Special Guest: Dr. Carolyn Porco is the leader of the Cassini Imaging Science team and the Director of the Cassini Imaging Central Laboratory for Operations (CICLOPS) at the Space Science Institute in Boulder, Colorado.
View showing actual flight structure of mirror backplane unit for NASA's James Webb Space Telescope (JWST) that holds 18 segment primary mirror array and secondary mirror mount at front, in stowed-for-launch configuration. JWST is being assembled here by technicians inside the world’s largest cleanroom at NASA Goddard Space Flight Center, Greenbelt, Md. Credit: Ken Kremer/kenkremer.com
View showing actual flight structure of mirror backplane unit for NASA’s James Webb Space Telescope (JWST) that holds 18 segment primary mirror array and secondary mirror mount at front, in stowed-for-launch configuration. JWST is being assembled here by technicians inside the world’s largest cleanroom at NASA Goddard Space Flight Center, Greenbelt, Md. Credit: Ken Kremer/kenkremer.com
Story/imagery updated[/caption]
NASA GODDARD SPACE FLIGHT CENTER, MD – The construction pace for NASA’s James Webb Space Telescope (JWST) took a major leap forward with delivery of the actual flight structure that serves as the observatory’s critical mirror holding backbone – to NASA’s Goddard Space Flight Center in Greenbelt, Maryland and observed by Universe Today.
“We are in good shape with the James Webb Space Telescope,” said Dr. John Mather, NASA’s Nobel Prize Winning scientist, in an exclusive interview with Universe Today at NASA Goddard during a visit to the flight structure – shown in my photos herein. Note: Read an Italian language version of this story – here at Alive Universe
And the mammoth $8.6 Billion Webb telescope has mammoth scientific objectives as the scientific successor to NASA’s Hubble Space Telescope (HST) – now celebrating its 25th anniversary in Earth orbit.
“JWST has the capability to look back towards the very first objects that formed after the Big Bang,” Mather told Universe Today.
How is that possible?
“James Webb has a much bigger mirror than Hubble. So its resolution is much better,” said astronaut and NASA science chief John Grunsfeld, during an exclusive interview at NASA Goddard. Grunsfeld flew on a trio of Hubble servicing missions aboard the Space Shuttle, including the final one during STS-125 in 2009.
“JWST can look back further in time, and a greater distance than Hubble, so we can see those first stars and galaxies formed in the Universe.”
These discoveries are only possible with Webb, which will become the most powerful telescope ever sent to space when it launches in 2018.
Up close view of actual side wing backplane of NASA’s James Webb Space Telescope (JWST) that will hold 3 of the observatory’s 18 primary mirrors, as technicians work inside cleanroom at NASA Goddard Space Flight Center, Greenbelt, Md. Credit: Ken Kremer/kenkremer.com
The massive JWST flight structure unit includes the “backplane assembly” that clasps in place all of the telescopes primary and secondary mirrors, as well as its ISIM science module loaded with the observatory’s quartet of state-of-the-art research instruments.
“The backplane looks really great,” Grunsfeld told me.
Numerous NASA centers and aerospace companies are involved in building the observatory and its backplane structure holding the mirrors that will search back some 13.4 billion years.
“The backplane structure just arrived in late August from Northrop Grumman Aerospace Systems in Redondo Beach, California,” said Sandra Irish, JWST lead structural engineer during an interview with Universe Today at the NASA Goddard cleanroom facility.
“This is the actual flight hardware.”
Side view of flight unit mirror backplane assembly structure for NASA’s James Webb Space Telescope (JWST) that holds primary mirror array and secondary mirror mount in stowed-for-launch configuration. JWST is being assembled technicians inside the cleanroom at NASA Goddard Space Flight Center, Greenbelt, Md. Credit: Ken Kremer/kenkremer.com
The purpose of JWST’s backplane assembly is to hold the telescopes 18 segment, 21-foot (6.5-meter) diameter primary mirror nearly motionless while floating in the utterly frigid space environment, thereby enabling the observatory to peer out into deep space for precise science gathering measurements never before possible.
The massive telescope structure “includes the primary mirror backplane assembly; the main backplane support fixture; and the deployable tower structure that lifts the telescope off of the spacecraft. The three arms at the top come together into a ring where the secondary mirror will reside,” say officials.
The backplane traveled a long and winding road before arriving at Goddard.
“The backplane structure was designed and built at Orbital ATK with NASA oversight,” Irish explained. The assembly work was done at the firms facilities in Magna, Utah.
“Then it was sent to Northrop Grumman in Redondo Beach, California for static testing. Then it came here to Goddard. Orbital ATK also built the composite tubes for the ISIM science module structure.”
The observatory’s complete flight structure measures about 26 feet (nearly 8 meters) from its base to the tip of the tripod arms and mirror mount holding the round secondary mirror.
Artist’s concept of the James Webb Space Telescope (JWST) with Sunshield at bottom. Credit: NASA/ESA
The flight structure and backplane assembly arrived at Goddard in its stowed-for-launch configuration after being flown cross country from California.
“It is here for the installation of all the mirrors to build up the entire telescope assembly here at Goddard. It will be fully tested here before it is delivered to the Johnson Space Center in Houston and then back to California,” Irish elaborated.
The overall assembly is currently attached to a pair of large yellow and white fixtures that firmly secure the flight unit, to stand it upright and rotate as needed, as it undergoes acceptance testing by engineers and technicians before commencement of the next big step – the crucial mirror installation that starts soon inside the world’s largest cleanroom at NASA Goddard.
Overhead cranes are also used to maneuver the observatory structure as engineers inspect and test the unit.
But several weeks of preparatory work are in progress before the painstakingly precise mirror installation can begin under the most pristine cleanroom operating conditions.
“Right now the technicians are installing harnesses that we need to mount all over the structure,” Irish told me.
“These harnesses will go to our electronic systems and the mirrors in order to monitor their actuation on orbit. So that’s done first.”
What is the construction sequence at Goddard for the installation of the mirrors and science instruments and what comes next?
“This fall we will be installing every mirror, starting around late October/early November. Then next April 2016 we will install the ISIM science module inside the backplane structure.”
“The ISIM mounts all four of the telescope science instrument. So the mirrors go on first, then the ISIM gets installed and then it will really be the telescope structure.” ISIM carries some 7,500 pounds (2400 kg) of telescope optics and instruments.
“Then starting about next July/August 2016 we start the environmental testing.”
The actual flight mirror backplane is comprised of three segments – the main central segment and a pair of outer wing-like parts holding three mirrors each. They will be unfolded from the stowed-for-launch configuration to the “deployed” configuration to carry out the mirror installation. Then be folded back over into launch configuration for eventual placement inside the payload fairing of the Ariane V ECA booster rocket.
The telescope will launch from the Guiana Space Center in Kourou, French Guiana in 2018.
Gold coated flight spare of a JWST primary mirror segment made of beryllium and used for test operations inside the NASA Goddard clean room. Credit: Ken Kremer- kenkremer.com
The telescopes primary and secondary flight mirrors have already arrived at Goddard.
The mirrors must remained precisely aligned and nearly motionless in order for JWST to successfully carry out science investigations. While operating at extraordinarily cold temperatures between -406 and -343 degrees Fahrenheit the backplane must not move more than 38 nanometers, approximately 1/1,000 the diameter of a human hair.
To account for the tiniest of errors and enhance science, each of the primary mirrors is equipped with actuators for minute adjustments.
“A beautiful advantage of Webb that’s different from Hubble is the fact that we do have actuation [capability] of every single one of our mirrors. So if we are off by just a little bit on either our calculations or from misalignment from launch or the zero gravity release, we can do some fine adjustments on orbit.”
“We can adjust every mirror within 50 nanometers.”
“That’s important because we can’t send astronauts to fix our telescope. We just can’t.”
“The telescope is a million miles away.”
NASA’s team at Goddard has already practiced mirror installation because there are no second chances.
“We only have one shot to get this right!” Irish emphasized.
Watch for more on the mirror installation in my upcoming story.
JWST is the successor to the 25 year old Hubble Space Telescope and will become the most powerful telescope ever sent to space.
Webb is designed to look at the first light of the Universe and will be able to peer back in time to when the first stars and first galaxies were forming.
The Webb Telescope is a joint international collaborative project between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
NASA has overall responsibility and Northrop Grumman is the prime contractor for JWST.
“The telescope is on schedule for its launch in 2018 in October,” Mather told me.
And the payoff from JWST will be monumental!
“On everything from nearby planets to the most distant universe, James Webb will transform our view of the Universe,” Grunsfeld beams.
Watch for more on JWST construction and mirror installation in part 2 soon.
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
A comparison of the primary mirror used by Hubble and the primary mirror array used by the James Webb Space Telescope. Photo Credit: NASANASA Science chief and astronaut John Grunsfeld discusses James Webb Space Telescope project at NASA Goddard Space Flight Center in Maryland. Credit: Ken Kremer/kenkremer.com
The atmosphere keeps us alive and breathing, but it really sucks for astronomy. Fortunately, humanity has built and launched space telescopes that get above the pesky atmosphere, where the skies are really clear. Let’s take a look at the past, current and future of orbital observation.
An artist's conception of 2007 OR10, nicknamed Snow White. Astronomers suspect that its rosy color is due to the presence of irradiated methane. [Credit: NASA]
Over the course of the past decade, more and more objects have been discovered within the Trans-Neptunian region. With every new find, we have learned more about the history of our Solar System and the mysteries it holds. At the same time, these finds have forced astronomers to reexamine astronomical conventions that have been in place for decades.
Consider 2007 OR10, a Trans-Neptunian Object (TNO) located within the scattered disc that at one time went by the nicknames of “the seventh dwarf” and “Snow White”. Approximately the same size as Haumea, it is believed to be a dwarf planet, and is currently the largest object in the Solar System that does not have a name.
Discovery and Naming:
2007 OR10 was discovered in 2007 by Meg Schwamb, a PhD candidate at Caltech and a graduate student of Michael Brown, while working out of the Palomar Observatory. The object was colloquially referred to as the “seventh dwarf” (from Snow White and the Seven Dwarfs) since it was the seventh object to be discovered by Brown’s team (after Quaoar in 2002, Sedna in 2003, Haumea and Orcus in 2004, and Makemake and Eris in 2005).
Comparison of Sedna with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon
At the time of its discovery, the object appeared to be very large and very white, which led to Brown giving it the other nickname of “Snow White”. However, subsequent observation has revealed that the planet is actually one of the reddest in the Kuiper Belt, comparable only to Haumea. As a result, the nickname was dropped and the object is still designated as 2007 OR10.
The discovery of 2007 OR10 would not be formally announced until January 7th, 2009.
Size, Mass and Orbit:
A study published in 2011 by Brown – in collaboration with A.J. Burgasser (University of California San Diego) and W.C. Fraser (MIT) – 2007 OR10’s diameter was estimated to be between 1000-1500 km. These estimates were based on photometry data obtained in 2010 using the Magellan Baade Telescope at the Las Campanas Observatory in Chile, and from spectral data obtained by the Hubble Space Telescope.
However, a survey conducted in 2012 by Pablo Santos Sanz et al. of the Trans-Neptunian region produced an estimate of 1280±210 km based on the object’s size, albedo, and thermal properties. Combined with its absolute magnitude and albedo, 2007 OR10 is the largest unnamed object and the fifth brightest TNO in the Solar System. No estimates of its mass have been made as of yet.
2007 OR10 also has a highly eccentric orbit (0.5058) with an inclination of 30.9376°. What this means is that at perihelion, it is roughly 33 AU (4.9 x 109 km/30.67 x 109 mi) from our Sun while at aphelion, it is as distant as 100.66 AU (1.5 x 1010 km/9.36 x 1010 mi). It also has an orbital period of 546.6 years, which means that the last time it was at perihelion was 1857 and it won’t reach aphelion until 2130. As such, it is currently the second-farthest known large body in the Solar System, and will be farther out than both Sedna and Eris by 2045.
Composition:
According to the spectral data obtained by Brown, Burgasser and Fraser, 2007 OR10 shows infrared signatures for both water ice and methane, which indicates that it is likely similar in composition to Quaoar. Concurrent with this, the reddish appearance of 2007 OR10 is believed to be due to presence of tholins in the surface ice, which are caused by the irradiation of methane by ultraviolet radiation.
The presence of red methane frost on the surfaces of both 2007 OR10 and Quaoar is also seen as an indication of the possible existence of a tenuous methane atmosphere, which would slowly evaporate into space when the objects are closer to the Sun. Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible.
Also, the presence of water ice on the surface is believed to imply that the object underwent a brief period of cryovolcanism in its distant past. According to Brown, this period would have been responsible not only for water ice freezing on the surface, but for the creation of an atmosphere that included nitrogen and carbon monoxide. These would have been depleted rather quickly, and a tenuous atmosphere of methane would be all that remains today.
However, more data is required before astronomers can say for sure whether or not 2007 OR10 has an atmosphere, a history of cryovolcanism, and what its interior looks like. Like other KBOs, it is possible that it is differentiated between a mantle of ices and a rocky core. Assuming that there is sufficient antifreeze, or due to the decay of radioactive elements, there may even be a liquid-water ocean at the core-mantle boundary.
Classification:
Though it is too difficult to resolve 2007 OR10’s size based on direct observation, based on calculations of 2007 OR10’s albedo and absolute magnitude, many astronomers believe it to be of sufficient size to have achieved hydrostatic equilibrium. As Brown stated in 2011, 2007 OR10 “must be a dwarf planet even if predominantly rocky”, which is based on a minimum possible diameter of 552 km and what is believed to be the conditions under which hydrostatic equilibrium occurs in cold icy-rock bodies.
That same year, Scott S. Sheppard and his team (which included Chad Trujillo) conducted a survey of bright KBOs (including 2007 OR10) using the Palomar Observatory’s 48 inch Schmidt telescope. According to their findings, they determined that “[a]ssuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus could be considered dwarf planets.”
Currently, nothing is known of 2007 OR10’s mass, which is a major factor when determining if a body has achieved hydrostatic equilibrium. This is due in part to there being no known satellite(s) in orbit of the object, which in turn is a major factor in determining the mass of a system. Meanwhile, the IAU has not addressed the possibility of accepting additional dwarf planets since before the discovery of 2007 OR10 was announced.
Alas, much remains to be learned about 2007 OR10. Much like it’s Trans-Neptunian neighbors and fellow KBOs, a lot will depend on future missions and observations being able to learn more about its size, mass, composition, and whether or not it has any satellites. However, given its extreme distance and fact that it is currently moving further and further away, opportunities to observe and explore it via flybys will be limited.
However, if all goes well, this potential dwarf planet could be joining the ranks of such bodies as Pluto, Eris, Ceres, Haumea and Makemake in the not-too-distant future. And with luck, it will be given a name that actually sticks!
This portrait looking down on Saturn and its rings was created from images obtained by NASA's Cassini spacecraft on Oct. 10, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic
The farthest planet from the Sun that can be observed with the naked eye, the existence of Saturn has been known for thousands of years. And much like all celestial bodies that can be observed with the aid of instruments – i.e. Mercury, Venus, Mars, Jupiter and the Moon – it has played an important role in the mythology and astrological systems of many cultures.
Saturn is one of the four gas giants in our Solar System, also known as the Jovian planets, and the sixth planet from the Sun. It’s ring system, which is it famous for, is also the most observable – consisting of nine continuous main rings and three discontinuous arcs.
Saturn’s Size, Mass and Orbit:
With a polar radius of 54364±10 km and an equatorial radius of 60268±4 km, Saturn has a mean radius of 58232±6 km, which is approximately 9.13 Earth radii. At 5.6846×1026 kg, and a surface area, at 4.27×1010 km2, it is roughly 95.15 as massive as Earth and 83.703 times it’s size. However, since it is a gas giant, it has significantly greater volume – 8.2713×1014 km3, which is equivalent to 763.59 Earths.
The sixth most distant planet, Saturn orbits the Sun at an average distance of 9 AU (1.4 billion km; 869.9 million miles). Due to its slight eccentricity, the perihelion and aphelion distances are 9.022 (1,353.6 million km; 841.3 million mi) and 10.053 AU (1,513,325,783 km; 940.13 million mi), on average respectively.
Saturn Compared to Earth. Image credit: NASA/JPL
With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days to complete a single revolution of the Sun. In other words, a single Cronian year is the equivalent of about 29.5 Earth years. However, as with Jupiter, Saturn’s visible features rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions.
The latest estimate of Saturn’s rotation as a whole are based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes. Saturn’s rotation causes it to have the shape of an oblate spheroid; flattened at the poles but bulging at the equator.
Saturn’s Composition:
As a gas giant, Saturn is predominantly composed of hydrogen and helium gas. With a mean density of 0.687 g/cm3, Saturn is the only planet in the Solar System that is less dense than water; which means that it lacks a definite surface, but is believed to have a solid core. This is due to the fact that Saturn’s temperature, pressure, and density all rise steadily toward the core.
Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Earth, but more dense due to the presence of metallic hydrogen, which as a result of the extreme pressure.
Diagram of Saturn’s interior. Credit: Kelvinsong/Wikipedia Commons
Saturn has a hot interior, reaching 11,700 °C at its core, and it radiates 2.5 times more energy into space than it receives from the Sun. This is due in part to the Kelvin-Helmholtz mechanism of slow gravitational compression, but may also be attributable to droplets of helium rising from deep in Saturn’s interior out to the lower-density hydrogen. As these droplets rise, the process releases heat by friction and leaves Saturn’s outer layers depleted of helium. These descending droplets may have accumulated into a helium shell surrounding the core.
In 2004, French astronomers Didier Saumon and Tristan Guillot estimated that the core must 9-22 times the mass of Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas.
Saturn’s Atmosphere:
The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The gas giant is also known to contain heavier elements, though the proportions of these relative to hydrogen and helium is not known. It is assumed that they would match the primordial abundance from the formation of the Solar System.
Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion.
NASA’s Cassini spacecraft captures a composite near-true-color view of the huge storm churning through the atmosphere in Saturn’s northern hemisphere. Image credit: NASA/JPL-Caltech/SSI
Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter and wider near the equator. As with Jupiter’s cloud layers, they are divided into the upper and lower layers, which vary in composition based on depth and pressure. In the upper cloud layers, with temperatures in range of 100–160 K and pressures between 0.5–2 bar, the clouds consist of ammonia ice.
Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in an aqueous solution.
On occasion, Saturn’s atmosphere exhibits long-lived ovals, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice.
These spots can be several thousands of kilometers wide, and have been observed in 1876, 1903, 1933, 1960, and 1990. Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed enveloping Saturn, which was spotted by the Cassini space probe. If the periodic nature of these storms is maintained, another one will occur in about 2020.
The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI
The winds on Saturn are the second fastest among the Solar System’s planets, after Neptune’s. Voyager data indicate peak easterly winds of 500 m/s (1800 km/h). Saturn’s northern and southern poles have also shown evidence of stormy weather. At the north pole, this takes the form of a hexagonal wave pattern, whereas the south shows evidence of a massive jet stream.
The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images. The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior.
The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope. These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter.
Saturn’s Moons:
Saturn has at least 150 moons and moonlets, but only 53 of these moons have been given official names. Of these moons, 34 are less than 10 km in diameter and another 14 are between 10 and 50 km in diameter. However, some of its inner and outer moons are rather large, ranging from 250 to over 5000 km.
Moons of Saturn (from left to right): Mimas, Enceladus, Tethys, Dione, Rhea, Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Credit: NASA/JPL/Space Science Institute
Traditionally, most of Saturn’s moons have been named after the Titans of Greek mythology, and are grouped based on their size, orbits, and proximity to Saturn. The innermost moons and regular moons all have small orbital inclinations and eccentricities and prograde orbits. Meanwhile, the irregular moons in the outermost regions have orbital radii of millions of kilometers, orbital periods lasting several years, and move in retrograde orbits.
The Inner Large Moons, which orbit within the E Ring (see below), includes the larger satellites Mimas, Enceladus, Tethys, and Dione. These moons are all composed primarily of water ice, and are believed to be differentiated into a rocky core and an icy mantle and crust. With a diameter of 396 km and a mass of 0.4×1020 kg, Mimas is the smallest and least massive of these moons. It is ovoid in shape and orbits Saturn at a distance of 185,539 km with an orbital period of 0.9 days.
Enceladus, meanwhile, has a diameter of 504 km, a mass of 1.1×1020 km and is spherical in shape. It orbits Saturn at a distance of 237,948 km and takes 1.4 days to complete a single orbit. Though it is one of the smaller spherical moons, it is the only Cronian moon that is endogenously active – and one of the smallest known bodies in the Solar System that is geologically active. This results in features like the famous “tiger stripes” – a series of continuous, ridged, slightly curved and roughly parallel faults within the moon’s southern polar latitudes.
Large geysers have also been observed in the southern polar region that periodically release plumes of water ice, gas and dust which replenish Saturn’s E ring. These jets are one of several indications that Enceladus has liquid water beneath it’s icy crust, where geothermal processes release enough heat to maintain a warm water ocean closer to its core. With a geometrical albedo of more than 140%, Enceladus is one of the brightest known objects in the Solar System.
Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Image Credit: NASA/JPL
At 1066 km in diameter, Tethys is the second-largest of Saturn’s inner moons and the 16th-largest moon in the Solar System. The majority of its surface is made up of heavily cratered and hilly terrain and a smaller and smoother plains region. Its most prominent features are the large impact crater of Odysseus, which measures 400 km in diameter, and a vast canyon system named Ithaca Chasma – which is concentric with Odysseus and measures 100 km wide, 3 to 5 km deep and 2,000 km long.
With a diameter and mass of 1,123 km and 11×1020 kg, Dione is the largest inner moon of Saturn. The majority of Dione’s surface is heavily cratered old terrain, with craters that measure up to 250 km in diameter. However, the moon is also covered with an extensive network of troughs and lineaments which indicate that in the past it had global tectonic activity.
The Large Outer Moons, which orbit outside of the Saturn’s E Ring, are similar in composition to the Inner Moons – i.e. composed primarily of water ice and rock. Of these, Rhea is the second largest – measuring 1,527 km in diameter and 23 × 1020 kg in mass – and the ninth largest moon of the Solar System. With an orbital radius of 527,108 km, it is the fifth-most distant of the larger moons, and takes 4.5 days to complete an orbit.
Like other Cronian satellites, Rhea has a rather heavily cratered surface, and a few large fractures on its trailing hemisphere. Rhea also has two very large impact basins on its anti-Saturnian hemisphere – the Tirawa crater (similar to Odysseus on Tethys) and an as-yet unnamed crater – that measure 400 and 500 km across, respectively.
A composite image of Titan’s atmosphere, created using blue, green and red spectral filters to create an enhanced-color view. Image Credit: NASA/JPL/Space Science Institute
At 5150 km in diameter, and 1,350×1020 kg in mass, Titan is Saturn’s largest moon and comprises more than 96% of the mass in orbit around the planet. Titan is also the only large moon to have its own atmosphere, which is cold, dense, and composed primarily of nitrogen with a small fraction of methane. Scientists have also noted the presence of polycyclic aromatic hydrocarbons in the upper atmosphere, as well as methane ice crystals.
The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters, evidence of cryo-volcanoes, and longitudinal dune fields that were apparently shaped by tidal winds. Titan is also the only body in the Solar System beside Earth with bodies of liquid on its surface, in the form of methane–ethane lakes in Titan’s north and south polar regions.
With an orbital distance of 1,221,870 km, it is the second-farthest large moon from Saturn, and completes a single orbit every 16 days. Like Europa and Ganymede, it is believed that Titan has a subsurface ocean made of water mixed with ammonia, which can erupt to the surface of the moon and lead to cryovolcanism.
Hyperion is Titan’s immediate neighbor. At an average diameter of about 270 km, it is smaller and lighter than Mimas. It is also irregularly shaped and quite odd in composition. Essentially, the moon is an ovoid, tan-colored body with an extremely porous surface (which resembles a sponge). The surface of Hyperion is covered with numerous impact craters, most of which are 2 to 10 km in diameter. It also has a highly unpredictable rotation, with no well-defined poles or equator.
The two sides of Iapetus, which is known as “Saturn’s yin yang moon” because of the contrast in its color composition. Credit: NASA/JPL
At 1,470 km in diameter and 18×1020 kg in mass, Iapetus is the third-largest of Saturn’s large moons. And at a distance of 3,560,820 km from Saturn, it is the most distant of the large moons, and takes 79 days to complete a single orbit. Due to its unusual color and composition – its leading hemisphere is dark and black whereas its trailing hemisphere is much brighter – it is often called the “yin and yang” of Saturn’s moons.
Beyond these larger moons are Saturn’s Irregular Moons. These satellites are small, have large-radii, are inclined, have mostly retrograde orbits, and are believed to have been acquired by Saturn’s gravity. These moons are made up of three basic groups – the Inuit Group, the Gallic Group, and the Norse Group.
The Inuit Group consists of five irregular moons that are all named from Inuit mythology – Ijiraq, Kiviuq, Paaliaq, Siarnaq, and Tarqeq. All have prograde orbits that range from 11.1 to 17.9 million km, and from 7 to 40 km in diameter. They are all similar in appearance (reddish in hue) and have orbital inclinations of between 45 and 50°.
The Gallic group are a group of four prograde outer moons named for characters in Gallic mythology -Albiorix, Bebhionn, Erriapus, and Tarvos. Here too, the moons are similar in appearance and have orbits that range from 16 to 19 million km. Their inclinations are in the 35°-40° range, their eccentricities around 0.53, and they range in size from 6 to 32 km.
Saturns rings and moons, shown to scale. Credit: NASA
Last, there is the Norse group, which consists of 29 retrograde outer moons that take their names from Norse mythology. These satellites range in size from 6 to 18 km, their distances from 12 and 24 million km, their inclinations between 136° and 175°, and their eccentricities between 0.13 and 0.77. This group is also sometimes referred to as the Phoebe group, due to the presence of a single larger moon in the group – which measures 240 km in diameter. The second largest, Ymir, measures 18 km across.
Within the Inner and Outer Large Moons, there are also those belonging to Alkyonide group. These moons – Methone, Anthe, and Pallene – are named after the Alkyonides of Greek mythology, are located between the orbits of Mimas and Enceladus, and are among the smallest moons around Saturn.
Some of the larger moons even have moons of their own, which are known as Trojan moons. For instance, Tethys has two trojans – Telesto and Calypso, while Dione has Helene and Polydeuces.
Saturn’s Ring System:
Saturn’s rings are believed to be very old, perhaps even dating back to the formation of Saturn itself. There are two main theories as to how these rings formed, each of which have variations. One theory is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces.
In version of this theory, the moon was struck by a large comet or asteroid – possible during the Late Heavy Bombardment – that pushed it beneath the Roche Limit. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed billions of years ago.
The structure is subdivided into seven smaller ring sets, each of which has a division (or gap) between it and its neighbor. The A and B Rings are the densest part of the Cronian ring system and are 14,600 and 25,500 km in diameter, respectively. They extend to a distance of 92,000 – 117,580 km (B Ring) and 122,170 – 136,775 km (A Ring) from Saturn’s center, and are separated by the 4,700 km wide Cassini Division.
Saturn’s rings. Credit: NASA/JPL/Space Science Institute.
The C Ring, which is separated from the B Ring by the 64 km Maxwell Gap, is approximately 17,500 km in width and extends 74,658 – 92,000 from Saturn’s center. Together with the A and B Rings, they comprise the main rings, which are denser and contain larger particles than the “dusty rings”.
These tenuous rings are called “dusty” due to the small particles that make them up. They include the D Ring, a 7,500 km ring that extends inward to Saturn’s cloud tops (66,900 – 74,510 km from Saturn’s center) and is separated from the C Ring by the 150 km Colombo Gap. On the other end of the system, the G and E Rings are located, which are also “dusty” in composition.
The G Ring is 9000 km in width and extends 166,000 – 175,000 km from Saturn’s center. The E Ring, meanwhile, is the largest single ring section, measuring 300,000 km in width and extending 166,000 to 480,000 km from Saturn’s center. It is here where the majority of Saturn’s moons are located (see above).
The narrow F Ring, which sits on the outer edge of the A Ring, is more difficult to categorize. While some parts of it are very dense, it also contains a great deal of dust-size particles. For this reason, estimates on its width range from 30 to 500 km, and it extends roughly 140,180 km from Saturn’s center.
History of Observing Saturn:
Because it is visible to the naked eye in the night sky, human beings have been observing Saturn for thousands of years. In ancient times, it was considered the most distant of five known the planets, and thus was accorded special meaning in various mythologies. The earliest recorded observations come from the Babylonians, where astronomers systematically observed and recorded its movements through the zodiac.
Roman astrological calendar, from the stone plate of the 3rd—4th centuries CE, Rome. Credit: Museo della civiltà romana
To the ancient Greeks, this outermost planet was named Cronus (Kronos), after the Greek god of agriculture and youngest of the Titans. The Greek scientist Ptolemy made calculations of Saturn’s orbit based on observations of the planet while it was in opposition.The Romans followed in this tradition, identifying it with their equivalent of Cronos (named Saturnus).
In ancient Hebrew, Saturn is called ‘Shabbathai’, whereas in Ottoman Turkish, Urdu and Malay, its name is ‘Zuhal’, which derived is from the original Arabic. In Hindu astrology, there are nine astrological objects known as Navagrahas. Saturn, which is one of them, is known as “Shani”, who judges everyone based on the good and bad deeds performed in life. In ancient China and Japan, the planet was designated as the “earth star” – based on the Five Elements of earth, air, wind, water and fire.
However, the planet was not directly observed until 1610, when Galileo Galilee first discerned the presence of rings. At the time, he mistook them for two moons that were located on either side. It was not until Christiaan Huygens used a telescope with greater magnification that this was corrected. Huygens also discovered Saturn’s moon Titan, and Giovanni Domenico Cassini later discovered the moons of Iapetus, Rhea, Tethys and Dione.
No further discoveries of significance were made again until the 181th and 19th centuries. The first occurred in 1789 when William Herschel discovered the two distant moons of Mimas and Enceladus, and then in 1848 when a British team discovered the irregularly-shaped moon of Hyperion.
Drawing of Saturn by Robert Hook, taken from Philosophical Transactions (1666). Credit: Wikipedia Commons
In 1899 William Henry Pickering discovered Phoebe, noting that it had a highly irregular orbit that did not rotate synchronously with Saturn as the larger moons do. This was the first time any satellite had been found to move about a planet in retrograde orbit. And by 1944, research conducted throughout the early 20th century confirmed that Titan has a thick atmosphere – a feature unique among the Solar System’s moons.
Exploration of Saturn:
By the late 20th century, unmanned spacecraft began to conduct flybys of Saturn, gathering information on its composition, atmosphere, ring structure, and moons. The first flyby was conducted by NASA using the Pioneer 11 robotic space probe, which passed Saturn at a distance of 20,000 km in September of 1979.
Images were taken of the planet and a few of its moons, although their resolution was too low to discern surface detail. The spacecraft also studied Saturn’s rings, revealing the thin F Ring and the fact that dark gaps in the rings are bright when facing towards the Sun, meaning that they contain fine light-scattering material. In addition, Pioneer 11 measured the temperature of Titan.
The next flyby took place in November of 1980 when the Voyager 1 space probe passed through the Saturn system. It sent back the first high-resolution images of the planet, its rings and satellites – which included features of various moons that had never before been seen.
These six narrow-angle color images were made from the first ever ‘portrait’ of the solar system taken by Voyager 1 in November 1980. Credit: NASA/JPL
In August 1981, Voyager 2 conducted its flyby and gathered more close-up images of Saturn’s moons, as well as evidence of changes in the atmosphere and the rings. The probes discovered and confirmed several new satellites orbiting near or within the planet’s rings, as well as the small Maxwell Gap and Keeler gap (a 42 km wide gap in the A Ring).
In June of 2004, the Cassini–Huygens space probe entered the Saturn system and conducted a close flyby of Phoebe, sending back high-resolution images and data. By July 1st, 2004, the probe entered orbit around Saturn, and by December, it had completed two flybys of Titan before releasing the Huygens probe. This lander reached the surface and began transmitting data on the atmospheric and surface by by Jan. 14th, 2005. Cassini has since conducted multiple flybys of Titan and other icy satellites.
In 2006, NASA reported that Cassini had found evidence of liquid water reservoirs that erupt in geysers on Saturn’s moon Enceladus. Over 100 geysers have since been identified, which are concentrated around the southern polar region. In May 2011, NASA scientists at an Enceladus Focus Group Conference reported that Enceladus’ interior ocean may be the most likely candidate in the search for extra-terrestrial life.
In addition, Cassini photographs have revealed a previously undiscovered planetary ring, eight new satellites, and evidence of hydrocarbon lakes and seas near Titan’s north pole. The probe was also responsible for sending back high-resolution images of the intense storm activity at Saturn’s northern and southern poles.
Cassini’s primary mission ended in 2008, but the probe’s mission has been extended twice since then – first to September 2010 and again to 2017. In the coming years, NASA hopes to use the probe to study a full period of Saturn’s seasons.
Artist Illustration of the Cassini space probe to Saturn and Titan, a joint NASA, ESA mission. Credit: NASA/JPL
From being a very important part of the astrological systems of many cultures to becoming the subject of ongoing scientific fascination, Saturn continues to occupy a special place in our hearts and minds. Whether it’s Saturn’s fantastically large and beautiful ring system, its many many moons, its tempestuous weather, or its curious composition, this gas giant continues to fascinate and inspire.
In the coming years and decades, additional robotic explorer missions will likely to be sent to investigate Saturn, its rings and its system of moons in greater detail. What we find may constitute some of the most groundbreaking discoveries of all time, and will likely teach us more about the history of our Solar System.
Tenth planet? Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)
Ask a person what Dysnomia refers to, and they might venture that it’s a medical condition. In truth, they would be correct. But in addition to being a condition that affects the memory (where people have a hard time remembering words and names), it is also the only known moon of the distant dwarf planet Eris.
In fact, the same team that discovered Eris a decade ago – a discovery that threw our entire notion of what constitutes a planet into question – also discovered a moon circling it shortly thereafter. As the only satellite that circles one of the most distant objects in our Solar System, much of what we know about this ball of ice is still subject to debate.
Discovery and Naming:
In January of 2005, astronomer Mike Brown and his team discovered Eris using the new laser guide star adaptive optics system at the W. M. Keck Observatory in Hawaii. By September, Brown and his team were conducting observations of the four brightest Kuiper Belt Objects – which at that point included Pluto, Makemake, Haumea, and Eris – and found indications of an object orbiting Eris.
Provisionally, this body was designated S/2005 1 (2003 UB³¹³). However, in keeping with the Xena nickname that his team was already using for Eris, Brown and his colleagues nicknamed the moon “Gabrielle” after Xena’s sidekick. Later, Brown selected the official name of Dysnomia for the moon, which seemed appropriate for a number of reasons.
For one, this name is derived from the daughter of the Greek god Eris – a daemon who represented the spirit of lawlessness – which was in keeping with the tradition of naming moons after lesser gods associated with the primary god. It also seemed appropriate since the “lawless” aspect called to mind actress Lucy Lawless, who portrayed Xena on television. However, it was not until the IAU’s resolution on what defined a planet – passed in August of 2006 – that the planet was officially designated as Dysnomia.
Size, Mass and Orbit:
The actual size of Dysnomia is subject to dispute, and estimates are based largely on the planet’s albedo relative to Eris. For example, the IAU and Johnston’s Asteroids with Satellites Database estimate that it is 4.43 magnitudes fainter than Eris and has an approximate diameter of between 350 and 490 km (217 – 304 miles)
However, Brown and his colleagues have stated that their observations indicate it to be 500 times fainter and between 100 and 250 km (62 – 155 miles) in diameter. Using the Herschel Space Observatory in 2012, Spanish astronomer Pablo Santo Sanz and his team determined that, provided Dysnomia has an albedo five times that of Eris, it is likely to be 685±50 km in diameter.
Eris and its moon, Dysnomia, as imaged by the W.M. Keck Observatory in Hawaii. Credits:NASA/ESA and M. Brown/Caltech
In 2007, Brown and his team also combined Keck and Hubble observations to determine the mass of Eris, and estimate the orbital parameters of the system. From their calculations, they determined that Dysnomia’s orbital period is approximately 15.77 days. These observations also indicated that Dysnomia has a circular orbit around Eris, with a radius of 37350±140 km. In addition to being a satellite of a dwarf planet, Dysnomia is also a Kuiper Belt Object (KBO) like Eris.
Composition and Origin:
Currently, there is no direct evidence to indicate what Dysnomia is made of. However, based on observations made of other Kuiper Belt Objects, it is widely believed that Dysnomia is composed primarily of ice. This is based largely on infrared observations made of Haumea (2003 EL61), the fourth largest object in the Kuiper Belt (after Eris, Pluto and Makemake) which appears to be made entirely of frozen water.
Astronomers now know that three of the four brightest KBOs – Pluto, Eris and Haumea – have one or more satellites. Meanwhile, of the fainter members, only about 10% are known to have satellites. This is believed to imply that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across would throw off large amounts of material that would coalesce into a moon.
Artist’s concept of Kuiper Belt Object Eris and its tiny satellite Dysnomia. The Hubble Space Telescope and Keck Observatory took images of Dysnomia’s movement from which astronomer Mike Brown (Caltech) precisely calculated Eris to be 27 percent more massive than Pluto. Credit: NASA/ESA/Adolph Schaller (for STScI)
This could mean that Dysnomia was the result of a collision between Eris and a large KBO. After the impact, the icy material and other trace elements that made up the object would have evaporated and been ejected into orbit around Eris, where it then re-accumulated to form Dysnomia. A similar mechanism is believed to have led to the formation of the Moon when Earth was struck by a giant impactor early in the history of the Solar System.
Since its discovery, Eris has lived up to its namesake by stirring things up. However, it has also helped astronomers to learn many things about this distant region of the Solar System. As already mentioned, astronomers have used Dysnomia to estimate the mass of Eris, which in turn helped them to compare it to Pluto.
While astronomers already knew that Eris was bigger than Pluto, but they did not know whether it was more massive. This they did by measuring the distance between Dysnomia and how long it takes to orbit Eris. Using this method, astronomers were able to discover that Eris is 27% more massive than Pluto is.
With this knowledge in hand, the IAU then realized that either Eris needed to be classified as a planet, or that the term “planet” itself needed to be refined. Ergo, one could make that case that it was the discovery of Dysnomia more than Eris that led to Pluto no longer being designated a planet.
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).
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
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
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.
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 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. 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.
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
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.
Chances are that if you have lived on this planet for the past half-century, you’ve heard of NASA. As the agency that is in charge of America’s space program, they put a man on the Moon, launched the Hubble Telescope, helped establish the International Space Station, and sent dozens of probes and shuttles into space.
But do you know what the acronym NASA actually stands for? Well, NASA stands for the National Aeronautics and Space Administration. As such, it oversees America’s spaceflight capabilities and conducts valuable research in space. NASA also has various programs on Earth dedicated to flight, hence why the term “Aeronautics” appears in the agency’s name.
The Solar System is 4.5 billion years old, but the Universe is much older. What was here before our Solar System formed?
The Solar System is old. Like, dial-up-fax-machine-old. 4.6 billion years to be specific. The Solar System has nothing on the Universe. It’s been around for 13.8 billion years, give or take a few hundred million. That means the Universe is three times older than the Solar System.
Astronomers think the Milky Way, is about 13.2 billion years old; almost as old as the Universe itself. It formed when smaller dwarf galaxies merged together to create the grand spiral we know today. It turns out the Milky Way has about 8.6 billion years of unaccounted time. Billions and billions of years to get up to all kinds of mischief before the Solar System showed up to keep an eye on things.
Our Galaxy takes 220 million years to rotate, so it’s done this about 60 times in total. As it turns, it swirls and mixes material together like a giant space blender. Clouds of gas and dust come together into vast star forming regions, massive stars have gone supernova, and then the clusters themselves have been torn up again, churning the stars into the Milky Way. This happens in the galaxy’s spiral arms, where the areas of higher density lead to regions of star formation.
So let’s go back, more than 4.6 billion years, before there was an Earth, a Sun, or even a Solar System. Our entire region was gas and dust, probably within one of the spiral arms. Want to know what it looked like? Some of your favorite pictures from the Hubble Space Telescope should help.
Here’s the Orion, Eagle, and the Tarantula Nebulae. These are star forming regions. They’re clouds of hydrogen left over from Big Bang, with dust expended by aging stars, and seeded with heavier elements formed by supernovae.
The Orion Nebula. Image Credit: Vasco Soeiro
After a few million years, regions of higher density began forming into stars, both large and small. Let’s take a look at a star-forming nebula again. See the dark knots? Those are newly forming stars surrounded by gas and dust in the stellar nursery.
You’re seeing many many stars, some are enormous monsters, others are more like our Sun, and some smaller red dwarfs. Most will eventually have planets surrounding them – and maybe, eventually life? If this was the environment, where are all those other stars?
Why do I feel so alone? Where are all our brothers and sisters? Where’s all the other stuff that’s in that picture? Where’s all my stuff?
TRAPPIST First Light Image of the Tarantula Nebula. Credit: ESO
Apparently nature hates a messy room and a cozy stellar nest. The nebula that made the Sun was either absorbed into the stars, or blown away by the powerful stellar winds from the largest stars. Eventually they cleared out the nebula, like a fans blowing out a smoky room.
At the earliest point, our solar nebula looked like the Eagle Nebula, after millions of years, it was more like the Pleiades Star Cluster, with bright stars surrounded by hazy nebulosity. It was the gravitational forces of the Milky Way which tore the members of our solar nursery into a structure like the Hyades Cluster. Finally, gravitational interactions tore our cluster apart, so our sibling stars were lost forever in the churning arms of the Milky Way.
We’ll never know exactly what was here before the Solar System; that evidence has long been blown away into space. But we can see other places in the Milky Way that give us a rough idea of what it might have looked like at various stages in its evolution.
What should we call our original star forming nebula? Give our own nebula a name in the comments below.
