One of many new Cassini images received after yesterday’s successful Enceladus flyby. Image Credit: NASA/JPL/Space Science Institute - “W00043237.jpg“

Slow server speeds mark the arrival of new raw data on the Cassini-Huygens website taken during yesterday’s successful Enceladus flyby. In addition to the images, Cassini sampled the material in Enceladus’ water ice plumes erupting from the moon’s south pole. Images like the one above will be validated and calibrated while scientists pour over all the new data, hoping for insight into the process that leads to the geyser-like features.

Cassini took this image of Enceladus’ water ice plumes on November 27, 2005.  New pictures and other data from the most recent flyby on Wednesday, March 12, 2008 are expected on Thursday, March 13, 2008.  Image Credit: NASA/JPL/Space Science Institute - “Jet Blue“

NASA’s Cassini spacecraft has successfully completed the closest flyby of Saturn’s mysterious moon Enceladus yet. Coming as close as 52 kilometers (32.3 miles) from the surface of Enceladus, Cassini used its array of instruments to sample the water ice geysers that erupt from the moon’s south pole. The close, and somewhat risky, flyby maybe provide just the required data to begin understanding the source of these geysers. These data have started to arrive at the Earth and will be completely downloaded over the next several hours.

On Wednesday, March 12, 2008 around noon PST, Cassini flew away from Enceladus along the outer extent of the plume that surprised scientists just over two years ago. The surprise was due to the moon’s small size; small moons were generally thought to be inactive, as no internal forces would be present to drive any surface activities. Whatever is driving the spectacular activity on Enceladus remains a mystery.

Recently, two sources for the geysers have been proposed. The “dry” theory suggests that tidal forces along the “Tiger Stripes” fractures discovered at the moon’s south pole rub ice until it is heated sufficiently to escape. The “wet” theory suggest that these tidal forces instead heat a spot in the moon’s interior, resulting in enough heat to melt a lake or ocean of liquid water just below the surface. This pressurized water then escapes through the discovered fractures.

The latest flyby is intended to sample the geysers to determine which of these theories might be correct, or suggest alternative theories. An underground reservoir of liquid water and the forces required might create a potentially habitable location and an intriguing site to look for life. Cassini will look for the presence of sodium, among other elements and compounds, to support the “wet” theory.

Cassini is nearing the completion of its nominal four-year mission to explore Saturn, its rings, and its moons. The mission has been extended for two more years, allowing mission planners to take more risks. Scientists believe that the ice and other particles in the geyser are tiny enough to pose no harm to Cassini. If confirmed, this will allow scientists to fly Cassini closer yet in upcoming explorations of Enceladus. Raw data could start appearing on the Cassini website as early as 5:00 AM PST on Thursday and mission scientists hope to have a preliminary analysis of data completed by Thursday afternoon.

More Information

• Cassini-Huygens Website
  • Saturn’s Moons section
  • Enceladus Information
  • Press Release (NASA/JPL): “Cassini Spacecraft to Dive Into Water Plume of Saturn Moon“
  • Blog: Visiting Enceladus

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington - “MESSENGER’s First Look at Mercury’s Previously Unseen Side“

A heavily cratered side of the planet Mercury never before seen has been revealed by the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft. A single image was released by NASA this evening after the successful flyby of the innermost planet on Monday. Featuring rayed craters, a portion of one of the largest basins in the solar systems, and rings of dark material, the new image is one of over 2000 captured during the first flyby of Mercury in thirty-three years.

More data is expected to arrive on the Earth on Wednesday after MESSENGER’s scheduled contact over the Deep Space Network was postponed due to unexpected problems with other missions and a shift in priorities.  In addition to the global wide-angle image released this evening,  these data include approach and departure images that will be turned into movies and high resolution narrow-angle images taken from only 200 kilometers above Mercury’s surface during closest approach.

In 1975 Mariner 10 successfully completed its third and final flyby of Mercury after imaging less than 50 percent of the planet’s surface.  MESSENGER will complete this mapping task between yesterday’s flyby and two more flybys scheduled for October 06, 2008 and September 29, 2009.  Then, on March 18, 2011, MESSENGER will enter orbit around Mercury for a planned year-long science phase.

The data returned by MESSENGER are expected to answer several longstanding questions about Mercury.  MESSENGER will use its array of instruments protected by a sunshade to search for evidence of water ice trapped in deep and dark craters at the planet’s poles, a potentially counter intuitive finding given Mercury’s close proximity to the Sun.   Scientists will study the planet’s surface and composition as well as its inner structure.  Mercury has a dense core of iron thought to compose a more significant portion of the planet than the cores of the other inner planets do.  Why this should be the case is complicated by the presence of a magnetic field around Mercury.  Magnetic fields are thought to depend on molten cores, but models of Mercury indicate that due to its small size its core should have solidified by now.

More Information

• MESSENGER Website
  • Press Release and Image: “MESSENGER’s First Look at Mercury’s Previously Unseen Side“

With the moon visible overhead, Armadillo Aerospace unsuccessfully attempted to win the Northrop Grumman Lunar Lander Challenge at the Wirefly X PRIZE Cup this weekend at Holloman Air Force Base. The only competitor of nine ready to go for the event, Armadillo Aerospace, led by John Carmack of Doom and Quake fame, experienced both successes and failures during multiple launch attempts. While able to rise 50 meters from the launch pad, move laterally 50 meters, and land after staying aloft at least 90 seconds, the teams vehicle was not able to repeat this feat to return to the launch pad within two and a half hours as required by competition rules. Earlier failures included thrust vectoring problems due to a crack in the vehicle’s engine and an aborted launch soon after liftoff. The team was able to repair some damage rapidly to try again later, but their final attempt on Sunday ended in disaster, with flames engulfing the vehicle immediately after the launch sequence began.

Armadillo Aerospace, a private company started by Doom and Quake game developer John Carmack, has been the leading contender for the prize that is intended to accelerate techniques and innovations for future lunar landers. The other eight registrants were not ready by the time of the event to compete. At stake is $350,000 in prize money for first place in level one of the competition. Level two will award a larger prize but requires 180 seconds aloft over rough terrain. Peter Diamandis, Chairman and CEO of the X PRIZE Foundation, explained to the audience that the competition’s return flight requirement is meant to demonstrate reusability of the vehicle within a short amount of time by a small team of technicians. This contrasts with shuttle launches that require many people, several months, and approximately US$1,000,000,000 in costs for turnaround.

The failure by Armadillo Aerospace to walk away with the prize opens up the competition to other teams during the 2008 X PRIZE Cup. According to a representative for the Speed Up team, they only need a few more months to make “Laramie Rose,” their entry vehicle, ready for competition.

Image Credit: NASA/JPL/University of Arizona - “PSP_003086_2015: Color Image of Nili Fossae Trough, Candidate MSL Landing Site“

[Disclaimer: Richard Leis, Jr. is an Operations Specialist for HiRISE.]

The High Resolution Imaging Science Experiment (HiRISE) team today released a slew of new false color images of the surface of Mars to the public, the culmination of many months of software and automation development. Color products are now expected to be released at regular intervals, matching the previous release rate of black and white images. The images selected are of potential Mars Science Laboratory (MSL) landing sites, the upcoming rover mission planned for launch in 2009. Now that these images have been released, researchers suggesting landing sites for the mission will have new data to work with while developing their proposals.

Creating useful color products from HiRISE data has proven to be a difficult task that has involved many people. Sarah Mattson applied her continuing University of Arizona mathematics education to help develop algorithms for registering and stitching the various color products together, based on manual procedures developed by HiRISE Principal Investigator Alfred McEwen. Guy McArthur, a software developer for HiRISE, created a series of automated “pipelines” for turning calibrated image products into beautiful final color products. Eric Eliason, HiRISE Operations Center (HiROC) Manager oversaw the software development effort and participated in validation efforts. Operations Specialist Táhirih Motazedian reprocessed MSL image data through calibration, geometry, and the new color pipelines, after also conducting thorough testing of the pipelines, all while managing the HiROC systems resources that are pushed to their limits during such intense reprocessing efforts. Student Validators Alaina de Jong and Bryan Cardwell raced to validate new color products fresh out of the pipelines to ensure they were ready for today’s scheduled public release. Database Manager Rod Heyd ensured the database and procedures for releasing products were updated to handle the new color products. Finally, Website Guru Yisrael Espinoza updated the web backend and public site to include color images in an attractive and user-friendly way.

Image Credit: NASA/JPL/University of Arizona - “PSP_004052_2045: Layers Exposed in Crater Near Mawrth Vallis”

The HiRISE camera is currently in orbit around Mars on board the Mars Reconnaissance Orbiter (MRO). The camera is returning the highest resolution images of the surface ever taken from Mars orbit, with images reaching resolutions of nearly 25 centimeters per pixel. This equates to objects about one meter in size on the surface of Mars, since the human eye needs about three or four pixels to pick out an object in an image. The new color images are in enhanced and false color. Everyone knows well that the surface of Mars is a study in red, so choosing color filters that can pull out subtle differences between compositions was a priority when developing the camera. Red, near infrared, and blue-green filters down the center of the instrument’s CCD array create a false color swath in HiRISE images of about 1.2 kilometers in width. The remaining red CCDs create a black and white image 6 kilometers across.

The prospective landing sites targeted by HiRISE include materials like clays, sulfates, and other materials with high water content. MSL is expected to explore just such a location to determine the past and current role of water on Mars and whether or not the environment ever supported microbial life.

More Information

• High Resolution Imaging Science Experiment (HiRISE)
  • October 10, 2007 Color Release of MSL Observations
  • [PDF] “Information for Scientific Users of HiRISE Color Products” By Alfred McEwen and Eric Eliason, October 10, 2007
  • University of Arizona Press Release: “HiRISE Releases Color Images, Movie of Prospective Landing Sites on Mars“
  • HiBlog
• Mars Science Laboratory (MSL)
• Mars Reconnaissance Orbiter (MRO)

• Division for Planetary Sciences 40th Annual Meeting
• Ithaca, NY, USA
• October 11-15, 2008

• Division for Planetary Sciences 39th Annual Meeting
• The University of Central Florida, Orlando, FL, USA
• October 07-12, 2007

[Launch Coverage] | [Commentary]

2:10 AM PST

Too early! But despite the small hours of the morning here I am very excited for the big launch of the Dawn spacecraft planned for this morning. NASA TV playing in Windows Media Player, the oven heating for some waffles, and a groggy yet excited brain…here we go!

2:18 AM PST

Launch is still planned for 7:20 AM PST (4:20 AM EST.)

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 2:24 AM PST

2:38 AM PST

The launch vehicle is a Delta II Heavy 2925H (modified Delta II) that will lift 1,217.7 kilograms (2,684.6 pounds) of spacecraft plus fuel. Right now technicians are adding liquid oxygen in preparation for launch. Launch will be from Cape Canaveral Air Force Station in Florida, USA.

Dawn will visit the two largest objects in the Asteroid Belt: asteroid Vesta and dwarf planet Ceres. This is not just a flyby mission; Dawn will actually approach and then go into orbit around each body, meaning that after it finishes with its exploration of Vesta, it will need to restart its ion propulsion engine to leave orbit and travel on to Ceres. Dawn should reach Vesta in September 2011 and Ceres in February 2015.

Other coverage:

• Dawn Mission Home Page
• Space.com
• The Planetary Society Weblog

2:54 AM PST

Image Caption: “Hubble Images of Asteroids Help Astronomers Prepare for Spacecraft Visit”
Credits for Vesta: NASA, ESA, and L. McFadden (University of Maryland)
Credits for Ceres: : NASA, ESA, and J. Parker (Southwest Research Institute)

Notice that Ceres is large enough to be roughly spherical in shape. Vesta is just slightly too small to be a sphere. The Hubble images are some of the best images taken of these bodies to date. The journey from discovery of a light in the sky followed by improving telescope images culminating in close up images by spacecraft is the reason why I find planetary science so fascinating. Just take a moment to appreciate what we do not know about Ceres and Vesta, and what we do know, captured in these blurry images. In just a few years, pending a successful launch, we will finally gain a much clearer perspective of these mysterious planetary bodies when their surfaces are revealed in great detail by Dawn.

3:09 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 3:07 AM PST - venting oxygen vapor

3:22 AM PST

The operations teams heard during launch coverage sound like well-oiled machines, checking off items on their checklists with great confidence and professionalism. This indicates both the complexity of the logistics involved with any launch and the experience and abilities of highly skilled humans. A highlight of NASA TV coverage is when, at particular intervals in the activity leading up to launch, various teams report in that their subsystems are “Go!” This same sequence of “Go!” pronouncements just prior to launch was a highlight for those of us on the HiRISE team who attended the launch of Mars Reconnaissance Orbiter. Sometimes we try to do the same thing at work, to liven up the place, to various degrees of success.

3:32 AM PST

A built-in hold of 20 minutes is coming up soon, followed by the restart of countdown, a 10 minute hold, and then, potentially on schedule, launch!

3:35 AM PST

T minus 15 minutes and holding for twenty minutes…

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 3:35 AM PST - Logos through vapor

3:45 AM PST

The Dawn Mission website has a wealth of images, graphics, and video, including this graphic of the spacecraft:

Image Credit: Orbital Sciences Corporation - “Dawn Spacecraft“

3:55 AM PST

The countdown clock has restarted with 15 minutes and one last built-in hold expected prior to launch. Weather is reported to be good. And dawn is breaking behind Dawn!

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 3:53 AM PST - Dawn breaks behind Dawn

4:02 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 3:59 AM PST - Engineering

4:05 AM PST

Next built-in hold of ten minutes has begun, at T minus 4 minutes.

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:05 AM PST - Dawn nears launch

4:14 AM PST

The hold has been extended, possibly because of a small aircraft or boat nearby.

4:16 AM PST

According to NASA TV, a ship has been spotted in the area. The Coast Guard has contacted the ship, to make sure it moves out of the way of falling solid rocket boosters. The ship should be out of the area in a few minutes.

4:20 AM PST

New launch time: 7:34 AM EST (4:34 AM PST.)

4:27 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:24 AM PST

4:30 AM PST

T minus 4 minutes to launch!

4:31 AM PST

“Go!” for launch…everything seems to be ready…

4:34:00.372 AM PST

Launch!

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:34 AM PST - Launch!

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:34 AM PST - Launch

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:34 AM PST - Column rising

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:34 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:34 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:35 AM PST

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 4:35 AM PST - Solid motors jettison

4:38 AM PST

All seems to be well, with events happening as expected. Dawn is racing away up through the atmosphere and away from the Earth.

4:44 AM PST

Dawn has reached Earth orbit. It will coast there for 40 minutes before the second and third stage engines sends Dawn on its way to its first stop: Vesta.

5:10 AM PST

The second stage should reignite around 5:14 AM, followed by the third stage. Separation should occur 62 minutes after launch and then the solar arrays will begin deployment. Confirmation that everything is fine and Dawn is successfully on its way may not come until one hour and 34 minutes after launch, or later. Necessary Dawn autonomous actions mean that the spacecraft will be out of contact with the Earth for much of that time.

5:25 AM PST

Telemetry has been reacquired and all is well. Second stage restart has just occurred. Operations is following along with an animation of events created from telemetry.

5:33 AM PST

The second stage fired, shut down, and separated from the upper stages successfully.

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 5:26 AM PST - Second stage firing animation

Image Credit: NASA TV screen capture - Dawn Launch Coverage as of 5:29 AM PST - Second stage separation animation

5:37 AM PST

The third stage fired and separated successfully, and Dawn is on its way!

A spacecraft health check should occur in a few hours, followed by a press conference at 1:00 PM EST (10:00 AM PST.)

Despite a 24-hour delay, preparations continue for the launch later this week of the Dawn spacecraft to explore two members of the Asteroid Belt. Dawn is now scheduled to be launched between 7:25 and 7:54 AM EDT on Thursday, September 27, 2007 after weather today interrupted the planned completion of launch vehicle fueling. The spacecraft will be launched from Space Launch Complex 17B at Cape Canaveral Air Force Station, Florida, USA using the Delta 2925H launch vehicle.

The launch period between September 26 and October 15, 2007 will allow Dawn to reach both Asteroid Vesta and recently reclassified dwarf planet Ceres as planned. Dawn has been repeatedly postponed due to a slew of other mission launches this summer and fall. These delays follow the cancellation and surprise reinstatement of the mission after earlier cost concerns were capped and technical issues were addressed.

The Dawn mission is unique because a single spacecraft will enter orbit around two separate bodies. Dawn will use an advanced ion propulsion system to enter orbit around Vesta in 2011 and then Ceres in 2014. Vesta and Ceres are the two largest objects in the Asteroid Belt and are expected to give planetary scientists a glimpse at the early history of the solar system. Scientists believe Vesta and Ceres have had very different histories despite similar beginnings.

NASA TV will broadcast the launch live.

More Information

• Dawn Mission Home Page

In 2005 Saturn’s moon Enceladus was discovered to be an active world with water ice particle geysers at its south pole. The driver of this activity on a moon so small remains a mystery. One possible explanation has been suggested by Dr. Francis Nimmo, a planetary scientist from the University of California Santa Cruz. Nimmo visited the University of Arizona Lunar and Planetary Laboratory to present his model on Thursday, September 18, 2007 for the department’s weekly Planetary Sciences Colloquium. The talk was based on his recent publication [reprint PDF] “Shear heating as the origin of the plumes and heat flux on Enceladus” in Nature.

While the old view of the outer solar system as a cold and dead region devoid of most geological activity has eroded with surprising discoveries since the 1980’s, one bias persisted until 2005: only large moons in the outer solar system could potentially be active. Below a particular diameter, moons were not believed to be able to produce sufficient internal heating to drive surface activity. With a diameter of only 252 kilometers (157 miles), Enceladus was expected to have frozen solid long ago. The discover of geysers and a thin oxygen atmosphere at Enceladus proved that this was not the case.

Enceladus’ geysers do not appear to be a global phenomena, however. They are localized to the moon’s south pole, apparently along fractures referred to as “Tiger Stripes.” Taking into consideration the moon’s size, possible internal structures, orbital eccentricity, and other characteristics Nimmo has been working to develop a model that can explain the localized nature of this activity.

An important feature of his model is reorientation theory, where a mass such as a diapir rising to the surface from the mantle can reorient a body, driving the mass’ surface expression toward the poles or equator over time. The presence of such a mass would indicate some driving force such as convection. Applied to Enceladus, this could explain why the tiger stripes have reorientated to their present location at the south pole.

While this may explain the tectonic activity at the south pole, the presence of active water ice plumes requires further explanation. If the tiger stripes are strike-slip faults like the San Andreas Fault on the Earth, then rapid enough motion back and forth along the faults could lead to uplift and shear heating. This friction leads to sublimation of water ice, the primary component of the crust of Enceladus, with some of that vapor being released with heat along the tiger stripes in the form of the spectacular plumes photographed by the Cassini spacecraft.

After developing this model, which Nimmo believes is a better explanation than other theories that have been put forward, such as a near-surface ocean or clathrate decomposition, Nimmo and his colleagues explored possible predictions. While a near-surface ocean does not provide the water vapor to geysers in his model, the model still suggests the presence of an ocean underneath a solid ice crust of at least 5 kilometers (3 miles). The model suggests that this ocean may be transitory, with significant freezing out or remelting depending on the tidal dynamics that change as Enceladus’ orbit around Saturn changes over time.

Furthermore, the orientation of the tiger stripes should change over time, and their fault motions should result in hotter or colder relative temperatures depending on how fast they are moving. In the paper, the team of researchers specify two portions of stripes they predict will have the highest relative tempatures. Some researchers believe fossil tiger stripes may be present elsewhere on Enceladus. Further observations of Enceladus may allow them to test this prediction and confirm or deny the presence of fossil tiger stripes.

Nimmo acknowledged that at present this model of Enceladus is simplistic with several questions still outstanding. Why, for example, does heating appear only at the south pole and not also at the north pole, as predicted by some models of subsurface tidal heating? What prevents the ocean, if it exists, from freezing out completely? Enceladus remains a mystery and will continue to be an important study target for planetary scientists still marveling at a frigid but incredibly active outer solar system.

More Information

• Dr. Francis Nimmo at the University of California Santa Cruz
• Cassini-Huygens Website
  • Saturn’s Moons section
  • Enceladus Information