Special Guests:
Dr. Sara Seager, whose research focuses on computer models of exoplanet atmospheres, interiors, and biosignatures. Her favorite projects involve the search for planets like Earth with signs of life
on them.
Enhanced-color image from Cassini showing red streaks on Tethys (NASA/JPL-Caltech/Space Science Institute)
Resembling what the skin on my arms looks like after giving my cat a bath, the surface of Saturn’s moon Tethys is seen above in an extended-color composite from NASA’s Cassini spacecraft showing strange long red streaks. They stretch for long distances across the moon’s surface following the rugged terrain, continuing unbroken over hills and down into craters… and their cause isn’t yet known.
According to a NASA news release, “The origin of the features and their reddish color is currently a mystery to Cassini scientists. Possibilities being studied include ideas that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside Tethys. The streaks could also be associated with features like fractures that are below the resolution of the available images.”
The images were taken by Cassini during a flyby of the 660-mile-wide (1,062 km) Tethys on April 11, 2015 at a resolution of about 2,300 feet (700 meters) per pixel. They were acquired in visible green, infrared, and ultraviolet light wavelengths and so the composite image reveals colors our eyes can’t directly perceive. The combination of this and the solar illumination needed to image this particular area as the spacecraft passed by are why these features haven’t been seen so well until now.
“The red arcs really popped out when we saw the new images,” said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston. “It’s surprising how extensive these features are.”
Extended color mosaic of Tethys from Cassini images acquired on April 11, 2015. The region where the streaks are is outlined. Click for original hi-res version. (NASA/JPL-Caltech/SSI)
While the nature of Tethys’ streaks isn’t understood, the observations do indicate a relatively young age compared to the surrounding surface.
“The red arcs must be geologically young because they cut across older features like impact craters, but we don’t know their age in years.” said Paul Helfenstein, a Cassini imaging scientist at Cornell University in Ithaca. “If the stain is only a thin, colored veneer on the icy soil, exposure to the space environment at Tethys’ surface might erase them on relatively short time scales.”
Reprocessed Galileo image of Europa’s streaked surface by Ted Stryk (NASA/JPL/Ted Stryk)
Could these arcs be signs of an underground ocean or reservoir of briny liquid, like Enceladus’ tiger stripes (aka sulcae) or the streaks that crisscross Europa’s ice? Or are they the results of infalling material from one of Saturn’s other moons? More observations with Cassini, now in its eleventh year in orbit at Saturn, are being planned to “study the streaks.”
“We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings,” said Linda Spilker, Cassini project scientist at JPL.
Graphical comparison showing how Jupiter's Great Red Spot has shrunk in the past 125 years. Credit: Damian Peach
Maybe it’s too soon for a pity party, but the profound changes in the size and prominence of Jupiter’s Great Red Spot (GRS) in the past 100 years has me worried. After Saturn’s rings, Jupiter’s big bloody eye is one of astronomy’s most iconic sights.
This titanic hurricane-like storm has charmed earthlings since Giovanni Cassini first spotted it in the mid-1600s. Will our grandchildren turn their telescopes to Jove only to see a pale pink oval like so many others rolling around the planet’s South Tropical Zone?
An inspired image prompted this sad train of thought. UK astrophotographer Damian Peach came up with an ideal way to depict how the GRS would look to us now if it we could see it as it was in 1890, 125 years ago. Those were the glory days for the “Eye of Jupiter” as Cassini was fond of calling it. With a diameter of 22,370 miles (36,000 km), the GRS spanned nearly three Earths wide. What a sight it must have been in nearly any telescope.
Peach compared measurements of the Spot in black and white photos taken at Lick Observatory in California in 1890-91 with a photo he took on April 13 this year. He then manipulated his April 13 data using the Lick photos and WINJUPOS (Jupiter feature measuring program) to carefully match the storm to its dimensions and appearance 125 years ago. Voila! Now we have a good idea of what we missed by being born too late.
At left, A crude photograph of Jupiter’s enormous Great Red Spot in 1879 from Agnes Clerk’s Book ” A History of Astronomy in the 19th Century”.
“A century ago, it truly was deserving of its name!” wrote Peach.
Painting by Italian artist Donato Creti showing a telescopic view of Jupiter in 1711 above a nighttime landscape. The Great Red Spot is clearly visible above center.
The shrinking of the Great Red Spot isn’t breaking news. You read about it here in Universe Today more than year ago. Before that, Jupiter observers had grumbled for years that the once-easy feature had become anemic and not nearly as obvious as once remembered. Astronomers have been following its downsizing since the 1930s.
Dramatic fading of Jupiter’s South Equatorial Belt (SEB) between 2009 and 2010. The belt has since returned to view. The Red Spot is also seen in both images. Credit: Anthony Wesley
That doesn’t mean it’s necessarily going away, though if it did — at least temporarily — it wouldn’t be the first time. The Spot vanished in the 1680s only to reappear in 1708. Like clouds and weather fronts that keeps things lively on Earth, Jupiter’s atmosphere constantly cooks up new surprises. The entire South Equatorial Belt, one of Jupiter’s two most prominent “stripes”, has taken a leave of absence at least 17 times since the invention of the telescope, the last in 2010.
The Great Red Spot photographed by Voyager 1 in 1979 and reprocessed by Bjorn Jonsson shows an incredible wealth of detail. Credit: NASA
Perhaps we should turn the question around? How has the Red Spot managed to last this long? Hurricanes on Earth have lifetimes measured in days, while this whirling vortex has been around for hundreds of years. Any number of things should have killed it: loss of energy through radiation of heat to outer space, or energy-sapping turbulence from nearby jet streams. But the Eye persists. So what keeps it alive? Astronomers think the storm might gain energy by devouring smaller vortices, those small white dots and ovals you see in high resolution photos of the planet. Vertical winds that transport hot and cold gases in and out of the Spot may also restore its vigor.
Just in case it disappears unexpectedly, take one last look this observing season. Jupiter’s currently getting lower in the western sky as it approaches Venus for its grand conjunction on June 30. Below are times (Central Daylight or CDT) when it crosses or transits the planet’s central meridian. The GRS will be easiest to see for a 2-hour interval starting an hour before the times shown. It’s located in the planet’s southern hemisphere just south of the prominent South Equatorial Belt. Add an hour for Eastern time; subtract one hour for Mountain and two hours for Pacific. A complete list of transit times can be found HERE.
* June 13 at 8:58 p.m.
* June 18 at 12:16 a.m.
* June 18 at 8:08 p.m.
* June 20 at 9:47 p.m.
* June 22 at 11:26 p.m.
* June 25 at 8:57 p.m.
* June 27 at 10:36 p.m.
Enhanced-color image of Hyperion from Sept. 26, 2005. (NASA/JPL/SSI)
On Sunday, May 31, the Cassini spacecraft will perform its last close pass of Hyperion, Saturn’s curiously spongelike moon. At approximately 9:36 a.m. EDT (13:36 UTC) it will zip past Hyperion at a distance of about 21,000 miles (34,000 km) – not its closest approach ever but considerably closer (by 17,500 miles/28,160 km) than it was when the image above was acquired.*
This will be Cassini’s last visit of Hyperion. It will make several flybys of other moons within Saturn’s equatorial plane over the course of 2015 before shifting to a more inclined orbit in preparation of the end phase of its mission and its operating life in 2017.
At 255 x 163 x 137 miles (410 x 262 x 220 km) in diameter, Hyperion is the largest of Saturn’s irregularly-shaped moons. Researchers suspect it’s the remnant of a larger body that was blown apart by an impact. Hyperion’s craters appear to have a “punched-in” look rather than having been excavated, and have no visible ejecta or secondary craters nearby.
Impacts on Hyperion tend to “punch in” the surface material, rather than blasting it out. (NASA/JPL/SSI. Edit by J. Major.)
Hyperion orbits Saturn in an eccentric orbit at a distance of over 920,000 miles (1.48 million km)…that’s almost four times the distance our Moon is from us! This distance – as well as constant gravitational nudges from Titan – prevents Hyperion from becoming tidally locked with Saturn like nearly all of its other moons are. In fact its rotation is more of haphazard tumble than a stately spin, making targeted observations of any particular regions on its surface virtually impossible.
Images from the May 31 flyby are expected to arrive on Earth 24 to 48 hours later.
As small as it is Hyperion is Saturn’s eighth-largest moon, although it appears to be very porous and has a density half that of water. Read more about Hyperion here and see more images of it from Cassini here and here.
*Cassini did come within 310 miles (500 km) of Hyperion on Sept. 26, 2005, but the images to make up the view above were acquired during approach.
UPDATE June 1, 2015: the raw images from Cassini’s flyby have arrived on Earth, check out a few below. (Looks like Cassini ended up with the same side of Hyperion again!)
Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI. (Minor editing by J. Major.)Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI.Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI. (Minor editing by J. Major.)
The fascinating surface of Jupiter’s icy moon Europa looms large in this newly-reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. This is the color view of Europa from Galileo that shows the largest portion of the moon's surface at the highest resolution. Credits: NASA/JPL-Caltech/SETI Institute
In a major move forward on a long dreamed of mission to investigate the habitability of the subsurface ocean of Jupiter’s mysterious moon Europa, top NASA officials announced today, Tuesday, May 26, the selection of nine science instruments that will fly on the agency’s long awaited planetary science mission to an intriguing world that many scientists suspect could support life.
“We are on our way to Europa,” proclaimed John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington, at a media briefing today outlining NASA’s plans for a mission dedicated to launching in the early to mid-2020s. “It’s a mission to inspire.”
“We are trying to answer big questions. Are we alone?”
“The young surface seems to be in contact with an undersea ocean.”
The Europa mission goal is to investigate whether the tantalizing icy Jovian moon, similar in size to Earth’s moon, could harbor conditions suitable for the evolution and sustainability of life in the suspected ocean.
It will be equipped with high resolution cameras, radar and spectrometers, several generations beyond anything before to map the surface in unprecedented detail and determine the moon’s composition and subsurface character. And it will search for subsurface lakes and seek to sample erupting vapor plumes like those occurring today on Saturn’s tiny moon Enceladus.
“Europa has tantalized us with its enigmatic icy surface and evidence of a vast ocean, following the amazing data from 11 flybys of the Galileo spacecraft over a decade ago and recent Hubble observations suggesting plumes of water shooting out from the moon,” says Grunsfeld.
“We’re excited about the potential of this new mission and these instruments to unravel the mysteries of Europa in our quest to find evidence of life beyond Earth.”
Planetary scientists have long desired a speedy return on Europa, ever since the groundbreaking discoveries of NASA’s Galileo Jupiter orbiter in the 1990s showed that the alien world possessed a substantial and deep subsurface ocean beneath an icy shell that appears to interact with and alter the surface in recent times.
This 12-frame mosaic provides the highest resolution view ever obtained of the side of Jupiter’s moon Europa that faces the giant planet. It was obtained on Nov. 25, 1999 by the camera onboard the Galileo spacecraft, a past NASA mission to Jupiter and its moons. Credit: NASA/JPL/University of Arizona
NASA’s Europa mission would blastoff perhaps as soon as 2022, depending on the budget allocation and rocket selection, whose candidates include the heavy lift Space Launch System (SLS).
The solar powered probe will go into orbit around Jupiter for a three year mission.
“The mission concept is that it will conduct multiple flyby’s of Europa,” said Jim Green. director, Planetary Science Division, NASA Headquarters, during the briefing.
“The purpose is to determine if Europa is a habitable place. It shows few craters, a brown gum on the surface and cracks where the subsurface meet the surface. There may be organics and nutrients among the discoloration at the surface.”
Europa is at or near the top of the list for most likely places in our solar system that could support life. Mars is also near the top of the list and currently being explored by a fleet of NASA robotic probes including surface rovers Curiosity and Opportunity.
“Europa is one of those critical areas where we believe that the environment is just perfect for potential development of life,” said Green. “This mission will be that step that helps us understand that environment and hopefully give us an indication of how habitable the environment could be.”
The exact thickness of Europa’s ice shell and extent of its subsurface ocean is not known.
The ice shell thickness has been inferred by some scientists to be perhaps only 5 to 10 kilometers thick based on data from Galileo, the Hubble Space Telescope, a Cassini flyby and other ground and space based observations.
The global ocean might be twice the volume of all of Earth’s water. Research indicates that it is salty, may possess organics, and has a rocky sea floor. Tidal heating from Jupiter could provide the energy for mixing and chemical reactions, supplemented by undersea volcanoes spewing heat and minerals to support living creatures, if they exist.
This artist’s rendering shows a concept for a future NASA mission to Europa in which a spacecraft would make multiple close flybys of the icy Jovian moon, thought to contain a global subsurface ocean. Credits: NASA/JPL-Caltech
“Europa could be the best place in the solar system to look for present day life beyond our home planet,” says NASA officials.
The instruments chosen today by NASA will help answer the question of habitability, but they are not life detection instruments in and of themselves. That would require a follow on mission.
“They could find indications of life, but they’re not life detectors,” said Curt Niebur, Europa program scientist at NASA Headquarters in Washington. “We currently don’t even have consensus in the scientific community as to what we would measure that would tell everybody with confidence this thing you’re looking at is alive. Building a life detector is incredibly difficult.”
‘During the three year mission, the orbiter will conduct 45 close flyby’s of Europa,” Niebur told Universe Today. “These will occur about every two to three weeks.”
The close flyby’s will vary in altitude from 16 miles to 1,700 miles (25 kilometers to 2,700 kilometers).
“The mass spectrometer has a range of 1 to 2000 daltons, Niebur told me. “That’s a much wider range than Cassini. However there will be no means aboard to determine chirality.” The presence of Chiral compounds could be an indicator of life.
Right now the Europa mission is in the formulation stage with a budget of about $10 million this year and $30 Million in 2016. Over the next three years the mission concept will be defined.
The mission is expected to cost in the range of at least $2 Billion or more.
Jupiter Moon Europa, Ice Rafting View
Here’s a NASA description of the 9 instruments selected:
Plasma Instrument for Magnetic Sounding (PIMS) — principal investigator Dr. Joseph Westlake of Johns Hopkins Applied Physics Laboratory (APL), Laurel, Maryland. This instrument works in conjunction with a magnetometer and is key to determining Europa’s ice shell thickness, ocean depth, and salinity by correcting the magnetic induction signal for plasma currents around Europa.
Interior Characterization of Europa using Magnetometry (ICEMAG) — principal investigator Dr. Carol Raymond of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California. This magnetometer will measure the magnetic field near Europa and – in conjunction with the PIMS instrument – infer the location, thickness and salinity of Europa’s subsurface ocean using multi-frequency electromagnetic sounding.
Mapping Imaging Spectrometer for Europa (MISE) — principal investigator Dr. Diana Blaney of JPL. This instrument will probe the composition of Europa, identifying and mapping the distributions of organics, salts, acid hydrates, water ice phases, and other materials to determine the habitability of Europa’s ocean.
Europa Imaging System (EIS) — principal investigator Dr. Elizabeth Turtle of APL. The wide and narrow angle cameras on this instrument will map most of Europa at 50 meter (164 foot) resolution, and will provide images of areas of Europa’s surface at up to 100 times higher resolution.
Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) — principal investigator Dr. Donald Blankenship of the University of Texas, Austin. This dual-frequency ice penetrating radar instrument is designed to characterize and sound Europa’s icy crust from the near-surface to the ocean, revealing the hidden structure of Europa’s ice shell and potential water within.
Europa Thermal Emission Imaging System (E-THEMIS) — principal investigator Dr. Philip Christensen of Arizona State University, Tempe. This “heat detector” will provide high spatial resolution, multi-spectral thermal imaging of Europa to help detect active sites, such as potential vents erupting plumes of water into space.
MAss SPectrometer for Planetary EXploration/Europa (MASPEX) — principal investigator Dr. Jack (Hunter) Waite of the Southwest Research Institute (SwRI), San Antonio. This instrument will determine the composition of the surface and subsurface ocean by measuring Europa’s extremely tenuous atmosphere and any surface material ejected into space.
Ultraviolet Spectrograph/Europa (UVS) — principal investigator Dr. Kurt Retherford of SwRI. This instrument will adopt the same technique used by the Hubble Space Telescope to detect the likely presence of water plumes erupting from Europa’s surface. UVS will be able to detect small plumes and will provide valuable data about the composition and dynamics of the moon’s rarefied atmosphere.
SUrface Dust Mass Analyzer (SUDA) — principal investigator Dr. Sascha Kempf of the University of Colorado, Boulder. This instrument will measure the composition of small, solid particles ejected from Europa, providing the opportunity to directly sample the surface and potential plumes on low-altitude flybys.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Host: Fraser Cain (@fcain) Special Guest:Dr. Rhys Taylor, Former Arecibo Post Doc; Current research involves looking for galaxies in the 21cm waveband.
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It hard to think of a more influential modern planetary scientist than Carolyn Porco, the leader of the imaging team for NASA’s Cassini mission exploring Saturn. But before Cassini, Porco was involved in Voyager missions, and she’ll be leading up the imaging team for New Horizons.?
We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.
It hard to think of a more influential modern planetary scientist than Carolyn Porco, the leader of the imaging team for NASA’s Cassini mission exploring Saturn. But before Cassini, Porco was involved in Voyager missions, and she’ll be leading up the imaging team for New Horizons.
We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.
