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Date: Wednesday, 23 Apr 2014 12:28
Hubble used the Advance Camera for Surveys to get this look at NGC 3455.  Credit:  ESA/Hubble & NASA, Acknowledgement: Nick Rose

Hubble used the Advance Camera for Surveys to get this look at NGC 3455. Credit: ESA/Hubble & NASA, Acknowledgement: Nick Rose

Located at RA: 10 51 52/DEC: 17 33.1 in the constellation Leo. The photo caption at NASA and included below pegs the distance at 65 million light-years what it doesn’t say is the red-shift velocity is about 1102 km sec / 685 miles per second!

The companion galaxy mentioned in the press release NGC 3454 can be seen here. NGC 3455 is the galaxy just below center and above that you can see the bright star in the center and the cigar shaped NGC 3454 above that.  Image: Simbad

The companion galaxy mentioned in the press release NGC 3454 can be seen here. NGC 3455 is the galaxy at the  center and above that you can see the bright star (from the Hubble image) in the center and the cigar shaped NGC 3454 above that. Image: Simbad

A very nice image and you can get more sizes at the link below.

The NASA/Hubble press release:

Shown here is a spiral galaxy known as NGC 3455, which lies some 65 million light-years away from us in the constellation of Leo (the Lion).

Galaxies are classified into different types according to their structure and appearance. This classification system is known as the Hubble Sequence, named after its creator Edwin Hubble.
In this image released 14, April, 2014, NGC 3455 is known as a type SB galaxy — a barred spiral. Barred spiral galaxies account for approximately two thirds of all spirals. Galaxies of this type appear to have a bar of stars slicing through the bulge of stars at their center. The SB classification is further sub-divided by the appearance of a galaxy’s pinwheeling spiral arms; SBa types have more tightly wound arms, whereas SBc types have looser ones. SBb types, such as NGC 3455, lie in between.

NGC 3455 is part of a pair of galaxies — its partner, NGC 3454, lies out of frame. This cosmic duo belong to a group known as the NGC 3370 group, which is in turn one of the Leo II groups, a large collection of galaxies scattered some 30 million light-years to the right of the Virgo cluster.
This image is from Hubble’s Advanced Camera for Surveys.

Author: "Tom" Tags: "Space Telescope"
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Date: Tuesday, 22 Apr 2014 12:45
The peak-ring basin Scarlatti as seen from MESSENGER on 18 April 2014.  Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The peak-ring basin Scarlatti as seen from MESSENGER on 18 April 2014. Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

On 20 April 2014 the MESSENGER spacecraft completed 3,000 orbits of the planet Mercury and is about to get closer to the planet than ever before at an altitude of 199 km / 124 miles.

From the MESSENGER website:

“We are cutting through Mercury’s magnetic field in a different geometry, and that has shed new light on the energetic electron population,” said MESSENGER Project Scientist Ralph McNutt, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. “In addition, we are now spending more time closer to the planet in general — and that has, in turn, increased the opportunities for all of the remote sensing instruments to make higher-resolution observations of the planet.”

 

MESSENGER has been completing three orbits of Mercury every day since April 2012, when two orbit-correction maneuvers reduced its orbital period about Mercury from 12 hours to 8 hours. The shorter orbit has allowed the science team to explore new questions about Mercury’s composition, geological evolution, and environment that were raised by discoveries made during the first year of orbital operations.

APL’s Carolyn Ernst, the deputy instrument scientist for the Mercury Laser Altimeter (MLA), said the change from a 12- to an 8-hour orbit provided her team with 50% more altimetry tracks. “MLA coverage takes a long time to build up, and because of the small footprint of the laser, a lot of coverage is needed to obtain good spatial resolution. The more data we acquire, the better we resolve the topography of the planet,” she said. “The 8-hour orbit has also allowed us to make more MLA reflectivity measurements, which have provided critical clues for characterizing Mercury’s radar-bright deposits at high northern latitudes.”

The probe has been edging closer and closer to Mercury since March 2013, at about the time that the spacecraft orbit’s minimum altitude passed closest to Mercury’s north pole.

APL’s David Lawrence, a MESSENGER Participating Scientist, said he is excited about what the low-altitude orbits will reveal about Mercury’s surface composition. “To date our compositional measurements with neutron, X-ray, and gamma-ray data have resolved only very large regions on Mercury’s surface. Altitudes of less than 100 kilometers will enable us to pinpoint the compositional signatures of specific geologic features, which in turn will help us to understand how the surface formed and has changed over time.”

MESSENGER’s periapsis altitude will continue to decrease until the first orbit-correction maneuver of the low-altitude campaign, scheduled for June 17.

“The final year of MESSENGER’s orbital operations will be an entirely new mission,” added MESSENGER Principal Investigator Sean Solomon, of Columbia University’s Lamont-Doherty Earth Observatory. “With each orbit, our images, our surface compositional measurements, and our observations of the planet’s magnetic and gravity fields will be higher in resolution than ever before. We will be able to characterize Mercury’s near-surface particle environment for the first time. Mercury has stubbornly held on to many of its secrets, but many will at last be revealed.”

About Scarlatti

Author: "Tom" Tags: "MESSENGER"
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Date: Monday, 21 Apr 2014 12:47
Artist concept of LADEE.  Image Credit: NASA Ames/Dana Berry

Artist concept of LADEE. Image Credit: NASA Ames/Dana Berry

The Lunar Atmosphere and Dust Environment Explorer (LADEE) interfaced with lunar surface, NASA speak for it hit the moon – hard.

The impact occurred between 21:30 and 22:22 PDT on 17 April. Not bad, my guess was 19:20 on 18 April.

I was kind of hoping to hear where it hit this weekend, apparently I was over-simplifying things. The spacecraft was moving about 5,800 kmh or 3,600 mph. Not likely to be anything recognizable on the surface except for small impact craters.

We might get a good look at the impact site from the Lunar Reconnaissance Orbiter Camera as soon as mission managers figure out where it ended up and a LRO pass will occur.

The LADEE mission end at NASA.

Author: "Tom" Tags: "General"
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Date: Sunday, 20 Apr 2014 16:37

New Horizons: On the Space Frontier

Glad to hear anything about New Horizons as I patiently wait out the long journey.

Source

Author: "Tom" Tags: "New Horizons"
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Date: Saturday, 19 Apr 2014 17:01

In case you missed it, here’s yesterday’s Space X launch.

Part of the mission was to land the first stage successfully and according to Space X, the landing was good. A successful landing in this case is a vertical “soft” landing and telemetry indicated it looks like it did indeed transmitting for eight seconds after reaching the water and stopped transmitting when it tipped over horizontally — not all the data though. Last reports had ships heading to the location for the possible recovery of the first stage. The recovery effort is NOT expected to be successful, but who knows.

Nice look at the first stage separation and stage two engine starting up.

Video

Author: "Tom" Tags: "Launch / Landing"
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Date: Friday, 18 Apr 2014 09:20
Artist's concept of Kepler-186f , the first validated Earth-size exp-planet to orbit a distant star in the habitable zone.  Image Credit: NASA Ames/SETI Institute/JPL-Caltech

Artist’s concept of Kepler-186f , the first validated Earth-size exp-planet to orbit a distant star in the habitable zone. Click for larger. Image Credit: NASA Ames/SETI Institute/JPL-Caltech

NOTE There is a 40 percent chance of the Space X -3 mission today at 15:25 ET / 19:25 UTC.  

Big news! Kepler-186f is the FIRST rocky Earth-sized exo-planet found! I am hoping this is just the first of a new series of discovery.

Being in the habitable zone means there is a possibility first of an atmosphere. If there is an atmosphere the similar Earth size then it could be possible to have an atmosphere more like our own. At the very least Hydrogen and Helium should be lacking as it is here, because as you know both of those gases are made of small and light atoms; those atoms move fast and at Earth temperatures, that velocity exceeds Earth’s escape velocity. Planets like Jupiter and the other gas giants have more gravity and are colder so Hydrogen and Helium are retained.

Then of course that only after an atmosphere you have to have the rest of the pieces. Or Kepler-186f could be just a big rock.

We are a long way from knowing the details on Kepler-186f, but just finding a planet of Earth size and in the habitable zone is an excellent start!

Here’s the press release from NASA (great wallpaper too!):

The artist’s concept depicts Kepler-186f , the first validated Earth-size planet to orbit a distant star in the habitable zone—a range of distance from a star where liquid water might pool on the planet’s surface. The discovery of Kepler-186f confirms that Earth-size planets exist in the habitable zones of other stars and signals a significant step closer to finding a world similar to Earth.

The size of Kepler-186f is known to be less than ten percent larger than Earth, but its mass, composition and density are not known. Previous research suggests that a planet the size of Kepler-186f is likely to be rocky. Prior to this discovery, the “record holder” for the most “Earth-like” planet went to Kepler-62f, which is 40 percent larger than the size of Earth and orbits in its star’s habitable zone.
Kepler-186f orbits its star once every 130 days and receives one-third the energy that Earth does from the sun, placing it near the outer edge of the habitable zone. If you could stand on the surface of Kepler-186f, the brightness of its star at high noon would appear as bright as our sun is about an hour before sunset on Earth.
Kepler-186f resides in the Kepler-186 system about 500 light-years from Earth in the constellation Cygnus. The system is also home to four inner planets, seen lined up in orbit around a host star that is half the size and mass of the sun.
The artistic concept of Kepler-186f is the result of scientists and artists collaborating to imagine the appearance of these distant worlds.

Author: "Tom" Tags: "Exoplanets"
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Date: Thursday, 17 Apr 2014 12:45

The Tadpole and the Wriggler. Click for larger. Copyright NASA, ESA, the Hubble Heritage Team (STScI/AURA), and IPHAS

I want to see the Goldfish. Ok I spent five minutes looking for it until I re-read the press release and the bit about it being just out of view. Larger and full-res versions availble at the link below.

BTW, I LOVE the title from ESA for selfish reasons. LOL.

From ESA Spaceinimages (The Tadpole and the Wriggler):

A bright blue tadpole appears to swim through the inky blackness of space. Known as IRAS 20324+4057 but dubbed “the Tadpole”, this clump of gas and dust has given birth to a bright protostar, one of the earliest steps in building a star.

There are actually multiple protostars within this tadpole’s ‘head’, but the glowing yellow one in this image is the most luminous and massive. When this protostar has gathered together enough mass from its surroundings, it will eventually emerge as a fully-fledged young star.

The intense blue glow is caused by nearby stars firing ultraviolet radiation at IRAS 20324+4057, which also sculpts its tail into a long, wiggly shape. In total, this clump spans roughly a light-year from head to tail-tip, and contains gas weighing almost four times the mass of the Sun.

Framed against a background of distant stars, IRAS 20324+4057 is making its way through the Cygnus OB2 association, a loose cluster of stars some 4700 light-years from Earth in the constellation of Cygnus. This association is one of the largest clusters known, and is famed for its heavyweight members. It contains some of the hottest, most massive and most luminous stars known, some of which are some two million times more luminous than the Sun.

The Tadpole is not alone in this interstellar pond. Just out of view to the bottom right of this image lies another curious object dubbed “the Goldfish” by astronomers. The Goldfish is about half the length of IRAS 20324+4057, and is also thought to be a globule of gas that is being both lit up and sculpted by radiation from cluster stars.

Completing this trio is a small clump of blue gas, informally nicknamed “the Wriggler” by some astronomers, visible in the bottom left of this Hubble image. All three objects have the same orientation in the sky and appear to be brighter on their northern sides, leading astronomers to believe they are being shaped by aggressive winds and radiation flowing from hot Cygnus OB2 stars towards the top right of the frame.

This image was originally released in August 2013 at the Hubble Heritage website.

Author: "Tom" Tags: "ESA, NASA, Space Telescope"
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Date: Wednesday, 16 Apr 2014 10:33
The final journey of Cassini. Image: NASA

The final journey of Cassini. Image: NASA

As hard as it seems, the Cassini spacecraft soon enough enter the final phase of its mission.

The new and final mission will begin in 2016 and promises to be incredible.

During this final phase the spacecrafts orbit will take it well above the north pole of Saturn, it will then plunge between the inner ring and the planet itself.

You can get the details of the final months of Cassini  here.

In the mean time the Cassini team is looking for a name to call the mission and YOU can help.

You can:
Pick a name from a list.
or
Submit a name of your own.

Author: "Tom" Tags: "Cassini"
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Date: Tuesday, 15 Apr 2014 12:41
A small icy object named Peggy in the rings of Saturn.  Image: NASA/JPL-Caltech/Space Science Institute

A small icy object named Peggy in the rings of Saturn. Image: NASA/JPL-Caltech/Space Science Institute

An “object”, dubbed Peggy located at the edge of the rings seen here at the bottom is being described as a “Small Icy Object”; might it be a new moon forming? Maybe, although it’s not expected to grow any larger, Peggy gives a good look at how a moon could form. It’s all new to everybody because this has never been seen before – a common theme with the Cassini mission. An epic mission for sure.

Here’s the story at NASA.

Author: "Tom" Tags: "Cassini"
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Date: Monday, 14 Apr 2014 16:54

Great animation but a little on the large size. Patience. Image: Tomruen / Creative Commons

Tomorrow morning 15 April 2014 at 07:46 UTC / 03:46 EDT the moon will be at total eclipse. This will be the first of a Tetrad, four total lunar eclipses.

All of the tetrad eclipses will be visible from North America. With this particular eclipse portions of Western Europe and Africa will get to see a little bit at the start, for example the British Isles should get to see the moon enter the penumbral shadow at 04:54 UTC, just barely before the moon sets. As one travels west say viewers in France, Spain and western Africa should be able to see it for a little longer. The same can be said for eastern Asia except their opportunity will come briefly at the end of the eclipse.

Can you see it? Check the map.

As for me, well it is clouding up now and we are expected to get up to 5 cm of rain so I bet not.

You can watch live below at about 04:54 UTC / 12:54 EDT.

The Space X launch I mentioned earlier was scrubbed due to a helium leak, rescheduled for Friday.

Video streaming by Ustream

Author: "Tom" Tags: "Eclipse"
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Date: Sunday, 13 Apr 2014 16:42

Until now we thought only big things had rings, really big things like Saturn and Jupiter. Turns out rings can occur around much smaller objects, like the asteroid Chariklo.

Chariklo or more formally 10199 Chariklo is a minor planet orbiting beyond Saturn, in fact its orbit is such it gets out to the orbit of Uranus.

Chariklo is only about 248 to 258 km / 154 to 160 miles in diameter (plus or minus 18 km), it has not one but two ring named Oiapoque and Chuí. It is almost unbelievable the rings could be detected, especially since Charilko was found only relatively recently, in February of 1997 by James Scotti of Spacewatch.

NOTE: Not sure what is going on with the Space X launch scheduled for 20:58 UTC (4:58 EDT). The last I have heard is there is an 80 percent chance of launch (from KSC) due to weather. There will be a press conference in a little while, I hope to be back with more news then.

Space X update:  

Sounds like there are adding a “late load” to the spacecraft right now and are attempting to have things ready tomorrow.

Space X is go for launch.

Video

Author: "Tom" Tags: "History"
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Date: Saturday, 12 Apr 2014 15:29

What goes into a supersonic parachute test, more than I thought.

Go big (and to Mars) or go home.

Video

Author: "Tom" Tags: "Cool Stuff"
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Date: Friday, 11 Apr 2014 07:15

A pre-winter storm off the Australian coast on 29 march 2014. Click for larger. Image: International Space Station.

This was a “pre-winter” storm off the coast of southwestern Australia was photographed from the International Space Station while over the southeastern Indian Ocean (at about 45.6 deg south and 108.9 deg west) on March 29th. The clockwise cloud pattern is opposite for storms in the north. I don’t know what the scale of the image is but the strom looks pretty large.

You should go to the NASA page featuring this image and grab a copy for your desktop it looks AMAZING!

Author: "Tom" Tags: "ISS"
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Date: Thursday, 10 Apr 2014 05:54

The diamond ring look of planetary nebula Abell 33. Click for larger. Credit: ESO

The ESO’s Very Large Telescope in Chili gives is the nice look at the Planetary Nebula Abell 33.

Abell 33 is located in the constellation Hydra. You can look around the region with The Microsoft Research Worldwide Telescope – enjoy!

The description from the ESO is below, click here to look at and download a variety of desktop sized images too:

Most stars with masses similar to that of our Sun will end their lives as white dwarfs — small, very dense, and hot bodies that slowly cool down over billions of years. On the way to this final phase of their lives the stars throw their atmospheres out into the space and create planetary nebulae, colourful glowing clouds of gas surrounding the small, bright stellar relics.

This image, captured by ESO’s Very Large Telescope (VLT), shows the remarkably round planetary nebula Abell 33, located roughly 2500 light-years from Earth. Being perfectly round is uncommon for these objects — usually something disturbs the symmetry and causes the planetary nebula to display irregular shapes.

The strikingly bright star located along the rim of the nebula creates a beautiful illusion in this VLT image. This is just a chance alignment — the star, named HD 83535, lies in the foreground of the nebula, between Earth and Abell 33, in just the right place to make this view even more beautiful. Together, HD 83535 and Abell 33 create a sparkling diamond ring.

Author: "Tom" Tags: "ESO"
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Date: Wednesday, 09 Apr 2014 12:44

Watch this! They (Airanespace) call it remarkable, I call that an understatement!  This is astounding is what it is.

One of the many really cool video showing up recently.

This from Arianespace:

Remarkable images from on-board cameras provide a detailed “ride-along” view of Arianespace’s Flight VS07, which orbited Europe’s Sentinel-1A from the Spaceport in French Guiana.

Recorded during the 23-minute mission on April 3, multiple cameras covered the action from final countdown to separation of the mission’s payload.

The Arianespace/European Space Agency/Roscosmos-copyrighted video begins with the pre-launch steps as seen from two cameras – mounted on opposite sides of the medium-lift launcher.

Looking down from the launcher’s upper portion, the opening sequence includes separation of umbilical connections for Soyuz’ Fregat upper stage, followed by the tilt-back of two umbilical masts. One of these masts provides fluids and electrical connections for the launcher’s Block I third stage, while the second mast services the Soyuz vehicle’s Block A core stage.

Soyuz’ engine ignition is clearly seen in the video with the startup sequence for the first stage’s four boosters and central core second-stage. This is followed by liftoff and the opening of four arms that supported the vehicle while on the pad – and which are opened by Soyuz’ upward movement.

Major steps during the flight trajectory as shown by the video are the jettison of Soyuz’ first stage boosters; separation of the two-piece payload fairing that protected Sentinel-1A during the initial ascent (as viewed by an upward-looking camera); dropoff of the second and third stages; and the mission-concluding deployment of Sentinel-1A by Fregat for operation in Sun-synchronous orbit.

Flight VS07 was Arianespace’s seventh mission with the medium-lift vehicle from French Guiana, and its Sentinel-1A passenger is the first for a family of dedicated missions to form the core of Europe’s Copernicus environmental monitoring network.

Author: "Tom" Tags: "Cool Stuff, ESA"
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Date: Tuesday, 08 Apr 2014 10:05

An Solar Dynamics Observatory video (coming to us from NASA/Goddard of an M 6.5 solar flare. Not quite the strongest of flare classes but still pretty strong and had it been directed at Earth it certainly could have given us an aurora.

I doubt we will see any auroral activity from this event, however, a flare could re-occur from the area so one never knows for sure. Keep an eye to the sky, also these strong earthquakes can disrupt the geomagnetic field enough to cause an auroral event. Generally at my latitude these types are almost ghostlike.

One other noteworthy observation about this flare is it’s a mid-level flare. Generally when I see these mid-latitude sunspots and flares I know the peak of the solar cycle isn’t too far away.

Video source

Author: "Tom" Tags: "SDO"
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Date: Monday, 07 Apr 2014 10:04
Submit your guess!  Image: NASA

Submit your guess! Image: NASA

The LADEE spacecraft is coming to the end of it’s mission. The spacecraft is going to go out with a bang, literately, it is going to impact the surface of the moon.

You can be a part of end of the mission too. Go on, take the challenge!

How?

First, read the short background below from NASA on what is going on.

Then just make your best guess and SUBMIT IT HERE.

The NASA link below will take you to the complete press release as I only included enough to get you going.

My entry is in, that certificate of success is as good as mine. . . or not. LOL.

Good luck and have fun.

From NASA:

When will it impact the lunar surface? NASA wants to hear your best guess!

LADEE mission managers expect the spacecraft will impact the moon’s surface on or before April 21. On April 11, ground controllers at NASA’s Ames Research Center in Moffett Field, Calif., will command LADEE to perform its final orbital maintenance maneuver prior to a total lunar eclipse on April 15, when Earth’s shadow passes over the moon. This eclipse, which will last approximately four hours, exposes the spacecraft to conditions just on the edge of what it was designed to survive.

This final maneuver will ensure that LADEE’s trajectory will impact the far side of the moon, which is not in view of Earth and away from any previous lunar mission landings. There are no plans to target a particular impact location on the lunar surface, and the exact date and time depends on several factors.

“The moon’s gravity field is so lumpy, and the terrain is so highly variable with crater ridges and valleys that frequent maneuvers are required or the LADEE spacecraft will impact the moon’s surface,” said Butler Hine, LADEE project manager at Ames. “Even if we perform all maneuvers perfectly, there’s still a chance LADEE could impact the moon sometime before April 21, which is when we expect LADEE’s orbit to naturally decay after using all the fuel onboard.”

Anyone is eligible to enter the “Take the Plunge: LADEE Impact Challenge.” Winners will be announced after impact and will be e-mailed a commemorative, personalized certificate from the LADEE program. The submissions deadline is 3 p.m. PDT Friday, April 11.

Author: "Tom" Tags: "Cool Stuff"
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Date: Sunday, 06 Apr 2014 16:23

So far.

Mars driving map. Click for larger. Image Credit: NASA/JPL-Caltech/Univ. of Arizona

Here’s a update to Curiosity’s journey on Mars. Looks to be something around 5 kilometers (3.1 miles). Just a guess, I’m sure the actual odometer reading is available on the website, except I couldn’t locate it after a moderate bit of searching.  The Where is Curiosity page has a lot of great stuff and would seem to be the best place to find it. I could try to sift through the archives and see if I can figure it out, that’s a lot of work, maybe I will look around some more first.

If anybody knows what the distance traveled (so far) is OR where to look, please let me know in the comments,  Just curious is all :mrgreen:

From NASA:

This map shows the route driven by NASA’s Curiosity Mars rover from the “Bradbury Landing” location where it landed in August 2012 (the start of the line in upper right) to a major waypoint called “the Kimberley.” The rover reached the Kimberley with a 98-foot (30 meter) drive on the 589th Martian day, or sol, of the rover’s work on Mars (April 1, 2014).

The Kimberley (formerly called “KMS-9″) was selected as a major waypoint for the mission because of the diversity of rock types distinguishable in orbital images, exposed close together at this location in a decipherable geological relationship to each other.

The base image for this map is from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter. North is up. The dark ground south of the rover’s route has dunes of dark, wind-blown material at the foot of Mount Sharp. The scale bar at lower right represents one kilometer (0.62 mile).

Author: "Tom" Tags: "Mars Rovers"
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Date: Saturday, 05 Apr 2014 16:49

A video of the separation of the Sentinel-1A from the Fregat putting it into orbit. Spectacular video.

The launch, if you didn’t see it was equally spectacular, the video is one of the best ground based recordings of an ascent into space around. Have a look while you’re here.

Author: "Tom" Tags: "ESA"
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Date: Friday, 04 Apr 2014 10:05
Artist concept:  NASA/JPL-Caltech

A possible internal structure of Enceladus. Artist concept: NASA/JPL-Caltech

I love this! I know, it’s not “for sure positively” but close enough for me. I was in the “global ocean” camp, then I thought “why not” this seems perfectly reasonable.

I do have to take issue with the very last line of the ESA press release (included / linked below): “This experiment provides a crucial new piece of information towards understanding the formation of plumes on this intriguing moon,” says Nicolas Altobelli, ESA’s Cassini project scientist.  Yeah it does provide a piece, but seems like it brings up more questions than it answered. That’s awesome is what it is!

Here is the Enceladus image gallery from NASA.

The press release from ESA is excellent:

Saturn’s icy moon Enceladus has an underground sea of liquid water, according to the international Cassini spacecraft.

Understanding the interior structure of 500 km-diameter Enceladus has been a top priority of the Cassini mission since plumes of ice and water vapour were discovered jetting from ‘tiger stripe’ fractures at the moon’s south pole in 2005.

Subsequent observations of the jets showed them to be relatively warm compared with other regions of the moon and to be salty – strong arguments for there being liquid water below the surface.

But planetary scientists have now been able to investigate the interior of the enigmatic moon directly, using Cassini’s radio science experiment.

On three separate occasions in 2010 and 2012, the spacecraft passed within 100 km of Enceladus, twice over the southern hemisphere and once over the northern hemisphere.

During the flybys, Cassini was pulled slightly off course by the moon’s gravity, changing its velocity by just 0.2–0.3 millimetres per second.

As tiny as these deviations were, they were detectable in the spacecraft’s radio signals as they were beamed back to Earth, providing a measurement of how the gravity of Enceladus varied along the spacecraft’s orbit. These measurements could then be used to infer the distribution of mass inside the moon.

For example, a higher-than-average gravity ‘anomaly’ might suggest the presence of a mountain, while a lower-than-average reading implies a mass deficit.

On Enceladus, the scientists measured a negative mass anomaly at the surface of the south pole, accompanied by a positive one some 30-40 km below.

“By analysing the spacecraft’s motion in this way, and taking into account the topography of the moon we see with Cassini’s cameras, we are given a window into the internal structure of Enceladus,” says Luciano Iess, lead author of the results published in Science.

“The perturbations in the spacecraft’s motion can be most simply explained by the moon having an asymmetric internal structure, such that an ice shell overlies liquid water at a depth of around 30–40 km in the southern hemisphere.”

While the gravity data cannot rule out a global ocean, a regional sea extending from the south pole to 50ºS latitude is most consistent with the moon’s topography and high local temperatures observed around the tiger stripes.

“This experiment provides a crucial new piece of information towards understanding the formation of plumes on this intriguing moon,” says Nicolas Altobelli, ESA’s Cassini project scientist.

Author: "Tom" Tags: "Cassini"
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