the moon originated in the Kuiper Belt and later became trapped by Neptune’s gravity.
Another theory has it that Triton was once a dwarf planet with a companion. In this scenario, Neptune captured Triton and flung its companion away when the giant gas moved further out into the solar system, billions of years ago.
Also like Pluto, 55% of Triton’s surface is covered with frozen nitrogen, with water ice comprising 15–35% and dry ice (aka. frozen carbon dioxide) forming the remaining 10–20%. Trace amounts of methane and carbon monoxide ice are believed to exist there as well, as are small amounts of ammonia (in the form of ammonia dihydrate in the lithosphere).
Triton’s density suggests that its interior is differentiated between a solid core made of rocky material and metals, a mantle composed of ice, and a crust. There is enough rock in Triton’s interior for radioactive decay to power convection in the mantle, which may even be sufficient to maintain a subterranean ocean. As with Jupiter’s moon of Europa, the proposed existence of this warm-water ocean could mean the presence of life beneath the icy crusts.
Atmosphere and Surface Features:
Triton has a considerably high albedo, reflecting 60–95% of the sunlight that reaches it. The surface is also quite young, which is an indication of the possible existence of an interior ocean and geological activity. The moon has a reddish tint, which is probably the result of the methane ice turning to carbon due to exposure to ultraviolet radiation.
Triton is considered to be one of the coldest places in the Solar System. The moon’s surface temperature is approx. -235°C while Pluto averages about -229°C. Scientists say that Pluto may drop as low as -240°C at the furthest point from the Sun in its orbit, but it also gets much warmer closer to the Sun, giving it a higher overall temperature average.
It is also one of the few moons in the Solar System that is geologically active, which means that its surface is relatively young due to resurfacing. This activity also results in cryovolcanism, where water ammonia and nitrogen gas burst forth from the surface instead of liquid rock. These nitrogen geysers can send plumes of liquid nitrogen 8 km above the surface of the moon.
Triton (lower left) compared to the Moon (upper left) and Earth (right), to scale. Credit: NASA/JPL/USGS
Because of the geological activity constantly renewing the moon’s surface, there are very few impact craters on Triton. Like Pluto, Triton has an atmosphere that is thought to have resulted from the evaporation of ices from its surface. Like its surface ices, Triton’s tenuous atmosphere is made up of nitrogen with trace amounts of carbon monoxide and small amounts of methane near the surface.
This atmosphere consists of a troposphere rising to an altitude of 8km, where it then gives way to a thermosphere that reaches out to 950 km from the surface. The temperature of Triton’s upper atmosphere, at 95-100 K (ca.-175 °C/-283 °F) is higher than that at the surface, due to the influence of solar radiation and Neptune’s magnetosphere.
A haze permeates most of Triton’s troposphere, thought to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane. Triton’s atmosphere also has clouds of condensed nitrogen that lie between 1 and 3 km from the surface.
Observations taken from Earth and by the Voyager 2 spacecraft have shown that Triton experiences a warm summer season every few hundred years. This could be the result of a periodic change in the planet’s albedo (i.e. its gets darker and redder) which could be caused by either frost patterns or geological activity.
Using the CRIRES instrument on ESO’s Very Large Telescope, a team of astronomers has been able to see that the summer is in full swing in Triton’s southern hemisphere. Credit: ESO
This change would allow more heat to be absorbed, followed by an increase in sublimation and atmospheric pressure. Data collected between 1987 and 1999 indicated that Triton was approaching one of these warm summers.
Exploration:
When NASA’s Voyager 2 made a flyby of Neptune in August of 1989, the mission controllers also decided to conduct a flyby of Triton – similar to Voyager 1‘s encounter with Saturn and Titan. When it made its flyby, most of the northern hemisphere was in darkness and unseen by Voyager.
Because of the speed of Voyager’s visit and the slow rotation of Triton, only one hemisphere was seen clearly at close distance. The rest of the surface was either in darkness or seen as blurry markings. Nevertheless, the Voyager 2 spacecraft managed to capture several images of the moon and spotted geysers of liquid nitrogen blasting out of two distinct features on the surface.
In August of 2014, in anticipation of New Horizons impending encounter with Pluto, NASA restored these photos and used them to create the first global color map of Triton. Produced by Paul Schenk, a scientist at the Lunar and Planetary Institute in Houston, the map was also used to make a movie (shown below) that recreated the historic Voyager 2 encounter in time for the 25th anniversary of the event.
Yes, Triton is indeed an unusual moon. Aside from its rather unique characteristics (retrograde motion, geological activity) the moon’s landscape is likely to be an amazing sight. For anyone standing on the surface, surrounded by colorful ices, plumes of nitrogen and ammonia, a nitrogen haze and Neptune’s big blue disc hanging on the sky, the experience would seem like something akin to a hallucination.
In the end, it is too bad that the Solar System will one day be saying good-bye to this moon. Because of the nature of its orbit, the moon will eventually fall into Neptune’s gravity well and break up. At which point, Neptune will have a huge ring like Saturn, until those particles crash into the planet as well.
That too would be something to behold. One can only hope that humanity will still be around in 3.6 billion years to witness it!
Like splitting double stars, hunting for the faint lesser known moons of the solar system offers a supreme challenge for the visual observer.
Sure, you’ve seen the Jovian moons do their dance, and Titan is old friend for many a star party patron as they check out the rings of Saturn… but have you ever spotted Triton or Amalthea?
Welcome to the challenging world of moon-spotting. Discovering these moons for yourself can be an unforgettable thrill.
One of the key challenges in spotting many of the fainter moons is the fact that they lie so close inside the glare of their respective host planet. For example, +11th magnitude Phobos wouldn’t be all that tough on its own, were it not for the fact that it always lies close to dazzling Mars. 10 magnitudes equals a 10,000-fold change in brightness, and the fact that most of these moons are swapped out is what makes them so tough to see. This is also why many of them weren’t discovered until later on.
But don’t despair. One thing you can use that’s relatively easy to construct is an occulting bar eyepiece. This will allow you to hide the dazzle of the planet behind the bar while scanning the suspect area to the side for the faint moon. Large aperture, steady skies, and well collimated optics are a must as well, and don’t be afraid to crank up the magnification in your quest. We mentioned using such a technique previously as a method to tease out the white dwarf star Sirius b in the years to come.
A homemade occulting bar eyepiece with the barrel removed. One bar is a strip of foil, and the other is a E-string from a guitar. Image credit: Dave Dickinson
What follows is a comprehensive list of the well known ‘easy ones,’ along with some challenges.
We included a handy drill down of magnitudes, orbital periods and maximum separations for the moons of each planet right around opposition. For the more difficult moons, we also noted the circumstances of their discovery, just to give the reader some idea what it takes to see these fleeting worlds. Remember though, many of those old scopes used speculum metal mirrors which were vastly inferior to commercial optics available today. You may have a large Dobsonian scope available that rivals these scopes of yore!
The orbits of the Martian moons. Image credit: Starry Night Education Software
Mars- The two tiny moons of Mars are a challenge, as it’s only possible to nab them visually near opposition, which occurs about once every 26 months. Mars next reaches opposition on May 22nd, 2016.
Phobos:
Magnitude: +11.3
Orbital period: 7 hours 39 minutes
Maximum separation: 16”
Deimos:
Magnitude: +12.3
Orbital period: 1 day 6 hours and 20 minutes
Maximum separation: 54”
The moons of Mars were discovered by American astronomer Asaph Hall during the favorable 1877 opposition of Mars using the 26-inch refracting telescope at the U.S. Naval Observatory.
Jupiter- Though the largest planet in our solar system also has the largest number of moons at 67, only the four bright Galilean moons are easily observable, although owners of large light buckets might just be able to tease out another two. Jupiter next reaches opposition March 8th, 2016.
Ganymede:
Magnitude: +4.6
Orbital period: 7.2 days
Maximum separation: 5’
Callisto
Magnitude: +5.7
Orbital period: 16.7 days
Maximum separation: 9’
Io
Magnitude: +5.0
Orbital period: 1.8 days
Maximum separation: 1’ 50”
Europa
Magnitude: +5.3
Orbital period: 3.6 days
Maximum separation: 3’
Amalthea
Magnitude: +14.3
Orbital period: 11 hours 57 minutes
Maximum separation: 33”
Himalia
Magnitude: +15
Orbital period: 250.2 days
Maximum separation: 52’
Note that Amalthea was the first of Jupiter’s moons discovered after the four Galilean moons. Amalthea was first spotted in 1892 by E. E. Barnard using the 36” refractor at the Lick Observatory. Himalia was also discovered at Lick by Charles Dillon Perrine in 1904.
Titan and Rhea imaged via Iphone and a Celestron NexStar 8SE telescope. Image credit: Andrew Symes (@failedprotostar)
Saturn- With a total number of moons at 62, six moons of Saturn are easily observable with a backyard telescope, though keen-eyed observers might just be able to tease out another two:
(Note: the listed separation from the moons of Saturn is from the limb of the disk, not the rings).
Titan
Magnitude: +8.5
Orbital period: 16 days
Maximum separation: 3’
Rhea
Magnitude: +10.0
Orbital period: 4.5 days
Maximum separation: 1’ 12”
Iapetus
Magnitude: (variable) +10.2 to +11.9
Orbital period: 79 days
Maximum separation: 9’
Enceladus
Magnitude: +12
Orbital period: 1.4 days
Maximum separation: 27″
Dione
Magnitude: +10.4
Orbital period: 2.7 days
Maximum separation: 46”
Tethys
Magnitude: +10.2
Orbital period: 1.9 days
Maximum separation: 35”
Mimas
Magnitude: +12.9
Orbital period: 0.9 days
Maximum separation: 18”
Hyperion
Magnitude: +14.1
Orbital period: 21.3 days
Maximum separation: 3’ 30”
Phoebe
Magnitude: +16.6
Orbital period: 541 days
Maximum separation: 27’
Hyperion was discovered by William Bond using the Harvard observatory’s 15” refractor in 1848, and Phoebe was the first moon discovered photographically by William Pickering in 1899.
Uranus- All of the moons of the ice giants are tough. Though Uranus has a total of 27 moons, only five of them might be spied using a backyard scope. Uranus next reaches opposition on October 12th, 2015.
Titania
Magnitude: +13.9
Orbital period:
Maximum separation: 28”
Oberon
Magnitude: +14.1
Orbital period: 8.7 days
Maximum separation: 40”
Umbriel
Magnitude: +15
Orbital period: 4.1 days
Maximum separation: 15”
Ariel
Magnitude: +14.3
Orbital period: 2.5 days
Maximum separation: 13”
Miranda
Magnitude: +16.5
Orbital period: 1.4 days
Maximum separation: 9”
The first two moons of Uranus, Titania and Oberon, were discovered by William Herschel in 1787 using his 49.5” telescope, the largest of its day.
Triton in orbit around Neptune near opposition in 2011. Image credit: Efrain Morales
Neptune- With a total number of moons numbering 14, two are within reach of the skilled amateur observer. Opposition for Neptune is coming right up on September 1st, 2015.
Triton
Magnitude: +13.5
Orbital period: 5.9 days
Maximum separation: 15”
Nereid
Magnitude: +18.7
Orbital period: 0.3 days
Maximum separation: 6’40”
Triton was discovered by William Lassell using a 24” reflector in 1846, just 17 days after the discovery of Neptune itself. Nereid wasn’t found until 1949 by Gerard Kuiper.
Pluto-Yes… it is possible to spy Charon from Earth… as amateur astronomers proved in 2008.
Charon
Magnitude: +16
Orbital period: 6.4 days
Maximum separation: 0.8”
Pluto! Click here for a (possible) capture of Charon as well. Image credit: Wendy Clark
In order to cross off some of the more difficult targets on the list, you’ll need to know exactly when these moons are at their greatest elongation. Sky and Telescope has some great apps in the case of Jupiter and Saturn… the PDS Rings node can also generate corkscrew charts of lesser known moons, and Starry Night has ‘em as well. In addition, we tend to publish cork screw charts for moons right around respective oppositions, and our ephemeris for Charon elongations though July 2015 is still active.
Good luck in crossing off some of these faint moons from your astronomical life list!
Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon Charon taken by New Horizons on July 11, 2015. The annotated version includes a diagram showing Charon’s north pole, equator, and central meridian, with the features highlighted. Credits: NASA/JHUAPL/SWRI
Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon Charon taken by New Horizons on July 11, 2015. The annotated version includes a diagram showing Charon’s north pole, equator, and central meridian, with the features highlighted. Credits: NASA/JHUAPL/SWRI
Story/imagery updated[/caption]
Indeed the largest of Charon’s chasms stretches farther than Earth’s Grand Canyon. And it’s taken New Horizons over nine years speeding through space – since launching back in 2006 as the fastest spacecraft departing Earth – to get close enough to see these wonders for the first time.
“The most pronounced chasm, which lies in the southern hemisphere, is longer and miles deeper than Earth’s Grand Canyon,” says William McKinnon, deputy lead scientist with New Horizon’s Geology and Geophysics investigation team, in a NASA statement.
To put that into perspective, consider this; Charon is only about 750 miles (1200 kilometers) across, about half the diameter of Pluto. The Grand Canyon stretches 277 miles (446 km) across the western United States and is up to 18 miles (29 km) wide and attains a depth of over a mile (6093 feet or 1857 meters). Thus Charon’s ‘Grand Canyon’ is truly gargantuan in comparison to its moons size when compared to our Grand Canyon.
At 1471 miles (2368 km) across, Pluto is about half the diameter of the United States. Both Pluto and Charon and largely composed of icy materials, with much less rock compared to the terrestrial planets like Earth.
“This is the first clear evidence of faulting and surface disruption on Charon,” says McKinnon, who is based at the Washington University in St. Louis.
“New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity.”
Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon Charon taken by New Horizons on July 11, 2015. Credits: NASA/JHUAPL/SWRI
The exquisite new image of Charon’s chasms and canyons was just released by NASA this evening, Sunday, July 12. It was taken yesterday, Saturday, July 11, by New Horizons Long Range Reconnaissance Imager (LORRI) at a distance of 2.5 million miles (4 million kilometers) from Pluto and Charon, and radioed back to Earth today.
The largest crater seen in the July 11 images lies near Charon’s south pole and is about 60 miles (96.5 kilometers) across.
“The brightness of the rays of material blasted out of the crater suggest it formed relatively recently in geologic terms, during a collision with a small body some time in the last billion million years,” says the team.
“The darkness of the crater’s floor is especially intriguing,” says McKinnon.
“One explanation is that the crater has exposed a different type of icy material than the more reflective ices that lie on the surface. Another possibility is that the ice in the crater floor is the same material as its surroundings but has a larger ice grain size, which reflects less sunlight. In this scenario, the impactor that gouged the crater melted the ice in the crater floor, which then refroze into larger grains.”
New Horizons is now merely one day and one million miles (1.6 million km) out from its history making encounter with the Pluto planetary system – some three billion miles (4.8 billion km) from Earth. It passed the million mile milestone at 11:23 p.m. EDT, Sunday night July 12.
And its closing in fast on its quarry at a whopping 31,000 mph (49,600 kph) after a nine year interplanetary voyage.
Facts about Pluto. Credit: NASA
The high resolution LORRI imager is achieving an image resolution of 5 mile per pixel at this moment at a million miles away. And it will gets thousands of times better during the closest approach.
“Features as small as the lakes in New York’s Central Park and wharfs on the Hudson will be resolved,” said New Horizons principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, during a live mission update today, July 12. The image resolution will reach a maximum of about 230 feet (70 meters).
New Horizons suite of seven science instruments will collected 44 gigabits of data during the flyby encounter period lasting from July 7 to July 16, from Pluto, Charon and the four tiny moons – Hydra, Styx, Nix and Kerberos.
New Horizons will swoop to within about 12,500 kilometers (nearly 7,750 miles) of Pluto’s surface and about 17,900 miles (28,800 kilometers) from Charon during closest approach at approximately 7:49 a.m. EDT (11:49 UTC) on July 14.
Pluto and Charon are gravitationally locked with an orbital period of 6.4 days, so they always show the same face to one another. They orbit about 12,160 mi (19,570 kilometers) apart but about a center of gravity, or barycenter, above the surface of Pluto, unlike any of the other major bodies in our solar system.
Image of Pluto and Charon from July 8, 2015; color information obtained earlier in the mission from the Ralph instrument has been added. Credits: NASA-JHUAPL-SWRI
Charon is by far the largest of Pluto’s five moons. The new July 11 image also shows that it sports a “mysterious dark region” stretching some 200 miles across near the north pole.
Pluto is the last of the nine classical planets to be explored up close and completes the initial the initial reconnaissance of the solar system nearly six decades after the dawn of the space age. It represents a whole new class of objects known as the ice dwarfs, located in the Kuiper Belt – a relic of solar system formation replete with countless bodies.
It has been three decades since we last visited planetary bodies at the outer reaches of our solar system when Voyager 2 flew past Uranus and Neptune in 1986 and 1989.
New Horizons trajectory to the Pluto System. Credit: NASA
The New Frontiers spacecraft was built by a team led by Stern and included researchers from SwRI and the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. APL also operates the New Horizons spacecraft and manages the mission.
Watch for Ken’s continuing onsite coverage of the Pluto flyby on July 14 from the Johns Hopkins University Applied Physics Laboratory (APL).
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
These six narrow-angle color images were made from the first ever "portrait" of the solar system taken by Voyager 1 on Valentine’s Day on Feb. 14, 1990, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. Venus, Earth, Jupiter, and Saturn, Uranus, Neptune are seen in these blown-up images, from left to right and top to bottom. Credit: NASA/JPL-Caltech
A quarter of a century has passed since NASA’s Voyager 1 spacecraft snapped the iconic image of Earth known as the “Pale Blue Dot” that shows all of humanity as merely a tiny point of light.
The outward bound Voyager 1 space probe took the ‘pale blue dot’ image of Earth 25 years ago on Valentine’s Day, on Feb. 14, 1990 when it looked back from its unique perch beyond the orbit of Neptune to capture the first ever “portrait” of the solar system from its outer realms.
Voyager 1 was 4 billion miles from Earth, 40 astronomical units (AU) from the sun and about 32 degrees above the ecliptic at that moment.
The idea for the images came from the world famous astronomer Carl Sagan, who was a member of the Voyager imaging team at the time.
He head the idea of pointing the spacecraft back toward its home for a last look as a way to inspire humanity. And to do so before the imaging system was shut down permanently thereafter to repurpose the computer controlling it, save on energy consumption and extend the probes lifetime, because it was so far away from any celestial objects.
Sagan later published a well known and regarded book in 1994 titled “Pale Blue Dot,” that refers to the image of Earth in Voyagers series.
This narrow-angle color image of the Earth, dubbed “Pale Blue Dot,” is a part of the first ever “portrait” of the solar system taken by Voyager 1 on Valentine’s Day on Feb. 14, 1990. Credit: NASA/JPL-Caltech
“Twenty-five years ago, Voyager 1 looked back toward Earth and saw a ‘pale blue dot,’ ” an image that continues to inspire wonderment about the spot we call home,” said Ed Stone, project scientist for the Voyager mission, based at the California Institute of Technology, Pasadena, in a statement.
Six of the Solar System’s nine known planets at the time were imaged, including Venus, Earth, Jupiter, and Saturn, Uranus, Neptune. The other three didn’t make it in. Mercury was too close to the sun, Mars had too little sunlight and little Pluto was too dim.
Voyager snapped a series of images with its wide angle and narrow angle cameras. Altogether 60 images from the wide angle camera were compiled into the first “solar system mosaic.”
Voyager 1 was launched in 1977 from Cape Canaveral Air Force Station in Florida as part of a twin probe series with Voyager 2. They successfully conducted up close flyby observations of the gas giant outer planets including Jupiter, Saturn, Uranus and Neptune in the 1970s and 1980s.
Both probes still operate today as part of the Voyager Interstellar Mission.
“After taking these images in 1990, we began our interstellar mission. We had no idea how long the spacecraft would last,” Stone said.
Hurtling along at a distance of 130 astronomical units from the sun, Voyager 1 is the farthest human-made object from Earth.
Solar System Portrait – 60 Frame Mosaic. The cameras of Voyager 1 on Feb. 14, 1990, pointed back toward the sun and took a series of pictures of the sun and the planets, making the first ever “portrait” of our solar system as seen from the outside. Missing are Mercury, Mars and Pluto. Credit: NASA/JPL-Caltech
Voyager 1 still operates today as the first human made instrument to reach interstellar space and continues to forge new frontiers outwards to the unexplored cosmos where no human or robotic emissary as gone before.
Here’s what Sagan wrote in his “Pale Blue Dot” book:
“That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. … There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.”
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
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At least two unknown planets could exist in our solar system beyond Pluto. / Credit: NASA/JPL-Caltech.
Could there be another Pluto-like object out in the far reaches of the Solar System? How about two or more?
Earlier this week, we discussed a recent paper from planet-hunter Mike Brown, who said that while there aren’t likely to be any bright, easy-to-find objects, there could be dark ones “lurking far away.” Now, a group of astronomers from the UK and Spain maintain at least two planets must exist beyond Neptune and Pluto in order to explain the orbital behavior of objects that are even farther out, called extreme trans-Neptunian objects (ETNO).
The presently known largest small bodies in the Kuiper Belt are likely not to be surpassed by any future discoveries. This is the conclusion of Dr. Michael Brown, et al. (Illustration Credit: Larry McNish, Data: M.Brown)
We do know that Pluto shares its region Solar System with more than 1500 other tiny, icy worlds along with likely countless smaller and darker ones that have not yet been detected.
In two new paper published this week, scientists at the Complutense University of Madrid and the University of Cambridge noted that the most accepted theory of trans-Neptunian objects is that they should orbit at a distance of about 150 AU, be in an orbital plane – or inclination – similar to the planets in our Solar System, and they should be randomly distributed.
But that differs from what is actually observed. What astronomers see are groupings of objects with widely disperse distances (between 150 AU and 525 AU) and orbital inclinations that vary between 0 to 20 degrees.
“This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNO,” said Carlos de la Fuente Marcos, scientist at UCM and co-author of the study, “ and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto.”
He added that the exact number is uncertain, but given the limited data that is available, their calculations suggest “there are at least two planets, and probably more, within the confines of our solar system.”
In their studies, the team analyzed the effects of what is called the ‘Kozai mechanism,’ which is related to the gravitational perturbation that a large body exerts on the orbit of another much smaller and further away object. They looked at how the highly eccentric comet 96P/Machholz1 is influenced by Jupiter (it will come near the orbit of Mercury in 2017, but it travels as much as 6 AU at aphelion) and it may “provide the key to explain the puzzling clustering of orbits around argument of perihelion close to 0° recently found for the population of ETNOs,” the team wrote in one of their papers.
The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth’s perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science
They also looked at the dwarf planet discovered last year called 2012 VP113 in the Oort cloud (its closest approach to the Sun is about 80 astronomical units) and how some researchers say it appears its orbit might be influenced by the possible presence of a dark and icy super-Earth, up to ten times larger than our planet.
“This Sedna-like object has the most distant perihelion of any known minor planet and the value of its argument of perihelion is close to 0°,” the team writes in their second paper. “This property appears to be shared by almost all known asteroids with semimajor axis greater than 150 au and perihelion greater than 30 au (the extreme trans-Neptunian objects or ETNOs), and this fact has been interpreted as evidence for the existence of a super-Earth at 250 au. In this scenario, a population of stable asteroids may be shepherded by a distant, undiscovered planet larger than the Earth that keeps the value of their argument of perihelion librating around 0° as a result of the Kozai mechanism.”
Of course, the theory put forth in two papers published by the team goes against the predictions of current models on the formation of the Solar System, which state that there are no other planets moving in circular orbits beyond Neptune.
But the team pointed to the recent discovery of a planet-forming disk around the star HL Tauri that lies more than 100 astronomical units from the star. HL Tauri is more massive and younger than our Sun and the discovery suggests that planets can form several hundred astronomical units away from the center of the system.
The team based their analysis by studying 13 different objects, so what is needed is more observations of the outer regions of our Solar System to determine what might be hiding out there.
An artist's concept of a trans-Neptunian object(TNOs). The distant sun is reduced to a bright star at a distance of over 3 billion miles. The Dark Energy Survey (DES) has now released discovery of more TNOs. (Illustration Credit: NASA)
Sometimes when you stare at something long enough, you begin to see things. This is not the case with optical sensors and telescopes. Sure, there is noise from electronics, but it’s random and traceable. Stargazing with a telescope and camera is ideal for staring at the same patches of real estate for very long and repeated periods. This is the method used by the Dark Energy Survey (DES), and with less than one percent of the target area surveyed, astronomers are already discovering previously unknown objects in the outer Solar System.
The Dark Energy Survey is a five year collaborative effort that is observing Supernovae to better understand the structures and expansion of the universe. But in the meantime, transient objects much nearer to home are passing through the fields of view. Trans-Neptunian Objects (TNOs), small icy worlds beyond the planet Neptune, are being discovered. A new scientific paper, released as part of this year’s American Astronomical Society gathering in Seattle, Washington, discusses these newly discovered TNOs. The lead authors are two undergraduate students from Carleton College of Northfield, Minnesota, participating in a University of Michigan program.
The Palomar Sky Survey (POSS-1, POSS-2), the Sloan Digital Sky Survey, and every other sky survey have mapped not just the static, nearly unchanging night sky, but also transient events such as passing asteroids, comets, or novae events. The Dark Energy Survey is looking at the night sky for structures and expansion of the Universe. As part of the five year survey, DES is observing ten select 3 square degree fields for Type 1a supernovae on a weekly basis. As the survey proceeds, they are getting more than anticipated. The survey is revealing more trans-Neptunian objects. Once again, deep sky surveys are revealing more about our local environment – objects in the farther reaches of our Solar System.
DES is an optical imaging survey in search of Supernovae that can be used as weather vanes to measure the expansion of the universe. This expansion is dependent on the interaction of matter and the more elusive exotic materials of our Universe – Dark Energy and Dark Matter. The five year survey is necessary to achieve a level of temporal detail and a sufficient number of supernovae events from which to draw conclusions.
In the mean time, the young researchers of Carleton College – Ross Jennings and Zhilu Zhang – are discovering the transients inside our Solar System. Led by Professor David Gerdes of the University of Michigan, the researchers started with a list of nearly 100,000 observations of individual transients. Differencing software and trajectory analysis helped identify those objects that were trans-Neptunian rather than asteroids of the inner Solar System.
While asteroids residing in the inner solar system will pass quickly through such small fields, trans-Neptunian objects (TNOs) orbit the Sun much more slowly. For example, Pluto, at an approximate distance of 40 A.U. from the Sun, along with the object Eris, presently the largest of the TNOs, has an apparent motion of about 27 arc seconds per day – although for a half year, the Earth’s orbital motion slows and retrogrades Pluto’s apparent motion. The 27 arc seconds is approximately 1/60th the width of a full Moon. So, from one night to the next, TNOs can travel as much as 100 pixels across the field of view of the DES survey detectors since each pixel has a width of 0.27 arc seconds.
Composite Dark Energy Camera image of one of the sky regions that the collaboration will use to study supernovae, exploding stars that will help uncover the nature of dark energy. The outlines of each of the 62 charge-coupled devices can be seen. This picture spans 2 degrees across on the sky and contains 520 megapixels. (Credit: Fermilab)
The scientific sensor array, DECam, is located at Cerro Tololo Inter-American Observatory (CTIO) in Chile utilizing the 4-meter (13 feet) diameter Victor M. Blanco Telescope. It is an array of 62 2048×4096 pixel back-illuminated CCDs totaling 520 megapixels, and altogether the camera weighs 20 tons.
A simple plot of the orbit of one of sixteen TNOs discovered by DES observations. (Credit: Dark Energy Detectives)
With a little over 2 years of observations, the young astronomers stated, “Our analysis revealed sixteen previously unknown outer solar system objects, including one Neptune Trojan, several objects in mean motion resonances with Neptune, and a distant scattered disk object whose 1200-year orbital period is among the 50 longest known.”
Object 2013 TV158 is one of the objects discovered by the Carleton College and University of Michigan team. Observed more than a dozen times over 10 months, the animated gif shows two image frames from August 2014 taken two hours apart. 2013 TV158 takes 1200 years to orbit the Sun and is likely a few hundred kilometers across – about the size of the Grand Canyon. (Credit: Dark Energy Detectives)
“So far we’ve examined less than one percent of the area that DES will eventually cover,” says Dr. Gerdes. “No other survey has searched for TNOs with this combination of area and depth. We could discover something really unusual.”
Illustration of color distribution of the trans-Neptunian objects. The horizontal axis represents the difference in intensity between visual (green & yellow) and blue of the object, while the vertical axis is the difference between visual and red. The distribution indicates how TNOs share a common origin and physical makeup, as well as common weathering in space. Yellow objects serve as reference: Neptune’s moon Triton, Saturn’s moon Phoebe, centaur Pholus, and the planet Mars. The object’s color represents the hue of the object. The size of the objects are relative – the larger objects are more accurate estimates, while smaller objects are simply based on absolute magnitude. (Credit: Wikimedia, Eurocommuter)
What does it all mean? It is further confirmation that the outer Solar System is chock-full of rocky-icy small bodies. There are other examples of recent discoveries, such as the search for a TNO for the New Horizons mission. As New Horizons has been approaching Pluto, the team turned to the Hubble space telescope to find a TNO to flyby after the dwarf planet. Hubble made short shrift of the work, finding three that the probe could reach. However, the demand for Hubble time does not allow long term searches for TNOs. A survey such as DES will serve to uncover many thousands of more objects in the outer Solar System. As Dr. Michael Brown of Caltech has stated, there is a fair likelihood that a Mars or Earth-sized object will be discovered beyond Neptune in the Oort Cloud.
A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute
Could there be an ocean hidden somewhere in that Death Star-like picture? This is an image of Mimas, a moon of Saturn, and just yesterday (Oct. 15) newly released data from the Cassini spacecraft suggests there are big liquid reservoirs underneath its surface.
“The amount of the to-and-fro motion indicates that Mimas’ interior is not uniform. These wobbles can be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell,” said Cornell University in a press release. More flybys with the Cassini spacecraft will be required to learn more about what lies beneath.
You can read more about the study (led by Cornell astronomy research associate Radwan Tajeddine) in Science, where it was published. Below, learn more about other worlds in the Solar System that could host oceans under their surface.
Enceladus
Cassini images of Saturn’s moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. This image was taken looking more or less broadside at the “tiger stripe” fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb (edge) of the moon. This image was acquired on Nov. 27, 2005. Image Credit: NASA/JPL/Space Science Institute
After nearly a decade of speculation, this year the Cassini spacecraft returned gravity data suggesting Enceladus (another moon of Saturn) does have a large subsurface ocean near its south pole, if not a global ocean. If confirmed, that could help explain why scientists see water gushing out of fractures in that area. As this recent paper by Cassini scientists shows, Enceladus is a promising location for habitability.
Titan
A halo of light surrounds Saturn’s moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute
By the way, anyone noticed that we still haven’t even left Saturn’s system? Titan is usually high on astrobiology wish lists for researchers because its hydrocarbon chemistry could be precursors to how life evolved. What’s not talked about as much, though, is at least two research findings pointing to evidence of a hidden ocean. Evidence comes from Titan’s tidal flexing from interacting with Saturn — which is 10 times more than what would be expected with a solid core — and the way that it moves on its own axis as well as around Saturn.
Europa
Rendering showing the location and size of water vapor plumes coming from Europa’s south pole. Credit: NASA/ESA/L. Roth/SWRI/University of Cologne
That Minecraft-looking object floating beside Europa there is a rendering showing where water vapor erupted from the Jovian moon, spotted by the Hubble Space Telescope in 2013. We were lucky enough to have a close-up view of Europa in the 1990s and early 2000s courtesy of NASA’s Galileo spacecraft. What we know for sure is there’s thick ice on Europa. What’s underneath is not known, but there’s long been speculation that it could be a subsurface ocean that may have more water than our own planet.
Io
Jupiter’s volcanic moon Io , imaged by the Galileo spacecraft in 1997. Credit: NASA/JPL/University of Arizona
Still flying around Jupiter here, we now turn our attention to Io — a place that is often remarked upon because of its blotchy appearance as well as all of the volcanoes on its surface. A newer analysis of Galileo data in 2011 — looking at some of the lesser-understood magnetic field data signatures — led one research team to conclude there could be a magma ocean lurking underneath that violence.
Triton
A glimpse of Triton from the Voyager 2 spacecraft, which flew by the Neptunian moon in August 1989. Credit: NASA/JPL
Little is known about Triton because only one spacecraft whizzed by it — Voyager 2, which took a running pass through the Neptune system in August 1989. An Icarus paper two years ago speculated that the world could host a subsurface ocean, but more data is needed. The energy of Neptune (which captured Triton long ago) could have melted its interior through tidal heating, possibly creating water from the ice in its crust.
Charon
Hubble image of Pluto and some of its moons, Charon, Nix and Hydra. Image Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team
We don’t have any close-up pictures of this moon of Pluto yet, but just wait a year. The New Horizons spacecraft will zoom past Charon and the rest of the system in July 2015. In the meantime, however, findings based on a model came out this summer in Icarus suggesting Charon — despite being so far from the Sun — might have had a subsurface ocean in the past. Or even now. The key is its once eccentric orbit, which would have produced tidal heating while interacting with Pluto. The science team plans to look for cracks that could be indicative of “the structure of the moon’s interior and how easily it deforms, and how its orbit evolved,” stated Alyssa Rhoden of NASA’s Goddard Space Flight Center in Maryland, who led the research.
Artist's impression of the New Horizons spacecraft. Image Credit: NASA
Another milestone for the Pluto-bound New Horizons mission — it’s crossing the orbit of Neptune today, as it prepares to fly by Pluto next August. In celebration, NASA is holding two live events at headquarters in Washington, D.C. starting at 1 p.m. EDT (5 p.m. UTC) today, and livestreamed above. More details below the jump.
The panel at 1 p.m. EDT will include:
Jim Green, director, NASA Planetary Division, Science Mission Directorate, NASA Headquarters, Washington
Ed Stone, Voyager project scientist, California Institute of Technology, Pasadena
Alan Stern, New Horizons principal investigator, Southwest Research Institute, Boulder, Colorado
Between 2 p.m. and 3 p.m. EDT, New Horizons team members will recall what happened when Voyager 2 passed by Neptune 25 years ago, and also talk about where they are working today on the Pluto mission. The members will include:
Moderator: David Grinspoon, Planetary Science Institute, Tucson, Arizona
Fran Bagenal, University of Colorado, Boulder
Bonnie Buratti, NASA Jet Propulsion Laboratory, Pasadena, California
Jeffrey Moore, NASA Ames Research Center, Moffett Field, California
John Spencer, Southwest Research Institute, Boulder, Colorado
The southern hemisphere of Neptune's moon Triton, at a resolution of 600 meters (1,969 feet) per pixel. Credit: Paul Schenk (LPI, Houston) from Voyager 2 images acquired August 1989
Talk about recycling! Twenty-five years after Voyager 2 zinged past Neptune’s moon Triton, scientists have put together a new map of the icy moon’s surface using the old data. The information has special relevance right now because the New Horizons spacecraft is approaching Pluto fast, getting to the dwarf planet in less than a year. And it’s quite possible that Pluto and Triton will look similar.
Triton has an exciting history. Scientists believed it used to be a lone wanderer until Neptune captured it, causing tidal heating that in turn created fractures, volcanoes and other features on the surface. While Triton and Pluto aren’t twins — this certainly didn’t happen to Pluto — Pluto also has frozen volatiles on its surface such as carbon monoxide, methane and nitrogen.
What you see in the map is a slightly enhanced version of Triton’s natural colors, bearing in mind that Voyager’s sensors are a little different from the human eye. Voyager 2 only did a brief flyby, so only about half the planet has been imaged. Nonetheless, the encounter was an exciting time for Paul Schenk, a planetary scientist at the Lunar and Planetary Institute in Houston. He led the creation of the new Triton map, and wrote about the experience of Voyager 2 in a blog post.
“Triton is a near twin of Pluto,” wrote Schenk. “Triton and Pluto are both slightly smaller than Earth’s Moon, have very thin nitrogen atmospheres, frozen ices on the surface (carbon monoxide, carbon dioxide, methane and nitrogen), and similar bulk composition (a mixture of ices, including water ice, and rock. Triton however was captured by Neptune long time ago and has been wracked by intense heating ever since. This has remade its surface into a tortured landscape of overturned layers, volcanism, and erupting geysers.”
He also added speculation about what will be seen at Pluto. Will it be a dead planet, or will geology still be affecting its surface? How close will Triton be to Pluto, particularly regarding its volcanoes? Only a year until we know for sure.
