Artist’s impression shows the distant dwarf planet Eris. Credit: ESO
In 2005, astronomer Mike Brown and his colleagues Chad Trujillo and David Rabinowitz announced the discovery of a previously unknown planetoid in the Kuiper Belt beyond Neptune’s orbit. The team named this object Eris after the Greek personification of strife and discord, which was assigned by the IAU a year later. Along with Haumea and Makemake, which they similarly observed in 2004 and 2005 (respectively), this object led to the “Great Planet Debate,” which continues to this day. Meanwhile, astronomers have continued to study the Trans-Neptunian region to learn more about these objects.
While subsequent observations have allowed astronomers to get a better idea of Eris’ size and mass, there are many unresolved questions about the structure of this “dwarf planet” and how it compares to Pluto. In a recent study, Mike Brown and University of California Santa Cruz professor Francis Nimmo presented a series of models based on new mass estimates for Eris’ moon Dysnomia. According to their results, Eris is likely differentiated into a convecting icy shell and rocky core, which sets it apart from Pluto’s conductive shell.
This artist’s impression shows the dwarf planet Quaoar and its ring. Quaoar’s moon Weywot is shown on the left. Quaoar’s ring was discovered through a series of observations that took place between 2018 to 2021. Image Credit: http://www.esa.int/spaceinvideos/Terms_and_Conditions
Quaoar is one of about 3,000 dwarf planets in our Solar System’s Kuiper Belt. Astronomers discovered it in 2002. It’s only half as large as Pluto, about 1,121 km (697 mi) in diameter. Quaoar has a tiny moon named Weywot, and the planet and its moon are very difficult to observe in detail.
Astronomers took advantage of an occultation to study the dwarf planet Quaoar and found that it has something unexpected: a ring where a moon should be.
There’s still a raging debate in some circles as to whether Pluto should be a planet or not. Ask an astronomer, and their typical answer would be something like – if Pluto is a planet, then there are plenty of other bodies out there in the solar system that should be considered one too. One of those is Haumea, a little explored rock in the Kuiper belt that is one of the strangest large objects out there. Now, a team from NASA has a new idea as to how it got that way.
A new and thorough analysis of high-resolution images and data from NASA’s Dawn mission have now provided fresh insights into the dwarf planet Ceres, with intriguing evidence that Ceres has a global subsurface salty ocean, and has been geologically active in the recent past.
An artful image of dwarf planet Vesta, with an image of micrometeorite overlaid. Image Credit: Ogliore Lab
One of the most enduring questions about Earth regards the origins of its water. Where did it come from? One widely-held theory gives comets the honor of bringing water to Earth. Another one says that Earth’s water came when a protoplanet crashed into early Earth, not only delivering a vast quantity of water, but creating the Moon.
Now a new study shows that the minor planet Vesta got its water from space dust. Could that help explain the origin of Earth’s water?
This is an artist's concept of a craggy piece of Solar System debris that belongs to a class of bodies called trans-Neptunian objects (TNOs).Credit: NASA, ESA, and G. Bacon (STScI)
Hey Pluto, Sedna, Haumea, Makemake Et al.: You’ve got company!
While searching for distant galaxies and supernovae, the Dark Energy Survey’s powerful 570-megapixel digital camera spotted a few other moving “dots” in its field of view. Turns out, the DES has found more than 100 previously unknown trans-Neptunian objects (TNOs), minor planets located in Kuiper Belt of our Solar System.
A new paper describes how the researchers connected the moving dots to find the new TNOs, and also says this new approach could help look for the hypothetical Planet Nine and other undiscovered worlds.
Guess you never know what you’ll find once you start looking!
A new SPHERE/VLT image of Hygiea, which could be the Solar System’s smallest dwarf planet yet. As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighbourhood around its orbit. The final requirement is that it have enough mass that its own gravity pulls it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.
Within the Main Asteroid Belt, there are a number of larger bodies that have defied traditional classification. The largest among them is Ceres, which is followed by Vesta, Pallas, and Hygeia. Until recently, Ceres was thought to be the only object in the Main Belt large enough to undergo hydrostatic equilibrium – where an object is sufficiently massive that its gravity causes it to collapse into a roughly spherical shape.
However, it now seems that there is another body in the Main Belt that has earned the designation of “dwarf planet”. Using data from the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT), an international team of astronomers found compelling evidence that Hygeia is actually round, making it the smallest dwarf planet in the Solar System.
Artist concept of Haumea, with the correct proportions of the main body and the ring. The ring is at a distance of 2287 kilometers from the center of the main body and is darker than the surface of the dwarf planet itself. Credit: Instituto de Astrofísica de Andalucía.
A unique opportunity to study the dwarf planet Haumea has led to an intriguing discovery: Haumea is surrounded by a ring.
Add this to the already long list of unique things about the weird-shaped world with a dizzying rotation and a controversial discovery.
On January 21, 2017 Haumea passed in front of a distant star, in an event known as an occultation. The background star can – pardon the pun – shine a light on the object passing in front, providing information about a distant object — such as size, shape, and density — that is otherwise difficult to obtain. Since an occultation with Haumea had never been observed before, scientists were first eager, and then surprised.
“One of the most interesting and unexpected findings was the discovery of a ring around Haumea,” said said Pablo Santos-Sanz, from the Institute of Astrophysics of Andalusia (IAA-CSIC) in a statement.
This is the first time a ring has been discovered around a trans-neptunian object, and the team said this discovery shows that the presence of rings could be much more common than was previously thought, in our Solar System as well as in other planetary systems.
“Twelve telescopes from ten different European observatories converged on the phenomenon,” said José Luis Ortiz, who led the observational effort, and is also from IAA-CSIC. “This deployment of technical means allowed us to reconstruct with a very high precision the shape and size of dwarf planet Haumea, and discover to our surprise that it is considerably bigger and less reflecting than was previously believed. It is also much less dense than previously thought, which answered questions that had been pending about the object.”
The team said their data shows that the egg-shaped Haumea measures 2,320 kilometers in its largest axis. Previous estimates from various observations put the size at roughly 1,400 km. It takes 3.9 hours for Haumea rotate around its axis, much less than any other body in the Solar System that measures more than a hundred kilometers long. This rotational speed likely caused Haumea to flatten out, giving it an ellipsoid shape. It orbits the Sun in an elliptical loop that takes 284 years to complete. Additionally Haumea has two small moons.
Artist’s impression of the dwarf planet Haumea and its moons, Hi’aka and Namaka. Credit: NASA
Ortiz and team say their data shows the newly discovered ring lies on the equatorial plane of the dwarf planet, and it “displays a 3:1 resonance with respect to the rotation of Haumea, which means that the frozen particles which compose the ring rotate three times slower around the planet than it rotates around its own axis.”
Ortiz says there might be a few possible explanations for the formation of the ring; it may have originated in a collision with another object, or in the dispersal of surface material due to the planet’s high rotational speed.
Of course, other objects in our Solar System have rings: all the giant planets have rings, with Saturn’s being the most massive and well know. But small centaur asteroids located between Jupiter and Neptune were found to have rings, too.
“Now we have discovered that bodies even farther away than the centaurs, bigger and with very different general characteristics, can also have rings,” said Santos-Sanz.
You may recall there was great controversy over the discovery of Haumea. The discovery was originally announced in 2005 by Mike Brown from Caltech, along with his colleagues Chad Trujillo of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of Yale University.
But then Ortiz and Santos-Sanz attempted to scoop Brown et. al by sending in their claim to discovery to the Minor Planet Center before Brown’s paper was published. It was later learned that Ortiz and colleagues had accessed the Caltech observing logs remotely, looking at when and where Brown was looking with his telescopes. Ortiz and team initially denied the claims, but later conceded accessing the observation logs, maintaining they were just verifying whether they had discovered a new object in observations from 2003.
I asked Brown today if anything was ever officially resolved about the controversy.
“I think the resolution is that it is generally accepted that they stole our positions, but no one wants to think about it anymore,” he said via email.
But the discovery of a ring Haumea, Brown said, looks solid.
“I will admit to being wary of anything Ortiz says, so I checked the data very carefully,” Brown said. “Even I have to agree that the detection looks pretty solid. Haumea is weird, so it’s less surprising than, say, finding rings around something like Makemake. But, still, this was not something I was expecting!”
Ahuna Mons towers over the Cerean landscape in this photo taken by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI
Whoa – what a sight! Ceres’ lonely mountain, Ahuna Mons, is seen in this simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission in August from an altitude of 240 miles (385 km) in August 2016. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI
An isolated 3-mile-high (5 km) mountain Ahuna Mons on Ceres is likely volcanic in origin, and the dwarf planet may have a weak, temporary atmosphere. These are just two of many new insights about Ceres from NASA’s Dawn mission published this week in six papers in the journal Science.
Ahuna Mons is seen in this mosaic of images from NASA’s Dawn spacecraft. On its steepest side, this mountain is about 3 miles (5 km) high. Its average overall height is 2.5 miles (4 km). The diameter of the mountain is about 12 miles (20 km). Dawn took these images from its low-altitude mapping orbit, 240 miles (385 kilometers) above the surface, in December 2015. Credits: NASA/JPL/Dawn mission
“Dawn has revealed that Ceres is a diverse world that clearly had geological activity in its recent past,” said Chris Russell, principal investigator of the Dawn mission, based at the University of California, Los Angeles.
The Ahuna Mons dome compared to a dome in Russia. The similarity in appearance is striking though the difference in size is large. Credit: NASA
Ahuna Mons is a volcanic dome similar to earthly and lunar volcanic domes but unique in the solar system, according to a new analysis led by Ottaviano Ruesch of NASA’s Goddard Space Flight Center and the Universities Space Research Association. While those on Earth erupt with molten rock, Ceres’ grandest peak likely formed as a salty-mud volcano. Instead of molten rock, salty-mud volcanoes, or “cryovolcanoes,” release frigid, salty water sometimes mixed with mud.
Learn more about Ahuna Mons
“This is the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past,” Ruesch said. Estimates place the mountain formation within the past billion years.
Dawn may also have detected a weak, temporary atmosphere; the probe’s gamma ray and neutron (GRaND) detector observed evidence that Ceres had accelerated electrons from the solar wind to very high energies over a period of about six days. In theory, the interaction between the solar wind’s energetic particles and atmospheric molecules could explain the GRaND observations.
Dwarf planet Ceres is located in the asteroid belt, between the orbits of Mars and Jupiter. Observations by ESA’s Herschel Space Observatory between 2011 and 2013 found that the dwarf planet has a thin water-vapor atmosphere, the first detection ever of water vapor around an asteroid in the asteroid belt. Copyright ESA/ATG medialab/Küppers et al.
A temporary atmosphere would confirm the water vapor the Herschel Space Observatory detected at Ceres in 2012-2013. The electrons that GRaND detected could have been produced by the solar wind hitting the water molecules that Herschel observed, but scientists are also looking into alternative explanations.
While Ahuna Mons may have erupted liquid water in the not-too-distant past, Dawn found probable water ice right now in the mid-latitude Oxo Crater using its visible and infrared mapping spectrometer (VIR).
The small, bright crater Oxo (6 miles / 10 km wide) on Ceres is seen in this perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Dawn’s visible and infrared mapping spectrometer (VIR) has found evidence of water ice at this crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Exposed water-ice is rare on the dwarf planet, but the low density of Ceres — 2.08 grams/cm3 vs. 5.5 for Earth — the impact-generated ice detection and the the existence of Ahuna Mons suggest that Ceres’ crust does contain a significant amount of water ice.
Impact craters are clearly the most abundant geological feature on Ceres, and their different shapes help tell the complex story of Ceres’ past. Craters that are roughly polygonal — shapes bounded by straight lines — hint that Ceres’ crust is heavily fractured. In addition, several Cerean craters display fractures on their floors. There are craters with flow-like features. Bright areas are peppered across Ceres, with the most reflective ones in Occator Crater. Some crater shapes could indicate water-ice in the subsurface.
In this illustration, a mud slurry rises up through Ceres’ crust to build a dome like Ahuna Mons. Click to see the animation. Credit: Goddard Media Studios
All these crater forms imply an outer shell for Ceres that is not purely ice or rock, but rather a mixture of both. Scientists also calculated the ratio of various craters’ depths to diameters, and found that some amount of crater relaxation must have occurred as icy walls gradually slump.
“The uneven distribution of craters indicates that the crust is not uniform, and that Ceres has gone through a complex geological evolution,” Hiesinger said.
The rim of Hamori Crater on Ceres is seen in the upper left portion of this image, which was taken by NASA’s Dawn spacecraft. Clay is found at many locations on the dwarf planet. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Ceres’ crust also appears loaded with clay-forming minerals called phyllosilicates. These phyllosilicates are rich in magnesium and also have some ammonium embedded in their crystalline structure. Their distribution throughout the dwarf planet’s crust indicates Ceres’ surface material has been altered by a global process involving water.
Now in its extended mission, the Dawn spacecraft has been increasing its altitude since Sept. 2 as scientists stand back once again for a broader look at Ceres under different lighting conditions now compared to earlier in the mission.
2015 RR245's orbit takes it 120 times further from the Sun than the Earth is. Image: OSSOS/Alex Parker
A new dwarf planet has been discovered beyond Neptune, in the disk of small icy worlds that resides there. The planet was discovered by an international team of astronomers as part of the Outer Solar Systems Origins Survey (OSSOS). The instrument that found it was the Canada-France Hawaii Telescope at Maunakea, Hawaii.
The planet is about 700 km in size, and has been given the name 2015 RR245. It was first sighted by Dr. JJ Kavelaars, of the National Research Council of Canada, in images taken in 2015. Dwarf planets are notoriously difficult to spot, but they’re important pieces of the puzzle in tracing the evolution of our Solar System.
Dr. Michele Bannister, of the University of Victoria in British Columbia, describes the moment when the planet was discovered: “There it was on the screen— this dot of light moving so slowly that it had to be at least twice as far as Neptune from the Sun.”
These images show 3 hours of RR245’s movement. Image: OSSOS
“The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the Sun. They let us piece together the history of our Solar System. But almost all of these icy worlds are painfully small and faint: it’s really exciting to find one that’s large and bright enough that we can study it in detail.” said Bannister.
As the New Horizons mission has shown us, these far-flung, cold bodies can have exotic features in their geological landscapes. Where once Pluto, king of the dwarf planets, was thought to be a frozen body locked in time, New Horizons revealed it to be a much more dynamic place. The same may be true of RR245, but for now, not much is known about it.
The 700 km size number is really just a guess at this point. More measurements will need to be taken of its surface properties to verify its size. “It’s either small and shiny, or large and dull.” said Bannister.
As our Solar System evolved, most dwarf planets like RR245 were destroyed in collisions, or else flung out into deep space by gravitational interactions as the gas giants migrated to their current positions. RR245 is one of the few that have survived. It now spends its time the same way other dwarf planets like Pluto and Eris do, among the tens of thousands of small bodies that orbit the sun beyond Neptune.
RR245 has not been observed for long, so much of what’s known about its orbit will be refined by further observation. But at this point it appears to have a 700 year orbit around the Sun. And it looks like for at least the last 100 million years it has travelled its current, highly elliptical orbit. For hundreds of years, it has been further than 12 billion km (80 AU)from the Sun, but by 2096 it should come within 5 billion km (34 AU) of the Sun.
The discovery of RR 245 came as a bit of a surprise to the OSSOS team, as that’s not their primary role. “OSSOS was designed to map the orbital structure of the outer Solar System to decipher its history,” said Prof. Brett Gladman of the University of British Columbia in Vancouver. “While not designed to efficiently detect dwarf planets, we’re delighted to have found one on such an interesting orbit”.
OSSOS has discovered over 500 hundred trans-Neptunian objects, but this is the first dwarf planet it’s found. “OSSOS is only possible due to the exceptional observing capabilities of the Canada-France-Hawaii Telescope. CFHT is located at one of the best optical observing locations on Earth, is equipped with an enormous wide-field imager, and can quickly adapt its observing each night to new discoveries we make. This facility is truly world leading.” said Gladman.
If RR 245’s diameter is conclusively measured as 700 km, it will be smaller than the dwarf planet Ceres, which is 945 km in diameter. Image courtesy of NASA.
A lot of work has been done to find dwarf planets in the far reaches of our Solar System. It may be that RR 245 is the last one we find. If there are any more out there, they may have to wait until larger and more powerful telescopes become available. In the mid-2020’s, the Large Synoptic Survey Telescope (LSST) will come on-line in Chile. That ‘scope features a 3200 megapixel camera, and each image it captures will be the size of 40 full Moons. It’ll be hard for any remaining dwarf planets to hide from that kind of imaging power.
As for RR 245’s rather uninspiring name, it will have to do for a while. But as the discoverers of the new dwarf planet, the OSSOS team will get to submit their preferred name for the planet. After that, it’s up the International Astronomical Union (IAU) to settle on one.
What do you think? If this is indeed the last dwarf planet to be found in our Solar System what should we call it?
