New Horizons Flight Controllers celebrate after they received confirmation from the spacecraft that it had successfully completed the flyby of Pluto, Tuesday, July 14, 2015 in the Mission Operations Center (MOC) of the Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Maryland. Credit: NASA/Bill Ingalls
Watch Pluto grow in this series of photos taken during New Horizons’ approach
Whew! We’re out of the woods. On schedule at 9 p.m. EDT, New Horizons phoned home telling the mission team and the rest of the on-edge world that all went well. The preprogrammed “phone call” — a 15-minute series of status messages beamed back to mission operations at the Johns Hopkins University Applied Physics Laboratoryin Maryland through NASA’s Deep Space Network — ended a tense 21-hour waiting period.
The team deliberately suspended communications with New Horizons until it was beyond the Pluto system, so the spacecraft could focus solely on data gathering. With a mountain of information now queued up, it’s estimated it will take 16 months to get it all back home. As the precious morsels arrive bit by byte, New Horizons will sail deeper into the Kuiper Belt looking for new targets until it ultimately departs the Solar System.
After Pluto, NASA hopes to send New Horizons to another asteroid or two in the Kuiper Belt to perform a flyby and reconnaissance similar to the Pluto mission. Credit: Alex Parker / SwRI
Assuming NASA funds a continuing mission, the team hopes to direct the spacecraft to one or two additional Kuiper Belt objects (KBO) over the next five to seven years. There are presently three possible targets – PT1, PT2, and PT3. (PT = potential target). PT1, imaged by the Hubble Space Telescope, looks like the best option at the moment and could by reached by January 2019. If you thought Pluto was small, PT 1 is only about 25 miles (40 km) across. Much lies ahead.
The image at left shows a KBO at an estimated distance of approximately 4 billion miles from Earth. Its position noticeably shifts between exposures taken approximately 10 minutes apart. The image at right shows a second KBO at roughly a similar distance. Credit: NASA, ESA, SwRI, JHU/APL, and the New Horizons KBO Search Team
Graphic showing New Horizons' busy schedule before and during the flyby. Credit: NASA
Countdown to discovery! Not since Voyager 2’s flyby of Neptune in 1989 have we flung a probe into the frozen outskirts of the Solar System. Speeding along at 30,800 miles per hour New Horizons will pierce the Pluto system like a smartly aimed arrow.
Newest view of Pluto seen from New Horizons on July 11, 2015 shows a world that continues to grow more fascinating and look stranger every day. See annotated version below. Credits: NASA/JHUAPL/SWRIFor the first time on Pluto, this view reveals linear features that may be cliffs, as well as a circular feature that could be an impact crater. Rotating into view is the bright heart-shaped feature that will be seen in more detail during New Horizons’ closest approach on July 14. The annotated version includes a diagram indicating Pluto’s north pole, equator, and central meridian. Credits: NASA/JHUAPL/SWRI
Edging within 7,800 miles of its surface at 7:49 a.m. EDT, the spacecraft’s long-range telescopic camera will resolve features as small as 230 feet (70 meters). Fourteen minutes later, it will zip within 17,930 miles of Charon as well as image Pluto’s four smaller satellites — Hydra, Styx, Nix and Kerberos.
This image shows New Horizons’ current position (3 p.m. EDT July 12) along its planned Pluto flyby trajectory. The green segment of the line shows where New Horizons has traveled; the red indicates the spacecraft’s future path. The Pluto system is tilted on end because the planet’s axis is tipped 123° to the plane of its orbit. Credit: NASA/JHUAPL/SWRI
After zooming past, the craft will turn to photograph Pluto eclipsing the Sun as it looks for the faint glow of rings or dust sheets illuminated by backlight. At the same time, sunlight reflecting off Charon will faintly illuminate Pluto’s backside. What could be more romantic than Charonshine?
Six other science instruments will build thermal maps of the Pluto-Charon pair, measure the composition of the surface and atmosphere and observe Pluto’s interaction with the solar wind. All of this will happen autopilot. It has to. There’s just no time to send a change instructions because of the nearly 9-hour lag in round-trip communications between Earth and probe.
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 studies); 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
Want to go along for the ride? Download and install NASA’s interactive app Eyes on Pluto and then click the launch button on the website. You’ll be shown several options including a live view and preview. Click preview and sit back to watch the next few days of the mission unfold before your eyes.
American astronomer Clyde Tombaugh discovered Pluto in 1930 from Lowell Observatory. Tombaugh died in 1997, but an ounce of his ashes, affixed to the spacecraft in a 2-inch aluminum container. “Interned herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system’s ‘third zone.’ Adelle and Muron’s boy, Patricia’s husband, Annette and Alden’s father, astronomer, teacher, punster, and friend: Clyde Tombaugh (1906-1997)”
Like me, you’ve probably wondered how daylight on Pluto compares to that on Earth. From 3 billion miles away, the Sun’s too small to see as a disk with the naked eye but still wildly bright. With NASA’s Pluto Time, select your city on an interactive mapand get the time of day when the two are equal. For my city, daylight on Pluto equals the gentle light of early evening twilight six minutes after sunset. An ideal time for walking, but step lightly. In Pluto’s gentle gravity, you only weigh 1/15 as much as on Earth.
Pluto and its inclined orbit are highlighted among the hundreds of thousands of icy asteroids in the Kuiper Belt beyond Neptune. Credit: NASA
New Horizons is the first mission to the Kuiper Belt, a gigantic zone of icy bodies and mysterious small objects orbiting beyond Neptune. This region also is known as the “third” zone of our solar system, beyond the inner rocky planets and outer gas giants. Pluto is its most famous member, though not necessarily the largest. Eris, first observed in 2003, is nearly identical in size. It’s estimated there are hundreds of thousands of icy asteroids larger than 61 miles (100 km) across along with a trillion comets in the Belt, which begins at 30 a.u. (30 times Earth’s distance from the Sun) and reaches to 55 a.u.
During its fleeting flyby, New Horizons will slice across the Pluto system, turning this way and that to photograph and gather data on everything it can. Crucial occultations are shown that will be used to determine the structure and composition of Pluto’s (and possibly Charon’s) atmosphere. Sunlight reflected from Charon will also faintly illuminate Pluto’s backside. Credit: NASA with additions by the author
Below you’ll find a schedule of events in Eastern Time. (Subtract one hour for Central, 2 hours for Mountain and 3 hours for Pacific). Keep in mind the probe will be busy shooting photos and gathering data during the flyby, so we’ll have to wait until Wednesday July 15 to see the the detailed close ups of Pluto and its moons. Even then, New Horizons’ recorders will be so jammed with data and images, it’ll take months to beam it all back to Earth.
A new photo of Charon, too! Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon taken by New Horizons on July 11, 2015. The annotated version includes a diagram showing Charon’s north pole, equator, and central meridian, with the features highlighted. The prominent crater is about 60 miles (96 km) across; the chasms appear to be geological faults. Credits: NASA/JHUAPL/SWRI
Fasten your seat belts — we’re in for an exciting ride.
We’ll be reporting on results and sharing photos from the flyby here at Universe Today, but you’ll also want to check out NASA’s live coverage on NASA TV, its website and social media.
Monday, July 13
10:30 a.m. to noon – Media briefing on mission status and what to expect broadcast live on NASA TV
Tuesday, July 14
7:30 to 8 a.m. – Arrival at Pluto! Countdown program on NASA TV
At approximately 7:49 a.m., New Horizons is scheduled to be as close as the spacecraft will get to Pluto, approximately 7,800 miles (12,500 km) above the surface, after a journey of more than 9 years and 3 billion miles. For much of the day, New Horizons will be out of communication with mission control as it gathers data about Pluto and its moons.
The moment of closest approach will be marked during a live NASA TV broadcast that includes a countdown and discussion of what’s expected next as New Horizons makes its way past Pluto and potentially dangerous debris.
8 to 9 a.m. – Media briefing, image release on NASA TV
Wednesday, July 15
3 to 4 p.m. – Media Briefing: Seeing Pluto in a New Light; live on NASA TV and release of close-up images of Pluto’s surface and moons, along with initial science team reactions.
We’ll have the latest Pluto photos for you, but you can also check these excellent sites:
New Horizons scientists combined the latest black and white map of Pluto’s surface features (left) with a map of the planet’s colors (right) to produce a detailed color portrait of the planet’s northern hemisphere (center).
Credits: NASA/JHUAPL/SWRI
Hey, Mars, you’ve got company. Looks like there’s a second “red planet” in the Solar System — Pluto. Color images returned from NASA’s New Horizons spacecraft, now just 10 days from its encounter with the dwarf planet, show a distinctly ruddy surface with patchy markings that strongly resemble Mars’ appearance in a small telescope.
Animation of Pluto’s rotation from photos taken by New Horizons two weeks before the flyby. What are those four nearly parallel dark streaks? Credit: NASA/JHUAPL/SWRI
On Mars, iron oxide or rust colors the planet’s soil, while Pluto’s coloration is likely caused by hydrocarbon molecules called tholins that are formed when cosmic rays and solar ultraviolet light interact with methane in Pluto’s atmosphere and on its surface. Airborne tholins fall out of the atmosphere and coat the surface with a reddish gunk.
Scientists at Johns Hopkins University’s Hörst Laboratory have produced complex chemical compounds called tholins, which may give Pluto its reddish hue. Credits: Chao He, Xinting Yu, Sydney Riemer, and Sarah Hörst, Johns Hopkins University
A particular color or wavelength of UV light called Lyman-alpha is most effective at stimulating the chemical reactions that build hydrocarbons at Pluto. Recent measurements with New Horizons’ Alice instrument reveal the diffuse glow of Lyman-alpha light all around the dwarf planet coming from all directions of space, not just the Sun.
Since one of the main sources of Lyman-alpha light besides the Sun are regions of vigorous star formation in young galaxies, Pluto’s cosmetic rouge may originate in events happening millions of light years away.
Triton’s pink too! Montage of Neptune’s largest moon, Triton (1,683 miles in diameter) and the planet Neptune showing the moon’s sublimating south polar cap (bottom) and enigmatic “cantaloupe terrain”. Photo taken by Voyager 2 in 1989. Credit: NASA
“Pluto’s reddish color has been known for decades, but New Horizons is now allowing us to correlate the color of different places on the surface with their geology and soon, with their compositions,” said New Horizons principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado.
Tholins have been found on other bodies in the outer Solar System, including Titan and Triton, the largest moons of Saturn and Neptune, respectively, and made in laboratory experiments that simulate the atmospheres of those bodies.
True color photos showing the two hemispheres of Pluto photographed on June 27, 2015. At left, a large, dark red patch is visible. The four streaks in a row are seen at right. New Horizons will fly by the hemisphere in the left image. Credit: NASA/JHUAPL/SWRI
As you study the photos and animation, you’ll notice that Pluto’s largest dark spot is redder than the most of the surface; you also can’ help but wonder what’s going on with those four evenly-spaced dark streaks in the equatorial zone. When I first saw them, my reaction was “no way!” They look so neatly lined up I assumed it was an image artifact, but after seeing the rotating movie, maybe not. It’s more likely that low resolution enhances the appearance of alignment.
Dark streaks on Triton deposited downwind from ice or cryovolcanos. Credit: NASA
But what are they? Located as they are on the Charon-facing side of Pluto, they may be related to long-ago tidal stresses induced by each body on the other as they slowly settled into their current tidally-locked embrace or something as current as seasonal change.
Voyager 2 photographed cyrovolcanos at Triton during its 1989 flyby of the Neptune system. Nitrogen geysers and plumes of gas and ice as high as 5 miles (8 km) were seen erupting from active volcanoes, leaving dark streaks on its icy surface.
Images showing the increase in detail from late June through July 1 as New Horizons homes in on Pluto. That possible big crater (seen in bottom middle photo) now looks more like a large, dark patch, BUT we still don’t know for sure what it is. Credit: NASA / JHUAPL / SwRI / Björn JónssonIt’s instructive to compare these images, based on observations with the Hubble Space Telescope made well before New Horizons’s arrival, with current photos. They appear to record the large dark spot and possibly the multiple streaks. Credit: NASA/ESA
Seasonal heating from the Sun is the most likely cause for Triton’s eruptions; Pluto’s dark streaks may have a similar origin.
Animation of Pluto and Charon from images taken between June 23 and June 29. Credit: NASA/JHUAPL/SWRTo better picture in your head how big these small bodies really are, Pluto and Charon would both fit within the United States with room to spare. Credit: Laboratory for Atmospheric and Space Physics (LASP)
Today, New Horizons lies just 7.4 million miles (11.9 million km) from its target. Sharpness and detail visible will rapidly improve in just a few days.
“Even at this resolution, Pluto looks like no other world in our Solar System,” said mission scientist Marc Buie of the Southwest Research Institute, Boulder in a recent press release.
Eris is the largest dwarf planet in the Solar System, and the ninth largest body orbiting our Sun. Sometimes referred to as the “tenth planet”, it’s discovery is responsible for upsetting the traditional count of nine planets in our Solar System, as well as leading the way to the creation of a whole new astronomical category.
Located beyond the orbit of Pluto, this “dwarf planet” is both a trans-Neptunian object (TNO), which refers to any planetary object that orbits the Sun at a greater distance than Neptune – or 30 astronomical units (AU). Because of this distance, and the eccentricity of its orbit, it is also a member of a the population of objects (mostly comets) known as the “scattered disk”.
The discovery of Eris was so important because it was a celestial body larger than Pluto, which forced astronomers to consider, for the first time in history, what the definition of a planet truly is.
Discovery:
Eris, which has the full title of 136199 Eris, was first observed in 2003 during a Palomar Observatory survey of the outer solar system by a team led by Mike Brown, a professor of planetary astronomy at the California Institute of Technology. The discovery was confirmed in January 2005 after the team examined the pictures obtained from the survey in detail.
Classification:
At the time of it’s discovery, Brown and his colleagues believed that they had located the 10th planet of our solar system, since it was the first object in the Kuiper Belt found to be bigger than Pluto. Some astronomers agreed and liked the designation, but others objected since they claimed that Eris was not a true planet. At the time, the definition of “planet” was not a clear-cut since there had never been an official definition issued by the International Astronomical Union (IAU).
The matter was settled by the IAU in the summer of 2006. They defined a planet as an object that orbits the Sun, which is large enough to make itself roughly spherical. Additionally, it would have to be able to clear its neighborhood – meaning it has enough gravity to force any objects of similar size or that are not under its gravitational control out of its orbit.
In addition to finally defining what a planet is, the IAU also created a new category of “dwarf planets“. The only difference between a planet and a dwarf planet is that a dwarf planet has not cleared its neighborhood. Eris was assigned to this new category, and Pluto lost its status as a planet. Other celestial bodies, including Haumea, Ceres, and Makemake, have been classified as dwarf planets.
Artist’s impression shows the distant dwarf planet Eris, highlighting its bright surface. Credit: ESO
Naming:
Eris is named after the Greek goddess of strife and discord. The name was assigned on September 13th, 2006, following an unusually long consideration period that arose over the issue of classification. During this time, the object became known to the wider public as Xena, which was the name given to it by the discovery team.
The team had been saving this name, which was inspired by the title character of the television series Xena: Warrior Princess, for the first body they discovered that was larger than Pluto. They also chose it because it started with the letter X, a reference to Percival Lowell’s hunt for a planet he believed to exist the edge of the Solar System (which he referred to as “Planet X“).
According to fellow astronomer and science writer Govert Schilling, Brown initially wanted to call the object “Lila”. This name was inspired by a concept in Hindu mythology that described the cosmos as the outcome of a game played by Brahma, and also because it was similar to “Lilah” – the name of Brown’s newborn daughter.
Size and Orbit:
The actual size and mass of Eris has been the subject of debate, as official estimates have changed with time and subsequent viewing. In 2005, using images from the Hubble Space Telescope. the diameter of Eris was measured to be 2397 ± 100 km (1,489 miles). In 2007, a series of observations of the largest trans-Neptunian objects with the Spitzer Space Telescope estimated Eris’s diameter at 2600 (+400/-200) km (1616 miles).
A diagram showing solar system orbits. The highly tilted orbit of Eris is in red. Credit: NASA
The most recent observation took place in November of 2010, when Eris was the subject of one of the most distant stellar occultations yet achieved from Earth. The teams findings were announced on October 2011, and contradicted previous findings with an estimated diameter of 2326 ± 12 km (1445 miles).
Because of these differences, astronomers have been hard-pressed to maintain that Eris is more massive than Pluto. According to the latest estimates, the Solar System’s “ninth planet” has a diameter of 2368 km (1471 miles), placing it on par with Eris. Part of the difficulty in accurately assessing the planet’s size comes from interference from Pluto’s atmosphere. Astronomers expect a more accurate appraisal when the New Horizons space probe arrives at Pluto in July 2015.
Eris has an orbital period of 558 years. Its maximum possible distance from the Sun (aphelion) is 97.65 AU, and its closest (perihelion) is 37.91 AU. This means that Eris and its moon are currently the most distant known objects in the Solar System, apart from long-period comets and space probes.
Eris’s orbit is highly eccentric, and brings Eris to within 37.9 AU of the Sun, a typical perihelion for scattered objects. This is within the orbit of Pluto, but still safe from direct interaction with Neptune (29.8-30.4 AU). Unlike the eight planets, whose orbits all lie roughly in the same plane as the Earth’s, Eris’s orbit is highly inclined – the planet is tilted at an angle of about 44° to the ecliptic.
Moons:
Eris has one moon called Dysnomia, which is named after the daughter of Eris in Greek mythology, which was first observed on September 10th, 2005 – a few months after the discovery of Eris. The moon was spotted by a team using the Keck telescopes in Hawaii, who were busy carrying out observations of the four brightest TNOs (Pluto, Makemake, Haumea, and Eris) at the time.
Eris (center) and its moon of Dysnomia (left of center), taken by the Hubble Space Telescope. Credit: NASA/ESA/Mike Brown
Interesting Facts:
The dwarf planet is rather bright and can be detected using something as simple as a small telescope. Models of internal heating via radioactive decay suggest that Eris may be capable of sustaining an internal ocean of liquid water at the mantle-core boundary. These studies were conducted by Hauke Hussmann and colleagues from the Institute of Astronomy, Geophysics and AtmosphericSciences (IAG) at the University of SãoPaulo.
Brown and the discovery team followed up their initial identification of Eris with spectroscopic observations of the planet, which were made on January 25th, 2005. Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto and of Neptune’s moon Triton.
Due to Eris’s distant eccentric orbit, its surface temperature is estimated to vary between about 30 and 56 K (?243.2 and ?217.2 °C). This places it on par with Pluto’s surface temperature, which ranges from 33 to 55 K (-240.15 and -218.15 °C).
We have many interesting articles on planets here at Universe Today, including this article on What is the newest planet and the 10th planet.
If you are looking for more information, try Eris and NASA’s Solar System Exploration entry.
The presently known largest trans-Neptunian objects (TNO) - are likely to be surpassed by future discoveries. Which of these trans-Neptunian objects (TNO) would you call planets and which "dwarf planets"? (Illustration Credit: Larry McNish, Data: M.Brown)
The self-professed “Pluto Killer” is at it again. Dr. Michael Brown is now reminiscing about the good old days when one could scour through sky survey data and discover big bright objects in the Kuiper Belt. In his latest research paper, Brown and his team have concluded that those days are over.
Ten years ago, Brown discovered what is now known as the biggest Kuiper Belt object – Eris. Brown’s team found others that rivaled Pluto in size and altogether, these discoveries led to the demotion of Pluto to dwarf planet. Now, using yet another sky survey data set but with new computer software, Brown says that its time to move on.
Instigators of the big heist – Rabinowitz, Brown and Trujillo, left to right. The researchers co-discovered dozens of Kuiper Belt objects (KBO) including nine of the ten largest KBOs including the largest, Eris.
Like the famous Bugs Bunny cartoon, its no longer Rabbit Season or Duck Season and as Bugs exclaims to Elmer Fudd, there is no more bullets. Analyzing seven years worth of data, Brown and his team has concluded we are fresh out of Pluto or Charon-sized objects to be discovered in the Kuiper Belt. But for Dr. Brown, perhaps it now might be Oort Cloud season.
His latest paper, A Serendipitous All Sky Survey For Bright Objects In The Outer Solar System, in pre-print, describes the completion of analysis of two past sky surveys covering the northern and southern hemisphere down to 20 degrees in Galactic latitude. Using revised computer software, his team scoured through the data sets from the Catalina Sky Survey (CSS) and the Siding Spring Survey (SSS). The surveys are called “fast cadence surveys” and they primarily search for asteroids near Earth and out to the asteroid belt. Instead Brown’s team used the data to look at image frames spaced days and months apart.
Update: In a Twitter communique, Dr. Brown stated, “I would say we’re out of BRIGHT ones, not big ones. Could be big ones lurking far away!” His latest work involved a southern sky survey (SSS) to about magnitude 19 and the northern survey (CSS) to 21. Low albedo (dark) and more distant KBOs might be lurking beyond the detectability of these surveys that are in the range of Charon to Pluto in size.
Animation showing the movement of Eris on the images used to discover it. Eris is indicated by the arrow. The three frames were taken over a period of three hours. More images over several weeks were necessary to determine its orbit.(Credit: Brown, et al.)
Objects at Kuiper Belt distances move very slowly. For example, Pluto orbits the Sun at about 17,000 km/hr (11,000 mph), taking 250 years to complete one orbit. These are speeds that are insufficient to maintain ven a low-Earth orbit. Comparing two image frames spaced just hours apart will find nearby asteroids moving relative to the star fields but not Kuiper belt objects. So using image frames spaced days, weeks or even months apart, they searched again. Their conclusion is that all the big Kuiper belt objects have been found.
The only possibility of finding another large KBO lies in a search of the galactic plane which is difficult due to the density of Milky Way’s stars in the field of view. The vast number of small bodies in the Kuiper belt and Oort Cloud lends itself readily to statistical analysis. Brown states that there is a 32% chance of finding another Pluto-sized object hiding among the stars of the Milky Way.
Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)
Dr. Brown also released a blog story in celebration of the discovery of the largest of the Kuiper Belt objects, Eris, ten years ago last week. Ten years of Eris, reminisces about the great slew of small body discoveries by Dr. Brown, Dr. Chad Trujillo of Gemini Observatory and Dr. David Rabinowitz of Yale Observatory.
Brown encourages others to take up this final search right in the galactic plane but apparently his own intentions are to move on. What remains to be seen — that is, to be discovered — are hundreds of large “small” bodies residing in the much larger region of the Oort Cloud. These objects are distributed more uniformly throughout the whole spherical region that the Cloud defines around the Sun.
Furthermore, Dr. Brown maintains that there is a good likelihood that a Mars or Earth-sized object exists in the Oort Cloud.
Small bodies within our Solar System along with exo-planets are perhaps the hottest topics and focuses of study in Planetary Science at the moment. Many graduate students and seasoned researchers alike are gravitating to their study. There are certainly many smaller Kuiper belt objects remaining to be found but more importantly, a better understanding of their makeup and origin are yet to be revealed.
Artist’s concept of the Dawn spacecraft at the protoplanet Ceres Illustration of Dawn’s approach phase and RC3 orbit This artist’s concept of NASA’s Dawn spacecraft shows the craft orbiting high above Ceres, where the craft will arrive in early 2015 to begin science investigations. (Image credit: NASA/JPL-Caltech)
Presently, the Dawn spacecraft is making final approach to the dwarf planet Ceres in the Asteroid belt. The first close up images of Ceres are only a few days away as Dawn is now just a couple of 100 thousand miles away approaching at a modest speed. And much farther from our home planet, scientists led by Dr. Alan Stern of SWRI are on final approach to the dwarf planet Pluto with their space probe, New Horizons. The Pluto system is now touted as a binary dwarf planet. Pluto and its moon Charon orbit a common point (barycenter) in space that lies between Pluto and Charon.
So Dr. Brown and team exits stage left. No more dwarf planets – at least not soon and not in the Kuiper belt. Will that upstage what is being called the year of the Dwarf Planet?
But next up for close inspection for the first time are Ceres, Pluto and Charon. It should be a great year.
The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)
Two spacecraft, Dawn and New Horizon will reach their final objectives in 2015 - Dwarf Planets - Ceres and Pluto. (Credit: NASA, Illustration - T.Reyes)
Together, the space probes Dawn and New Horizons have been in flight for a collective 17 years. One remained close to home and the other departed to parts of the Solar System of which little is known. They now share a common destination in the same year: dwarf planets.
At the time of these NASA probes’ departures, Ceres had just lost its designation as the largest asteroid in our Solar System. Pluto was the ninth planet. Both probes now stand to deliver measures of new data and insight that could spearhead yet another revision of the definition of planet.
A comparison of the trajectories of New Horizons (left) and the Dawn missions (right). (Credit: NASA/JPL, SWRI, Composite- T.Reyes)
Certainly, NASA’s Year of the Dwarf Planet is an unofficial designation and NASA representatives would be quick to emphasize another dozen or more missions that are of importance during the year 2015. However, these two missions could determine the fate of billions or more small bodies just within our galaxy, the Milky Way.
If Ceres and Pluto are studied up close – mission success is never a sure thing – then what is observed could lead to a new, more certain and accepted definition of planet, dwarf planet, and possibly other new definitions.
The New Horizons mission became the first mission of NASA’s New Frontiers program, beginning development in 2001. The probe was launched on January 19, 2006, atop an Atlas V 551 (5 solid rocket boosters plus a third stage). Utilizing more compact and lightweight electronics than its predecessors to the outer planets – Pioneer 10 & 11, and Voyager 1 & 2 – the combination of reduced weight, a powerful launch vehicle, plus a gravity assist from Jupiter has lead to a nine year journey. On December 6, 2014, New Horizons was taken out of hibernation for the last time and now remains powered on until the Pluto encounter.
This “movie” of Pluto and its largest moon, Charon, by NASA’s New Horizons spacecraft taken in July 2014 clearly shows that the barycenter – the center of mass of the two bodies – resides outside (between) both bodies. The 12 images that make up the movie were taken by the spacecraft’s best telescopic camera – the Long Range Reconnaissance Imager (LORRI) – at distances ranging from about 267 million to 262 million miles (429 million to 422 million kilometers). Charon is orbiting approximately 11,200 miles (about 18,000 kilometers) above Pluto’s surface. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
The arrival date of New Horizon is July 14, 2015. A telescope called the Long Range Reconnaissance Imager (LORRI) has permitted the commencement of observations while still over 240 million kilometers (150 million miles) from Pluto. The first stellar-like images were taken while still in the Asteroid belt in 2006.
Pluto was once the ninth planet of the Solar System. From its discovery in 1930 by Clyde Tombaugh until 2006, it maintained this status. In that latter year, the International Astronomical Union undertook a debate and then a membership vote that redefined what a planet is. The change occurred 8 months after New Horizons’ launch. There were some upset mission scientists, foremost of which was the principal investigator, Dr. Alan Stern, from the Southwest Research Institute in San Antonio, Texas. In a sense, the rug had been pulled from under them.
A gentleman’s battle ensued between opposing protagonists Dr. Stern and Dr. Michael Brown from Caltech. In 2001, Dr. Brown’s research team began to discover Kuiper belt objects (Trans-Neptunian objects) that rivaled the size of Pluto. Pluto suddenly appeared to be one of many small bodies that could likely number in the trillions within just one galaxy – ours. According to Dr. Brown, there could be as many as 200 objects in our Solar System similar to Pluto that, under the old definition, could be defined as planets. Dr. Brown’s work was the straw that broke the camel’s back – that is, it led to the redefinition of planet, and the native of Huntsville, Alabama, went on to write a popular book, How I Killed Pluto and Why It Had It Coming.
Dr. Stern’s story involving Pluto and planetary research is a longer and more circuitous one. Stern was the Executive Director of the Southwest Research Institute’s Space Science and Engineering Division and then accepted the position of Associate Administrator of NASA’s Science Mission Directorate in 2007. Clearly, after a nine year journey, Stern is now fully committed to New Horizons’ close encounter. More descriptions of the two protagonists of the Pluto debate will be included in a follow on story.
Artist’s concept depicting the Dawn spacecraft thrusting with its ion propulsion system as it travels from Vesta (lower right) to Ceres (upper left). The galaxies in the background are part of the Virgo supercluster. Dawn, Vesta, and Ceres are currently in the constellation Virgo from the perspective of viewers on Earth. (Image credit: NASA/JPL)
The JPL and Orbital Science Corporation developed Dawn space probe began its journey to the main asteroid belt on September 27, 2007. It has used gravity assists and flew by the planet Mars. Dawn spent 14 months surveying Vesta, the 4th largest asteroid of the main belt (assuming Ceres is still considered the largest). While New Horizons has traveled over 30 Astronomical Units (A.U.) – 30 times the distance from the Earth to the Sun – Dawn has remained closer and required reaching a little over 2 A.U. to reach Vesta and now 3 A.U. to reach Ceres.
The Dawn mission had the clear objective of rendezvous and achieving orbit with two asteroids in the main belt between Mars and Jupiter. Dawn was also sent packing the next generation of Ion Propulsion. It has proven its effectiveness very well, having used ion propulsion for the first time to achieve an orbit. Pretty simple, right? Not so fast.
As Dawn was passing critical design reviews during development, the redefinition of planet lofted its second objective – the asteroid 1 Ceres – to a new status. While Pluto was demoted, Ceres was promoted from its scrappy status of biggest of the asteroids – the debris, the leftovers of our solar system’s development – to dwarf planet. Even 4 Vesta is now designated a proto-planet.
Artist rendition of Dawn spacecraft orbiting Vesta. (Credit: NASA/JPL-Caltech)
So now the stage is set. Dawn will arrive first at a dwarf planet – Ceres – in April. With a small, low gravity body and ion propulsion, the arrival is slow and cautious. If the two missions fair well and achieve their goals, 2015 is likely to become a pivotal year in the debate over the classification of non-stellar objects throughout the universe.
Just days ago, at the American Geophysical Union Conference in San Francisco, Dr. Stern and team described the status and more details of the goals of New Horizons. Since arriving, more moons of Pluto have been discovered. There is the potential that faint rings exist and Pluto may even harbor an interior ocean due to the tidal forces from its largest moon, Charon. And Dawn mission scientists have seen the prospects for Ceres’ change. Not just the status, the latest Hubble images of Ceres is showing bright spots which could be water ice deposits and could also harbor an internal ocean.
The Solar System is becoming a more crowded place. This picture shows the sizes of dwarf planets Pluto, Ceres, Eris, and Makemake as compared to Earth and Earth’s Moon, here called “Luna.” None of the distances between objects are to scale. (Credit: NASA)
So other NASA missions notwithstanding, this is the year of the dwarf planet. NASA will provide Humanity with its first close encounters with the most numerous of small round – by their self-gravity – bodies in the Universe. They are now called dwarf planets but ask Dr. Stern and company, the public, and many other planetary scientists and you will discover that the jury is still out.
Two potential targets for the New Horizons mission emerge in these Hubble Space Telescope multiple-exposure images. Both are about four billion miles (6.4 billion kilometers) away. NASA, ESA, SwRI, JHU/APL, and the New Horizons KBO Search Team
Where could New Horizons visit after it flies by Pluto next year? NASA’s Hubble Space Telescope is on the case. In a program that pushed the limits of the 24-year-old observatory, Hubble found three potential Kuiper Belt Objects for the spacecraft to visit.
The wrinkle is there is no money approved yet for New Horizons to do an extended mission yet, but team members (including Alex Parker from the Southwest Research Institute, who is quoted from Twitter below) are celebrating the milestone. To them, the most promising target (PT1) is the one on the left of the images you see above. Read more about it below the jump.
The Kuiper Belt is a zone of icy objects about four billion miles (6.4 billion kilometers) from the Sun, considered to be leftovers of the building blocks that put together the Solar System billions of years ago. It’s an area that Pluto itself drifts through from time to time on its elliptical orbit around the Sun. Roughly 1,000 objects there have been cataloged, although many more are believed to exist.
The team used Hubble from June 16 to 26 in a test program to look at 20 sky zones for evidence of KBOs, finding two that had never been spotted before by ground-based telescopes. More searching between July and September revealed one object that is “definitely reachable”, NASA stated, and two others that require more scrutiny.
We estimate that PT1 is several 10s of kilometers across. Here’s what that looks like next to Cape Cod and #Comet67P: pic.twitter.com/IHUx6uymO7
Here is where PT1 lies in relation to the rest of the solar system. The yellow path is New Horizons’ trajectory. pic.twitter.com/4aQDEj8oPZ — Alex Parker (@Alex_Parker) October 15, 2014
Here is a gif of the Hubble Space Telescope discovery images of our New Horizons-targetable Kuiper Belt Object PT1. http://t.co/ifw8I4a8Wz
An important and sobering note: even though New Horizons can reach this Kuiper Belt Object, there is no guarantee of an extended mission. — Alex Parker (@Alex_Parker) October 15, 2014
Each of the three candidates would take a while to reach, as they are all about one billion miles (1.6 billion km) beyond Pluto. They’re also tiny, with two estimated at 34 miles (55 kilometers) across and the third at 15 miles (25 kilometers). This makes them 10 times bigger than the average comet, but only 1-2% the size of small Pluto.
“This was a needle-in-haystack search for the New Horizons team because the elusive KBOs are extremely small, faint, and difficult to pick out against a myriad background of stars in the constellation Sagittarius, which is in the present direction of Pluto,” NASA wrote in a press release.
New Horizons’ team plans to ask for the extended mission in late 2016. Meanwhile, the spacecraft (which has been flying ever outwards since 2006) will finally zoom past its main target of Pluto in July 2015.
Artist's conception of the New Horizons spacecraft flying past Pluto and Charon, one of the dwarf planet's moons. Credit: Johns Hopkins University/APL
Here’s Hydra! The New Horizons team spotted the tiny moon of Pluto in July, about six months ahead of when they expected to. You can check it out in the images below. The find is exciting in itself, but it also bodes well for the spacecraft’s search for orbital debris to prepare for its close encounter with the system in July 2015.
Most of Pluto’s moons were discovered while New Horizons was under development, or already on its way. Mission planners are thus concerned that there could be moons out there that aren’t discovered yet — moons that could pose a danger to the spacecraft if it ended up in the wrong spot at the wrong time. That’s why the team is engaging in long-range views to see what else is lurking in Pluto’s vicinity.
“We’re thrilled to see it, because it shows that our satellite-search techniques work, and that our camera is operating superbly. But it’s also exciting just to see a third member of the Pluto system come into view, as proof that we’re almost there,” stated science team member John Spencer, of the Southwest Research Institute.
Watch the difference: Pluto’s moon Hydra stands out in these images taken by the New Horizons spacecraft on July 18 and 20, 2014. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Hydra was spotted using the spacecraft’s Long Range Reconnaissance Imager (LORRI), which took 48 images of 10 seconds apiece between July 18 and July 20. Then the team used half the images, the ones that show Hydra better, to create the images you see above.
The spacecraft was still 267 million miles (430 million kilometers) from Pluto when the images were taken. Another moon discovered around the same time as Hydra — Nix — is still too close to be seen given it’s so close to Pluto, but just wait.
Meanwhile, scientists are busily trying to figure out where to send New Horizons after Pluto. In July, researchers using the Hubble Space Telescope began a full-scale search for a suitable Kuiper Belt Object, which would be one of trillions of icy or rocky objects beyond Neptune’s orbit. Flying past a KBO would provide more clues as to how the Solar System formed, since these objects are considered leftovers of the chunks of matter that came together to form the planets.
Artist's impression of the New Horizons spacecraft. Image Credit: NASA
After almost nine years on the road, New Horizons is in what NASA calls “Pluto-space”! Earlier today (July 7), the spacecraft Twitter account announced New Horizons is now 29.8 Earth-sun distances (astronomical units) away from the Sun, putting it within the boundaries of Pluto’s eccentric orbit — exciting, since Pluto is the primary science target.
“Didn’t get the word? We’re farther out than Pluto’s minimum distance to the Sun. We’re in ‘Pluto-space’ now!” tweeted the New Horizons account. We’ve included some of the best Pluto pictures below, to date, to celebrate.
And while many are focused on the Pluto encounter itself, NASA is already planning for what to do next for the spacecraft. In mid-June, we reported that the Hubble Space Telescope was doing a test search for icy Kuiper Belt objects that New Horizons could possibly fly to next.
That test search was successful enough, with two objects found, that Hubble is now doing a full-blown investigation, according to an announcement last week. Hubble will begin that work in July and conclude observations in August. New Horizons is expected to fly by Pluto and its moons in July 2015.
Pluto’s surface as viewed from the Hubble Space Telescope in several pictures taken in 2002 and 2003. Though the telescope is a powerful tool, the dwarf planet is so small that it is difficult to resolve its surface. Astronomers noted a bright spot (180 degrees) with an unusual abundance of carbon monoxide frost. Credit: NASAPluto and its moons, most of which were discovered while New Horizons was in development and en route. Charon was found in 1978, Nix and Hydra in 2005, Kerberos in 2011 and Styx in 2012. The New Horizons mission launched in 2006. Picture taken by the Hubble Space Telescope. Credit: NASAPluto and moons Charon, Hydra and Nix (left) compared to the dwarf planet Eris and its moon Dysnomia (right). This picture was taken before Kerberos and Styx were discovered in 2011 and 2012, respectively. Credit: International Astronomical UnionPluto appears as a faint white dot (see arrow) in this image taken by New Horizons in September 2006, nine months after launch. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research InstitutePluto and Charon are visible in this 2013 image from New Horizons’ LOng Range Reconnaissance Imager (LORRI). It was the first image from the spacecraft showing Charon separated from Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Distribution of Kuiper belt objects (green), along with various other outer Solar System bodies, based on data from the Minor Planet Center. [Credit: Minor Planet Center; Murray and Dermott]
The Kuiper belt — the region beyond the orbit of Neptune inhabited by a number of small bodies of rock and ice — hides many clues about the early days of the Solar System. According to the standard picture of Solar System formation, many planetesimals were born in the chaotic region where the giant planets now reside. Some were thrown out beyond the orbit of Neptune, while others stayed put in the form of Trojan asteroids (which orbit in the same trajectory as Jupiter and other planets). This is called the Nice model.
However, not all Kuiper belt objects (KBOs) play nicely with the Nice model.
(I should point out that the model is named named for the city in France and therefore pronounced “neese”.) A new study of large scale surveys of KBOs revealed that those with nearly circular orbits lying roughly in the same plane as the orbits of the major planets don’t fit the Nice model, while those with irregular orbits do. It’s a puzzling anomaly, one with no immediate resolution, but it hints that we need to refine our Solar System formation models.
This new study is described in a recently released paper by Wesley Fraser, Mike Brown, Alessandro Morbidelli, Alex Parker, and Konstantin Baygin (to be published in the Astrophysical Journal, available online). These researchers combined data from seven different surveys of KBOs to determine roughly how many of each size of object are in the Solar System, which in turn is a good gauge of the environment in which they formed.
The difference between this and previous studies is the use of absolute magnitudes — a measure of how bright an object really is — as opposed to their apparent magnitudes, which are simply how bright an object appears. The two types of magnitude are related by the distance an object is from Earth, so the observational challenge comes down to accurate distance measurements. Absolute magnitude is also related to the size of an KBO and its albedo (how much light it reflects), both important physical quantities for understanding formation and composition.
Finding the absolute magnitudes for KBOs is more challenging than apparent magnitudes for obvious reasons: these are small objects, often not resolved as anything other than points of light in a telescope. That means requires measuring the distance to each KBO as accurately as possible. As the authors of the study point out, even small errors in distance measurements can have a large effect on the estimated absolute magnitude.
The bodies in the Kuiper Belt. Credit: Don Dixon
In terms of orbits, KBOs fall into two categories: “hot” and “cold”, confusing terms having nothing to do with temperature. The “cold” KBOs are those with nearly circular orbits (low eccentricity, in mathematical terms) and low inclinations, meaning their trajectories lie nearly in the ecliptic plane, where the eight canonical planets also orbit. In other words, these objects have nearly planet-like orbits. The “hot” KBOs have elongated orbits and higher inclinations, behavior more akin to comets.
The authors of the new study found that the hot KBOs have the same distribution of sizes as the Trojan asteroids, meaning there are the same relative number of small, medium, and large KBOs and similarly sized Trojans. That hints at a probable common origin in the early days of the Solar System. This is in line with the Nice model, which predicts that, as they migrated into their current orbits, the giant planets kicked many planetesimals out beyond Neptune.
However, the cold KBOs don’t match that pattern at all: there are fewer large KBOs relative to smaller objects. To make matters more strange, both hot and cold seem to follow the same pattern for the smaller bodies, only deviating at larger masses, which is at odds with expectations if the cold KBOs formed where they orbit today.
To put it another way, the Nice model as it stands could explain the hot KBOs and Trojans, but not the cold. That doesn’t mean all is lost, of course. The Nice model seems to do very well except for a few nagging problems, so it’s unlikely that it’s completely wrong. As we’ve learned from studying exoplanet systems, planet formation models are a work in progress — and astronomers are an ingenious lot.
