Neptune’s Moon Triton

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. June 23, 2010. Credit: NASA
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 book Astronomie 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
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
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!

We have many interesting articles on Triton, Neptune, and the outer planets of the Solar System here at Universe Today.

Here’s one about the New Map of Triton, and one about the Underground Ocean it might be hiding, and 40 Years of Summer on Triton. And here’s Why You Shouldn’t Buy Real Estate on Triton.

In the Observatory also has an interview with Emily Lakdawalla, the senior editor and planetary evangelist for the Planetary Society, titled “Where Should We Look for Life in the Solar System?

Sources:

New Horizons Mission to Pluto

Artist's impression of the New Horizons spacecraft in orbit around Pluto (Charon is seen in the background). Credit: NASA/JPL

Humans have been sending spacecraft to other planets, as well as asteroid and comets, for decades. But rarely have any of these ventured into the outer reaches of our Solar System. In fact, the last time a probe reached beyond the orbit of Saturn to explore the worlds of Neptune, Uranus, Pluto and beyond was with the Voyager 2 mission, which concluded back in 1989.

But with the New Horizons mission, humanity is once again peering into the outer Solar System and learning much about its planets, dwarf planets, planetoids, moons and assorted objects. And as of July 14th, 2015, it made its historic rendezvous with Pluto, a world that has continued to surprise and mystify astronomers since it was first discovered.

Background:

In 1980, after Voyager 1‘s flyby of Saturn, NASA scientists began to consider the possibility of using Saturn to slingshot the probe towards Pluto to conduct a flyby by 1986. This would not be the case, as NASA decided instead to conduct a flyby of Saturn’s moon of Titan – which they considered to be a more scientific objective – thus making a slingshot towards Pluto impossible.

Because no mission to Pluto was planned by any space agency at the time, it would be years before any missions to Pluto could be contemplated. However, after Voyager 2′s flyby of Neptune and Triton in 1989, scientists once again began contemplating a mission that would take a spacecraft to Pluto for the sake of studying the Kuiper Belt and Kuiper Belt Objects (KBOs).

Voyager 2. Credit: NASA
Artist’s impression of the Voyager spacecraft in flight. Credit: NASA/JPL

In May 1989, a group of scientists, including Alan Stern and Fran Bagenal, formed an alliance called the “Pluto Underground”. Committed to the idea of mounting an exploratory mission to Pluto and the Kuiper Belt, this group began lobbying NASA and the US government to make it this plan a reality. Combined with pressure from the scientific community at large, NASA began looking into mission concepts by 1990.

During the course of the late 1990s, a number of Trans-Neptunian Objects (TNOs) were discovered, confirming the existence of the Kuiper Belt and spurring interest in a mission to the region. This led NASA to instruct the JPL to re-purpose the mission as a Pluto and KBO flyby. However, the mission was scrapped by 2000, owing to budget constraints.

Backlash over the cancellation led NASA’s Science Mission Directorate to create the New Frontiers program which began accepting mission proposals. Stamatios “Tom” Krimigis, head of the Applied Physics Laboratory’s (APL) space division, came together with Alan Stern to form the New Horizons team. Their proposal was selected from a number of submissions, and officially selected for funding by the New Frontiers program in Nov. 2001.

Despite additional squabbles over funding with the Bush administration, renewed pressure from the scientific community allowed the New Horizons team managed to secure their funding by the summer of 2002. With a commitment of $650 million for the next fourteen years, Stern’s team was finally able to start building the spacecraft and its instruments.

Engineers working on the New Horizons spacecraft's Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument. Credit: NASA
Engineers working on the New Horizons spacecraft’s Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument. Credit: NASA

Mission Profile:

New Horizons was planned as a voyage to the only unexplored planet in the Solar System, and was originally slated for launch in January 2006 and arrival at Pluto in 2015. Alan Stern was selected as the mission’s principal investigator, and construction of the spacecraft was handled primarily by the Southwest Research Institute (SwRI) and the Johns Hopkins Applied Physics Laboratory, with various contractor facilities involved in the navigation of the spacecraft.

Meanwhile, the US Naval Observatory (USNO) Flagstaff Station – in conjunction with NASA and JPL – was responsible for performing navigational position data and related celestial frames. Coincidentally, the UNSO Flagstaff station was where the photographic plates that led to the discovery of Pluto’s moon Charon came from.

In addition to its compliment of scientific instruments (listed below), there are several cultural artifacts traveling aboard the spacecraft. These include a collection of 434,738 names stored on a compact disc, a piece of Scaled Composites’s SpaceShipOne, and a flag of the USA, along with other mementos. In addition, about 30 g (1 oz) of Clyde Tombaugh’s ashes are aboard the spacecraft, to commemorate his discovery of Pluto in 1930.

The New Horizons spacecraft takes off on Jan. 19, 2006 from the Kennedy Space Center for its planned close encounter with Pluto. Credit: NIKON/Scott Andrews/NASA
The New Horizons spacecraft takes off on Jan. 19, 2006 from the Kennedy Space Center for its planned close encounter with Pluto. Credit: NIKON/Scott Andrews/NASA

Instrumentation:

The New Horizons science payload consists of seven instruments. They are (in alphabetically order):

  • Alice: An ultraviolet imaging spectrometer responsible for analyzing composition and structure of Pluto’s atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects (KBOs).
  • LORRI: (Long Range Reconnaissance Imager) a telescopic camera that obtains encounter data at long distances, maps Pluto’s farside and provides high resolution geologic data.
  • PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation) an energetic particle spectrometer which measures the composition and density of plasma (ions) escaping from Pluto’s atmosphere.
  • Ralph: A visible and infrared imager/spectrometer that provides color, composition and thermal maps.
  • REX: (Radio Science EXperiment) a device that measures atmospheric composition and temperature; passive radiometer.
  • SDC: (Student Dust Counter) built and operated by students, this instrument measures the space dust peppering New Horizons during its voyage across the solar system.
  • SWAP: (Solar Wind Around Pluto) a solar wind and plasma spectrometer that measures atmospheric “escape rate” and observes Pluto’s interaction with solar wind.
Instruments New Horizons will use to characterize Pluto are REX (atmospheric composition and temperature; PEPSSI (composition of plasma escaping Pluto's atmosphere); SWAP (solar wind); LORRI (close up camera for mapping, geological data); Star Dust Counter (student experiment measuring space dust during the voyage); Ralph (visible and IR imager/spectrometer for surface composition and thermal maps and Alice (composition of atmosphere and search for atmosphere around Charon). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The instruments New Horizons will use to characterize Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Launch:

Due to a series of weather-related delays, the New Horizons mission launched on January 19th, 2006, two days later than originally scheduled. The spacecraft took off from Cape Canaveral Air Force Station, Florida, at 15:00 EST (19:00 UTC) atop an Atlas V 551 rocket. This was the first launch of this particular rocket configuration, which has a third stage added to increase the heliocentric (escape) speed.

The spacecraft left Earth faster than any spacecraft to date, achieving a launch velocity of 16.5 km/s. It took only nine hours to reach the Moon’s orbit, passing lunar orbit before midnight (EST) on the same day it was launched. It has not, however, broken Voyager 1‘s record – which is currently traveling at 17.145 km/s (61,720 km/h, 38,350 mph) relative to the Sun – for being the fastest spacecraft to leave the Solar System.

Inner Solar System:

Between January and March, 2006, mission controllers guided the probe through a series of trajectory-correction maneuvers (TCMs). During the week of February 20th, 2006, controllers conducted in-flight tests on three of the major on board science instruments. On April 7th, the spacecraft passed the orbit of Mars, moving at roughly 21 km/s (76,000 km/h; 47,000 mph) away from the Sun.

At this point in its journey, the spacecraft had reached a distance of 243 million kilometers from the Sun, and approximately 93.4 million km from Earth. On June 13th, 2006, the New Horizons spacecraft passed the tiny asteroid 132524 APL at a distance of 101,867 km (63,297 mi) when it was closest.

Using the Ralph instrument, New Horizons was able to capture images of the asteroid, estimating to be 2.5 km (1.6 mi) in diameter. The spacecraft also successfully tracked the asteroid from June 10th-12th, 2006, allowing the mission team to test the spacecraft’s ability to track rapidly moving objects.

First images of Pluto in September 2006. Credit: NASA
First images of Pluto taken by New Horizons in September 2006. Credit: NASA

From September 21st-24th, New Horizons managed to capture its first images of Pluto while testing the LORRI instruments. These images, which were taken from a distance of approximately 4,200,000,000 km (2.6×109 mi) or 28.07 AU and released on November 28th, confirmed the spacecraft’s ability to track distant targets.

Outer Solar System:

On September 4th, 2006, New Horizons took its first pictures of Jupiter at a distance of 291 million kilometers (181 million miles). The following January, it conducted more detailed surveys of the system, capturing an infrared image of the moon Callisto, and several black and white images of Jupiter itself.

By February 28th, 2007, at 23:17 EST (03:17, UTC) New Horizons made its closest approach to Europa, at a distance of 2,964,860 km (1,842,278 mi). At 01:53:40 EST (05:43:40 UTC), the spacecraft made its flyby of Jupiter, at a distance of 2.3 million km (1.4 million mi) and received a gravity assist.

The Jupiter flyby increased New Horizons‘ speed by 4 km/s (14,000 km/h; 9,000 mph), accelerating the probe to a velocity of 23 km/s (83,000 km/h; 51,000 mph) relative to the Sun and shortening its voyage to Pluto by three years.

The encounter with Jupiter not only provided NASA with the opportunity to photograph the planet using the latest equipment, it also served as a dress rehearsal for the spacecraft’s encounter with Pluto. As well as testing the imaging instruments, it also allowed the mission team to test the communications link and the spacecraft’s memory buffer.

Black and white image of Jupiter viewed by LORRI in January 2007
Black and white image of Jupiter viewed by LORRI in January 2007. Credit: NASA/John Hopkins University Applied Physics Laboratory/Southwest Research Institute

One of the main goals during the Jupiter encounter was observing its atmospheric conditions and analyzing the structure and composition of its clouds. Heat-induced lightning strikes in the polar regions and evidence of violent storm activity were both observed. In addition, the Little Red Spot,  was imaged from up close for the first time. The New Horizons spacecraft also took detailed images of Jupiter’s faint ring system. Traveling through Jupiter’s magnetosphere, the spacecraft also managed to collect valuable particle readings.

The flyby of the Jovian systems also gave scientists the opportunity to examine the structure and motion of Io’s famous lava plumes. New Horizons measured the plumes coming from the Tvashtar volcano, which reached an altitude of up to 330 km from the surface, while infrared signatures confirmed the presence of 36 more volcanoes on the moon.

Callisto’s surface was also analyzed with LEISA, revealing how lighting and viewing conditions affect infrared spectrum readings of its surface water ice. Data gathered on minor moons such as Amalthea also allowed NASA scientists to refine their orbit solutions.

After passing Jupiter, New Horizons spent most of its journey towards Pluto in hibernation mode. During this time, New Horizons crossed the orbit of Saturn (June 8, 2008) and Uranus on (March 18, 2011). In June 2014, the spacecraft emerged from hibernation and the team began conducting instrument calibrations and a course correction,. By August 24th, 2014, it crossed Neptune’s orbit on its way to Pluto.

Capturing Callisto
New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter’s outermost large moon, Callisto, during its flyby in February 2007. Credit: NASA/JPL

Rendezvous with Pluto:

Distant-encounter operations at Pluto began on January 4th, 2015. Between January 25th to 31st, the approaching probe took several images of Pluto, which were released by NASA on February 12th. These photos, which were taken at a distance of more than 203,000,000 km (126,000,000 mi) showed Pluto and its largest moon, Charon.

Investigators compiled a series of images of the moons Nix and Hydra taken from January 27th through February 8th, 2015, beginning at a range of 201,000,000 km (125,000,000 mi), while Kerberos and Styx were captured by photos taken on April 25.

On July 4th, 2015, NASA lost contact with New Horizons after it experienced a software anomaly and went into safe mode. On the following day, NASA announced that they had determined it to be the result of a timing flaw in a command sequence. By July 6th, the glitch had been fixed and the probe had exited safe mode and began making its approach.

The New Horizons spacecraft made its closest approach to Pluto at 07:49:57 EDT (11:49:57 UTC) on July 14th, 2015, and then Charon at 08:03:50 EDT (12:03:50 UTC). Telemetries confirming a successful flyby and a healthy spacecraft reached Earth on 20:52:37 EDT (00:52:37 UTC).

During the flyby, the probe captured the clearest pictures of Pluto to date, and full analyses of the data obtained is expected to take years to process. The spacecraft is currently traveling at a speed of 14.52 km/s (9.02 mi/s) relative to the Sun and at 13.77 km/s (8.56 mi/s) relative to Pluto.

Full trajectory of New Horizons space probe (sideview). Credit: pluto.jhuapl.edu
Full trajectory of New Horizons space probe (sideview). Credit: pluto.jhuapl.edu

Future Objectives:

With its flyby of Pluto now complete, the New Horizons probe is now on its way towards the Kuiper Belt. The goal here is to study one or two other Kuiper Belt Objects, provided suitable KBOs are close to New Horizons‘ flight path.

Three objects have since been selected as potential targets, which were provisionally designated PT1 (“potential target 1”), PT2 and PT3 by the New Horizons team. These have since been re-designated as 2014 MU69 (PT1), 2014 OS393 (PT2), and 2014 PN70 (PT3).

All of these objects have an estimated diameter of 30–55 km, are too small to be seen by ground telescopes, and are 43–44 AU from the Sun, which would put the encounters in the 2018–2019 period. All are members of the “cold” (low-inclination, low-eccentricity) classical Kuiper Belt, and thus very different from Pluto.

Even though it was launched far faster than any outward probe before it, New Horizons will never overtake either Voyager 1 or Voyager 2 as the most distant human-made object from Earth. But then again, it doesn’t need to, given that what it was sent out to study all lies closer to home.

What’s more, the probe has provided astronomers with extensive and updated data on many of planets and moons in our Solar System – not the least of which are the Jovian and Plutonian systems. And last, but certainly not least, New Horizons is the first spacecraft to have it made it out to such a distance since the Voyager program.

And so we say so long and good luck to New Horizons, not to mention thanks for providing us with the best images of Pluto anyone has ever seen! We can only hope she fares well as she makes its way into the Kuiper Belt and advances our knowledge of the outer Solar System even farther.

We have many interesting articles about the New Horizons spacecraft and Pluto here on Universe Today. For example, here are some Interesting Facts About PlutoHow Long Does it Take to Get to Pluto, Why Pluto is No Longer Considered a Planet, and Is There Life on Pluto?

For more information on the Kuiper Belt, check out What is The Kuiper Belt? and NASA’s Solar System Exploration entry on the Kuiper Belt and Oort Cloud.

Astronomy Cast also has some fascinating episodes on Pluto, including On Pluto’s Doorstep – Live Hangout with New Horizons Team

And be sure to check out the New Horizons mission homepage at NASA.

25 Years Since Voyager’s ‘Pale Blue Dot’ Images

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
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
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.

Ken Kremer

What Does a Supernova Sounds Like?

What Does a Supernova Sounds Like?

We’ve all been ruined by science fiction, with their sound effects in space. But if you could watch a supernova detonate from a safe distance away, what would you hear?

Grab your pedantry tinfoil helmet and say the following in your best “Comic Book Guy” voice: “Don’t be ridiculous. Space does not have sound effects. You would not hear the Death Star exploding. That is wrong.” There are no sounds in space. You know that. Why did you even click on this?

Wait! I still have thing I want to teach you. Keep that tinfoil on and stick around. First, a quick review. Why are there sounds? What are these things we detect with our ear shell-flaps which adorn the sides of our hat-resting orb?

Sounds are pressure waves moving through a medium, like air, water or beer. Talking, explosions, and music push air molecules into other molecules. Through all that “stuff” pushing other “stuff” it eventually pushes the “stuff” that we call our eardrum, and that lets us hear a thing. So, much like how there’s not enough “stuff” in space to take a temperature reading. There’s not enough “stuff” in space to be considered a medium for sound to move through.

Don’t get me wrong there’s “stuff” there. There’s particles. Even in intergalactic depths there are a few hundred particles every cubic meter, and there’s much more in a galaxy. They’re so far apart though, the particles don’t immediately collide with each other allowing a sound wave to pass through a grouping of them.

So, even if you did watch the Death Star explode, you couldn’t hear it. This includes zapping lasers, and exploding rockets. Unless two astronauts touched helmets together, then they could talk. The sound pressure moves through the air molecules in one helmet, through the glass transferring from one helmet to the other, and then pushes against the air inside the helmet of the listening astronaut. Then they could talk, or possibly hear one another scream, or just make muffled noises under the face-hugger that had been hiding in their boot.

There’s no sound in space, so you can’t hear what a supernova sounds like. But if you’re willing to consider swapping out your listening meats for other more impressive cybernetic components, there are possibilities. Perhaps I could offer you something in a plasma detection instrument, and you could hear the Sun.

Artist's concept of NASA's Voyager spacecraft. Image credit: NASA/JPL-Caltech
Artist’s concept of NASA’s Voyager spacecraft. Image credit: NASA/JPL-Caltech

Voyager 1 detects waves of particles streaming from the Sun’s solar wind. It was able to hear when it left the heliosphere, the region where the Sun’s solar wind buffets against the interstellar medium.

Or you could try something in the Marconi Auralnator 2000 which is the latest in radio detector implants I just made up. If there was such a thing, you could hear the plasma waves in Earth’s radiation belts. Which would be pretty amazing, but perhaps somewhat impractical for other lifestyle purposes such as watching Ellen.

So, if you wanted to hear a supernova you’d need a different kind of ear. In fact, something that’s not really an ear at all. There are some exceptions out there. With dense clouds of gas and dust at the heart of a galaxy cluster, you could have a proper medium. NASA’s Chandra X-Ray Observatory has detected sound waves moving through these dust clouds. But you would need ears millions of billions of times more sensitive to hear them.

NASA and other space agencies work tirelessly to convert radio, plasma and other activity into a sound pressure format that we can actually hear. There are beautiful things happening space. I’ve included a few links below which will take you to a few of these, and they are really quite incredible.

Earthsong

Lightning on Saturn, Helium in the atmosphere, etc.

Stunning Amateur Timelapse of Jupiter ‘Re-enacts’ Voyager Flyby

This animated gif shows Voyager 1's approach to Jupiter during a period of over 60 Jupiter days in 1979. Credit: NASA.

Back in the 1970’s when NASA launched the two Voyager spacecraft to Jupiter, Saturn, Uranus, and Neptune, I remember being mesmerized by a movie created from Voyager 1 images of the movement of the clouds in Jupiter’s atmosphere. Voyager 1 began taking pictures of Jupiter as it approached the planet in January 1979 and completed its Jupiter encounter in early April. During that time it took almost 19,000 pictures and many other scientific measurements to create the short movie, which you can see below, showing the intricate movement of the bright band of clouds for the first time.

Now, 35 years later a group of seven Swedish amateur astronomers achieved their goal of replicating the Voyager 1 footage, not with another flyby but with images taken with their own ground-based telescopes.

“We started this joint project back in December of 2013 to redo the NASA Voyager 1 flyby of Jupiter,” amatuer astronomer Göran Strand told Universe Today. “During 90 days we captured 560 still images of Jupiter and turned them into 90 complete maps that covered the whole of Jupiter’s surface.”

Their newly released film, above details the work they did and the hurdles they overcame (including incredibly bad weather in Sweden this winter) to make their dream a reality. They called their project “Voyager 3.”

Animated gif of the 'Voyager 3' team re-enactment of the Voyager 1 flyby. Credit: Voyager 3 team, via Kristoffer Åberg.
Animated gif of the ‘Voyager 3’ team re-enactment of the Voyager 1 flyby. Credit: Voyager 3 team, via Kristoffer Åberg.
It is really an astonishing project and those of you who do image processing will appreciate the info in the video about the tools they used and how they did their processing to create this video.

The seven Swedish astronomers who participated in the Voyager 3 project are (from left to right in the photo below) Daniel Sundström, Torbjörn Holmqvist, Peter Rosén (the project initiator), Göran Strand, Johan Warell and his daughter Noomi, Martin Högberg and Roger Utas.

The Swedish team of amateur astronomers who compiled the 'Voyager 3' project. Image courtesy Peter Rosén.
The Swedish team of amateur astronomers who compiled the ‘Voyager 3’ project. Image courtesy Peter Rosén.

Congrats to the team of Voyager 3!

You can read more about the Voyagers visits to Jupiter here from NASA.

Voyager3Movie from Peter Rosén on Vimeo.

How Would Earth Send Messages To A Starship — Or A Distant Civilization?

USS Enterprise-D, a starship of the Star Trek: The Next Generation era. Credit: MemoryAlpha.Org/Paramount Pictures/CBS Studios

I have a new exercise routine where I watch Star Trek: The Next Generation most mornings of the week while doing my thing. Besides serving as awesome distraction, the episodes do get me thinking about how humans would talk to extraterrestrials. It likely wouldn’t be as easy as the show portrays to zoom across space to conduct diplomatic negotiations at the planet “Parliament”, for example, so interstellar communication would be a problem.

Luckily for non-engineers such as me, there are folks out there (on Earth, at least) that are examining the problem of talking between stars. David Messerschmitt, of the University of California at Berkeley, is one of those people. A new paper by him on Arxiv examines the issue. Note this is a preprint site and not a peer-reviewed journal, but all the same it provides an intriguing addition to how to communicate outside of Earth.

Messerschmitt explains that humans already communicate with probes that are a fair distance from Earth (say, Voyager 1 in interstellar space) at radio frequencies, and there is some usage now of laser/optical communications (namely between the Earth and the moon).

Across greater distances, however, you lose information, the interstellar medium gets in the way, and stars shift due to relative motion. Besides all that, at first you wouldn’t know how the other civilization designs its systems and you could therefore send a message that wouldn’t be picked up.

This sequence of images, showing a region where fewer stars are forming near the constellation of Perseus, illustrates how the structure and distribution of the interstellar medium can be distilled from the images obtained with Planck. Credit: ESA / HFI and LFI Consortia
This sequence of images, showing a region where fewer stars are forming near the constellation of Perseus, illustrates how the structure and distribution of the interstellar medium can be distilled from the images obtained with Planck. Credit: ESA / HFI and LFI Consortia

He further explains that starships and civilizations would have different communications requirements. Starship communication would be two-way and based on a similar design, so success comes by having high “uplink and downlink transmit times”. The more information, the better it would be for scientific observations and keeping down errors.

Civilization-to-civilization chats, however, would present headaches. As with all diplomatic negotiations, crafting suitable messages would take time. Then we’d have to send the message out repeatedly to make sure it is heard (which actually means that reliability is not as big of a problem.) Then the ISM would have to be contended with (something that pulsar astronomers and astrophysicists are already working on, he said).

In either case — talking to starships or other civilizations — one can assume there’d be a lot of energy involved, he added. “Starships are likely to be much closer than the nearest civilizations, but the cost of either a large transmit antenna or transmit energy is likely to be considerably greater for the starship than for a terrestrial-based transmitter,” he said, suggesting that a solution would be to minimize the energy delivered to the receiver. Other civilizations may have found more efficient ways to overcome this problem, he added.

You can read more details of the research on Arxiv, where Messerschmitt talks about Gaussian noise, channel coding and other parameters to keep in mind during communication.

Weekly Space Hangout – September 13, 2013: Voyager is Out, LADEE Launches (a Frog), Asteroid 324 Bamberga

Once again, we have gathered together the forces of space journalism to report on the big news stories of the week. And there were lots of big stories indeed, with the launch of NASA’s LADEE mission to the Moon, and the awesome fact that Voyager 1 has totally left the Solar System.

Host: Fraser Cain

Journalists: Amy Shira Teitel, Nicole Gugliucci, Matthew Francis, David Dickinson, Nancy Atkinson

Frog Launches with LADEE
LADEE Launch Trajectory
Asteroid 334’s Close Approach
Voyager Has Left the Heliosphere
New Comet Lovejoy Discovered
Lots of Globular Clusters

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern as a live Google+ Hangout on Air. You can watch the show from right here on Universe Today, or on our YouTube channel.

10 Historic Moments in Voyager’s Journey to Interstellar Space

The Voyager spacecraft have been on an extensive mission of discovery that has lasted some 36 years. Image Credit: NASA/JPL

Yesterday, NASA announced that as of August 2012, Voyager 1 is in a new frontier to humanity: interstellar space. Our most distant spacecraft is now in a region where the plasma (really hot gas) environment comes more from between the stars than from the sun itself. (There’s still debate as to whether it’s in or out of the solar system, as this article explains.)

The plucky spacecraft is close to 12 billion miles (19 million kilometers) from home, and in its 36 years of voyaging has taught us a lot about the planets, their moons and other parts of space. Here are 10 of some of its most historic moments. Did we miss any? Let us know in the comments.

10. The launch: Aug. 20, 1977

Voyager 1 launches from the Kennedy Space Center on Sept. 5, 1977. Credit: NASA
Voyager 1 launches from the Kennedy Space Center on Sept. 5, 1977. Credit: NASA

Voyager 1 blasted off from Cape Canaveral on Sept. 5, 1977. Its twin, Voyager 2, departed Earth 16 days earlier. Each spacecraft carried various scientific instruments on board as well as a “Golden Record” that had sounds of Earth on it, as well as a diagram showing where Earth is in the universe.

9. Capturing the Earth and Moon together for the first time

On Sept. 18, 1977, Voyager 1 took three images of the Earth and Moon that were combined into this one image. The moon is artificially brightened to make it show up better. Credit: NASA
On Sept. 18, 1977, Voyager 1 took three images of the Earth and Moon that were combined into this one image. The moon is artificially brightened to make it show up better. Credit: NASA

About two weeks after launching, Voyager 1 turned back towards Earth and took three images, which were combined into this single view of the Earth and Moon together in space. This was the first time both bodies were pictured together, NASA said.

8. The ‘Pale Blue Dot’ image

Voyager 1 pale blue dot. Image credit: NASA/JPL
Voyager 1 pale blue dot. Image credit: NASA/JPL

On February 14, 1990, Voyager 1 was about 3.7 billion miles (6 billion kilometers) away from Earth. Scientists commanded the spacecraft to turn its face towards the solar system and snap some pictures of the planets. Among them was this famous image of Earth, which astronomer Carl Sagan called the Pale Blue Dot. “Look again at that dot. That’s here. That’s home. That’s us,” wrote Sagan in his 1997 book of the same name. In 2013, the spacecraft Cassini also took a picture of Earth, and NASA encouraged everyone to wave back.

7. Finding moons “shepherding” Saturn’s F ring

Prometheus, a small potato-shaped moon of Saturn, shown in this Voyager 1 picture interacting with the planet's F ring. Credit: NASA/JPL/SSI
Prometheus, a small potato-shaped moon of Saturn, shown in this Voyager 1 picture interacting with the planet’s F ring. Credit: NASA/JPL/SSI

Voyager 1 spotted Prometheus and Pandora, two moons of Saturn that keep the F ring separate from the rest of the debris, as well as Atlas, which “shepherds” the A ring. More recently, astronomers have found even more interesting things in Saturn’s rings — such as rain.

6. Spotting what appeared to be a LOT of water ice on Saturn’s moons

Encaladus, a moon of Saturn, as shown in this Voyager 1 image. Credit: NASA
Encaladus, a moon of Saturn, as shown in this Voyager 1 image. Credit: NASA

After many years of seeing Saturn’s moons as mere points of light, Voyager 1 buzzed several of them in its quick flyby through the system: Dione, Enceladus, Mimas, Rhea, Tethys and Titan among them. Many of these moons appeared to be icy, which was a surprising find since astronomers previously thought water was pretty rare in the Solar System. We know better now.

5. Imaging Titan’s orange haze

Saturn's moon Titan lies under a thick blanket of orange haze in this Voyager 1 picture. Credit: NASA
Saturn’s moon Titan lies under a thick blanket of orange haze in this Voyager 1 picture. Credit: NASA

Voyager 1 pictures such as this tortured astronomers for decades — what lies beneath this mysterious haze surrounding Titan, Saturn’s moon? That mystery, in fact, inspired the European Space Agency to send a lander to the moon, called Huygens, which successfully reached the surface in 2005.

4. Finding active volcanoes on Io

Io's blotchy volcanoes are clearly visible in this image from Voyager 1. Credit: NASA
Io’s blotchy volcanoes are clearly visible in this image from Voyager 1. Credit: NASA

Voyager 1 helped show us that the Solar System is full of very interesting moons. At Io — a moon of Jupiter — it turns out the moon flexes during its 42-hour orbit of massive Jupiter, which powers a lot of volcanic activity.

3. Voyager 1 becomes the most distant human object

A 2013 snapshot riding along with Voyager 1's looking back at the Sun and inner solar system. The positions of Voyager 2 and Pioneers 10 and 11 show within the viewport as well.
A 2013 computer-generated snapshot riding along with Voyager 1’s looking back at the Sun and inner solar system. The positions of Voyager 2 and Pioneers 10 and 11 show within the viewport as well.

On Feb. 17, 1998, Voyager 1’s distance surpassed that of another long-flying probe, Pioneer 10. This made Voyager 1 the farthest-flung human object in space.

2. Riding the “magnetic highway”

Artist concept of NASA’s Voyager 1 spacecraft exploring a new region in our solar system called the “magnetic highway.” Credit: NASA/JPL-Caltech
Artist concept of NASA’s Voyager 1 spacecraft exploring a new region in our solar system called the “magnetic highway.” Credit: NASA/JPL-Caltech

In December, NASA said Voyager 1 had reached an area (as of July 28, 2012) where high-energy magnetic particles were starting to bleed through the bubble of lower-energy particles from our sun. “Voyager’s discovered a new region of the heliosphere that we had not realized was there. It’s a magnetic highway where the magnetic field of the Sun is connected to the outside. So it’s like a highway, letting particles in and out,” said project scientist Ed Stone at the time. After that point, as more measurements were analyzed by different teams, there was a lot of debate as to whether Voyager had reached interstellar space.

1. Reaching interstellar space

This graphic shows the main evidence that Voyager 1 has reached interstellar space. The blue line shows particle density, which dropped as Voyager 1 moved away from the sun, and then jumped again after it crossed the "termination shock" that is where the sun's solar wind (particles streaming from the sun) slows down. Credit: NASA/JPL-Caltech
This graphic shows the main evidence that Voyager 1 has reached interstellar space. The blue line shows particle density, which dropped as Voyager 1 moved away from the sun, and then jumped again after it crossed the “termination shock” that is where the sun’s solar wind (particles streaming from the sun) slows down. Credit: NASA/JPL-Caltech

With Voyager 1 now known to be in interstellar space, we’re lucky enough to have a few years left to communicate with it before it runs out of power. All of the instruments will be turned off by 2025, and then engineering data will be available for about 10 years beyond that. The silent emissary from humanity will then come within 1.7 light years of an obscure star in the constellation Ursa Minor (the Little Bear) called AC+79 3888 in the year 40,272 AD and then orbit the center of the Milky Way for millions of years.

Astro Poetry: The First Starship

Artist's concept of NASA's Voyager spacecraft. Image credit: NASA/JPL-Caltech

Our favorite astro-poet, Stuart Atkinson, has written a wonderful ode to Voyager 1 in commemoration of the spacecraft reaching interstellar space. Stu has a knack for turning science into poetry!

The First Starship

I needed no nacelles to push me onwards;
No dilithium crystals crackled in my heart.
Yet I have left Sol so far behind me she is
Just a star now, a golden spark in a salt grain sea,
And I can feel her gentle breath on my cheek
No more.

In my ears now the whalesong of the universe
Drowns out the sounds of distant, troubled Earth.
Oh, the blissful peace!
Out here all I can hear
Is the fabled music of the spheres.
Each trembling tone rolling under me,
Every mellow note washing over me
Was sung somewhere Out There.
Melodies ripped from ravenous black holes’ throats,
Screamed from the broken hearts of dying stars
Swirl around me, multi-wavelength whispers
In the dark and endless night.

My head is full of memories…
Skimming Titan’s marmalade-haze atmosphere;
My first sight of Jove’s great bloodshot eye,
Staring back at me, into me, as I flew by;
Earth as Pale Blue Dot, a Sagan sequin
Dancing in a sunbeam…

Ahead now – the solar system’s Barrier Reef.
Terra will whip around Sol 300 times before
I reach the Oort’s icy inner harbour wall
And tens of thousands of times more before
I finally leave port, sailing on in serene silence
For forty millennia more before I venture anywhere
Near another star…

And in ten million years, when Earth’s proud citadels
And cities have crumbled and whatever evolves
In their dust to take Mankind’s place
Stares out into space with curious, alien eyes,
I will still be flying through the stars.
Your legacy. Proof that once you dared to dream
Noble, Camelot dreams
And reached out, through me, to explore eternity.

(c) Stuart Atkinson Sept 13th 2013

Written to commemorate and celebrate the Sept 12, 2013 announcement that Voyager 1 had entered interstellar space.

Read more of Stu’s poetry at this Astropoetry website and his other musings at Cumbrian Sky.

Messages To Voyager: Welcome to Interstellar Space

On the Voyager spacecraft are the famous Voyager Golden Records, which send messages from planet Earth to … whatever or whoever may find it in the future. In celebration of Voyager 1 making it into interstellar space (read all the details here) a few friends put together a video to congratulate the spacecraft and the team. Neil deGrasse Tyson, Wil Wheaton, Carl Sagan’s son and others shared their messages to the Voyager 1 spacecraft.

Feel free to leave your message to Voyager in the (new and improved) comment section.