What is a Butte?

What is a Butte?

During the 16h century, Spanish explorers ventured north from Mexico looking for gold and the legendary “Seven cities of Cibola”. What they found instead were some of the most amazing natural formations in the world, which are today known as “buttes”. To the local Hopi, Navajo, and other indigenous nations, these features – which resemble tall, isolated plateaus – have been regarded as sacred sites since time immemorial.

By the beginning of the 19th century, the term “butte” entered common parlance and quickly became adopted by the geological community. And while their existence was something of a mystery for thousands of years, spawning mythological connections and folk tales, improvements in the fields of Earth sciences and geology have led scientists to understand what these features are and how they are formed.


By definition, a Butte is a conspicuous isolated hill with steep, often vertical sides and a small, relatively flat top. The word “butte” comes from a French word meaning “small hill”. They are not to be confused with Mesas or Plateaus, which are typically differentiated based on the fact that their top surfaces are larger than their vertical faces, while a butte is taller than it is wide. However, definitions of the surface areas of mesas and buttes vary.

The Courthouse Butte, located near the town of Sedona, Arizona. Credit: Wikipedia Commons

One source states that a mesa has a surface area of less than 10 square kilometers, while a butte has a surface area less than 1,000 square meters. Another source states that the surface area of a mesa is larger than 2.59 square kilometers. However, all sides are in agreement that is the difference between their vertical and horizontal measurements that are key.


Both buttes and mesas are formed by the same geological process, which involves the physical weathering of rock formations. Essentially, this involves the surface material of a hill or mountain (the cap rock) resists wind and water erosion, but the underlying materials do not. Over time, the underlying material is stripping away, leaving an isolated, standing feature with a flat top.

The top layer of a butte is a hardened layer of rock that is resistant to erosion. This top layer, called the cap rock, is usually composed of sedimentary rock, but sometimes is the remains of cooled and hardened lava that had spread out across the landscape in repeated flows from fissures or cracks in the ground.

Beneath this flat, protective cap of rock, horizontal layers of softer sedimentary rock are found. To varying degrees, these layers are not as resistant to wind and water erosion. As a result, when the softer rock is stripped away, a standing, isolated rock is left behind. Typically, buttes are found in arid and semiarid regions.

Merrick’s Butte, in Monument Valley, Utah. Credit: Wikipedia Commons/Ernst Brötz

Because water evaporates quickly in these normally dry environments, plants and other ground cover are scarce. Left exposed to the action of running water, the bare sides of the softer rock layers of buttes are eroded away over time. The base of these landforms is often gently sloped, contrasting with the almost-vertical sides leading down from the top. Rock material that has been eroded from the sides is carried downward, forming this sloping base.

Notable Buttes:

Because of their isolated and imposing nature, many buttes have become geographical land markers and major tourist destinations. They also figured prominently in the spiritual beliefs and creation myths of the indigenous peoples across North America. Buttes can be found all over North America, though they are most commonly found in the arid regions of the American Southwest.

For example, there is the Courthouse Butte, a prominent feature located just north of the Village of Oak Creek, and south of the town of Sedona in Yavapai County. Then there’s the Elephant Butte, which is located in the Elephant Butte Lake State Park in Sierra Country, New Mexico,. This geographical feature is so-named because of the combination of a vertical side and a sloping side, which resemble the shape of an elephant.

Bear Butte in South Dakota also has a long history of being a geological and cultural significant feature. Long before the arrival of European settlers, Bear Butte featured prominently in the religious and mythological traditions of the Lakota, Sioux and Cheyenne nations. To the Lakota and Sioux, the feature was known as “Matho Paha” (literally, Bear Mountain), while the Cheyenne referred to it as Nahkohe-vose (“bear hill”).

Bear Butte (aka. Bear Mountain or Bear Hill),, located in South Dakota. Credit: Jerrye & Roy Klotz, MD.

According to Cheyenne mythology, it was here that Ma’heo’o (God, or the Great Spirit) imparted the knowledge from which the Cheyenne base their religion, political, social and economic customs to the prophet Sweet Medicine. Today, the location remains a sacred site for many indigenous peoples, who make pilgrimages to leave prayer cloths and tobacco bundles tied to branches taken from the trees that surround the butte.

To the north, buttes can be found in the Canadian provinces of Saskatchewan, Alberta and British Columbia, in regions that are arid and semi-arid. For example, there is the Pilot Butte, which is located in southern Saskatchewan, near the town of the same name. This feature’s name is derived from the fact that the flat-topped butte served as a lookout for hunting buffalo and as a landmark for planes approaching the provincial capitol of Regina.

And there’s Lone Butte, a prehistoric basalt feature located in the southern Cariboo Plateau in central British Columbia. A part of the geological formation known as the Chilcotin Group, this feature was formed roughly six million years ago as a result of the extensive volcanic activity in the region.

Buttes on Other Planets:

Buttes have also been spotted on other planets in the Solar System, where they are also linked to geological activity and erosion. For example, NASA’s Curiosity rover mission has taken extensive images of the area currently known as the “Murray Buttes” region on Mars, which is located in the lower region of Mount Sharp (in the Gale Crater). In addition, Curiosity has taken drill samples from the surface rock in the region.

Wide-angle mosaic of a butte with sandstone layers showing cross-bedding, in the Murray Buttes region on lower Mount Sharp. Credit: NASA/JPL/MSSS/Ken Kremer/Marco Di Lorenzo

At one time, this crater was believed to be a standing body of water, which was largely responsible for the creation of these features. As Ashwin Vasavada, the Curiosity Project Scientist of NASA’s Jet Propulsion Laboratory, described the area as being “reminiscent of parts of the American southwest because of its butte and mesa landscape. In both areas, thick layers of sediment were deposited by wind and water, eventually resulting in a “layer cake” of bedrock that then began to erode away as conditions changed.  In both places, more resistant sandstone layers cap the mesas and buttes because they protect the more easily eroded, fine-grained rock underneath. ”

Buttes have also been photographed by the Mars Reconnaissance Orbiter’s (MRO) HiRISE instrument. These include the many buttes spotted in the Candor Chasma region – part of the Valles Marineris canyon system – back in 2007. The Viking 1 orbiter also noted the presence of many buttes in the Cydonia region during its flyby in 1976 – the occasion when it took pictures of the “Face of Mars” (later revealed to be a mesa).

Much like polygonal ridges that have been observed in the Medusae Fossae region and other locations across Mars (and Earth), these features are believed to be the remains of volcanic rock that remained in place after the surrounding rock was stripped away by erosion.

Ongoing studies into the various forces that shape our planet has allowed us to understand just how dynamic and changing it is. In addition, developments in space exploration and the planetary sciences have helped us to realize that Earth has a lot in common with other planets in our Solar System.

We have written many articles about geological formations for Universe Today. Here’s What is the Bakken Formation?, What is a Volcanic Neck?, What is the Earth’s Mantle Made Of?, What are Volcanoes?, What is the Difference Between Active and Dormant Volcanoes? and Stunning New Images of Mars from Curiosity Rover.

If you’d like more info on the Butte, check out the U.S. Geological Survey Website. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.


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Vortex Coronagraph A Game Changer For Seeing Close In Exoplanets

Vortex Coronagraph A Game Changer For Seeing Close In Exoplanets

The study of exoplanets has advanced a great deal in recent years, thanks in large part to the Kepler mission. But that mission has its limitations. It’s difficult for Kepler, and for other technologies, to image regions close to their stars. Now a new instrument called a vortex coronagraph, installed at Hawaii’s Keck Observatory, allows astronomers to look at protoplanetary disks that are in very close proximity to the stars they orbit.

The problem with viewing disks of dust, and even planets, close to their stars is that stars are so much brighter than objects that orbit them. Stars can be billions of times brighter than the planets near them, making it almost impossible to see them in the glare. “The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet,” said Gene Serabyn of NASA’s Jet Propulsion Laboratory (JPL). “The vortex coronagraph may be key to taking the first images of a pale blue dot like our own.”

“The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet.” – Gene Serabyn, JPL.

“The vortex coronagraph allows us to peer into the regions around stars where giant planets like Jupiter and Saturn supposedly form,” said Dmitri Mawet, research scientist at NASA’s Jet Propulsion Laboratory and Caltech, both in Pasadena. “Before now, we were only able to image gas giants that are born much farther out. With the vortex, we will be able to see planets orbiting as close to their stars as Jupiter is to our sun, or about two to three times closer than what was possible before.”

Rather than masking the light of stars, like other methods of viewing exoplanets, the vortex coronagraph redirects light away from the detectors by combining light waves and cancelling them out. Because there is no occulting mask, the vortex coronagraph can capture images of regions much closer to stars than other coronagraphs can. Dmitri Mawet, research scientist who invented the new coronagraph, compares it to the eye of a storm.

The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the "vortex" microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University

The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the “vortex” microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University

“The instrument is called a vortex coronagraph because the starlight is centered on an optical singularity, which creates a dark hole at the location of the image of the star,” said Mawet. “Hurricanes have a singularity at their centers where the wind speeds drop to zero — the eye of the storm. Our vortex coronagraph is basically the eye of an optical storm where we send the starlight.”

The results from the vortex coronagraph are presented in two papers (here and here) published in the January 2017 Astronomical Journal. One of the studies was led by Gene Serabyn of JPL, who is also head of the Keck vortex project. That study presented the first direct image of HIP79124 B, a brown dwarf that is 23 AU from its star, in the star-forming region called Scorpius-Centaurus.

The vortex coronagraph captured this image of the brown dwarf PIA21417.

The vortex coronagraph captured this image of the brown dwarf PIA21417. Image: NASA/JPL-Caltech

“The ability to see very close to stars also allows us to search for planets around more distant stars, where the planets and stars would appear closer together. Having the ability to survey distant stars for planets is important for catching planets still forming,” said Serabyn.

“Having the ability to survey distant stars for planets is important for catching planets still forming.” – Gene Serabyn, JPL.

The second of the two vortex studies presented images of a protoplanetary disk around the young star HD141569A. That star actually has three disks around it, and the coronagraph was able to capture an image of the innermost ring. Combining the vortex data with data from the Spitzer, WISE, and Herschel missions showed that the planet-forming material in the disk is made up pebble-size grains of olivine. Olivine is one of the most abundant silicates in Earth’s mantle.

“The three rings around this young star are nested like Russian dolls and undergoing dramatic changes reminiscent of planetary formation,” said Mawet. “We have shown that silicate grains have agglomerated into pebbles, which are the building blocks of planet embryos.”

These images and studies are just the beginning for the vortex coronagraph. It will be used to look at many more young planetary systems. In particular, it will look at planets near so-called ‘frost lines’ in other solar systems. The is the region around star systems where it’s cold enough for molecules like water, methane, and carbon dioxide to condense into solid, icy grains. Current thinking says that the frost line is the dividing line between where rocky planets and gas planets are formed. Astronomers hope that the coronagraph can answer questions about hot Jupiters and hot Neptunes.

Hot Jupiters and Neptunes are large gaseous planets that are found very close to their stars. Astronomers want to know if these planets formed close to the frost line then migrated inward towards their stars, because it’s impossible for them to form so close to their stars. The question is, what forces caused them to migrate inward? “With a bit of luck, we might catch planets in the process of migrating through the planet-forming disk, by looking at these very young objects,” Mawet said.

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Carnival of Space #494

Carnival of Space #494

This week’s Carnival of Space is hosted by Brian Wang at his Next Big Future blog.

Click here to read Carnival of Space #494

And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to carnivalofspace@gmail.com, and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, sign up to be a host. Send an email to the above address.

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SpaceX Shuffles Falcon 9 Launch Schedule, NASA Gets 1st Launch from Historic KSC Pad 39A

SpaceX Shuffles Falcon 9 Launch Schedule, NASA Gets 1st Launch from Historic KSC Pad 39A

SpaceX is repurposing historic pad 39A at the Kennedy Space Center, Florida for launches of the Falcon 9 rocket. Ongoing pad preparation by work crews is seen in this current view taken on Jan. 27, 2017. Credit: Ken Kremer/kenkremer.com

KENNEDY SPACE CENTER, FL – SpaceX announced Sunday (Jan. 29) a significant shuffle to the Falcon 9 launch schedule, saying that a key NASA mission to resupply the space station is moving to the head of the line and will now be their first mission to launch from historic pad 39A at the Kennedy Space Center- formerly used to launch space shuttles.

The late breaking payload shuffle will allow SpaceX additional time to complete all the extensive ground support work needed for repurposing pad 39A from launching the NASA Space Shuttle to the SpaceX Falcon 9.

Blastoff of the SpaceX Falcon 9 carrying an unmanned Dragon cargo freighter with NASA as customer on the CRS-10 resupply mission to the International Space Station (ISS) could come as soon as mid-February, said SpaceX
“SpaceX announced today that its first launch from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida will be the CRS-10 mission to the International Space Station,” said SpaceX in a statement.

SpaceX is renovating Launch Complex 39A at the Kennedy Space Center for launches of commercial and human rated Falcon 9 rockets as well as the Falcon Heavy, as seen here during Dec 2016 with construction of a dedicated new transporter/erector. Credit: Ken Kremer/kenkremer.com

Crews have been working long hours to get pad 39A ready for Falcon 9 launches, and the newly built transporter erector was seen raised at the pad multiple times in recent days.

“This schedule change allows time for additional testing of ground systems ahead of the CRS-10 mission,” SpaceX announced in a statement.

The surprise switch in customers means that the previously planned first Falcon 9 launch from pad 39A of the commercial EchoStar 23 communications satellite is being pushed off to a later date – perhaps late February.

Until now, EchoStar 23 was slated to be the first satellite launched by a Falcon 9 from Launch Complex 39A on NASA’s Kennedy Space Center. It could have come as soon as by the end of this week.

However, the Falcon 9 launch date from pad 39A has slipped repeatedly in January, with this week on Feb. 3 as the most recently targeted ‘No Earlier Than’ NET date.

SpaceX successfully resumed launches of the Falcon 9 earlier this month when the first flock of Iridium NEXT mobile voice and data relay satellites blasted off on the Iridium 1 mission from Vandenberg Air Force Base in California on Jan. 14, 2017.

NASA now gets the first dibs for using pad 39A which has lain dormant for nearly six years since Space Shuttle Atlantis launched on the final shuttle mission STS 135 in July 2011.

SpaceX leased pad 39A from NASA for launches of the Falcon 9 and Falcon Heavy back in 2014 and was already employing pad 40 on Cape Canaveral Air Force Station for Falcon 9 launches to the ISS.

But following the Sept 1, 2016 launch pad explosion that destroyed a Falcon 9 and the Amos-6 payload, pad 40 suffered extensive damage. And it is not known when the pad will be ready to resume launches.

So SpaceX has had to press pad 39A into service much more urgently, and the refurbishing and repurposing work is not yet complete.

To date SpaceX has not rolled a Falcon 9 rocket to pad 39A, not raised it to launch position, not conducted a fueling exercise and not conducted a static fire test.

So the current launch target of mid-February for CRS-10 remains a target date and not a firm launch date. EchoStar 23 is next in line.

“The launch is currently targeted for no earlier than mid-February,” SpaceX elaborated.

“Following the launch of CRS-10, first commercial mission from 39A is currently slated to be EchoStar XXIII.”

Once the pad is ready, SpaceX plans an aggressive launch schedule in 2017.

“The launch vehicles, Dragon, and the EchoStar satellite are all healthy and prepared for launch,” SpaceX stated.

The history making first use of a recycled Falcon 9 carrying the SES-10 communications satellite could follow as soon as March, if all goes well.

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.

Ken Kremer

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What is a Planet?

What is a Planet?

Humanity’s understanding of what constitutes a planet has changed over time. Whereas our most notable magi and scholars once believed that the world was a flat disc (or ziggurat, or cube), they gradually learned that it was in fact spherical. And by the modern era, they came to understand that the Earth was merely one of several planets in the known Universe.

And yet, our notions of what constitutes a planet are still evolving. To put it simply, our definition of planet has historically been dependent upon our frame of reference. In addition to discovering extra-solar planets that have pushed the boundaries of what we consider to be normal, astronomers have also discovered new bodies in our own backyard that have forced us to come up with new classification schemes.

History of the Term:

To ancient philosophers and scholars, the Solar Planets represented something entirely different than what they do today. Without the aid of telescopes, the planets looked like particularly bright stars that moved relative to the background stars. The earliest records on the motions of the known planets date back to the 2nd-millennium BCE, where Babylonian astronomers laid the groundwork for western astronomy and astrology.

These include the Venus tablet of Ammisaduqa, which catalogued the motions of Venus. Meanwhile, the 7th-century BCE MUL.APIN tablets laid out the motions of the Sun, the Moon, and the then-known planets over the course of the year (Mercury, Venus, Mars, Jupiter and Saturn). The Enuma anu enlil tablets, also dated to the 7th-century BCE, were a collection of all the omens assigned to celestial phenomena and the motions of the planets.

By classical antiquity, astronomers adopted a new concept of planets as bodies that orbited the Earth. Whereas some advocated a heliocentric system – such as 3rd-century BCE astronomer Aristarchus of Samos and 1st-century BCE astronomer Seleucus of Seleucia – the geocentric view of the Universe remained the most widely-accepted one. Astronomers also began creating mathematical models to predict their movements during this time.

This culminated in the 2nd century CE with Ptolemy’s (Claudius Ptolemaeus) publication of the Almagest, which became the astronomical and astrological canon in Europe and the Middle East for over a thousand years. Within this system, the known planets and bodies (even the Sun) all revolved around the Earth. In the centuries that followed, Indian and Islamic astronomers would added to this system based on their observations of the heavens.

By the time of the Scientific Revolution (ca. 15th – 18th centuries), the definition of planet began to change again. Thanks to Nicolaus Copernicus, Galileo Galilei, and Johannes Kepler, who proposed and advanced the heliocentric model of the Solar System, planets became defined as objects that orbited the Sun and not Earth. The invention of the telescope also led to an improved understanding of the planets, and their similarities with Earth.

A comparison of the geocentric and heliocentric models of the universe. Credit: history.ucsb.edu

Between the 18th and 20th centuries, countless new objects, moons and planets were discovered. This included Ceres, Vesta, Pallas (and the Main Asteroid Belt), the planets Uranus and Neptune, and the moons of Mars and the gas giants. And then in 1930, Pluto was discovered by Clyde Tombaugh, which was designated as the 9th planet of the Solar System.

Throughout this period, no formal definition of planet existed. But an accepted convention existed where a planet was used to described any “large” body that orbited the Sun. This, and the convention of a nine-planet Solar System, would remain in place until the 21st century. By this time, numerous discoveries within the Solar System and beyond would lead to demands that a formal definition be adopted.

Working Group on Extrasolar Planets:

While astronomers have long held that other star systems would have their own system of planets, the first reported discovery of a planet outside the Solar System (aka. extrasolar planet or exoplanet) did not take place until 1992. At this time, two radio astronomers working out of the Arecibo Observatory (Aleksander Wolszczan and Dale Frail) announced the discovery of two planets orbiting the pulsar PSR 1257+12.

The first confirmed discovery took place in 1995, when astronomers from the University of Geneva (Michel Mayor and Didier Queloz) announced the detection of 51 Pegasi. Between the mid-90s and the deployment of the Kepler space telescope in 2009, the majority of extrasolar planets were gas giants that were either comparable in size and mass to Jupiter or significantly larger (i.e. “Super-Jupiters”).

Earlier today, NASA announced that Kepler had confirmed the existence of 1,284 new exoplanets, the most announced at any given time. Credit: NASA

These new discoveries led the International Astronomical Union (IAU) to create the Working Group of Extrasolar Planets (WGESP) in 1999. The stated purpose of the WGESP was to “act as a focal point for international research on extrasolar planets.” As a result of this ongoing research, and the detection of numerous extra-solar bodies, attempts were made to clarify the nomenclature.

As of February 2003, the WGESP indicated that it had modified its position and adopted the following “working definition” of a planet:

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are “planets” (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are “brown dwarfs”, no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not “planets”, but are “sub-brown dwarfs” (or whatever name is most appropriate).

As of January 22nd, 2017, more than 2000 exoplanet discoveries have been confirmed, with 3,565 exoplanet candidates being detected in 2,675 planetary systems (including 602 multiple planetary systems).

The number of confirmed exoplanet discoveries, by year. Credit: NASA

2006 IAU Resolution:

During the early-to-mid 2000s, numerous discoveries were made in the Kuiper Belt that also stimulated the planet debate. This began with the discovery of Sedna in 2003 by a team of astronomers (Michael Brown, Chad Trujillo and David Rabinowitz) working at the Palomar Observatory in San Diego. Ongoing observations confirmed that it was approx 1000 km in diameter, and large enough to undergo hydrostatic equilibrium.

This was followed by the discovery of Eris – an even larger object (over 2000 km in diameter) – in 2005, again by a team consisting of Brown, Trujillo, and Rabinowitz. This was followed by the discovery of Makemake on the same day, and Haumea a few days later. Other discoveries made during this period include Quaoar in 2002, Orcus in 2004,  and 2007 OR10 in 2007.

The discovery of a several objects beyond Pluto’s orbit that were large enough to be spherical led to efforts on behalf of the IAU to adopt a formal definition of a planet. By October 2005, a group of 19 IAU members narrowed their choices to a shortlist of three characteristics. These included:

  • A planet is any object in orbit around the Sun with a diameter greater than 2000 km. (eleven votes in favour)
  • A planet is any object in orbit around the Sun whose shape is stable due to its own gravity. (eight votes in favour)
  • A planet is any object in orbit around the Sun that is dominant in its immediate neighbourhood. (six votes in favour)

After failing to reach a consensus, the committee decided to put these three definitions to a wider vote. This took place in August of 2006 at the 26th IAU General Assembly Meeting in Prague. On August 24th, the issue was put to a final draft vote, which resulted in the adoption of a new classification scheme designed to distinguish between planets and smaller bodies. These included:

(1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and  (d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.

In accordance with this resolution, the IAU designated Pluto, Eris, and Ceres into the category of “dwarf planet”, while other Trans-Neptunian Objects (TNOs) were left undeclared at the time. This new classification scheme spawned a great deal of controversy and some outcries from the astronomical community, many of whom challenged the criteria as being vague and debatable in their applicability.

The presently-known largest trans-Neptunian objects (TNO), the discovery of which prompted the current IAU definition of planet. Credit: Larry McNish, Data: M.Brown)

For instance, many have challenged the idea of a planet clearing its neighborhood, citing the existence of near-Earth Objects (NEOs), Jupiter’s Trojan Asteroids, and other instances where large planets share their orbit with other objects. However, these have been countered by the argument that these large bodies do not share their orbits with smaller objects, but dominate them and carry them along in their orbits.

Another sticking point was the issue of hydrostatic equilibrium, which is the point where a planet has sufficient mass that it will collapse under the force of its own gravity and become spherical. The point at which this takes place remains entirely unclear thought, and some astronomers therefore challenge it being included as a criterion.

In addition, some astronomers claim that these newly-adopted criteria are only useful insofar as Solar planets are concerned. But as exoplanet research has shown, planets in other star star systems can be significantly different. In particular, the discovery of numerous “Super Jupiters” and “Super Earths” has confounded conventional notions of what is considered normal for a planetary system.

In June 2008, the IAU executive committee announced the establishment of a subclass of dwarf planets in the hopes of clarifying the definitions further. Comprising the recently-discovered TNOs, they established the term “plutoids”, which would thenceforth include Pluto, Eris and any other future trans-Neptunian dwarf planets (but excluded Ceres). In time, Haumea, Makemake, and other TNOs were added to the list.

Despite these efforts and changes in nomenclature, for many, the issue remains far from resolved. What’s more, the possible existence of Planet 9 in the outer Solar System has added more weight to the discussion. And as our research into exoplanets continues – and uncrewed (and even crewed) mission are made to other star systems – we can expect the debate to enter into a whole new phase!

We have written many interesting articles about the planets here at Universe Today. Here’s How Many Planets are there in the Solar System?, What are the Planets of the Solar System, The Planets of our Solar System in Order of Size, Why Pluto is no Longer a Planet, Evidence Continues to Mount for Ninth Planet, and What are Extrasolar Planets?.

For more information, take a look at this article from Scientific American, What is a Planet?, and the video archive from the IAU.

Astronomy Cast has an episode on Pluto’s planetary identity crisis.


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Unprecedented Views of Saturn’s Rings as Cassini Dances Death Spiral

Unprecedented Views of Saturn’s Rings as Cassini Dances Death Spiral

As the Cassini spacecraft moves ever closer to Saturn, new images provide some of the most-detailed views yet of the planet’s spectacular rings. From its “Ring-Grazing” orbit phase, Cassini’s cameras are resolving details in the rings as small as 0.3 miles (550 meters), which is on the scale of Earth’s tallest buildings.

On Twitter, Cassini Imaging Team Lead Carolyn Porco called the images “outrageous, eye-popping” and the “finest Cassini images of Saturn’s rings.”

Project Scientist Linda Spilker said the ridges and furrows in the rings remind her of the grooves in a phonograph record.

These images are giving scientists the chance to see more details about ring features they saw earlier in the mission, such as waves, wakes, and things they call ‘propellers’ and ‘straw.’

This Cassini image features a density wave in Saturn’s A ring (at left) that lies around 134,500 km from Saturn. Density waves are accumulations of particles at certain distances from the planet. This feature is filled with clumpy perturbations, which researchers informally refer to as “straw.” Credit: NASA/JPL-Caltech/Space Science Institute

As of this writing, Cassini just started the 10th orbit of the 20-orbit ring-grazing phase, which has the spacecraft diving past the outer edge of the main ring system. The ring-grazing orbits began last November, and will continue until late April, when Cassini begins its grand finale. During the 22 finale orbits, Cassini will repeatedly plunge through the gap between the rings and Saturn. The first of these plunges is scheduled for April 26.

The spacecraft is actually close enough to the ‘F’ ring that occasionally tenuous particle strike Cassini, said project scientist Linda Spilker, during a Facebook Live event today.

“These are very small and tenuous, only a few microns in size,” Spilker said, “like dust particles you’d see in the sunlight. We can actually ‘hear’ them hitting the spacecraft in our data, but these particles are so small, they won’t hurt Cassini.”

Stardust melody: @CassiniSaturn took these images as it stared at #Saturn’s faint & dusty G Ring. More on the rings: https://t.co/rH9bqqQCQd pic.twitter.com/ftMZMwYB1W

— NASA JPL (@NASAJPL) January 27, 2017

I talked with Spilker about ring particles for my book “Incredible Stories From Space:”

Spilker has envisioned holding a ring particle in her hand. What would it look like?

“We have evidence of the particles that have an icy core covered with fluffy regolith material that is very porous,” she said, “and that means the particle can heat up and cool down very quickly compared to a solid ice cube.”

The straw features are caused by clumping ring particles and the propellers are caused by small, embedded moonlets that creates propeller shaped wakes in the rings.

The wavemaker moon, Daphnis, is featured in this view, taken as NASA’s Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn’s rings on Jan. 16, 2017. This is the closest view of the small moon obtained yet. Daphnis is 5 miles or 8 kilometers across. Credit: NASA/JPL-Caltech/Space Science Institute

This stunning view of the moon Daphnis shows the moon interacting with the ring particles, creating waves in the rings around it.

A close-up of Saturn and its rings. Assembled using raw uncalibrated RGB filtered images taken by the Cassini spacecraft on January 18 2017. Credit:
NASA/JPL-Caltech/SSI/image editing by Kevin M. Gill

“These close views represent the opening of an entirely new window onto Saturn’s rings, and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet,” said Matthew Tiscareno, a Cassini scientist who studies Saturn’s rings at the SETI Institute, Mountain View, California. Tiscareno planned the new images for the camera team.

Further reading: JPL, CICLOPS

The post Unprecedented Views of Saturn’s Rings as Cassini Dances Death Spiral appeared first on Universe Today.

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Messier 33 – The Triangulum Galaxy

Messier 33 – The Triangulum Galaxy

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Triangulum Galaxy, also known as Messier 33. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these is the Triangulum Galaxy, a spiral galaxy located approximately 3 million light-years from Earth in the direction of the Triangulum constellation. As the third-largest member of the Local Group of galaxies (behind the Andromeda Galaxy and the Milky Way), it is the one of the most distant objects that can be seen with the naked eye. Much like M32, M33 is very close to Andromeda, and is believed to be a satellite of this major galaxy.


At some 3 million light years away from Earth, the Triangulum Galaxy is the third largest galaxy in our Local Group and it may be a gravitationally bound companion of the Andromeda Galaxy. Its beautiful spiral arms show multitudes of red HII regions and blue clouds of young stars. The largest of these HII regions (NGC 604) spans nearly 1500 across and is the largest so far known.

The Triangulum Galaxy (M33), taken by the Swift Gamma-Ray Burst Mission. Credit: NASA/Swift

It has a spectrum similar to the Orion Nebula – our own Milky Way’s most celebrated starbirth region. “M33 is a gigantic laboratory where you can watch dust being created in novae and supernovae, being distributed in the winds of giant stars, and being reborn in new stars,” said University of Minnesota researcher and lead author Elisha Polomski. By studying M33, “you can see the Universe in a nutshell.”

Of course, our curiousity about our neighboring galaxy has driven us to try to understand more over the years. Once Edwin Hubble set the standard with Cepheid variables, we began measuring distance by discovering about 25 of them in M33. By 2004 we were studying the red giant star branch to peer even further. As A.W. McConnachie said in a 2004 study of the galaxy:

“The absolute bolometric luminosity of the point of core helium ignition in old, metal-poor, red giant stars is of roughly constant magnitude, varying only very slightly with mass or metallicity. It can thus be used as a standard candle. This technique then allows for the determination of realistic uncertainties which reflect the quality of the luminosity function used. Finally, we apply our technique to the Local Group spiral galaxy M33 and the dwarf galaxies Andromeda I and II, and derive distance. The result for M33 is in excellent agreement with the Cepheid distances to this galaxy, and makes the possibility of a significant amount of reddening in this object unlikely.”

By 2005, astronomers had detected two water masers on either side of M33 and for the first time ever – revealed what direction it as going in. According to Andreas Brunthaler (et al), who published a study about the distance and proper motion of the galaxy in 2005:

“We measured the angular rotation and proper motion of the Triangulum Galaxy (M33) with the Very Long Baseline Array by observing two H2O masers on opposite sides of the galaxy. By comparing the angular rotation rate with the inclination and rotation speed, we obtained a distance of 730 +/- 168 kiloparsecs. This distance is consistent with the most recent Cepheid distance measurement. This distance is consistent with the most recent Cepheid distance measurement. M33 is moving with a velocity of 190 +/- 59 kilometers per second relative to the Milky Way. These measurements promise a method to determine dynamical models for the Local Group and the mass and dark-matter halos of M31, M33, and the Milky Way.”

Composite image of the Triangulum Galaxy (Messier 33), taken at Mount Lemmon Observatory. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Yes, it’s moving toward the Andromeda Galaxy, much like how Andromeda is moving towards us! In 2006, a group of astronomers announced the discovery of an eclipsing binary star in M33. As A.Z. Bonanos, the lead author of the study that detailed the discovery, said:

“We present the first direct distance determination to a detached eclipsing binary in M33, which was found by the DIRECT Project. Located in the OB 66 association, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its 4.8938 day period.”

By studying the eclipsing binary, astronomers soon knew their size, distance, temperature and absolute magnitude. But more was yet to come! In 2007, the Chandra X-ray Observatory revealed even more when a black hole nearly 16 times the mass of the Sun was revealed. The black hole, named M33 X-7, orbits a companion star which it eclipses every 3.5 days. This means the companion star must also have an incredibly large mass as well….

Yet how huge must the parent star have been to have formed a black hole in advance of its companion? As Jerome Orosz, of San Diego State University, was quoted as saying in a 2007 Chandra press release:

“This discovery raises all sorts of questions about how such a big black hole could have been formed. Massive stars can be much less extravagant than people think by hanging onto a lot more of their mass toward the end of their lives. This can have a big effect on the black holes that these stellar time-bombs make.”

Artist’s rendering of the black hole found in orbit of the large blue star in M33 . Credit: Chandra/Harvard/HST

Stellar bombs? You bet. Gigantic stellar explosions even. Although no supernovae events have been detected in the Triangulum galaxy, it certainly doesn’t lack for evidence of supernova remnants. According to a 2004 study by F. Haberl and W. Pietsch of the Max-Planck-Institute:

“We present a catalogue of 184 X-ray sources within 50′ of the nucleus of the local group spiral galaxy M 33. The catalogue is derived from an analysis of the complete set of ROSAT archival data pointed in the direction of M 33 and contains X-ray position, existence likelihood, count rates and PSPC spectral hardness ratios. To identify the sources the catalog was correlated with previous X-ray catalogues, optical and radio catalogues. In addition sources were classified according to their X-ray properties. We find seven candidates for supersoft X-ray sources, of which two may be associated with known planetary nebulae in M 33. The majority of X-ray detected supernova remnants is also detected at radio frequencies and seen in optical lines. The low overall X-ray detection rate of optically selected SNRs can probably be attributed to their expansion into interstellar matter of low density.”

Or the creation of black holes…

History of Observation:

While the Triangulum Galaxy was probably first observed by Hodierna before 1654 (back when skies were dark), it was independently rediscovered by Charles Messier, and cataloged by him on August 25, 1764. As he recorded in his notes on the occasion:

“I have discovered a nebula between the head of the northern Fish and the large Triangle, a bit distant from a star which had not been known, of sixth magnitude, of which I have determined the position; the right ascension of that star was 22d 7′ 13″, and its declination 29d 54′ 10″ north: near that star, there is another one which is the first of Triangulum, described by the letter b. Flamsteed described it in his catalog, of sixth magnitude; it is less beautiful than that of which I have given the position, and one should set it to the rank of the stars of the eighth class. The nebula is a whitish light of 15 minutes in diameter, of an almost even density, despite a bit more luminous at two third of its diameter; it doesn’t contain any star: one sees it with difficulty with an ordinary refractor of one foot.”

The location of the Triangulum Galaxy in the night sky. Credit: Wikisky

While Sir William Herschel wouldn’t publish papers on Messier’s findings, he was an astronomically curious soul and couldn’t help but study M33 intently on his own, writing:

“There is a suspicion that the nebula consists of exceedingly small stars. With this low power it has a nebulous appearance; and it vanishes when I put on the higher magnifying powers of 278 and 460.” He would continue to observe this grand galaxy again and again over the years, cataloging its various regions with their own separate numbers and keeping track of his findings: “The stars of the cluster are the smallest points imaginable. The diameter is nearly 18 minutes.”

Yet it would take a very special observer, one named Bill Parsons – the third Earl of Rosse – to become the very first to describe it as spiral. As he wrote of it:

“September 16, 1849. – New spiral: Alpha the brighter branch; Gamma faint; Delta short but pretty bright; Beta pretty distinct; Epsilon but suspected; the whole involved in a faint nebula, which probably extends past several knots which lie about it in different directions. Faint nebula seems to extend very far following: drawing taken.”

Quite the description indeed, since it would eventually lead to Rosse’s description of M33 being “…full of knots. Spiral arrangement. Two similar curves like an “S” cross in the center”, and to other astronomers discovering that these “spiral nebulae” were extra-galactic!

The location of Messier 33 in the Triangulum constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 33:

While actually locating Messier 33 isn’t so difficult, seeing Messier 33 can be. Even though it is billed at nearly unaided eye magnitude, this huge, low surface brightness galaxy requires some experience with equipment and observing conditions or you may hunt forever in the right place and never find it. Let’s begin first by getting you in the proper area! First locate the Great Square of Pegasus – and its easternmost bright star, Alpha. About a hand span further east you will see the brightest star in Triangulum – Alpha.

M33 is just a couple of degrees (about 2 finger widths) west. Now, the most important part to understand is that you must use the lowest magnification possible, or you won’t be able to see the proverbial forest because of the trees. The image you see here at the top of the page is around a full degree of sky – about 1/3 the field of view of average binoculars and far larger than your average telescope eyepiece.

However, by using the least amount of magnification with a telescope you are causing M33 to appear much smaller – allowing it to fit within eyepiece field of view range. The larger the aperture, the more light it gathers and the brighter the image will be. The next thing to understand is M33 really is low surface brightness… Light pollution, a fine haze in the sky, moonlight… All of these things will make it difficult to find. Yet, there are places left here on Earth where the Triangulum Galaxy can be seen with no optical aid at all!

Enjoy your quest for M33. You may find it your first time out and it may be years before you see it in all its glory. But when you do, we guarantee you’ll never forget! Be sure to enjoy this video of the Triangulum galaxy too, courtesy of the European Southern Observatory:

Enjoy your quest for M33. You may find it your first time out and it may be years before you see it in all its glory. But when you do, we guarantee you’ll never forget!

And here are the quick facts on M33 to help you get started:

Object Name: Messier 33
Alternative Designations: M33, NGC 598, Triangulum Galaxy, Pinwheel Galaxy
Object Type: Type Sc, Spiral Galaxy
Constellation: Triangulum
Right Ascension: 01 : 33.9 (h:m)
Declination: +30 : 39 (deg:m)
Distance: 3000 (kly)
Visual Brightness: 5.7 (mag)
Apparent Dimension: 73×45 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.


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NASA Tribute Exhibit Honors Fallen Crew 50 Years After Apollo 1 Tragedy

NASA Tribute Exhibit Honors Fallen Crew 50 Years After Apollo 1 Tragedy

The new tribute to Apollo 1 at NASA’s Kennedy Space Center was opened during a dedication ceremony on Jan. 27, 2017, 50 years after the crew was lost – with a keynote speech by Kennedy Space Center Director and former astronaut Bob Cabana. The entrance to the Apollo 1 tribute shows the three astronauts who perished in a fire at the launch pad on Jan. 27, 1967 during training for the mission. The astronauts are, from left, Gus Grissom, Ed White II and Roger Chaffee. Credit: Ken Kremer/kenkremer.com

KENNEDY SPACE CENTER VISITOR COMPLEX, FL – NASA unveiled a new tribute exhibit honoring three fallen astronaut heroes 50 years to the day of the Apollo 1 tragedy on January 27, 1967 when the three man crew perished in a flash fire on the launch pad during a capsule test that was not considered to be dangerous.

The Apollo 1 prime crew comprising NASA astronauts Gus Grissom, Ed White II and Roger Chaffee were killed during routine practice countdown testing when a fire suddenly erupted inside the cockpit as they were strapped to their seats in their Apollo command module capsule, on a Friday evening at 6:31 p.m. on January 27, 1967.

“It’s been 50 years since the crew of Apollo 1 perished in a fire at the launch pad, but the lives, accomplishments and heroism of the three astronauts are celebrated in a dynamic, new tribute that is part museum, part memorial and part family scrapbook,” says a NASA narrative that aptly describes the exhibit and the memorial ceremony I attended at the Apollo/Saturn V Center at NASA’s Kennedy Space Center in Florida on Friday, Jan. 27, 2017 on behalf of Universe Today.

It was the first disaster with a human crew and the worst day in NASA’s storied history to that point.

The tribute is named called “Ad Astra Per Aspera – A Rough Road Leads to the Stars.”

A new tribute to the crew of Apollo 1, who perished in a fire at the launch pad on Jan. 27, 1967, opened at NASA’s Kennedy Space Center on the 50th anniversary of that fatal day that cost the lives of all three crewmembers. The tribute exhibit at the Apollo/Saturn Center highlights the lives and careers of NASA astronauts Gus Grissom, Ed White II and Roger Chaffee with artifacts and photos. Credit: Ken Kremer/kenkremer.com

At the tribute dedication ceremony Kennedy Space Center Director and former astronaut Bob Cabana said the families of the fallen crew gave their approvals and blessing to the efforts that would at last tell the story of Apollo 1 to all generations – those who recall it and many more to young or not yet born to remember the tragedy of the early days of America’s space program.

“It’s long overdue,” said Cabana. “I’m proud of the team that created this exhibit.”

“Ultimately, this is a story of hope, because these astronauts were dreaming of the future that is unfolding today,” said former astronaut Bob Cabana, center director at Kennedy. “Generations of people around the world will learn who these brave astronauts were and how their legacies live on through the Apollo successes and beyond.”

The exhibit “showcases clothing, tools and models that define the men as their parents, wives and children saw them as much as how the nation viewed them.”

The main focus was to introduce the astronauts to generations who never met them and may not know much about them or the early space program, says NASA.

“This lets you now meet Gus Grissom, Ed White and Roger Chaffee as members of special families and also as members of our own family,” said NASA’s Luis Berrios, who co-led the tribute design that would eventually involve more than 100 designers, planners and builders to realize.

“You get to know some of the things that they liked to do and were inspired by. You look at the things they did and if anyone does just one of those things, it’s a lifetime accomplishment and they did all of it and more.”

The crew and the Apollo 1 command module were stacked atop the Saturn 1B rocket at Launch Complex 34 on what is now Cape Canaveral Air Force Station in Florida.
During the “plugs out” test the Saturn1B rocket was not fueled. But the fatal flaw was the atmosphere of pure oxygen for the astronauts to breath inside the sealed Apollo 1 command module which was pressurized to 16.7 psi.
Another significantly contributing fatal flaw was the inward opening three layered hatch that took some 90 seconds to open under the best of conditions.
After working all afternoon through the practice countdown and encountering numerous problems, something went terribly awry. Without warning a flash fire erupted in the cockpit filled with 100 percent oxygen and swiftly spread uncontrollably creating huge flames licking up the side of the capsule, acrid smoke and a poisonous atmosphere that asphyxiated, burned and killed the crew.
With the scorching temperatures spiking and pressures rapidly rising in a closed system, the capsule exploded some 20 seconds after the fire started. And because of the pressure buildup inside with flames licking up the sides and the toxic atmosphere generated from burning materials, the crew succumbed and could not turn the latch to pull open the hatch against the pressure.

The pad crew tried bravely in vain to save them, fighting heavy smoke and fire and fearing that the attached launch abort system on top of the capsule would ignite and kill them all too.

An investigation would determine that the fire was likely caused by a spark from frayed wiring, perhaps originating under Grissom’s seat.

NASA and contractor North American Aviation completely redesigned the capsule with major engineering changes including an atmosphere of 60 percent oxygen and 40 percent nitrogen at 5 psi blower pressure, new hatch that could open outwards in 5 seconds, removing flammable materials among many others that would make the Apollo spacecraft much safer for the upcoming journeys to the moon.

The multi-layed hatch serves as the centerpiece of the tribute exhibit. No piece of Apollo 1 has ever before been put on public display. Alongside the old hatch, the new hatch is displayed that was used on all the remaining Apollo missions.

Display cases highlights the lives and careers of the three astronauts in these NASA descriptions.

Gus Grissom was “one of NASA’s Original Seven astronauts who flew the second Mercury mission, a hunting jacket and a pair of ski boots are on display, along with a small model of the Mercury spacecraft and a model of an F-86 Sabre jet like the one he flew in the Korean War. A slide rule and engineering drafts typify his dedication to detail.”

“The small handheld maneuvering thruster that Ed White II used to steer himself outside his Gemini capsule during the first American spacewalk features prominently in the display case for the West Point graduate whose athletic prowess nearly equaled his flying acumen. An electric drill stands alongside the “zip gun,” as he called the thruster.”

“It was great to juxtaposition it with a drill which was also a tool that Ed loved to use,” Berrios said. “He had a tremendous passion for making things for his family.”

“Roger Chaffee, for whom Apollo 1 would have been his first mission into space, was an esteemed Naval aviator who became a test pilot in his drive to qualify as an astronaut later. Displayed are board games he played with his wife and kids on rare evenings free of training.”

Grissom, White and Chaffee composed NASA’s first three person crew following the one man Mercury program and two man Gemini program, that had just concluded in November 1966 with Gemini 12.

The trio had been scheduled to blastoff in late February 1967 on a 14 day long mission in Earth orbit to thoroughly check out the Apollo command and service modules.

Apollo 1 was to be the first launch in NASA’s Apollo moon landing program initiated by President John F. Kennedy in 1961.

Apollo 1 was planned to pave the way to the Moon so that succeeding missions would eventually “land a man on the Moon and return him safely to Earth before this decade is out” as Kennedy eloquently challenged the nation to do.

I remember seeing the first news flashes about the Apollo 1 fire on the TV as a child, as it unfolded on the then big three networks. It is indelibly marked in my mind. This new exhibit truly tells the story of these astronaut heroes vividly to those with distant memories and those with little or no knowledge of Apollo 1.

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.

Ken Kremer

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A Proposal For Juno To Observe The Volcanoes Of Io

A Proposal For Juno To Observe The Volcanoes Of Io

To accomplish its science objectives, NASA’s Juno spacecraft orbits over Jupiter’s poles and passes repeatedly through repeatedly hazardous radiation belts. Two Boston University researchers propose using Juno to probe the ever-changing flux of volcanic gases-turned-ions spewed by Io’s volcanoes. Credit: NASA/JPL-Caltech

Jupiter may be the largest planet in the Solar System with a diameter 11 times that of Earth, but it pales in comparison to its own magnetosphere. The planet’s magnetic domain extends sunward at least 3 million miles (5 million km) and on the back side all the way to Saturn for a total of 407 million miles or more than 400 times the size of the Sun.

Jupiter’s large magnetic field interacts with the solar wind to form an invisible magnetosphere. If we were able to see it, it would span a large distance across the sky. In the artist’s depiction, the planet would be located between the two “purple eyes,” but it’s too small to see at this scale. Credit: NASA.

If we had eyes adapted to see the Jovian magnetosphere at night, assuming Saturn was positioned at a right angle to Jupiter (rising or setting when Jupiter was on the meridian), its teardrop-like shape would cover 40° of sky! No surprise then that Jove’s magnetic aura has been called one of the largest structures in the Solar System.

A 5-frame sequence taken by the New Horizons spacecraft in May 2007 shows a cloud of volcanic debris from Io’s Tvashtar volcano. The plume extends some 200 miles (330 km) above the moon’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Io, Jupiter’s innermost of the planet’s four large moons, orbits deep within this giant bubble. Despite its small size — about 200 miles smaller than our own Moon — it doesn’t lack in superlatives. With an estimated 400 volcanoes, many of them still active, Io is the most volcanically active body in the Solar System. In the moon’s low gravity, volcanoes spew sulfur, sulfur dioxide gas and fragments of basaltic rock up to 310 miles (500 km) into space in beautiful, umbrella-shaped plumes.

This schematic of Jupiter’s magnetic environments shows the planets looping magnetic field lines (similar to those generated by a simple bar magnet), Io and its plasma torus and flux tube. Credit: John Spencer / Wikipedia CC-BY-SA3.0 with labels by the author

Once aloft, electrons whipped around by Jupiter’s powerful magnetic field strike the neutral gases and ionize them (strips off their electrons). Ionized atoms and molecules (ions) are no longer neutral but possess a positive or negative electric charge. Astronomers refer to swarms of ionized atoms as plasma.

Jupiter rotates rapidly, spinning once every 9.8 hours, dragging the whole magnetosphere with it. As it spins past Io, those volcanic ions get caught up and dragged along for the ride, rotating around the planet in a ring called the Io plasma torus. You can picture it as a giant donut with Jupiter in the “hole” and the tasty, ~8,000-mile-thick ring centered on Io’s orbit.

That’s not all. Jupiter’s magnetic field also couples Io’s atmosphere to the planet’s polar regions, pumping Ionian ions through two “pipelines” to the magnetic poles and generating a powerful electric current known as the Io flux tube. Like firefighters on fire poles, the ions follow the planet’s magnetic field lines into the upper atmosphere, where they strike and excite atoms, spawning an ultraviolet-bright patch of aurora within the planet’s overall aurora. Astronomers call it Io’s magnetic footprint. The process works in reverse, too, spawning auroras in Io’s tenuous atmosphere.

The tilt of Juno’s orbit relative to Jupiter changes over the course of the mission, sending the spacecraft increasingly deeper into the planet’s intense radiation belts. Orbits are numbered from early in the mission to late. Credit: NASA/JPL-Caltech

Io is the main supplier of particles to Jupiter’s magnetosphere. Some of the same electrons stripped from sulfur and oxygen atoms during an earlier eruption return to strike atoms shot out by later blasts. Round and round they go in a great cycle of microscopic bombardment! The constant flow of high-speed, charged particles in Io’s vicinity make the region a lethal environment not only for humans but also for spacecraft electronics, the reason NASA’s Juno probe gets the heck outta there after each perijove or closest approach to Jupiter.

Io’s flux tube directs ions down Jupiter’s magnetic field lines to create magnetic footprints of enhanced aurora in Jupiter’s polar regions. An electric current of 5 million amps flows along Io’s flux tube.Credit: NASA/J.Clarke/HST

But there’s much to glean from those plasma streams.  Astronomy PhD student Phillip Phipps and assistant professor of astronomy Paul Withers of Boston University have hatched a plan to use the Juno spacecraft to probe Io’s plasma torus to indirectly study the timing and flow of material from Io’s volcanoes into Jupiter’s magnetosphere. In a paper published on Jan. 25, they propose using changes in the radio signal sent by Juno as it passes through different regions of the torus to measure how much stuff is there and how its density changes over time.

The technique is called a radio occultation. Radio waves are a form of light just like white light. And like white light, they get bent or refracted when passing through a medium like air (or plasma in the case of Io). Blue light is slowed more and experiences the most bending; red light is slowed less and refracted least, the reason red fringes a rainbow’s outer edge and blue its inner. In radio occultations, refraction results in changes in frequency caused by variations in the density of plasma in Io’s torus.

The best spacecraft for the attempt is one with a polar orbit around Jupiter, where it cuts a clean cross-section through different parts of the torus during each orbit. Guess what? With its polar orbit, Juno’s the probe for the job! Its main mission is to map Jupiter’s gravitational and magnetic fields, so an occultation experiment jives well with mission goals. Previous missions have netted just two radio occultations of the torus, but Juno could potentially slam dunk 24.

New Horizons took this photo of Io in infrared light. The Tvastar volcano is bright spot at top. At least 10 other volcanic hot spots dot the moon’s night side. Credit: NASA/JHUPL/SRI

Because the paper was intended to show that the method is a feasible one, it remains to be seen whether NASA will consider adding a little extra credit work to Juno’s homework. It seems a worthy and practical goal, one that will further enlighten our understanding of how volcanoes create aurorae in the bizarre electric and magnetic environment of the largest planet.

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